Colloidal Interactions of Microplastic Particles with Anionic Clays in Electrolyte Solutions

Click to copy article linkArticle link copied!

This article references 64 other publications.

1. 1

   Brahney, J.; Hallerud, M.; Heim, E.; Hahnenberger, M.; Sukumaran, S. Plastic rain in protected areas of the United States. Science 2020, 368, 1257– 1260,  DOI: 10.1126/science.aaz5819

   Google Scholar

   1

   Plastic rain in protected areas of the United States

   Brahney, Janice; Hallerud, Margaret; Heim, Eric; Hahnenberger, Maura; Sukumaran, Suja

   Science (Washington, DC, United States) (2020), 368 (6496), 1257-1260CODEN: SCIEAS; ISSN:1095-9203. (American Association for the Advancement of Science)

   Eleven billion metric tons of plastic are projected to accumulate in the environment by 2025. Because plastics are persistent, they fragment into pieces that are susceptible to wind entrainment. Using high-resoln. spatial and temporal data, we tested whether plastics deposited in wet vs. dry conditions have distinct atm. life histories. Further, we report on the rates and sources of deposition to remote U.S. conservation areas. We show that urban centers and resuspension from soils or water are principal sources for wet-deposited plastics. By contrast, plastics deposited under dry conditions were smaller in size, and the rates of deposition were related to indexes that suggest longer-range or global transport. Deposition rates averaged 132 plastics per square meter per day, which amts. to >1000 metric tons of plastic deposition to western U.S. protected lands annually.
2. 2

   Mitrano, D. M.; Wick, P.; Nowack, B. Placing nanoplastics in the context of global plastic pollution. Nat. Nanotechnol. 2021, 16, 491– 500,  DOI: 10.1038/s41565-021-00888-2

   Google Scholar

   2

   Placing nanoplastics in the context of global plastic pollution

   Mitrano, Denise M.; Wick, Peter; Nowack, Bernd

   Nature Nanotechnology (2021), 16 (5), 491-500CODEN: NNAABX; ISSN:1748-3387. (Nature Portfolio)

   A review. Numerous studies have made the ubiquitous presence of plastic in the environment undeniable, and thus it no longer comes as a surprise when scientists measure the accumulation of macroplastic litter and microplastic fragments in both urban and remote sites. Nanoplastics have recently emerged in the discussions of scientists, regulators and the public, as the weathering of macroplastics may lead to a substantial burden of nanoplastics in various ecosystems. While nanoplastics particles themselves have not (yet) been extensively measured in the environment, there is increased concern that this size fraction of plastic may be more extensively distributed and hazardous that larger-sized particles. This assessment may emanate from an unease with the term 'nano', which may elicit a neg. response over uncertainties of the pervasiveness of nanoplastics specifically, or from the lessons learned by many years of intensive environmental health and safety research of engineered nanomaterials. Ultimately, the different phys. and chem. characteristics of the different size classes of plastic pollution (macroplastics, microplastics and nanoplastics) will result in divergent fate and hazards. As nanoscientists specializing in understanding the fate, transport and interactions of nanoparticles in human and environmental systems, in this Perspective, we try to place nanoplastics in the context of global plastic pollution by assessing its sources and risks, and by assessing commonalities nanoplastics may share with other nanosized objects in environmental systems, such as engineered nanomaterials and natural colloids.
3. 3

   Sharma, S.; Chatterjee, S. Microplastic pollution, a threat to marine ecosystem and human health: a short review. Environ. Sci. Pollut. Res. 2017, 24, 21530– 21547,  DOI: 10.1007/s11356-017-9910-8

   Google Scholar

   3

   Microplastic pollution, a threat to marine ecosystem and human health: a short review

   Sharma Shivika; Chatterjee Subhankar

   Environmental science and pollution research international (2017), 24 (27), 21530-21547 ISSN:.

   Human populations are using oceans as their household dustbins, and microplastic is one of the components which are not only polluting shorelines but also freshwater bodies globally. Microplastics are generally referred to particles with a size lower than 5 mm. These microplastics are tiny plastic granules and used as scrubbers in cosmetics, hand cleansers, air-blasting. These contaminants are omnipresent within almost all marine environments at present. The durability of plastics makes it highly resistant to degradation and through indiscriminate disposal they enter in the aquatic environment. Today, it is an issue of increasing scientific concern because these microparticles due to their small size are easily accessible to a wide range of aquatic organisms and ultimately transferred along food web. The chronic biological effects in marine organisms results due to accumulation of microplastics in their cells and tissues. The potential hazardous effects on humans by alternate ingestion of microparticles can cause alteration in chromosomes which lead to infertility, obesity, and cancer. Because of the recent threat of microplastics to marine biota as well as on human health, it is important to control excessive use of plastic additives and to introduce certain legislations and policies to regulate the sources of plastic litter. By setup various plastic recycling process or promoting plastic awareness programmes through different social and information media, we will be able to clean our sea dustbin in future.
4. 4

   Gewert, B.; Plassmann, M. M.; MacLeod, M. Pathways for degradation of plastic polymers floating in the marine environment. Environ. Sci.: Processes Impacts 2015, 17, 1513– 1521,  DOI: 10.1039/C5EM00207A

   Google Scholar

   4

   Pathways for degradation of plastic polymers floating in the marine environment

   Gewert, Berit; Plassmann, Merle M.; MacLeod, Matthew

   Environmental Science: Processes & Impacts (2015), 17 (9), 1513-1521CODEN: ESPICZ; ISSN:2050-7895. (Royal Society of Chemistry)

   Each year vast amts. of plastic are produced worldwide. When released to the environment, plastics accumulate, and plastic debris in the world's oceans is of particular environmental concern. More than 60% of all floating debris in the oceans is plastic and amts. are increasing each year. Plastic polymers in the marine environment are exposed to sunlight, oxidants and phys. stress, and over time they weather and degrade. The degrdn. processes and products must be understood to detect and evaluate potential environmental hazards. Some attention has been drawn to additives and persistent org. pollutants that sorb to the plastic surface, but so far the chems. generated by degrdn. of the plastic polymers themselves have not been well studied from an environmental perspective. In this paper we review available information about the degrdn. pathways and chems. that are formed by degrdn. of the six plastic types that are most widely used in Europe. We extrapolate that information to likely pathways and possible degrdn. products under environmental conditions found on the oceans' surface. The potential degrdn. pathways and products depend on the polymer type. UV-radiation and oxygen are the most important factors that initiate degrdn. of polymers with a carbon-carbon backbone, leading to chain scission. Smaller polymer fragments formed by chain scission are more susceptible to biodegrdn. and therefore abiotic degrdn. is expected to precede biodegrdn. When heteroatoms are present in the main chain of a polymer, degrdn. proceeds by photo-oxidn., hydrolysis, and biodegrdn. Degrdn. of plastic polymers can lead to low mol. wt. polymer fragments, like monomers and oligomers, and formation of new end groups, esp. carboxylic acids.
5. 5

   Pfohl, P.; Wagner, M.; Meyer, L.; Domercq, P.; Praetorius, A.; Huffer, T.; Hofmann, T.; Wohlleben, W. Environmental degradation of microplastics: How to measure fragmentation rates to secondary micro- and nanoplastic fragments and dissociation into dissolved organics. Environ. Sci. Technol. 2022, 56, 11323– 11334,  DOI: 10.1021/acs.est.2c01228

   Google Scholar

   5

   Environmental degradation of microplastics: how to measure fragmentation rates to secondary micro- and nanoplastic fragments and dissociation into dissolved organics

   Pfohl, Patrizia; Wagner, Marion; Meyer, Lars; Domercq, Prado; Praetorius, Antonia; Hueffer, Thorsten; Hofmann, Thilo; Wohlleben, Wendel

   Environmental Science & Technology (2022), 56 (16), 11323-11334CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)

   Understanding the environmental fate of microplastics is essential for their risk assessment. It is essential to differentiate size classes and degrdn. states. Still, insights into fragmentation and degrdn. mechanisms of primary and secondary microplastics into micro- and nanoplastic fragments and other degrdn. products are limited. Here, we present an adapted NanoRelease protocol for a UV-dose-dependent assessment and size-selective quantification of the release of micro- and nanoplastic fragments down to 10 nm and demonstrate its applicability for polyamide and thermoplastic polyurethanes. The tested cryo-milled polymers do not originate from actual consumer products but are handled in industry and are therefore representative of polydisperse microplastics occurring in the environment. The protocol is suitable for various types of microplastic polymers, and the measured rates can serve to parameterize mechanistic fragmentation models. We also found that primary microplastics matched the same ranking of weathering stability as their corresponding macroplastics and that dissolved orgs. constitute a major rate of microplastic mass loss. The results imply that previously formed micro- and nanoplastic fragments can further degrade into water-sol. orgs. with measurable rates that enable modeling approaches for all environmental compartments accessible to UV light.
6. 6

   Zhang, F.; Wang, Z.; Wang, S.; Fang, H.; Wang, D. G. Aquatic behavior and toxicity of polystyrene nanoplastic particles with different functional groups: Complex roles of pH, dissolved organic carbon and divalent cations. Chemosphere 2019, 228, 195– 203,  DOI: 10.1016/j.chemosphere.2019.04.115

   Google Scholar

   6

   Aquatic behavior and toxicity of polystyrene nanoplastic particles with different functional groups: Complex roles of pH, dissolved organic carbon and divalent cations

   Zhang, Fan; Wang, Zhuang; Wang, Se; Fang, Hao; Wang, Degao

   Chemosphere (2019), 228 (), 195-203CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)

   Herein we systematically examd. the roles of water chem. (pH, DOC, and divalent cations) and particle surface functionality that control the aq. stability, aggregation, and toxicity of engineered nanoplastic particles in simulated natural environmental conditions. Results indicate that the presence of only DOC increased the surface charge and exhibited negligible effects on the size distribution of the PLNPs in aq. suspensions. The presence of the divalent cations (Ca2+ and Mg2+) was obsd. to decrease the surface charge and increase the size of the PLNPs. The coexistence of DOC and the divalent cations enhanced the extent of aggregation of the PLNPs in the water columns. The surface modification and pH were sensitive factors influencing the stability of PLNPs during long-term suspension when DOC and the divalent cations coexisted. Direct visual further testified the conclusions on the combined effects of soln. and surface chem. parameters. Furthermore, in situ transmission electron microscope observations revealed that the enhancement of PLNP aggregation in the presence of DOC and the divalent cation was caused by bridge formation. Toxicity test indicated the PLNPs exhibited acute toxicity and phys. damage to Daphnia magna. The more complex the soln. conditions, the more toxicity the aPLNPs and cPLNPs. Anal. of mode of toxic action implied that the PLNPs mainly caused the accumulation of oxidative damage to the gut of D. magna.
7. 7

   Singh, N.; Tiwari, E.; Khandelwal, N.; Darbha, G. K. Understanding the stability of nanoplastics in aqueous environments: effect of ionic strength, temperature, dissolved organic matter, clay, and heavy metals. Environ. Sci.: Nano 2019, 6, 2968– 2976,  DOI: 10.1039/C9EN00557A

   Google Scholar

   7

   Understanding the stability of nanoplastics in aqueous environments: effect of ionic strength, temperature, dissolved organic matter, clay, and heavy metals

   Singh, Nisha; Tiwari, Ekta; Khandelwal, Nitin; Darbha, Gopala Krishna

   Environmental Science: Nano (2019), 6 (10), 2968-2976CODEN: ESNNA4; ISSN:2051-8161. (Royal Society of Chemistry)

   Nanoplastics (NPs) are one of the most dangerous fractions of plastics because of their possible eco-toxicol. impacts. NP stability and transport are highly influenced by various environmental factors, which warrants the necessity to understand their fate in ambient water systems. This study investigates the polystyrene (PS) NP stability under the effect of varying ionic strength, temp., dissolved org. matter (DOM), inorg. soil colloids and heavy metal salts using the dynamic light scattering technique. Controlled studies were used to examine the aggregation of NPs in the presence of natural river water (RW), groundwater (GW), and seawater (SW). Results highlight that, at all studied temps., divalent cations had a greater influence on the aggregation rate of NPs as compared to monovalent cations whereas for the same salt, a drop in temp. tended to increase the stability. A rise in crit. coagulation concn. (CCC) by 1.6 and 2.4 times for NaCl and CaCl2 was obsd., resp., at 15°C as compared to 35°C. Steric repulsion produced by DOM stabilizes NPs shifting the CCC value to a higher salt concn. for NaCl. However, faster aggregation with CaCl2 due to complexation was notable. The clay colloids participate in heteroaggregation with NPs under the influence of salts; this was confirmed using cryo-TEM. Heavy metal salts such as ZnCl2 and CdCl2 had interactions with PS NPs similar to that presented by CaCl2 but showed independent behavior in the presence of HgCl2, due to metal speciation under different redox conditions. The concn. of salts and org. substances in the complex matrix of natural water results in the least stable NPs in SW > RW > GW. The results of this study contribute to the fundamental understanding of the fate of NPs in complex aquatic environments.
8. 8

   Hirai, H.; Takada, H.; Ogata, Y.; Yamashita, R.; Mizukawa, K.; Saha, M.; Kwan, C.; Moore, C.; Gray, H.; Laursen, D.; Zettler, E. R.; Farrington, J. W.; Reddy, C. M.; Peacock, E. E.; Ward, M. W. Organic micropollutants in marine plastics debris from the open ocean and remote and urban beaches. Mar. Pollut. Bull. 2011, 62, 1683– 1692,  DOI: 10.1016/j.marpolbul.2011.06.004

   Google Scholar

   8

   Organic micropollutants in marine plastics debris from the open ocean and remote and urban beaches

   Hirai, Hisashi; Takada, Hideshige; Ogata, Yuko; Yamashita, Rei; Mizukawa, Kaoruko; Saha, Mahua; Kwan, Charita; Moore, Charles; Gray, Holly; Laursen, Duane; Zettler, Erik R.; Farrington, John W.; Reddy, Christopher M.; Peacock, Emily E.; Ward, Marc W.

   Marine Pollution Bulletin (2011), 62 (8), 1683-1692CODEN: MPNBAZ; ISSN:0025-326X. (Elsevier Ltd.)

   To understand the spatial variation in concns. and compns. of org. micropollutants in marine plastic debris and their sources, we analyzed plastic fragments (∼10 mm) from the open ocean and from remote and urban beaches. Polychlorinated biphenyls (PCBs), polycyclic arom. hydrocarbons (PAHs), dichloro-diphenyl-trichloroethane and its metabolites (DDTs), polybrominated di-Ph ethers (PBDEs), alkylphenols and bisphenol A were detected in the fragments at concns. from 1 to 10,000 ng/g. Concns. showed large piece-to-piece variability. Hydrophobic org. compds. such as PCBs and PAHs were sorbed from seawater to the plastic fragments. PCBs are most probably derived from legacy pollution. PAHs showed a petrogenic signature, suggesting the sorption of PAHs from oil slicks. Nonylphenol, bisphenol A, and PBDEs came mainly from additives and were detected at high concns. in some fragments both from remote and urban beaches and the open ocean.
9. 9

   Liu, Q.; Wu, H. W.; Chen, J. J.; Guo, B. H.; Zhao, X. F.; Lin, H.; Li, W.; Zhao, X.; Lv, S. H.; Huang, C. Adsorption mechanism of trace heavy metals on microplastics and simulating their effect on microalgae in river. Environ. Res. 2022, 214, 113777,  DOI: 10.1016/j.envres.2022.113777

   Google Scholar

   9

   Adsorption mechanism of trace heavy metals on microplastics and simulating their effect on microalgae in river

   Liu, Qian; Wu, Haowen; Chen, Jiajiao; Guo, Biaohu; Zhao, Xiufang; Lin, Hui; Li, Wei; Zhao, Xin; Lv, Sihao; Huang, Cong

   Environmental Research (2022), 214 (Part_1), 113777CODEN: ENVRAL; ISSN:0013-9351. (Elsevier Inc.)

   Microplastics (MPs) and heavy-metal contamination in freshwater is an increasing concern. Heavy metals are common heavy metals that can easily flow into rivers, causing water pollution, like Fe, Mn, Pb, Zn, Cr, and Cd. Microplastics act as carriers for heavy metals and increase the transport of contaminants in freshwater systems. We investigated the adsorption mechanisms of three kinds of MPs having similar particle sizes, namely polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), with respect to trace heavy metals of Pb, Cu, Cr, and Cd under different temp. and salinity conditions. The reaction kinetics of the adsorption of different trace heavy metals on different MPs were consistent with both the quasi primary and quasi secondary kinetic models, indicating the complexity of heavy metal adsorption by MPs. The adsorption rate of heavy metal on MPs was mainly controlled by intra-particle diffusion, and the isotherm model indicated that the adsorption of Pb, Cu, Cr, and Cd by MPs occurred in the form of monolayer phys. adsorption. Addnl., an increase in temp. and decrease in salinity were favorable to improve the affinity of MPs toward heavy metals (through adsorption). Zeta potential measurements and Fourier transform IR (FTIR) and XPS analyses indicated that electrostatic force interaction was the main mechanism of the adsorption process; oxygen-contg. functional groups, π-π interaction, and halogen bonds played important roles in the process of adsorption. Furthermore, the growth inhibition and oxidative stress of microalgae Chlorella vulgaris (GY-D27) due to PP, PS, and PVC were analyzed; notably, MPs or Pb inhibited the growth of Chlorella vulgaris. However, the reduced toxicity to Chlorella vulgaris, with respect to a mixt. of Pb and MPs, was confirmed using superoxide dismutase and catalase enzyme activities. Our results can be applied for the risk assessment of heavy metals and MPs in aquatic environments.
10. 10

    Holmes, L. A.; Turner, A.; Thompson, R. C. Adsorption of trace metals to plastic resin pellets in the marine environment. Environ. Pollut. 2012, 160, 42– 48,  DOI: 10.1016/j.envpol.2011.08.052

    Google Scholar

    10

    Adsorption of trace metals to plastic resin pellets in the marine environment

    Holmes, Luke A.; Turner, Andrew; Thompson, Richard C.

    Environmental Pollution (Oxford, United Kingdom) (2012), 160 (), 42-48CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)

    Plastic prodn. pellets collected from beaches of south west England contain variable concns. of trace metals (Cr, Co, Ni, Cu, Zn, Cd and Pb) that, in some cases, exceed concns. reported for local estuarine sediments. The rates and mechanisms by which metals assoc. with virgin and beached polyethylene pellets were studied by adding a cocktail of 5 μg L-1 of trace metals to 10 g L-1 pellet suspensions in filtered seawater. Kinetic profiles were modelled using a pseudo-first-order equation and yielded response times of less than about 100 h and equil. partition coeffs. of up to about 225 mL g-1 that were consistently higher for beached pellets than virgin pellets. Adsorption isotherms conformed to both the Langmuir and Freundlich equations and adsorption capacities were greater for beached pellets than for virgin pellets. Results suggest that plastics may represent an important vehicle for the transport of metals in the marine environment. Trace metals accumulate on plastic resin pellets in the marine environment through adsorption to the polymer and to chem. and biol. attritions thereon.
11. 11

    Rahman, M. M.; Sultan, M. B.; Alam, M. Microplastics and adsorbed micropollutants as emerging contaminants in landfill: A mini review. Curr. Opin. Environ. Sci. Health 2023, 31, 100420,  DOI: 10.1016/j.coesh.2022.100420

    Google Scholar

    There is no corresponding record for this reference.
12. 12

    Bere, K.; Xiong, X.; Sáringer, S.; Douglas, G.; Szilagyi, I. Microplastics as an adsorption and transport medium for per- and polyfluoroalkyl substances in aquatic systems: Polystyrene and undecafluorohexanoic acid interactions. J. Mol. Liq. 2023, 384, 122285,  DOI: 10.1016/j.molliq.2023.122285

    Google Scholar

    12

    Microplastics as an adsorption and transport medium for per- and polyfluoroalkyl substances in aquatic systems: Polystyrene and undecafluorohexanoic acid interactions

    Bere, Katalin; Xiong, Xiong; Saringer, Szilard; Douglas, Grant; Szilagyi, Istvan

    Journal of Molecular Liquids (2023), 384 (), 122285CODEN: JMLIDT; ISSN:0167-7322. (Elsevier B.V.)

    The assessment of possible interactions between microplastic particles (MPP) and other emerging contaminants such as per- and polyfluoroalkyl substances (PFAS) is of great importance due to their potentially conjunctive harmful effects on the environment. Here, the colloidal behavior of a polystyrene MPP in the presence of undecafluorohexanoic acid (UFHA), an alternative to the widely used C8 PFAS, was studied in aq. dispersions. Adsorption of UFHA on MPP was confirmed, where it induced charge neutralization with overcharging at higher UFHA concns. Rates of MPP aggregation were rapid with neutral particles, while slow at low and high UFHA doses, where considerable, alternate surface charge persisted and hence, fine particle dispersion was maintained. The addn. of multivalent ions influenced the surface charge and aggregation features of MPP, in both their native form and in the presence of UFHA. Concurrent adsorption of electrolytes and UFHA was obsd. and strongly affected the rate of MPP aggregation under some exptl. conditions. This study provides new insights into the possible interactions of PFAS with MPP, which may fundamentally influence the migration of these contaminants in aq. environments. Aggregated particles will more likely accumulate in the sediments or at the air-water interface, while individual, highly stable MPP-PFAS composites have the potential to migrate together in the water column.
13. 13

    Li, X.; He, E. K.; Jiang, K.; Peijnenburg, W.; Qiu, H. The crucial role of a protein corona in determining the aggregation kinetics and colloidal stability of polystyrene nanoplastics. Water Res. 2021, 190, 116742,  DOI: 10.1016/j.watres.2020.116742

    Google Scholar

    13

    The crucial role of a protein corona in determining the aggregation kinetics and colloidal stability of polystyrene nanoplastics

    Li, Xing; He, Erkai; Jiang, Ke; Peijnenburg, Willie J. G. M.; Qiu, Hao

    Water Research (2021), 190 (), 116742CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)

    Nanosized plastics are considered as being a class of contaminants of emerging concern. The interaction between nanoplastics and proteins may significantly influence the environmental behavior and fate of nanoplastics. Here, we employed time-resolved dynamic light scattering to explore the aggregation kinetics and stability of polystyrene nanoparticles (PSNPs) exposed to a model globular protein (bovine serum albumin, BSA) in the presence of a no. of typical electrolytes (NaCl, CaCl2, and Na2SO4). With the increase of the BSA concn., the amt. of BSA adsorbed on the surface of neg. charged PS-Bare (non-modified) and PS-COOH (carboxyl-modified) increased, resulting in higher dispersibility in comparison to the treatment without BSA. This stabilization effect derived from the protein corona structure was revealed by combining characterization techniques and visualized by transmission electron microscopy. Upon addn. of NaCl and CaCl2, the aggregation of pos. charged PS-NH2 (amino-modified) was inhibited by the BSA addn. possibly due to the screening of the attractive patch-charge force and the competition for adsorption of cations between PS-NH2 and the protein. When Na2SO4 was present in the suspension, BSA addn. significantly increased PS-NH2 aggregation rate due to patch-charge attraction and the high performance of SO2-4 in attaching to particles and charge neutralization. These findings shed light on the interactions between PSNPs and proteins, which were shown to vary with the compn. of the surface coatings of PSNPs. The newly gained knowledge will help us to forecast the transport and fate of PSNPs in natural aq. systems.
14. 14

    Chang, X.; Fang, Y.; Wang, Y.; Wang, F.; Shang, L. Y.; Zhong, R. Z. Microplastic pollution in soils, plants, and animals: A review of distributions, effects and potential mechanisms. Sci. Total Environ. 2022, 850, 157857,  DOI: 10.1016/j.scitotenv.2022.157857

    Google Scholar

    14

    Microplastic pollution in soils, plants, and animals: A review of distributions, effects and potential mechanisms

    Chang, Xiao; Fang, Yi; Wang, Ying; Wang, Fei; Shang, Liyuan; Zhong, Rongzhen

    Science of the Total Environment (2022), 850 (), 157857CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)

    A review. Increasing prodn. of synthetic plastics and poor management of plastic wastes have dramatically increased the amt. of plastics in the environment. In 2014, at the first United Nations Environment Assembly, marine plastic waste pollution was listed as one of the 10 most pressing environmental issues. In addn., there is much plastic waste in terrestrial ecosystems due to substantial residues from agricultural mulching and packing. As a recently recognized pollutant, microplastics (MPs) have attracted significant attention from the public and various governments. Concns. of MPs in the environment vary among locations, from <100 to >1 x 106 particles per cubic meter. Many studies have addressed the impacts and potential mechanisms of MPs on the environment and organisms. Humans and other organisms can ingest or carry MPs in a variety of passive ways and these MPs can have a range of neg. effects on metab., function, and health. Addnl., given their large surface area, MPs can sorb various pollutants, including heavy metals and persistent org. pollutants, with serious implications for animals and human wellbeing. However, due to their complexity and a lack of accurate detn. methods, the systematic impacts of MP pollution on whole foodwebs are not clearly established. Therefore, this review summarizes current research advances in MP pollution, particularly the impact of MPs on soils, plants, and animals, and proposes potential future research prospects to better characterize MPs.
15. 15

    Alimi, O. S.; Farner Budarz, J.; Hernandez, L. M.; Tufenkji, N. Microplastics and nanoplastics in aquatic environments: Aggregation, deposition, and enhanced contaminant transport. Environ. Sci. Technol. 2018, 52, 1704– 1724,  DOI: 10.1021/acs.est.7b05559

    Google Scholar

    15

    Microplastics and Nanoplastics in Aquatic Environments: Aggregation, Deposition, and Enhanced Contaminant Transport

    Alimi, Olubukola S.; Farner Budarz, Jeffrey; Hernandez, Laura M.; Tufenkji, Nathalie

    Environmental Science & Technology (2018), 52 (4), 1704-1724CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    A review is given. Plastic litter is widely acknowledged as a global environmental threat, and poor management and disposal lead to increasing levels in the environment. Of recent concern is the degrdn. of plastics from macro- to micro- and even to nanosized particles <100 nm in size. At the nanoscale, plastics are difficult to detect and can be transported in air, soil, and water compartments. While the impact of plastic debris on marine and fresh waters and organisms has been studied, the loads, transformations, transport, and fate of plastics in terrestrial and subsurface environments are largely overlooked. Here, we 1st present estd. loads of plastics in different environmental compartments. We also provide a crit. review of the current knowledge vis-a-vis nanoplastic (NP) and microplastic (MP) aggregation, deposition, and contaminant cotransport in the environment. Important factors that affect aggregation and deposition in natural subsurface environments are identified and critically analyzed. Factors affecting contaminant sorption onto plastic debris are discussed, and we show how polyethylene generally exhibits a greater sorption capacity than other plastic types. We highlight key knowledge gaps that need to be addressed to improve our ability to predict the risks assocd. with these ubiquitous contaminants in the environment by understanding their mobility, aggregation behavior and their potential to enhance the transport of other pollutants.
16. 16

    Saavedra, J.; Stoll, S.; Slaveykova, V. I. Influence of nanoplastic surface charge on eco-corona formation, aggregation and toxicity to freshwater zooplankton. Environ. Pollut. 2019, 252, 715– 722,  DOI: 10.1016/j.envpol.2019.05.135

    Google Scholar

    16

    Influence of nanoplastic surface charge on eco-corona formation, aggregation and toxicity to freshwater zooplankton

    Saavedra, Juan; Stoll, Serge; Slaveykova, Vera I.

    Environmental Pollution (Oxford, United Kingdom) (2019), 252 (Part_A), 715-722CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)

    Concerns about possible environmental implications of nano- and micro-plastics are continuously raising. Hence, comprehensive understanding of their behavior, bioaccumulation and toxicity potential is required. The aims of the present study are thus two-fold: (i) to examine the role of the surface charge on nanoplastic stability and acute effects to freshwater zooplankton; (ii) to decipher the influence of the refractory natural org. matter (NOM) on the nanoplastic fate and effects. Amidine and carboxyl-stabilized polystyrene (PS) spheres of 200 nm diam. characterized by opposite primary surface charges and neutral buoyancy were selected as model nanoplastics. The results demonstrated that the surface functionalization of the polystyrene nanoplastics controls their aggregation behavior. Both amidine and carboxyl PS nanoplastics were ingested by the zooplankton and concd. mainly in the gut of water flea Daphnia magna and larvae Thamnocephalus platyurus, and the stomach of rotifer Brachionus calyciflorus. Amidine PS nanoplastic was more toxic than carboxyl one. The toxicity decreased in the order D. magna (48 h -immobilization) > B. calyciflorus (24 h - lethality) > T. platyurus (24 h - lethality). Alginate or SRHA reduced significantly the toxicity of both amidine and carboxyl PS nanoplastics to the studied zooplankton representatives. The implications of this lab. study findings to natural environment were discussed.
17. 17

    Mao, Y. F.; Li, H.; Huangfu, X. L.; Liu, Y.; He, Q. Nanoplastics display strong stability in aqueous environments: Insights from aggregation behaviour and theoretical calculations. Environ. Pollut. 2020, 258, 113760,  DOI: 10.1016/j.envpol.2019.113760

    Google Scholar

    17

    Nanoplastics display strong stability in aqueous environments: Insights from aggregation behaviour and theoretical calculations

    Mao, Yufeng; Li, Hong; Huangfu, Xiaoliu; Liu, Yao; He, Qiang

    Environmental Pollution (Oxford, United Kingdom) (2020), 258 (), 113760CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)

    Nanoplastics are inevitably released into aquatic environments due to their extensive use and the continuous fragmentation of plastics. Therefore, it is imperative to understand the aggregation behaviors that det. the transport and fate of nanoplastics in aquatic environments. In this study, the effects of various metal cations, pH, aging and extracellular polymeric substances (EPS) on the aggregation of polystyrene nanoplastics (nano-PS) in aq. solns. were systematically evaluated based on aggregation kinetics expts. and Derjaguin-Landau-Verwey-Overbeek (DLVO) theor. calcn. The concn., valence and hydration ability of metal cations jointly affected the aggregation of nano-PS. The crit. coagulation concn. (CCC) of nano-PS was significantly higher than the ionic strengths in aquatic environments, indicating that the aggregation rate of nano-PS is relatively low in aquatic environments. The results of the aggregation kinetics expts. were consistent with DLVO theory, which showed that the energy barrier of nano-PS was dependent on electrostatic repulsion forces and van der Waals forces, and increased with pH. Nano-PS was artificially aged by UV-H2O2, which reduced the hydrophobic nature of the particle surfaces, consequently enhancing the stability of the nanoplastics. Our results highlight the high stability of nano-PS in aquatic environments, which could help facilitate the evaluation of their environmental impact.
18. 18

    Wu, J. Y.; Ye, Q. Y.; Wu, P. X.; Xu, S. R.; Liu, Y. J.; Ahmed, Z.; Rehman, S.; Zhu, N. W. Heteroaggregation of nanoplastics with oppositely charged minerals in aquatic environment: Experimental and theoretical calculation study. Chem. Eng. J. 2022, 428, 131191,  DOI: 10.1016/j.cej.2021.131191

    Google Scholar

    18

    Heteroaggregation of nanoplastics with oppositely charged minerals in aquatic environment: Experimental and theoretical calculation study

    Wu, Jiayan; Ye, Quanyun; Wu, Pingxiao; Xu, Shanrong; Liu, Yanjun; Ahmed, Zubair; Rehman, Saeed; Zhu, Nengwu

    Chemical Engineering Journal (Amsterdam, Netherlands) (2022), 428 (), 131191CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)

    The transport, fate, and toxic effects of nanoplastics (NPs) would be affected by various environmental factors. In this study, the aggregation behaviors of polystyrene nanoplastics (PSNPs) with or without the presence of oppositely charged minerals (Mg/Al layered double hydroxides (LDH) and kaolin) in aq. phase were investigated through settling expt., and the influencing factors including pH and ionic strength (IS) were also analyzed systematically. Our results revealed that pH had a negligible effect on the fate of individual PSNPs under natural aquatic conditions, while high IS would cause homoaggregation. The pos. charged LDH decreased the stability of PSNPs, while neg. charged kaolin had a weak effect on it, suggesting that electrostatic interaction was directly related to the stability of PSNPs in aquatic environment. Further expts. of PSNPs with other metal oxides with different surface charges (Al2O3 and SiO2) confirmed the importance of electrostatic interaction for PSNPs-minerals heteroaggregation. Transmission electron microscopic (TEM), Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and D. function theory (DFT) calcns. were combined for the first time to explain the heteroaggregation mechanism, demonstrating that there were expected to exist hydrogen bond and van der Waals interaction in addn. to the dominant force of electrostatic interaction. Our findings are expected to shed light on the environmental behavior of PSNPs in a complex aquatic environment.
19. 19

    Oncsik, T.; Trefalt, G.; Borkovec, M.; Szilagyi, I. Specific ion effects on particle aggregation induced by monovalent salts within the Hofmeister series. Langmuir 2015, 31, 3799– 3807,  DOI: 10.1021/acs.langmuir.5b00225

    Google Scholar

    19

    Specific Ion Effects on Particle Aggregation Induced by Monovalent Salts within the Hofmeister Series

    Oncsik, Tamas; Trefalt, Gregor; Borkovec, Michal; Szilagyi, Istvan

    Langmuir (2015), 31 (13), 3799-3807CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    Ion specific effects of monovalent salts on charging and aggregation for two types of polystyrene latex particles were investigated by electrophoresis and time-resolved light scattering. The chem. compn. of the electrolytes was systematically varied in the expts. Accordingly, NaH2PO4, NaF, NaCl, NaBr, NaNO3, and NaSCN were used to vary the anions and N(CH3)4Cl, NH4Cl, CsCl, KCl, NaCl, and LiCl for the cations. The salt concn. dependence of the electrophoretic mobilities indicates that the surface charge was screened by the counterions when their concns. increased. For the SCN- ions, adsorption on pos. charged particles leads to charge reversal. The aggregation rates are small at low electrolyte concns. indicating stable dispersions under these conditions, and they increase with the salt concn. When viscosity corrections are taken into account, no ion specific effects in the fast aggregation regime can be established. The slow and fast aggregation regimes are sepd. by the crit. coagulation concn. (CCC). Within the exptl. error, the CCCs are the same in systems contg. different co-ions but the same counterions, with the exception of ammonium salts. However, the variation of counterions leads to different CCC values due to specific interaction of the counterions with the surface. These values follow the Hofmeister series for neg. charged sulfate latex particles, while the reversed order was obsd. for pos. charged amidine latex. Comparison between exptl. CCCs and those calcd. by the theory of Derjaguin, Landau, Verwey, and Owerbeek reveals that variations in the surface charge due to ionic adsorption are mainly responsible for the ion specific effects in the aggregation process.
20. 20

    Witzmann, T.; Ramsperger, A.; Wieland, S.; Laforsch, C.; Kress, H.; Fery, A.; Auernhammer, G. K. Repulsive Interactions of Eco-corona-Covered Microplastic Particles Quantitatively Follow Modeling of Polymer Brushes. Langmuir 2022, 38, 8748– 8756,  DOI: 10.1021/acs.langmuir.1c03204

    Google Scholar

    20

    Repulsive Interactions of Eco-corona-Covered Microplastic Particles Quantitatively Follow Modeling of Polymer Brushes

    Witzmann, Thomas; Ramsperger, Anja F. R. M.; Wieland, Simon; Laforsch, Christian; Kress, Holger; Fery, Andreas; Auernhammer, Guenter K.

    Langmuir (2022), 38 (29), 8748-8756CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    The environmental fate and toxicity of microplastic particles are dominated by their surface properties. In the environment, an adsorbed layer of biomols. and natural org. matter forms the so-called eco-corona. A quant. description of how this eco-corona changes the particles' colloidal interactions is still missing. Here, we demonstrate with colloidal probe-at. force microscopy that eco-corona formation on microplastic particles introduces a compressible film on the surface, which changes the mech. behavior. We measure single particle-particle interactions and find a pronounced increase of long-range repulsive interactions upon eco-corona formation. These force-sepn. characteristics follow the Alexander-de Gennes (AdG) polymer brush model under certain conditions. We further compare the obtained fitting parameters to known systems like polyelectrolyte multilayers and propose these as model systems for the eco-corona. Our results show that concepts of fundamental polymer physics, like the AdG model, also help in understanding more complex systems like biomols. adsorbed to surfaces, i.e., the eco-corona.
21. 21

    Wang, Y.; Chen, X. W.; Wang, F. F.; Cheng, N. S. Influence of typical clay minerals on aggregation and settling of pristine and aged polyethylene microplastics. Environ. Pollut. 2023, 316, 120649,  DOI: 10.1016/j.envpol.2022.120649

    Google Scholar

    21

    Influence of typical clay minerals on aggregation and settling of pristine and aged polyethylene microplastics

    Wang, Yi; Chen, Xingwei; Wang, Feifeng; Cheng, Niansheng

    Environmental Pollution (Oxford, United Kingdom) (2023), 316 (Part_2), 120649CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)

    Microplastics (MPs) are emerging as a class of pollutants that are a potential threat to biol. and human health. Aggregation and settling are crucial to controlling MPs transport and environmental fate. However, the influence of clay minerals in the aq. environment on the aggregation-settling processes of larger size MPs and its mechanisms remain unclear. In this study, homoaggregation of pristine and aged polyethylene microplastics (PEs) and heteroaggregation-settling of PEs with typical clay minerals (chlorite, illite, kaolinite, montmorillonite) under different hydrochem. conditions (NaCl, CaCl2, MgCl2) were systematically investigated. The results showed that the cation type has a greater influence on the homoaggregation system. In detail, the aged PEs is more stable than pristine PEs in monovalent electrolyte solns., but not in divalent electrolytes. In heteroaggregation systems, electrostatic repulsion dominates the interaction of PEs (pristine, aged) with clay minerals. However, the settling ratio of PEs (pristine, aged) contributed by clay minerals is not very dependent on the clay mineral type. Conversely, high NaCl concns. are more conducive to the heteroaggregation-settling of PEs, which can be explained by the DLVO theory. The findings of this study provide new insights into the environmental fate and distribution of MPs in natural waters.
22. 22

    Oriekhova, O.; Stoll, S. Heteroaggregation of nanoplastic particles in the presence of inorganic colloids and natural organic matter. Environ. Sci.: Nano 2018, 5, 792– 799,  DOI: 10.1039/C7EN01119A

    Google Scholar

    22

    Heteroaggregation of nanoplastic particles in the presence of inorganic colloids and natural organic matter

    Oriekhova, Olena; Stoll, Serge

    Environmental Science: Nano (2018), 5 (3), 792-799CODEN: ESNNA4; ISSN:2051-8161. (Royal Society of Chemistry)

    The presence and accumulation of micro- and nanoplastics in marine and fresh waters represent a huge environmental concern. Due to the complexity of nanoplastic surface chem. and impact of the surrounding aquatic environment, the fate of nanoplastics is still difficult to evaluate. Our study aims to explore the effect of different water components such as natural org. matter and inorg. colloids as well as water compn. on the stability of polystyrene nanoplastics. Heteroaggregation expts. are performed under contrasting conditions by considering mixts. of three components: nanoplastics, Fe2O3 and alginate and at different concn. ratios. It is found that the charge neutralization mechanism in most cases is responsible for the formation of large heteroaggregates. A shift in the optimal heteroaggregation concn. is obsd. in the presence of alginate indicating competitive effects between alginate and Fe2O3. The formation of primary heteroaggregates is found to be a requisite before the formation of large structures. The behavior of polystyrene nanoplastics is also studied here in natural water from the Rĥone river. Nanoplastic particles are found to rapidly change their surface charge from pos. to neg. and form small heteroaggregates at low concn. Increasing the nanoplastic particle concn. is found to result in the formation of large heteroaggregates when the isoelec. point is achieved indicating the importance of nanoplastic surface charge neutralization.
23. 23

    Li, M.; He, L.; Zhang, M. Y.; Liu, X. W.; Tong, M. P.; Kim, H. Cotransport and deposition of iron oxides with different-sized plastic particles in saturated quartz sand. Environ. Sci. Technol. 2019, 53, 3547– 3557,  DOI: 10.1021/acs.est.8b06904

    Google Scholar

    23

    Cotransport and Deposition of Iron Oxides with Different-Sized Plastic Particles in Saturated Quartz Sand

    Li, Meng; He, Lei; Zhang, Mengya; Liu, Xianwei; Tong, Meiping; Kim, Hyunjung

    Environmental Science & Technology (2019), 53 (7), 3547-3557CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)

    The present study was designed to investigate the cotransport and deposition of different-sized plastic particle from nano- (0.02 μm) to micrometer-scale (0.2 and 2 μm) with goethite and hematite (two types of representative iron oxides abundant in natural environment) in porous media at both low (5 mM) and high ionic strength (25 mM) in NaCl solns. We found that through different mechanisms (i.e., modification of surface properties of iron oxides, steric repulsion, or alteration in deposition sites on quartz sand), different-sized plastic particles induced different effects on the transport and deposition behaviors of iron oxides in quartz sand. Likewise, via different mechanisms such as change of surface properties or alteration in deposition sites on quartz sand, different transport behaviors for different sized plastic particles induced by the copresence of iron oxides were also obsd. The results of this study suggested that cotransport of iron oxides and plastic particles in porous media is far more complex than those of individual colloid transport. Since both plastic particles and iron oxides are ubiquitous presence in natural environment, it is expected that they would interact with each other and thus alter the surface properties, leading to the change of transport behaviors in porous media.
24. 24

    Nie, X.; Xing, X. H.; Xie, R. Y.; Wang, J. X.; Yang, S. G.; Wan, Q.; Zeng, E. Y. Impact of iron/aluminum (hydr)oxide and clay minerals on heteroaggregation and transport of nanoplastics in aquatic environment. J. Hazard. Mater. 2023, 446, 130649,  DOI: 10.1016/j.jhazmat.2022.130649

    Google Scholar

    24

    Impact of iron/aluminum (hydr)oxide and clay minerals on heteroaggregation and transport of nanoplastics in aquatic environment

    Nie, Xin; Xing, Xiaohui; Xie, Ruiyin; Wang, Jingxin; Yang, Shuguang; Wan, Quan; Zeng, Eddy Y.

    Journal of Hazardous Materials (2023), 446 (), 130649CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)

    Nanoplastics (NPs) are emerging contaminants in the environment, where the transport and fate of NPs would be greatly affected by interactions between NPs and minerals. In the present study, the interactions of two types of polystyrene nanoplastics (PSNPs), i.e., bare-PSNPs and carboxylated PSNPs-COOH, with iron (hydr)oxides (hematite, goethite, magnetite, and ferrihydrite), aluminum (hydr)oxides (boehmite and gibbsite), and clay minerals (kaolinite, montmorillonite, and illite) were investigated. The pos. charged iron/aluminum (hydr)oxide minerals could form heteroaggregates with neg. charged PSNPs. Electrostatic and hydrophobic interaction dominate for the heteroaggregation of bare-PSNPs with iron/aluminum (hydr)oxide minerals, while ligand exchange and electrostatic interaction are involved in the heteroaggregation of PSNPs-COOH with iron/aluminum (hydr)oxides minerals. However, heteroaggregation between PSNPs and neg. charged clay minerals was negligible. Humic acid markedly suppressed such heteroaggregation between PSNPs and minerals due to enhanced electrostatic repulsion, steric hindrance, and competition of surface attachment sites. The heteroaggregation rates of both bare-PSNPs and PSNPs-COOH with hematite decreased with increasing soln. pH. Increased ionic strength enhanced the heteroaggregation of PSNPs-COOH but inhibited that of bare-PSNPs. The results of the present study suggested that the heteroaggregation of PSNPs in environments could be strongly affected by minerals, soln. pH, humic acid, and ionic strength.
25. 25

    Zhang, Y. H.; Wang, X. J.; Li, Y.; Wang, H.; Shi, Y. X.; Li, Y.; Zhang, Y. J. Improving nanoplastic removal by coagulation: Impact mechanism of particle size and water chemical conditions. J. Hazard. Mater. 2022, 425, 127962,  DOI: 10.1016/j.jhazmat.2021.127962

    Google Scholar

    25

    Improving nanoplastic removal by coagulation: Impact mechanism of particle size and water chemical conditions

    Zhang, Yunhai; Wang, Xinjie; Li, Ying; Wang, Hao; Shi, Yuexiao; Li, Yang; Zhang, Yongjun

    Journal of Hazardous Materials (2022), 425 (), 127962CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)

    Plastic particles may bring potential threats to the ecosystem. Coagulation, as a widely used method to remove particles, has been rarely studied for plastic particles in the nanometer range. In this work, the coagulation removal of polystyrene nanoplastic particles (PSNPs, 50-1000 nm) was conducted in a model system contg. coagulants aluminum chlorohydrate (PAC) and polyacrylamide (PAM). The optimal removal efficiency (98.5%) was obsd. in the coagulation process at pH= 8.0, 0.4 g·L-1 PAC and 20 mg·L-1 PAM. The inhibition impact of humic acid was also noticed, due to its competitive adsorption with PSNPs onto flocs. The interaction energies between PSNPs and PAC were calcd. by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, which showed that elec. neutralization resulted in the difference of the remove efficiency in different sizes and coagulant concns. The formation of Al-O bond between PSNPs and PAC/PAM flocs promoted the removal of PSNPs. Excessive PAM (> 20 mg·L-1) increased clusters size and soln. viscosity, which resulted in the settling of clusters being controlled by buoyancy and the reduced remove efficiency. The findings suggest that the chem. coagulation dominants the removal of NPs, and the coagulation efficiency can be optimized by choosing suitable coagulant and water chem. conditions.
26. 26

    Wang, J.; Sun, C.; Huang, Q. X.; Chi, Y.; Yan, J. H. Adsorption and thermal degradation of microplastics from aqueous solutions by Mg/Zn modified magnetic biochars. J. Hazard. Mater. 2021, 419, 126486,  DOI: 10.1016/j.jhazmat.2021.126486

    Google Scholar

    26

    Adsorption and thermal degradation of microplastics from aqueous solutions by Mg/Zn modified magnetic biochars

    Wang, Jun; Sun, Chen; Huang, Qun-Xing; Chi, Yong; Yan, Jian-Hua

    Journal of Hazardous Materials (2021), 419 (), 126486CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)

    Microplastics (MPs) derived from plastic wastes have attracted wide attention throughout the world due to the wide distribution, easy transition, and potential threats to organisms. This study proposes efficient Mg/Zn modified magnetic biochar adsorbents for microplastic removal. For polystyrene (PS) microspheres (1μm, 100 mg/mL) in aq. soln., the removal efficiencies of magnetic biochar (MBC), Mg modified magnetic biochar (Mg-MBC), and Zn modified magnetic biochar (Zn-MBC) were 94.81%, 98.75%, and 99.46%, resp. It is supposed that the adsorption process was a result of electrostatic interaction and chem. bonding interaction between microplastics and biochar. The coexisting H2PO4- and org. matters in real water significantly affected the removal efficiency of Zn-MBC due to competitive adsorption effect. Microplastic degrdn. and adsorbent regeneration were accomplished by thermal treatment simultaneously. The degrdn. of adsorbed MPs was promoted by the catalytic active sites originated from Mg and Zn, releasing adsorption sites. Thermal regeneration maintained the adsorption capability. Even after five adsorption-pyrolysis cycles, MBC (95.02%), Mg-MBC (94.60%), and Zn-MBC (95.79%) showed high microplastic removal efficiency. Therefore, the low-cost, eco-friendly, and robust Mg/Zn-MBCs have promising potential for application in microplastic removal.
27. 27

    Chen, Z. Y.; Chen, C. Y.; Luo, X. W.; Liu, J. H.; Huang, Z. J. Flocculation of polystyrene nanoplastics in water using Mg/Al layered double hydroxides via heteroaggregation. Appl. Clay Sci. 2021, 213, 106264,  DOI: 10.1016/j.clay.2021.106264

    Google Scholar

    27

    Flocculation of polystyrene nanoplastics in water using Mg/Al layered double hydroxides via heteroaggregation

    Chen, Ziying; Chen, Chengyu; Luo, Xuewen; Liu, Junhong; Huang, Zhujian

    Applied Clay Science (2021), 213 (), 106264CODEN: ACLSER; ISSN:0169-1317. (Elsevier B.V.)

    Nanoplastics (NPs) nano-scale effects and have strong mobility, posing potential risks to ecosystems and human health. Therefore, it is of great significance to study the interactions of minerals and NPs in water to understand the migration, transformation, and fate of NPs in the environment. This study investigated the flocculation of NPs on layered double hydroxides (LDHs) in water via heteroaggregation under various conditions such as different Mg/Al ratios of LDHs, calcination temps., coexisting ions, soln. pH, and contact time. We found that the overall reaction achieved high efficiency that almost surpassed 70% and varied with soln. pH. The highest flocculation performance (85.87%) was achieved at a Mg:Al ratio of 3:1, followed by 4:1 and 2:1. Moreover, the highest removal rate (80.85%) of NPs on cLDHs was achieved at calcination temp. of 300°C. The heteroaggregation mechanism, bonding type, and interface reaction of the NPs-LDHs system were analyzed using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, spectroscopy, and microscopy. At short sepn. distance within 5 nm, the total interaction energy was governed by electrostatic repulsion. However, at longer distance, the interparticle forces became dominated by van der Waals and electrostatic attractions, leading to attachment of two types of particles. The NPs could be removed by attachment onto the surface of LDHs without forming other functional groups. However, the calcined LDHs and those prepd. by hydrothermal reactions showed different attachment morphologies under SEM, which revealed the mechanisms of surface attachment and encased pptn. These results provided new insights and theor. support for controlling NPs pollution in surface water, which could reduce the risks of NPs to ecosystems and human health.
28. 28

    Tiwari, E.; Singh, N.; Khandelwal, N.; Monikh, F. A.; Darbha, G. K. Application of Zn/Al layered double hydroxides for the removal of nanoscale plastic debris from aqueous systems. J. Hazard. Mater. 2020, 397, 122769,  DOI: 10.1016/j.jhazmat.2020.122769

    Google Scholar

    28

    Application of Zn/Al layered double hydroxides for the removal of nano-scale plastic debris from aqueous systems

    Tiwari, Ekta; Singh, Nisha; Khandelwal, Nitin; Monikh, Fazel Abdolahpur; Darbha, Gopala Krishna

    Journal of Hazardous Materials (2020), 397 (), 122769CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)

    Nano-scale plastic debris (NPDs) are emerging as potential contaminants as they can be easily ingested by aquatic organisms and carry many pollutants in the environment. This study is aimed to remove NPDs from aq. environment for the first time by using eco-friendly adsorption techniques. Initially, the interaction between NPDs and synthesized Zn-Al layered double hydroxide (LDH) was confirmed by pH titrn. of Zn-Al LDH against NPDs at varying mass ratio (50:1 to 50:7) and FTIR anal. for both before and after 2 h of contact time. Fast removal was obsd. in deionized water and synthetic freshwater with max. sorption capacity (Qmax) of 164.49 mg/g,162.62 mg/g, resp., according to Sips isotherm. Whereas, removal was least in synthetic hard water having a Qmax value of 53 mg/g. For 2 mM concn. of SO42- and PO43-, the adsorption capacity significantly decreased to 2%. The removal efficiency was found 100% at pH 4, while at pH 9, it reached 37% due to increased competitive binding and destabilization of LDH under alk. conditions. The process of sorption was spontaneous in different types of water studied. The study reveals that Zn-Al LDH can be used as potential adsorbent for the removal of NPDs from freshwater systems.
29. 29

    Wu, J. Y.; Liu, J. Y.; Wu, P. X.; Sun, L. Y.; Chen, M. Q.; Shang, Z. B.; Ye, Q. Y.; Zhu, N. W. The heteroaggregation and deposition behavior of nanoplastics on Al₂O₃ in aquatic environments. J. Hazard. Mater. 2022, 435, 128964,  DOI: 10.1016/j.jhazmat.2022.128964

    Google Scholar

    29

    The heteroaggregation and deposition behavior of nanoplastics on Al2O3 in aquatic environments

    Wu, Jiayan; Liu, Jieyu; Wu, Pingxiao; Sun, Leiye; Chen, Meiqing; Shang, Zhongbo; Ye, Quanyun; Zhu, Nengwu

    Journal of Hazardous Materials (2022), 435 (), 128964CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)

    The ubiquitous Al2O3 is anticipated to interact with nanoplastics, affecting their fate and transport in aquatic environments. In this study, the heteroaggregation and deposition behaviors of polystyrene nanoplastics (PSNPs) on Al2O3 were systematically investigated under different conditions (ionic strength, pH, and natural org. matter). The results showed that significant heteroaggregation occurred between PSNPs and Al2O3 particles under acidic and neutral conditions. When the NaCl concn. was increased from 50 to 500 mM, the heteroaggregation ratio gradually increased. However, poly (acrylic acid) (PAA) inhibited the heteroaggregation of PSNPs-Al2O3 due to steric repulsion. The deposition of PSNPs on Al2O3 surfaces was inhibited as the NaCl concn. or pH values increased. Due to charge reversal and steric repulsion, humic acid (HA) and fulvic acid (FA) prevented the deposition of PSNPs onto Al2O3 surfaces, and the former was more effective in reducing the deposition rate. The interaction mechanism between PSNPs and Al2O3 was revealed by using various characterization techniques and d. function theory (DFT) calcn. The results demonstrated that in addn. to the dominant electrostatic interaction, there were also weak hydrogen bonds and van der Waals interactions. Our research is of great significance for predicting the migration and fate of PSNPs in aquatic environments.
30. 30

    Wang, X. X.; Dan, Y. T.; Diao, Y. Z.; Liu, F. H.; Wang, H.; Sang, W. J.; Zhang, Y. L. Transport characteristics of polystyrene microplastics in saturated porous media with biochar/Fe₃O₄-biochar under various chemical conditions. Sci. Total Environ. 2022, 847, 157576,  DOI: 10.1016/j.scitotenv.2022.157576

    Google Scholar

    30

    Transport characteristics of polystyrene microplastics in saturated porous media with biochar/Fe3O4-biochar under various chemical conditions

    Wang, Xiaoxia; Dan, Yitong; Diao, Yinzhu; Liu, Feihong; Wang, Huan; Sang, Wenjing; Zhang, Yalei

    Science of the Total Environment (2022), 847 (), 157576CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)

    Magnetically modified biochar, with a rougher surface and more pos. surface charge, may interact with microplastics (MPs) after being applied to soil, potentially altering the fate and transport of MPs in porous media. In this study, the transport and retention behavior of polystyrene microplastics (PSMPs) in a sandy porous media mixed with biochar/Fe3O4 modified biochar (Fe3O4-biochar) was investigated under various chem. conditions (humic acid (HA), ionic strength (IS) and cationic types (Na+/Ca2+ )). The results showed that the addn. of biochar and Fe3O4-biochar can hinder the transport of PSMPs in porous media without HA, and that Fe3O4-biochar was more effective in inhibiting the transport of PSMPs through electrostatic adsorption and complexation, with an optimum retention efficiency of 92.36%. HA significantly attenuated the retention of PSMPs in both porous media through electrostatic repulsion, steric resistance and competitive adsorption under 1 mM Na+ solns., and the mobility of PSMPs in Fe3O4-biochar/sand was enhanced more significantly than in biochar/sand with the increase of HA concn. IS significantly inhibited the transport of PSMPs in both porous media in the absence of HA, but there was an antagonistic effect of HA and IS on the transport of PSMPs in the presence of HA, with the facilitative effect of HA being stronger than the inhibitory effect of IS. Ca2+ was consistently more effective in inhibiting the transport of PSMPs than Na+ under all test conditions, and HA promoted the transport of PSMPs in all Na+ solns., while it inhibited the transport of PSMPs in high IS (10 mM) with Ca2+ solns. In addn., HA, Fe3O4-biochar and PSMPs tend to form larger aggregates under the complex interactions of Ca2+ , leading to increased retention of PSMPs in porous media. The two-site kinetic retention models suggested that the retention of PSMPs in porous media with biochar was predominantly reversible attachment effect, while retention in porous media with Fe3O4-biochar was predominantly an irreversible straining effect.
31. 31

    Ye, X. Y.; Cheng, Z.; Wu, M.; Hao, Y. R.; Lu, G. P.; Hu, B. X.; Mo, C. H.; Li, Q. S.; Wu, J. F.; Wu, J. C. Effects of clay minerals on the transport of polystyrene nanoplastic in groundwater. Water Res. 2022, 223, 118978,  DOI: 10.1016/j.watres.2022.118978

    Google Scholar

    31

    Effects of clay minerals on the transport of polystyrene nanoplastic in groundwater

    Ye, Xinyao; Cheng, Zhou; Wu, Ming; Hao, Yanru; Lu, Guoping; Hu, Bill X.; Mo, Cehui; Li, Qusheng; Wu, Jianfeng; Wu, Jichun

    Water Research (2022), 223 (), 118978CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)

    Microplastics are widely detected in the soil-groundwater environment, which has attracted more and more attention. Clay mineral is an important component of the porous media contained in aquifers. The transport expts. of polystyrene nanoparticles (PSNPs) in quartz sand (QS) mixed with three kinds of clay minerals are conducted to investigate the effects of kaolinite (KL), montmorillonite (MT) and illite (IL) on the mobility of PSNPs in groundwater. Two-dimensional (2D) distributions of DLVO interaction energy are calcd. to quantify the interactions between PSNPs and three kinds of clay minerals. The crit. ionic strengths (CIS) of PSNPs-KL, PSNPs-MT and PSNPs-IL are 17.0 mM, 19.3 mM and 21.0 mM, resp. Exptl. results suggest KL has the strongest inhibition effect on the mobility of PSNPs, followed by MT and IL. Simultaneously, the change of ionic strength can alter the surface charge of PSNPs and clay minerals, thus affecting the interaction energy. Exptl. and model results indicate both the deposition rate coeff. (k) and max. deposition (Smax) linearly decrease with the logarithm of the DLVO energy barrier, while the mass recovery rate of PSNPs (Rm) exponentially increases with the logarithm of the DLVO energy barrier. Therefore, the mobility and assocd. kinetic parameters of PSNPs in complex porous media contg. clay minerals can be predicted by 2D distributions of DLVO interaction energy. These findings could help to gain insight into understanding the environmental behavior and transport mechanism of microplastics in the multicomponent porous media, and provide a scientific basis for the accurate simulation and prediction of microplastic contamination in the groundwater system.
32. 32

    Bansal, P.; Deshpande, A. P.; Basavaraj, M. G. Hetero-aggregation of oppositely charged nanoparticles. J. Colloid Interface Sci. 2017, 492, 92– 100,  DOI: 10.1016/j.jcis.2016.12.059

    Google Scholar

    32

    Hetero-aggregation of oppositely charged nanoparticles

    Bansal, Pooja; Deshpande, Abhijit P.; Basavaraj, Madivala G.

    Journal of Colloid and Interface Science (2017), 492 (), 92-100CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)

    Hetero-aggregation refers to aggregation of particles that are not identical i.e. particles of different phys.-chem. properties. The study of this phenomenon is important because of the fascinating structures that can be formed and their application in several fields including the synthesis of porous materials and particle stabilized emulsions. The authors report an exptl. study of hetero-aggregation behavior of oppositely charged nanoparticles of similar size. The hetero-aggregation phenomenon is studied using a combination of visual observation, zeta potential measurements, dynamic light scattering, SEM and rheol. measurements. The authors report details of aggregate size, structure, flow properties to provide understanding of hetero-aggregation by a careful examn. of different phases formed upon mixing oppositely charged particles. The expts. were carried out at different mixing fraction (defined as the mass of pos. particle in the dispersion divided by total mass of particles in the dispersion) varying from 0 to 1 with total concn. of particles ranging from 0.05 to 30% (0.023-13.82 vol.%). At low total particle concn., 4 different states of the mixt. were obsd. which includes sediment with turbid supernatant, sediment with clear supernatant, turbid sample with no sediment and a clear dispersion. However, at higher concn. ⪆7.5% (3.45 vol.%), the mixt. of oppositely charged particles form - a particulate gel with turbid supernatant at low mixing fraction (from 0.1 to 0.3), a solid-like gel at intermediate mixing fraction (from ∼0.3 to 0.7) and a turbid sample at high mixing fractions from 0.7 to 1.0.
33. 33

    Madhavan, N.; Deshpande, A. P.; Mani, E.; Basavaraj, M. G. Electrostatic heteroaggregation: fundamentals and applications in interfacial engineering. Langmuir 2023, 39, 2112– 2134,  DOI: 10.1021/acs.langmuir.2c02681

    Google Scholar

    33

    Electrostatic Heteroaggregation: Fundamentals and Applications in Interfacial Engineering

    Madhavan, Nithin; Deshpande, Abhijit P.; Mani, Ethayaraja; Basavaraj, Madivala G.

    Langmuir (2023), 39 (6), 2112-2134CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    A review. The aggregation of oppositely charged soft materials (particles, surfactants, polyelectrolytes, etc.) that differ in one or more phys. or chem. attributes, broadly referred to as electrostatic heteroaggregation, has been an active area of research for several decades now. While electrostatic heteroaggregation (EHA) is relevant to diverse fields such as environmental engineering, food technol., and pharmaceutical formulations, more recently there has been a resurgence to explore various aspects of this phenomenon in the context of interface stabilization and the development of functional materials. In this Feature Article, we provide an overview of the recent contributions of our group to this exciting field with particular emphasis on fundamental studies of electrostatic heteroaggregation between oppositely charged systems in the bulk, at interfaces, and across the bulk/interface. The influence of the size and shape of particles and the surface charge of heteroaggregates on the formation of Pickering emulsions and their utilization in the development of porous ceramics is discussed.
34. 34

    Zhang, Y. Y.; Luo, Y. Y.; Guo, X. T.; Xia, T. J.; Wang, T. C.; Jia, H. Z.; Zhu, L. Y. Charge mediated interaction of polystyrene nanoplastic (PSNP) with minerals in aqueous phase. Water Res. 2020, 178, 115861,  DOI: 10.1016/j.watres.2020.115861

    Google Scholar

    34

    Charge mediated interaction of polystyrene nanoplastic (PSNP) with minerals in aqueous phase

    Zhang, Yangyang; Luo, Yuanyuan; Guo, Xuetao; Xia, Tianjiao; Wang, Tiecheng; Jia, Hanzhong; Zhu, Lingyan

    Water Research (2020), 178 (), 115861CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)

    A large no. of plastic products potentially become smaller particles, including nanoplastics, under multiple actions in the environment. The interactions between nanoplastic particles and constituents in the environment, such as minerals, would greatly affect the transport, fate and toxic effects of nanoplastics. In this study, the interactions of polystyrene nanoplastic (PSNP) with four typical minerals, including goethite, magnetite, kaolinite and montmorillonite, in aq. phase were investigated. The stability of PSNP colloidal suspension decreased in the presence of the pos. charged goethite or magnetite, while it was not affected by the neg. charged montmorillonite and kaolinite, suggesting that there was a strong electrostatic attraction between PSNP and the two iron oxides. Incubation of PSNP with other three metal oxides with different surface charges, MnO2, Al2O3 and SiO2, confirmed the importance of electrostatic interaction in the stability of PSNP suspension. The transmission electron microscopy (TEM) anal. and batch adsorption expts. indicated that PSNP was effectively adsorbed on goethite or magnetite due to the strong electrostatic attraction between them. These findings shed light on the interactions of PSNP with mineral surfaces, and potential fate of PSNP under natural conditions in the water environment.
35. 35

    Lin, W.; Kobayashi, M.; Skarba, M.; Mu, C.; Galletto, P.; Borkovec, M. Heteroaggregation in binary mixtures of oppositely charged colloidal particles. Langmuir 2006, 22, 1038– 1047,  DOI: 10.1021/la0522808

    Google Scholar

    35

    Heteroaggregation in Binary Mixtures of Oppositely Charged Colloidal Particles

    Lin, Wei; Kobayashi, Motoyoshi; Skarba, Michal; Mu, Changdao; Galletto, Paolo; Borkovec, Michal

    Langmuir (2006), 22 (3), 1038-1047CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    Heteroaggregation (or heterocoagulation) rate consts. were measured in mixts. of well-characterized colloidal particles of opposite charge with multiangle static and dynamic light scattering. This technique permits routine measurements of abs. heteroaggregation rate consts., also in the presence of homoaggregation. Particularly with multiangle dynamic light scattering, one is able to est. abs. heteroaggregation rate consts. accurately in the fast aggregation regime for the 1st time. Heteroaggregation rate consts. also were measured over a wide range of parameters, for example, ionic strength and different surface charge densities. Amidine latex particles, sulfate latex particles, and silica particles were used for these expts., and they were well characterized with respect to their charging and homoaggregation behavior. Heteroaggregation rate consts. of oppositely charged particles increase slowly with decreasing ionic strength, and provided the surface charge is sufficiently large, the rate const. is largely independent of the surface charge. These trends can be well described with DLVO theory without adjustable parameters.
36. 36

    Cao, T. C.; Sugimoto, T.; Szilagyi, I.; Trefalt, G.; Borkovec, M. Heteroaggregation of oppositely charged particles in the presence of multivalent ions. Phys. Chem. Chem. Phys. 2017, 19, 15160– 15171,  DOI: 10.1039/C7CP01955F

    Google Scholar

    36

    Heteroaggregation of oppositely charged particles in the presence of multivalent ions

    Cao, Tianchi; Sugimoto, Takuya; Szilagyi, Istvan; Trefalt, Gregor; Borkovec, Michal

    Physical Chemistry Chemical Physics (2017), 19 (23), 15160-15171CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)

    Time-resolved dynamic light scattering is used to measure abs. heteroaggregation rate coeffs. and the corresponding stability ratios for heteroaggregation between amidine and sulfate latex particles. These measurements are complemented by the resp. quantities for the homoaggregation of the two systems and electrophoresis. Based on the latter measurements, the stability ratios are calcd. using Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. In monovalent salt solns., the two types of particles investigated are oppositely charged. In the presence of multivalent ions, however, one particle type reverses its charge, while the charge of the other particle type is hardly affected. In this region, the heteroaggregation stability ratio goes through a pronounced max. when plotted vs. concn. This region of slow aggregation is wider than the one obsd. in the corresponding homoaggregation process. One also finds that the onset of this region sensitively depends on the boundary conditions used to calc. the double layer force. The present results are more in line with const. potential boundary conditions.
37. 37

    Zhang, X. T.; Chen, Y. X.; Li, X. Y.; Zhang, Y. L.; Gao, W.; Jiang, J.; Mo, A. Y.; He, D. F. Size/shape-dependent migration of microplastics in agricultural soil under simulative and natural rainfall. Sci. Total Environ. 2022, 815, 152507,  DOI: 10.1016/j.scitotenv.2021.152507

    Google Scholar

    37

    Size/shape-dependent migration of microplastics in agricultural soil under simulative and natural rainfall

    Zhang, Xiaoting; Chen, Yingxin; Li, Xinyu; Zhang, Yalin; Gao, Wei; Jiang, Jie; Mo, Aoyun; He, Defu

    Science of the Total Environment (2022), 815 (), 152507CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)

    Agricultural soil is a sink of microplastics (MPs) in the environment. MPs in topsoil can be transferred deeply or into surrounding water by rainfall. However, little is known about rainfall-induced migration pattern of different MPs in agricultural soil. In this study, soil leaching expts. of 21 d were performed on Nile red-stained size-different polyethylene terephthalate (PET) particles, and shape-different polyethylene (PE) MPs under simulated or natural rainfall. Results showed that simulated rainfall of 5-25 mm/d caused intensity-dependent migration of MPs in horizontal and vertical directions. Maximum migration depth of MP particles arrived up to 4-7 cm. Rise of soil slopes could significantly increase horizontal mobility of MPs. Comparatively, natural rainfall of similar intensity caused relatively high mobility of MPs. Moreover, under both simulative and natural rainfall, mobility of MPs presented size/shape-different characteristics. Comparatively, small-size MPs (esp. <1 mm) showed relatively high mobility in horizontal or vertical direction, and had high-frequency presence in runoff water. Of four MPs' shapes, fiber and film had relatively high mobility in comparison to particles. These results indicate that rainfall can cause size/shape-dependent migration of MPs in agricultural soil. It suggests size/shape-different environment fate of MPs, and provides a ref. for MP control.
38. 38

    Wang, L. W.; Wu, W. M.; Bolan, N. S.; Tsang, D. C. W.; Li, Y.; Qin, M. H.; Hou, D. Y. Environmental fate, toxicity and risk management strategies of nanoplastics in the environment: Current status and future perspectives. J. Hazard. Mater. 2021, 401, 123415,  DOI: 10.1016/j.jhazmat.2020.123415

    Google Scholar

    38

    Environmental fate, toxicity and risk management strategies of nanoplastics in the environment: Current status and future perspectives

    Wang, Liuwei; Wu, Wei-Min; Bolan, Nanthi S.; Tsang, Daniel C. W.; Li, Yang; Qin, Muhan; Hou, Deyi

    Journal of Hazardous Materials (2021), 401 (), 123415CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)

    A review. Tiny plastic particles considered as emerging contaminants have attracted considerable interest in the last few years. Mech. abrasion, photochem. oxidn. and biol. degrdn. of larger plastic debris result in the formation of microplastics (MPs, 1μm to 5 mm) and nanoplastics (NPs, 1 nm to 1000 nm). Compared with MPs, the environmental fate, ecosystem toxicity and potential risks assocd. with NPs have so far been less explored. This review provides a state-of-the-art overview of current research on NPs with focus on currently less-investigated fields, such as the environmental fate in agroecosystems, migration in porous media, weathering, and toxic effects on plants. The co-transport of NPs with org. contaminants and heavy metals threaten human health and ecosystems. Furthermore, NPs may serve as a novel habitat for microbial colonization, and may act as carriers for pathogens (i.e., bacteria and viruses). An integrated framework is proposed to better understand the interrelationships between NPs, ecosystems and the human society. In order to fully understand the sources and sinks of NPs, more studies should focus on the total environment, including freshwater, ocean, groundwater, soil and air, and more attempts should be made to explore the aging and aggregation of NPs in environmentally relevant conditions. Considering the fact that naturally-weathered plastic debris may have distinct physicochem. characteristics, future studies should explore the environmental behavior of naturally-aged NPs rather than synthetic polystyrene nanobeads.
39. 39

    Wang, Q.; O’Hare, D. Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets. Chem. Rev. 2012, 112, 4124– 4155,  DOI: 10.1021/cr200434v

    Google Scholar

    39

    Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets

    Wang, Qiang; O'Hare, Dermot

    Chemical Reviews (Washington, DC, United States) (2012), 112 (7), 4124-4155CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    In this review, it was attempted to summarize the current methods that were developed for the prepn. of dispersed LDH nanosheets. In general, these methods can be divided into two general strategies. The "bottom-up" method tries to control the nucleation and growth conditions in such a way as to only allow the formation of dispersed nanosheets. To date, this is best achieved using an oil-water inverse micelle/microemulsion scheme. The more developed method and perhaps the easiest to scale up to com. relevant quantities is to develop suitably modified LDHs systems in which solvation forces enable the delamination of the LDHs to be thermodynamically favorable. However, the best systems tend to use highly polar solvents which makes it almost impossible to recover the nanosheets in bulk form. New and exciting applications for these materials are emerging all the time. Reviewed is the current literature in the areas of polymer/LDH nanocomposites, core-shell LDH materials, LDH thin films, nanodispersed LDH catalysts, LDH electrode materials, LDH hybrid magnets, and bioinorg. hybrid materials. Nanodispersed clay-based materials currently dominate the nanocomposite field, however it is anticipated that the use of LDH materials will rapid accelerate to catch up as new and cost-effective methods of prepg. stable LDHs dispersion are developed.
40. 40

    Takács, D.; Katana, B.; Szerlauth, A.; Sebők, D.; Tomšič, M.; Szilagyi, I. Influence of adsorption of ionic liquid constituents on the stability of layered double hydroxide colloids. Soft Matter 2021, 17, 9116– 9124,  DOI: 10.1039/D1SM01074C

    Google Scholar

    40

    Influence of adsorption of ionic liquid constituents on the stability of layered double hydroxide colloids

    Takacs, Dora; Katana, Bojana; Szerlauth, Adel; Sebok, Daniel; Tomsic, Matija; Szilagyi, Istvan

    Soft Matter (2021), 17 (40), 9116-9124CODEN: SMOABF; ISSN:1744-6848. (Royal Society of Chemistry)

    The influence of ionic liq. (IL) anions and cations on the charging and aggregation properties of layered double hydroxide (LDH) nanoparticles was systematically studied. Surface charge characteristics were explored using zeta potential measurements, while aggregation processes were followed in dynamic light scattering expts. in aq. IL solns. The results revealed that the aggregation rates of LDHs were sensitive to the compn. of ILs leading to IL-dependent crit. coagulation concn. (CCC) values being obtained. The origin of the interparticle forces was found to be electrostatic, in line with the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, as the exptl. aggregation kinetics were in good agreement with the predicted data. The ion specific adsorption of IL anions led to different surface charge densities for LDHs, which decreased in the order Cl- > Br- > DCA- > SCN- > NO3- for counterions and BMIM+ > BMPYR+ > BMPY+ > BMPIP+ in the case of coions resulting in weaker elec. double layer repulsion in these sequences. Since van der Waals forces are always present and their strength does not depend significantly on the ionic strength, the CCC values decreased in the above order. The present results shed light on the importance of the interfacial arrangement of the IL constituent ions on the colloidal stability of particle dispersions and provide important information on the design of stable or unstable particle-ionic liq. systems.
41. 41

    Li, L.; Gu, Z.; Gu, W. Y.; Xu, Z. P. Direct synthesis of layered double hydroxide nanosheets for efficient siRNA delivery. RSC Adv. 2016, 6, 95518– 95526,  DOI: 10.1039/C6RA19225D

    Google Scholar

    41

    Direct synthesis of layered double hydroxide nanosheets for efficient siRNA delivery

    Li, L.; Gu, Z.; Gu, W. Y.; Xu, Z. P.

    RSC Advances (2016), 6 (98), 95518-95526CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)

    In this paper, we have developed a simple yet efficient method to prep. stable single-sheet MgAl-layered double hydroxide (MA-NS) suspensions without using org. solvents or surfactants. This green approach involves a fast co-pptn. with hydrothermal treatment. The av. hydrodynamic diam. of mono-disperse fully-delaminated LDH nanosheets can be precisely tailored in the range of 25-300 nm. The reproducibility of making identical suspensions under identical conditions has been confirmed and the method has also been successfully applied to prep. stable and single-layered LDH nanosheet suspensions contg. various transition metal ions such as Ni2+, Fe2+, Fe3+ and Co2+ in the single hydroxide layer. MgAl-LDH nanosheets (MA-NSs) with various sizes do not exhibit any acute cytotoxicity at concns. up to 400 μg mL-1 as assayed by MTT. The cellular uptake and cell viability data have demonstrated MA-NSs can efficiently load and deliver small interfering RNA (siRNA) into osteosarcoma (U2OS) cancer cells, and significantly inhibit their growth. Thus, MA-NSs have great potential as an effective cellular delivery system for siRNA therapy, in addn. to their conventional applications in coatings, catalysis, composites and adsorption.
42. 42

    Delgado, A. V.; Gonzalez-Caballero, F.; Hunter, R. J.; Koopal, L. K.; Lyklema, J. Measurement and interpretation of electrokinetic phenomena. J. Colloid Interface Sci. 2007, 309, 194– 224,  DOI: 10.1016/j.jcis.2006.12.075

    Google Scholar

    42

    Measurement and interpretation of electrokinetic phenomena

    Delgado, A. V.; Gonzalez-Caballero, F.; Hunter, R. J.; Koopal, L. K.; Lyklema, J.

    Journal of Colloid and Interface Science (2007), 309 (2), 194-224CODEN: JCISA5; ISSN:0021-9797. (Elsevier)

    A review. The status quo and recent progress in electrokinetics are reviewed. Practical rules are recommended for performing electrokinetic measurements and interpreting their results in terms of well-defined quantities, the most familiar being the ζ-potential or electrokinetic potential. This potential is a property of charged interfaces and it should be independent of the technique used for its detn. However, often the ζ-potential is not the only property electrokinetically characterizing the elec. state of the interfacial region; the excess cond. of the stagnant layer is an addnl. parameter. The requirement to obtain the ζ-potential is that electrokinetic theories be correctly used and applied within their range of validity. Basic theories and their application ranges are discussed. A thorough description of the main electrokinetic methods is given; special attention is paid to their ranges of applicability as well as to the validity of the underlying theor. models. Electrokinetic consistency tests are proposed to assess the validity of the ζ-potentials obtained. The recommendations given in the report apply mainly to smooth and homogeneous solid particles and plugs in aq. systems; some attention is paid to nonaq. media and less ideal surfaces.
43. 43

    Russel, W. B.; Saville, D. A.; Schowalter, W. R. Colloidal dispersions; Cambridge University Press: Cambridge, 1989; pp 88– 123. DOI: 10.1017/CBO9780511608810.007 .

    Google Scholar

    There is no corresponding record for this reference.
44. 44

    Holthoff, H.; Egelhaaf, S. U.; Borkovec, M.; Schurtenberger, P.; Sticher, H. Coagulation rate measurements of colloidal particles by simultaneous static and dynamic light scattering. Langmuir 1996, 12, 5541– 5549,  DOI: 10.1021/la960326e

    Google Scholar

    44

    Coagulation Rate Measurements of Colloidal Particles by Simultaneous Static and Dynamic Light Scattering

    Holthoff, Helmut; Egelhaaf, Stefan U.; Borkovec, Michal; Schurtenberger, Peter; Sticher, Hans

    Langmuir (1996), 12 (23), 5541-5549CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    The kinetics of coagulation of monodisperse spherical colloids in aq. suspensions were studied at the early stage of coagulation. The measurements were performed with a multiangle static and dynamic light scattering instrument using a fiber-optics-based detection system which permits simultaneous time-resolved measurements at different angles. The abs. coagulation rate consts. are detd. from the change of the scattering light intensity as well as from the increase of the hydrodynamic radius at different angles. The combined evaluation of static and dynamic light scattering results permits the detn. of coagulation rate consts. without the explicit use of light scattering form factors for the aggregates. Fast coagulation rate consts. were estd for various electrolytes. Stability curves were measured as a function of ionic strength by using different particle concns.
45. 45

    Hassan, P. A.; Rana, S.; Verma, G. Making sense of Brownian motion: Colloid characterization by dynamic light scattering. Langmuir 2015, 31, 3– 12,  DOI: 10.1021/la501789z

    Google Scholar

    45

    Making Sense of Brownian Motion: Colloid Characterization by Dynamic Light Scattering

    Hassan, Puthusserickal A.; Rana, Suman; Verma, Gunjan

    Langmuir (2015), 31 (1), 3-12CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    A review. Dynamic light scattering (DLS) has evolved as a fast, convenient tool for particle size anal. of noninteracting spherical colloids. In this historical review, the basic principle, data anal., and important precautions to be taken while analyzing colloids using DLS are discussed. The effect of particle interaction, polydispersity, anisotropy, light absorption, and so forth, on measured diffusion coeff. is discussed. New developments in this area such as diffusing wave spectroscopy, particle tracking anal., microrheol. studies using DLS, and so forth, are discussed in a manner that can be understood by a beginner.
46. 46

    Grolimund, D.; Elimelech, M.; Borkovec, M. Aggregation and deposition kinetics of mobile colloidal particles in natural porous media. Colloids Surf., A 2001, 191, 179– 188,  DOI: 10.1016/S0927-7757(01)00773-7

    Google Scholar

    46

    Aggregation and deposition kinetics of mobile colloidal particles in natural porous media

    Grolimund, D.; Elimelech, M.; Borkovec, M.

    Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2001), 191 (1-2), 179-188CODEN: CPEAEH; ISSN:0927-7757. (Elsevier Science B.V.)

    A novel method for assessing the deposition kinetics of colloidal particles in natural porous media is presented. The method is applied for studying the deposition kinetics of in situ mobilized colloidal particles in a non-calcareous soil in mixed electrolytes contg. Na and Ca as counterions. Particle deposition rate consts. were measured by combining deposition expts. in packed columns and aggregation measurements by dynamic light scattering. The relative deposition and aggregation rate consts. follow very similar trends, featuring fast (favorable) and slow (unfavorable) regimes at high and low salt concns., resp. These regimes are sepd. by the crit. coagulation or deposition concns. (CCC or CDC, resp.), which sensitively depend on the type of counterion. In systems contg. a single electrolyte, the CCC and CDC follow the classical Schulze-Hardy rule. In mixed Na-Ca electrolytes, a gradual transition of the CCC and CDC between the values obtained for the corresponding pure (single) electrolyte systems is obsd. The present approach provides a facile route for assessing deposition rates of mobile colloidal particles in natural porous media.
47. 47

    Glatter, O. Data treatment. In Small angle x-ray scattering; Glatter, O., Kratky, O., Eds.; Academic Press Inc.: London, 1982; pp 119– 165.

    Google Scholar

    There is no corresponding record for this reference.
48. 48

    Orthaber, D.; Bergmann, A.; Glatter, O. SAXS experiments on absolute scale with Kratky systems using water as a secondary standard. J. Appl. Crystallogr. 2000, 33, 218– 225,  DOI: 10.1107/S0021889899015216

    Google Scholar

    48

    SAXS experiments on absolute scale with Kratky systems using water as a secondary standard

    Orthaber, Doris; Bergmann, Alexander; Glatter, Otto

    Journal of Applied Crystallography (2000), 33 (2), 218-225CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)

    For small-angle scattering, of x-rays (SAXS) and neutrons (SANS), the importance of abs. calibration was recognized since the inception of the technique. The work reported here focuses on SAXS measurements using Kratky slit systems. In former days, only mol. wts. or scattering per particle were detd., but today abs. calibration implies the use of the unit of cm-1 for the scattering curve. It is necessary to measure the so-called abs. intensity, which is the ratio of the scattering intensity to the primary intensity P0. Basically there are 2 possible ways to det. the abs. intensity. The 1st 1 is the direct method, which involves the mech. attenuation of the primary beam by a rotating disk or a moving slit. The 2nd is the indirect method, using secondary stds. H2O is well suited as a calibration std. because of the angle-independent scattering. The essential advantage is that the scattering of H2O only depends on the phys. property of isothermal compressibility. Before presenting an example of the practical performance of this method, the most important theor. equations for an SAS expt. on the abs. scale are summarized. With the slit collimation system, the scattering curve of H2O can be measured with high enough statistical accuracy. As a 1st example, the scattering curve of the protein lysozyme on the abs. scale is presented. The 2nd example is the detn. of the aggregation no. of a triblock copolymer P94 (EO17-PO42-EO17). Taking into account that at least 10% of the polymer sample consists of diblocks, the accuracy of ∼10% for the detd. aggregation no. is rather good. The data of P94 are considered on the particle scale to obtain the radial scattering-length d. distribution.
49. 49

    Derjaguin, B.; Landau, L. Theory of the stability of strongly charged lyophobic sols and of the adhesion of strongly charged particles in solutions of electrolytes. Prog. Surf. Sci. 1993, 43, 30– 59,  DOI: 10.1016/0079-6816(93)90013-L

    Google Scholar

    There is no corresponding record for this reference.
50. 50

    Behrens, S. H.; Borkovec, M.; Schurtenberger, P. Aggregation in charge-stabilized colloidal suspensions revisited. Langmuir 1998, 14, 1951– 1954,  DOI: 10.1021/la971237k

    Google Scholar

    50

    Aggregation in Charge-stabilized Colloidal Suspensions Revisited

    Behrens, S. H.; Borkovec, M.; Schurtenberger, P.

    Langmuir (1998), 14 (8), 1951-1954CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory commonly used to describe interactions of charged surfaces across liqs. has traditionally been reported to fail when used for quant. predictions of deposition and aggregation in aq. colloidal suspensions. Yet direct force measurements have recently confirmed the theory down to surface sepns. of a few nanometers. Aggregation studies on latex and hematite colloids now reconcile these contrasting findings. Well-known discrepancies between theory and expt. with respect to the dependence of aggregation rates on pH (or electrolyte concn.) and particle size are shown to disappear when charge densities are reduced.
51. 51

    Cao, T. C.; Elimelech, M. Colloidal stability of cellulose nanocrystals in aqueous solutions containing monovalent, divalent, and trivalent inorganic salts. J. Colloid Interface Sci. 2021, 584, 456– 463,  DOI: 10.1016/j.jcis.2020.09.117

    Google Scholar

    51

    Colloidal stability of cellulose nanocrystals in aqueous solutions containing monovalent, divalent, and trivalent inorganic salts

    Cao, Tianchi; Elimelech, Menachem

    Journal of Colloid and Interface Science (2021), 584 (), 456-463CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)

    Aggregation kinetics and surface charging properties of rod-like sulfated cellulose nanocrystals (CNCs) have been investigated in aq. suspensions contg. monovalent, divalent, or trivalent inorg. salts. Electrophoresis and time-resolved dynamic light scattering (DLS) were used to characterize the surface charge and colloidal stability of the CNCs, resp. The surface charge and aggregation kinetics of the sulfated CNCs were found to be independent of soln. pH (pH range 2-10). For the monovalent salts (CsCl, KCl, NaCl, and LiCl), the crit. coagulation concn. (CCC) followed the order of Cs+ < K+ < Na+ < Li+, which follows the direct Hofmeister series, indicating specific interaction of the cations with the CNCs surface. The exptl. aggregation kinetics of CNCs were in very good agreement with predictions based on the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. A Hamaker const. of 3.6 x 10-20 J for the CNCs in aq. medium was derived, for the first time, from the colloidal stability curves with monovalent salts. This value is consistent with a previous value detd. by direct force measurements for cellulose surfaces in aq. solns. For the divalent salts (MgCl2, CaCl2, and BaCl2), the CCC values followed the order Mg2+ > Ca2+ > Ba2+, which is in the reverse order of the counterion ionic size. For the trivalent salts (LaCl3, AlCl3, and FeCl3), the CNCs suspension was destabilized much more effectively. The obsd. complex stability curves with AlCl3 and FeCl3 are attributed to charge neutralization and charge reversal imparted by the adsorption of aluminum and ferric hydrolysis species on the CNC surface. The significant charge reversal induced by the ferric hydrolysis species led to the restabilization of suspensions. Our results on the colloidal stability of CNCs are of central importance to the nanotechnol. and materials science communities working on various applications of CNCs.
52. 52

    Trefalt, G.; Szilagyi, I.; Borkovec, M. Schulze-Hardy rule revisited. Colloid Polym. Sci. 2020, 298, 961– 967,  DOI: 10.1007/s00396-020-04665-w

    Google Scholar

    52

    Schulze-Hardy rule revisited

    Trefalt, Gregor; Szilagyi, Istvan; Borkovec, Michal

    Colloid and Polymer Science (2020), 298 (8), 961-967CODEN: CPMSB6; ISSN:0303-402X. (Springer)

    A review. The classical Schulze-Hardy rule suggests that the crit. coagulation concn. (CCC) decreases as the inverse 6th power of the counterion valence. While this dependence can be derived from the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), this derivation relies on unrealistic assumptions. In particular, one cannot assume that the electrolytes are sym., since one normally works with the better sol. asym. electrolytes. For such electrolytes, however, it is essential to distinguish between multivalent counterions and coions. For multivalent counterions, one must consider their strong tendency towards adsorption to the oppositely charged substrates, which leads to low charge densities. In this situation, the CCC increases with the surface charge d., inducing the strong decrease of the CCC with valence. For multivalent coions, the substrates are typically highly charged. In this case, the CCC decreases with increasing ionic valence and is in fact inversely proportional to the valence. This dependence is referred to as the inverse Schulze-Hardy rule.
53. 53

    Trefalt, G. Derivation of the inverse Schulze-Hardy rule. Phys. Rev. E 2016, 93, 032612,  DOI: 10.1103/PhysRevE.93.032612

    Google Scholar

    53

    Derivation of the inverse Schulze-Hardy rule

    Trefalt, Gregor

    Physical Review E (2016), 93 (3-B), 032612/1-032612/5CODEN: PREHBM; ISSN:2470-0045. (American Physical Society)

    The inverse Schulze-Hardy rule was recently proposed based on exptl. observations. This rule describes an interesting situation of the aggregation of charged colloidal particles in the presence of the multivalent coions. Specifically, it can be shown that the crit. coagulation concn. is inversely proportional to the coion valence. Here the derivation of the inverse Schulze-Hardy rule based on purely theor. grounds is presented. This derivation complements the classical Schulze-Hardy rule, which describes the multivalent counterion systems.
54. 54

    Yu, W. Y.; Du, N.; Gu, Y. T.; Yan, J. G.; Hou, W. G. Specific ion effects on the colloidal stability of layered double hydroxide single-layer nanosheets. Langmuir 2020, 36, 6557– 6568,  DOI: 10.1021/acs.langmuir.0c01089

    Google Scholar

    54

    Specific Ion Effects on the Colloidal Stability of Layered Double Hydroxide Single-layer Nanosheets

    Yu, Weiyan; Du, Na; Gu, Yongtao; Yan, Jingen; Hou, Wanguo

    Langmuir (2020), 36 (23), 6557-6568CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    The surface charge properties and aggregation behavior of pos. charged Mg-Al-NO3 layered double hydroxide (LDH) single-layer nanosheets dispersed in water were investigated in the presence of K+ salts with different mono-, di-, and trivalent anions, using electrophoresis and dynamic light scattering techniques. An increase in the salt concn. can significantly decrease the effective surface charge d. (σeff) of LDHs, leading to the aggregation of nanosheets. The crit. coagulation concn. (CCC) or ionic strength (CCIS) of salts for nanosheets significantly decreases with an increase in the valence of anions. Specific ion effects, with a partially reverse Hofmeister series, are obsd. On the basis of the Stern model and the DLVO theory, the relationship of CCC with σeff and the ionic valences of salts (zi) is theor. analyzed, which can accurately describe the dependence of CCC on the σeff and zi but cannot explain the origin of specific ion effects. To explore the origin of specific ion effects, a correlation between CCIS and the specific adsorption energy (Esc) of anions within the Stern layer is developed. Esp., an empirical relationship of Esc with the characteristic phys. parameters of anions is proposed. Our model can accurately predict the CCISs of at least monovalent anions and divalent anions (CO32- and SO42-), demonstrating that the specific ion effects obsd. can be attributed to the differences in ionic size, polarizability, and hydration free energy (or the formation capacity of anion-cation pairs) of different anions. This work not only deepens the understanding of specific ion effects on the colloidal stability but also provides useful information for the potential applications of LDH single-layer nanosheets.
55. 55

    Elzbieciak-Wodka, M.; Popescu, M. N.; Ruiz-Cabello, F. J. M.; Trefalt, G.; Maroni, P.; Borkovec, M. Measurements of dispersion forces between colloidal latex particles with the atomic force microscope and comparison with Lifshitz theory. J. Chem. Phys. 2014, 140, 104906,  DOI: 10.1063/1.4867541

    Google Scholar

    55

    Measurements of dispersion forces between colloidal latex particles with the atomic force microscope and comparison with Lifshitz theory

    Elzbieciak-Wodka, Magdalena; Popescu, Mihail N.; Ruiz-Cabello, F. Javier Montes; Trefalt, Gregor; Maroni, Plinio; Borkovec, Michal

    Journal of Chemical Physics (2014), 140 (10), 104906/1-104906/11CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)

    Interaction forces between carboxylate colloidal latex particles of about 2 μm in diam. immersed in aq. solns. of monovalent salts were measured with the colloidal probe technique, which is based on the at. force microscope. We have systematically varied the ionic strength, the type of salt, and also the surface charge densities of the particles through changes in the soln. pH. Based on these measurements, we have accurately measured the dispersion forces acting between the particles and estd. the apparent Hamaker const. to be (2.0 ± 0.5) × 10-21 J at a sepn. distance of about 10 nm. This value is basically independent of the salt concn. and the type of salt. Good agreement with Lifshitz theory is found when roughness effects are taken into account. The combination of retardation and roughness effects reduces the value of the apparent Hamaker const. and its ionic strength dependence with respect to the case of ideally smooth surfaces. (c) 2014 American Institute of Physics.
56. 56

    Evans, D. G.; Slade, R. C. T. Structural aspects of layered double hydroxides. In Layered Double Hydroxides; Duan, X., Evans, D. G., Eds.; Springer, 2006; Vol. 119, pp 1– 87.

    Google Scholar

    There is no corresponding record for this reference.
57. 57

    Pavlovic, M.; Huber, R.; Adok-Sipiczki, M.; Nardin, C.; Szilagyi, I. Ion specific effects on the stability of layered double hydroxide colloids. Soft Matter 2016, 12, 4024– 4033,  DOI: 10.1039/C5SM03023D

    Google Scholar

    57

    Ion specific effects on the stability of layered double hydroxide colloids

    Pavlovic, Marko; Huber, Robin; Adok-Sipiczki, Monika; Nardin, Corinne; Szilagyi, Istvan

    Soft Matter (2016), 12 (17), 4024-4033CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)

    Pos. charged layered double hydroxide particles composed of Mg2+ and Al3+ layer-forming cations and NO3- charge compensating anions (MgAl-NO3-LDH) were synthesized and the colloidal stability of their aq. suspensions was investigated in the presence of inorg. anions of different charges. The formation of the layered structure was confirmed by X-ray diffraction, while the charging and aggregation properties were explored by electrophoresis and light scattering. The monovalent anions adsorb on the oppositely charged surface to a different extent according to their hydration state leading to the Cl- > NO3- > SCN- > HCO3- order in surface charge densities. The ions on the right side of the series induce the aggregation of MgAl-NO3-LDH particles at lower concns., whereas in the presence of the left ones, the suspensions are stable even at higher salt levels. The adsorption of multivalent anions gave rise to charge neutralization and charge reversal at appropriate concns. For some di, tri and tetravalent ions, charge reversal resulted in restabilization of the suspensions in the intermediate salt concn. regime. Stable samples were also obsd. at low salt levels. Particle aggregation was fast near the charge neutralization point and at high concns. These results, which evidence the colloidal stability of MgAl-NO3-LDH in the presence of various anions, are of prime fundamental interest. These are also crit. for applications to develop stable suspensions of primary particles for water purifn. processes, with the aim of the removal of similar anions by ion exchange.
58. 58

    Pavlovic, M.; Rouster, P.; Oncsik, T.; Szilagyi, I. Tuning colloidal stability of layered double hydroxides: from monovalent ions to polyelectrolytes. ChemPlusChem 2017, 82, 121– 131,  DOI: 10.1002/cplu.201600295

    Google Scholar

    58

    Tuning Colloidal Stability of Layered Double Hydroxides: From Monovalent Ions to Polyelectrolytes

    Pavlovic, Marko; Rouster, Paul; Oncsik, Tamas; Szilagyi, Istvan

    ChemPlusChem (2017), 82 (1), 121-131CODEN: CHEMM5; ISSN:2192-6506. (Wiley-VCH Verlag GmbH & Co. KGaA)

    The growing no. of applications of layered double hydroxide (LDH) colloids demands for detailed understanding of particle aggregation processes in such samples. Tuning the colloidal stability in aq. suspensions is essential to design stable systems or to induce controlled aggregation of these elongated particles. In this review, recent progress in this field is summarized; in particular, the charging and aggregation of LDHs of various compns. and sizes in the presence of different aggregating agents are discussed. The review focuses on the effect of monovalent salts, multivalent ions, and polyelectrolytes on the suspension stability of LDHs. The provided information will help to better understand the origin of interparticle forces responsible for the colloidal stability and to design highly stable or aggregating LDH colloids according to the desired goals in certain applications. Moreover, potential future research directions to obtain a broader picture of LDH aggregation are also suggested.
59. 59

    Borkovec, M.; Papastavrou, G. Interactions between solid surfaces with adsorbed polyelectrolytes of opposite charge. Curr. Opin. Colloid Interface Sci. 2008, 13, 429– 437,  DOI: 10.1016/j.cocis.2008.02.006

    Google Scholar

    59

    Interactions between solid surfaces with adsorbed polyelectrolytes of opposite charge

    Borkovec, Michal; Papastavrou, Georg

    Current Opinion in Colloid & Interface Science (2008), 13 (6), 429-437CODEN: COCSFL; ISSN:1359-0294. (Elsevier B.V.)

    A review. Adsorption of polyelectrolytes to surfaces of opposite charge typically leads to charge neutralization and subsequent charge reversal. As can be shown by direct force measurements and stability studies, the interaction forces are dominated by repulsive forces originating from diffuse layer overlap and attractive van der Waals forces, in line with the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). Recently, the existence of an addnl. attractive non-DLVO force was demonstrated, and its likely origin is the attraction between patch-charge heterogeneities. With novel single mol. pulling expts. with the at. force microscope (AFM) polymer bridging forces could be shown to represent the most important contribution to the adhesion of surfaces coated by polyelectrolytes.
60. 60

    Gillies, G.; Lin, W.; Borkovec, M. Charging and aggregation of positively charged latex particles in the presence of anionic polyelectrolytes. J. Phys. Chem. B 2007, 111, 8626– 8633,  DOI: 10.1021/jp069009z

    Google Scholar

    60

    Charging and Aggregation of Positively Charged Latex Particles in the Presence of Anionic Polyelectrolytes

    Gillies, Graeme; Lin, Wei; Borkovec, Michal

    Journal of Physical Chemistry B (2007), 111 (29), 8626-8633CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)

    Charging behavior and colloidal stability of amidine latex particles are studied in the presence of poly(sodium styrene sulfonate) (PSS) and KCl. Detailed measurements of electrophoretic mobility, adsorbed layer thickness, and aggregation (or coagulation) rate const. on varying the polymer dose, mol. mass of the polymer, and ionic strength are reported. Polyelectrolyte adsorption leads to the characteristic charge reversal (or overcharging) of the colloidal particles at the isoelec. point (IEP). In accordance with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, uncharged particles tend to aggregate because of van der Waals attraction, whereas charged particles are stabilized by elec. double layer repulsion. Attractive patch-charge interactions originating from the laterally inhomogeneous structure of the adsorbed polymer substantially decrease the suspension stability or even accelerate the aggregation rate beyond diffusion control. These electrostatic non-DLVO forces become progressively important with increasing mol. mass of the polymer and the ionic strength of the soln. At higher polymer dose of typically 10 times the IEP, one observes the formation of a satd. layer of the adsorbed polymer with a thickness of several nanometers. Its thickness increases with increasing mol. mass, whereby the layer becomes increasingly porous. This layer does not seem to be involved in the suspension stabilization, since at such high polymer doses the double layer repulsion has attained sufficient strength to stabilize the suspension.
61. 61

    Pavlovic, M.; Rouster, P.; Bourgeat-Lami, E.; Prevot, V.; Szilagyi, I. Design of latex-layered double hydroxide composites by tuning the aggregation in suspensions. Soft Matter 2017, 13, 842– 851,  DOI: 10.1039/C6SM02608G

    Google Scholar

    61

    Design of latex-layered double hydroxide composites by tuning the aggregation in suspensions

    Pavlovic, Marko; Rouster, Paul; Bourgeat-Lami, Elodie; Prevot, Vanessa; Szilagyi, Istvan

    Soft Matter (2017), 13 (4), 842-851CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)

    Colloidal stability of polymeric latex particles was studied in the presence of oppositely charged layered double hydroxide (LDH) platelets of different interlayer anions. Adsorption of the LDH particles led to charge neutralization and to overcharging of the latex at appropriate concns. Mixing stable colloidal suspensions of individual particles results in rapid aggregation once the LDH adsorption neutralizes the neg. charges of the polymer spheres, while stable suspensions were obsd. at high and low LDH doses. The governing interparticle interactions included repulsive elec. double layer forces as well as van der Waals and patch-charge attractions, whose strength depended on the amt. of LDH particles adsorbed on the latex surface. The type of the LDH interlayer anions did not affect the colloidal stability of the samples. Structural investigation of the obtained latex-LDH composites revealed that the polymer spheres were completely coated with the inorg. platelets once their concn. was sufficiently high. These results are esp. important for designing synthetic routes for hybrid systems in suspensions, where stable colloids are required for uniform film-formation and for the homogeneous distribution of the inorg. filler within the composite materials.
62. 62

    Alsharif, N. B.; Bere, K.; Sáringer, S.; Samu, G. F.; Takács, D.; Hornok, V.; Szilagyi, I. Design of hybrid biocatalysts by controlled heteroaggregation of manganese oxide and sulfate latex particles to combat reactive oxygen species. J. Mater. Chem. B 2021, 9, 4929– 4940,  DOI: 10.1039/D1TB00505G

    Google Scholar

    62

    Design of hybrid biocatalysts by controlled heteroaggregation of manganese oxide and sulfate latex particles to combat reactive oxygen species

    Alsharif, Nizar B.; Bere, Katalin; Saringer, Szilard; Samu, Gergely F.; Takacs, Dora; Hornok, Viktoria; Szilagyi, Istvan

    Journal of Materials Chemistry B: Materials for Biology and Medicine (2021), 9 (24), 4929-4940CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)

    The prepn. of an antioxidant hybrid material by controlled heteroaggregation of manganese oxide nanoparticles (MnO2 NPs) and sulfate-functionalized polystyrene latex (SL) beads was accomplished. Neg. charged MnO2 NPs were prepd. by pptn. and initially functionalized with poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte to induce charge reversal allowing decoration of oppositely charged SL surfaces via simple mixing. The PDADMAC-functionalized MnO2 NPs (PMn) aggregated with the SL particles leading to the formation of neg. charged, neutral and pos. charged (SPMn) composites. The charge neutralization resulted in rapidly aggregating dispersions, while stable samples were obsd. once the composites possessed sufficiently high neg. and pos. charge, below and above the charge neutralization point, resp. The antioxidant assays revealed that SL served as a suitable substrate and that the PDADMAC functionalization and immobilization of MnO2 NPs did not compromise their catalase (CAT) and superoxide dismutase (SOD)-like activities, which were also maintained within a wide temp. range. The obtained SPMn composite is expected to be an excellent candidate as an antioxidant material for the efficient scavenging of reactive oxygen species at both lab. and larger scales, even under harsh conditions, where natural antioxidants do not function.
63. 63

    Huang, H.; Ruckenstein, E. Effect of steric double-layer and depletion interactions on the stability of colloids in systems containing a polymer and an electrolyte. Langmuir 2006, 22, 4541– 4546,  DOI: 10.1021/la0602057

    Google Scholar

    63

    Effect of Steric, Double-Layer, and Depletion Interactions on the Stability of Colloids in Systems Containing a Polymer and an Electrolyte

    Huang, Haohao; Ruckenstein, Eli

    Langmuir (2006), 22 (10), 4541-4546CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)

    Expts. carried out by Stenkamp et al. [Stenkamp, V. S.; McGuiggan, P.; Berg, J. C. Langmuir 2001, 17, 637.] have shown that polystyrene latexes can be restabilized at sufficiently high electrolyte concns. in the presence of an amphiphilic block copolymer [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO)] At even higher electrolyte concns., the systems can again be destabilized. The present paper attempts to explain the restabilization through the dominance of steric interactions and the destabilization through the dominance of depletion interactions. Because of salting out, as the concn. of electrolyte increases, the polymer mols. are increasingly pptd. onto the surface of the latex particles and, at sufficiently high electrolyte concns., form, in addn., aggregates. The pptn. onto the latex particles generates steric repulsion, which is responsible for the restabilization, whereas the formation of aggregates generates depletion interactions, which are responsible for destabilization.
64. 64

    Moazzami-Gudarzi, M.; Maroni, P.; Borkovec, M.; Trefalt, G. Depletion and double layer forces acting between charged particles in solutions of like-charged polyelectrolytes and monovalent salts. Soft Matter 2017, 13, 3284– 3295,  DOI: 10.1039/C7SM00314E

    Google Scholar

    64

    Depletion and double layer forces acting between charged particles in solutions of like-charged polyelectrolytes and monovalent salts

    Moazzami-Gudarzi, Mohsen; Maroni, Plinio; Borkovec, Michal; Trefalt, Gregor

    Soft Matter (2017), 13 (18), 3284-3295CODEN: SMOABF; ISSN:1744-6848. (Royal Society of Chemistry)

    Interaction forces between silica particles were measured in aq. solns. of the sodium salt of poly(styrene sulfonate) (PSS) and NaCl using the colloidal probe technique based on an at. force microscope (AFM). The obsd. forces can be rationalized through a superposition of damped oscillatory forces and double layer forces quant. The double layer forces are modeled using Poisson-Boltzmann (PB) theory for a mixt. of a monovalent sym. electrolyte and a highly asym. electrolyte, whereby the multivalent coions represent the polyelectrolyte chains. The effective charge of the polyelectrolyte is found to be smaller than the bare no. of charged groups residing on one polyelectrolyte mol. This effect can be explained by counterion condensation. The interplay between depletion and double layer forces can be further used to predict the phase of the depletion force oscillations. However, this picture holds only at not too elevated concns. of the polyelectrolyte and salt. At higher salt concns., attractive van der Waals forces become important, while at higher polyelectrolyte concns., the macromols. adsorb onto the like-charged silica interface.