The effect of dielectric confinement on the peak position of intramolecular and a lattice vibration in the infrared spectra of various condensed media is investigated. Liquid benzene, carbon disulfide, and chloroform, as well as amorphous SiO₂ and microcrystalline MgO particles, were characterized in this study. The absorption spectra of organic liquids and aqueous solutions of a silica submicrometer powder were measured under a variety of dielectric confinement configurations using Fourier transform Infrared spectroscopy. A significant shift of the resonant absorption band of liquid mesoparticles has been observed under dielectric confinement, which is in good agreement with model predictions. A corresponding expression for the dielectric loss spectrum of an absorbing composite medium was obtained using a Maxwell-Garnett generalized equation for the cases of one, two, and three-dimensional dielectric confinement in both ordered and disordered thin layers (disks), rods (wires or needles), and spheres of an absorbing medium. The experimental data on peak positions obtained from the infrared spectra of the organic liquids investigated in this work, as well as from the infrared spectra of amorphous quartz spherical particles and rods, are in good agreement with the calculated data. It is shown using simulations of the absorption spectrum of MgO powder that the approach suggested can be applied under certain conditions to the modeling of the spectra of microcrystalline particles of nonspheroidal shape.

Micelles of hydrophilic−hydrophobic block copolymers, such as poly(ethylene glycol)-block-poly(caprolactone) (PEG-b-PCL), are useful for delivery of hydrophobic drugs. Such micelles can be formed by liquid solvent displacement or dialysis. A more recent approach is to use supercritical fluids as solvents, but the selection criteria for solvents are not well understood. The compressible solvents studied in this work can induce pressure-tunable micellization of PEG-b-PCL. Their capacity and selectivity, and hence their ability to form micelles, depends on their density, polarity, and hydrogen bonding potential. By mixing two solvent components, such as dimethyl ether (good solvent) and trifluoromethane (selective antisolvent), one can control not only the micellization temperature and pressure, but also the bulk separation pressure (cloud pressure), crystallization temperature, and melting temperature. This can be utilized to develop efficient ways to prepare micellar precursors for drug-loaded nanoparticles.

¹H PFG NMR spectroscopy has been used to evidence the association of ditopic {(BuSn)₁₂O₁₄(OH)₆}²⁺ macrocations when sulfate or oxalate divalent anions are used to balance their positive charges. The existence of supramolecular species, the size of which can reach up to about 10 times the size of the individual building blocks, is clearly related to electrostatic interactions as the supramolecular species fully break down to their individual components in solvent with high dielectric constant.

We present a facile approach to the production of magnetic iron oxide short nanotubes (SNTs) employing an anion-assisted hydrothermal route by simultaneously using phosphate and sulfate ions. The size, morphology, shape, and surface architecture control of the iron oxide SNTs are achieved by simple adjustments of ferric ions concentration without any surfactant assistance. The result of a formation mechanism investigation reveals that the ferric ions concentrations, the amount of anion additive, and the reaction time make significant contributions to SNT growth. The shape of the SNTs is mainly regulated by the adsorption of phosphate ions on faces parallel to the long dimension of elongated α-Fe₂O₃ nanoparticles (c axis) during nanocrystal growth, and the hollow structure is given by the preferential dissolution along the c axis due to the strong coordination of the sulfate ions. Moreover, the as-synthesized hematite (α-Fe₂O₃) SNTs can be converted to magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) ferromagnetic SNTs by a reducing atmosphere annealing process while preserving the same morphology. The structures and magnetic properties of these iron oxide SNTs were characterized by various analytical techniques.

Silica dispersed copper nanomaterials with high dispersion and unusual thermal stability were prepared by a simple precipitation-gel method, and their physicochemical properties have been characterized by a variety of techniques including FTIR, XRD, XPS, TG-DSC, SEM, TEM, H₂-TPR, and N₂ adsorption. Both Cu(OH)₂ nanoparticles and amorphous copper phyllosilicate are confirmed to present in the dried samples, whereas CuO nanoparticles and undecomposed copper phyllosilicate are determined in the calcined samples. Cu(OH)₂ nanoparticles are prone to assemble to wire-like structure during sample preparation, and their structure can be well preserved after calcination and silica dispersed CuO nanowires were obtained. The preparation procedure of precipitation gel is favorable for the formation of copper phyllosilicate, which is rather stable and played a profound effect on both the structure and thermal stability of the samples. In addition, the high dispersion and the one-dimensional structure of copper also contribute to the high stability of the samples.

Confining the growth of inorganic materials in patterns using DNA as a molecular guide represents a versatile system for nanoscale construction. Here, we report the first example of efficiently attaching BaWO₄ nanocrystals to dsDNA skeleton forming in patterns of well-defined nano pair-linear arrays. We have studied the influences of solution temperatures and concentrations of reagents on the pair-linear morphology. Results indicate that the two factors play the important roles in synthesizing the stable and desired patterned pair-linear arrays. We have tested four kinds of oligonucleotides to investigate systematically how nucleotide functionalities influence nanoparticle growth. We find that the phosphate and possibly the amino moiety binding site on adenine are the favorable targets to feed nanoparticle growth. On the basis of our findings, possible mechanisms are discussed.

The identification and timely detection of pathogenic bacteria is critical to ensuring safe food, health, and water. Although surface enhanced Raman scattering (SERS) methods have been used for pathogen characterization and single molecule sensing, the challenge of detecting pathogens in very low numbers using an optimal substrate that is sensitive and reproducible is still a challenge. In this report, we have developed and explored a novel SERS active substrate of 60−80 nm diameter through the assembly of Ag nanocrystals (AgNCs) into Ag nanospheres (AgNSs). A finite difference time domain (FDTD) analysis of the electromagnetic field produced by these structures and the enhancement factor calculations indicated that an enhancement of 10⁸ was possible using the 633 or 785 nm excitation. The exact enhancement factors (EF) through the experimental results were calculated to be 2.47 × 10⁷, which is close to that obtained through the FDTD analysis. Preliminary characterization of the SERS substrate was demonstrated using various labels from the fluorescent dye and nonfluorescent small molecules. More importantly, these novel SERS active substrates when used for pathogenic bacteria detection could detect cells as few as 10 colony forming units/mL (CFU/mL). Using canonical variate analysis (CVA) in conjunction with Raman spectra, differentiation of three key pathogens (E. coli O157, S. typhimurium, and S. aureus) including live and dead cells was also accomplished. With further optimization of the SERS substrate, single cell detection is possible.

Precise control over the size and shape of nanoparticles from solution-phase synthetic approach is currently a major objective in nanoscience. Metal nanorods and nanowires have attracted much attention because of their outstanding catalytic, magnetic, optical, and electrical properties. We have reported here the microwave (MW) assisted gram quantity synthesis of 1D nanostructures composed of Rh(0) and Rh(I). Thus, the rod-like assembly evolves through Rh(I)−Rh(I) interaction as the building blocker for the 1D nanostructure by using cetyltrimethylammonium bromide (CTAB) as a reducing agent as well as soft template. Reduction of Rh(III) to Rh(0)/Rh(I) occurred on the glass surface as a result of decomposition of CTAB upon MW heating without any other reducing agent. Uniform heating and the presence of CTAB, a face selective adsorption additive, helped the formation of 1D Rh nanostructures. Here, CTAB upon decomposition produced ammonia which in turn acted as a reducing agent ((a) Bal, R.; Tada, M.; Iwasawa, Y. Chem. Commun. 2005, 3433. (b) Huang, Y.; Wang, W.; Liang, H.; Xu, H. Cryst. Growth Des. 2009, 9, 858), and the undecomposed CTAB stabilized the nanostructure moiety. Hydrothermal condition produced only spherical Rh(0) nanoparticles, and boiling condition prompted anisotropic growth of the Rh(0)/Rh(I) nanoparticles with ill-defined morphology. The presence of impurity such as NH₄Cl or CsCl produced distinct 1D nanorods or nanowires in microwave heating condition. Interestingly, the syntheses of different morphology of Rh nanomaterials have been obtained by keeping the Rh(III) ion precursor to CTAB molar ratio unaltered. It has been observed that the pH has a remarkable influence on the alteration of aspect ratio and sharpening of the edges of Rh nanorods. The evolved nanostructures in different stages were characterized ex situ by different physical methods. How and why thermodynamically rather unstable Rh nanorods and nanowires changed their shapes in a chosen redox environment is reported. Interesting shape transformation has also been shown in a selective redox environment for nanorods and nanowires to octahedral and spherical particles, respectively. Isolated intermediates, identified by FESEM and TEM measurements, supported and guarantee the rod-to-octahedral shape transformation. Cyclic voltammetric measurement shows that as-prepared nanorods can be used as a potential candidate for oxygen evolution.

Single-crystalline Li₄Mn₅O₁₂ nanosticks were prepared by a simple method of adding MnSO₄ to molten LiNO₃ and NaNO₃. FESEM and HRTEM investigations revealed that two-dimensional Li₄Mn₅O₁₂ nanosticks were generated in large quantity. The results of dc and ac magnetization as well as magnetic hysteresis measurements suggest spin-glass-like behavior at 9.8 K. Furthermore, an exchange-bias effect is observed over the material in applied magnetic field of H ≤ 5 T.

Vertically aligned, single-crystalline ZnO/MgZnO coaxial nanorod arrays were epitaxially grown on GaN substrates by hydrothermal synthesis combined with pulsed laser deposition. Well-defined core/shell heterostructures with high-quality interfaces and coherent epitaxial relationship were confirmed by Z-contrast scanning transmission electron microscopy and line-scan compositional analyses. It is interesting to note that the MgZnO shell thickness gradually decreases from the tip to the base of the nanorods, due to a shadow effect during the deposition. The nonuniform coating allows us to study the carrier confinement and surface passivation effects on a single nanorod. Spatially resolved cathodoluminescence measurements reveal that the band-edge emission intensity of ZnO cores is variable along their length, and depends strongly on the shell thickness. A model, which involves carrier tunneling, surface trapping, and radiative/nonradiative recombination processes, was developed to understand this phenomenon. However, a high-temperature thermal treatment may lead to the stress relaxation and the formation of interfacial defects, and enhance the interdiffusion of interfacial atoms. These degrade the optical quality of coaxial nanorods.

Highly intense ArF and KrF laser radiation-induced photolysis of gaseous dichloroethenes allows chemical vapor deposition of ultrafine amorphous Cl-substituted hydrogenated carbon soot, which was characterized by FTIR, Raman, X-ray photoelectron and Auger spectroscopy, and electron microscopy, and diagnosed for magnetic and thermal properties. The deposited submicroscopic material was shown to contain C(sp³)−H, C−Cl, C−O, and C═O bonds and upon heating to 700 °C to evolve H₂, HCl, Cl₂, and C/H fragments and transform to graphite-like carbon. The deposited soot is diamagnetic, has a large surface area, and has a potential for synthesis of soot modified at the C−Cl bonds by other substituents.

This paper reports the effect of ligands including oleic acid (OA), trioctylphosphine (TOP), and tributylphosphine (TBP) on the PbSe nanocrystal growth during synthesis, as well as the effect of OA ligands on the nanocrystal stability after synthesis. These ligands play important roles in the nucleation and growth mechanism of nanocrystals. We have discovered that the ligand effect on the growth of PbSe nanocrystals can differ from that on the mostly studied CdSe nanocrystals. Also, we present a method for producing relatively smaller and more monodisperse PbSe nanocrystals based on our new understanding that the use of TBP, instead of the generally reported TOP, can slow down the growth of PbSe nanocrystals. In addition, our postsynthetic investigation of OA ligand effects demonstrate the dominant desorption of OA-bonded Pb atoms, causing the shrinkage of PbSe nanocrystals. This provides some insight into stabilization strategies for labile PbSe nanocrystals.

Here we report on the synthesis of a graphene/polyaniline (PANI) nanocomposite and its application in the development of a hydrogen (H₂) gas sensor. Using a chemical synthetic route, graphene was prepared and ultrasonicated with a mixture of aniline monomer and ammonium persulfate to form PANI on its surface. The developed material was characterized by scanning electron microscopy (SEM), transmission electron microscopy, Raman spectroscopy, and X-ray photoemission spectroscopy. The SEM study revealed that the PANI in the composite has a nanofibrillar morphology. We investigated the H₂ gas sensing performance of this material and compare it with that of the sensors based on only graphene sheets and PANI nanofibers. We found that the graphene/PANI nanocomposite-based device sensitivity is 16.57% toward 1% of H₂ gas, which is much larger than the sensitivities of sensors based on only graphene sheets and PANI nanofibers.

We have synthesized nanoporous silica, SBA-15, in the 1 μm size range with the pore diameter of 7.6 nm. The redox enzyme horseradish peroxidase (HRP) was entrapped in the pores to form nanostructured hybrid materials. The catalytic activity of free and immobilized enzyme was first compared at room temperature. Details of the enzyme kinetics including the apparent Michaelis constant (K_M) and maximum rate (V_max) were determined. Both thermal stability and stability, toward the denaturing agents guanidinium chloride and urea, of free and immobilized enzymes were compared next. The thermal stability of the immobilized enzyme is significantly improved in comparison with free HRP. The catalytic kinetics is slowed down notably, but V_max is much more robust to heat than the free enzyme. The stability resistance of the enzyme toward the denaturing agents depends on the chemical nature of the denaturing agents and interactions between enzyme and silica nanopore walls. Guanidinium chloride showed similar attenuation of the catalytic activity of immobilized and free enzyme. In contrast, the immobilized HRP was much more resistant to urea than the free enzyme. The different behavior of free and immobilized enzyme is most likely due to different hydrogen bonding of water and increased hydration strength of the protein inside the nanopores.

Multi-temperature X-ray diffraction studies show that twisting, rotation, and libration cause negative thermal expansion (NTE) of the nanoporous metal−organic framework MOF-5, Zn₄O(1,4-benzenedicarboxylate)₃. The near-linear lattice contraction is quantified in the temperature range 80−500 K using synchrotron powder X-ray diffraction. Vibrational motions causing the abnormal expansion behavior are evidenced by shortening of certain interatomic distances with increasing temperature according to single-crystal X-ray diffraction on a guest-free crystal over a broad temperature range. Detailed analysis of the atomic positional and displacement parameters suggests two contributions to cause the effect: (1) local twisting and vibrational motion of the carboxylate groups and (2) concerted transverse vibration of the linear linkers. The vibrational mechanism is confirmed by calculations of the dynamics in a molecular fragment of the framework.

Self-assembled magnetic nanohead-FeSi nanowire (NW) epitaxial heterojunctions by chemical vapor deposition (CVD) are reported. Free-standing FeSi NWs, ∼30 nm in diameter and several micrometers long, were grown by reduction of Fe₂O₃ in a H₂ atmosphere on a heated silicon substrate at 750 °C. These NWs shows very uniform dimensions, which is thought to be due to a higher diffusion activation energy for the nanostructure. A magnetic Fe₃O₄ head with a diameter of ∼30 nm was observed on each FeSi NW. The epitaxial relationship of these junctions is Si[001]//Fe₃O₄[2̅01], Si(001)//Fe₃O₄(102). Ferromagnetic behavior of the nanoheads was identified, and the coercivity was characterized as ∼220 Oe at 10 K. This one-step CVD approach for self-assembling epitaxially magnetic heads could enable device integration for spintronics and sensors. Particularly, such FeSi nanowires with highly localized magnetic nanoheads are ideal for high resolution magnetic force microscopy (MFM).

The microstructure, growth mechanism, and ferromagnetic (FM)/antiferromagnetic (AFM) coupling have been discussed in Ni:ZnO nanorod/Zn:NiO nanowall composite structures. The composite structures were synthesized by a hydrothermal method at 90 °C. A systematic investigation of high-resolution transmission electron microscopy, X-ray absorption spectroscopy, and magnetization studies reveals that the as-synthesized product shows FM behavior at room temperature, whereas the annealed sample shows mixed (FM/AFM) magnetic behavior. A detectable magnetic exchange coupling between FM/AFM has been demonstrated by magnetization measurements in the annealed products. The observed room-temperature FM behavior in these nanostructures was interpreted in terms of bound magnetic polarons.

Structure and properties of small quantum dots are of fundamental and practical interest due to a broad range of applications that exploit their optical tunability. Although previous experimental and theoretical investigation of very small semiconductor quantum dots have shown relative stability for clusters that deviate from the bulk, these materials have not been systematically characterized. In this work, structures of (CdSe)_n (n = 1−37) clusters were studied using a combination of structure enumeration, Monte Carlo search, and local optimization. Binding energy (E_n and relative binding energy, ΔE_n = n(E_n+1 − E_n), per CdSe unit) calculations using density functional theory (DFT) were carried out to identify the so-called magic size (MS, ΔE_n > 0) quantum dots. (CdSe)_n with n = 9, 12, 16, 18, 21, 24, 28, 32, 33, 35, and 36 were found to have high relative stability. MS structural motifs were investigated further for clusters up to (CdSe)₅₄. In addition, time-dependent DFT calculations of one-photon absorption (OPA) spectra for MS clusters were carried out to compare with experimental spectra. Computational prediction provides insight into the cluster formation during early growth and serves as a starting point for further analysis of the nonlinear optical response. The effects of ligands/solvent on the structure, stability, and OPA spectra were also examined for selected clusters.

The temperature dependence of the Raman spectrum of a gelatin-based composite material doped with single-walled carbon nanotubes (SWNT@gelatin) is reported. A significant upshift of the G-mode frequency is observed when the temperature is decreased from room temperature to 20 K. This frequency shift is significantly stronger than the one found for pure thermal effects. In contrast, the features of the radial breathing modes (frequencies and width) display no significant change in the same temperature range. These results are well understood by considering a uniaxial strain on the nanotube induced by the thermal expansitivity mismatch between the nanotube and the surrounding matrix.

Single-walled carbon nanotube (SWCNT) hybrids with meso-5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4) and meso-5,10,15,20-tetraphenylporphyrin (TPP) have been studied by the resonance Raman spectroscopy and by ab initio and molecular dynamic calculations. A comparison of the intensities of the bands assigned in the Raman spectrum to the radial breathing mode, as well as the relative band positions corresponding to the tangential modes of the hybrids with respect to the positions of these modes in the spectrum of the pristine SWCNT, indicates that the interaction of the nanotube with TMPyP4 is stronger than with TPP. A structure calculation (by the DFT/M05-2X method) of the TMPyP4 molecule adsorbed to a fragment of the zigzag (10,0) SWCNT surface shows that porphyrin adapts a saddled structure with the binding energy to the nanotube of −72.0 kcal/mol. The interaction energy in the complex of a TPP molecule with SWCNT, whose molecular structure is similar to TMPyP4, is only −19.3 kcal/mol and TPP does not adapt the saddled structure on the nanotube surface. The calculated interaction energies of the nanotube surface with the porphin core (−14.3 kcal/mol), the charged fragment of TMPyP4 (methylpyridinium) (−25.8 kcal/mol) and a neutral benzene molecule (−4.6 kcal/mol), which mimic the side residues of TMPyP4 and TPP, respectively, suggest that the stronger interaction between SWCNT and the TMPyP4 molecule is due to the cation−π interaction. The SWCNT:TMPyP4 complex formation in the aqueous solution has been modeled by the molecular dynamics method. The modeling showed that the hybrid is also stable in the water solution.

This article explores the transverse thermal conductance between two parallel—bonded as well as nonbonded—carbon nanotubes, embedded in an epoxy matrix using nonequilibrium molecular dynamics simulations. Here, we study the effect of different organic linkers—connecting the two nanotubes—on the thermal interface conductance and compare these results with those of nonbonded nanotubes. Our results suggest that incorporation of linker molecules significantly modifies overall interface conductance between nanotubes. Specifically, we find that the conductance increases with the number of linking functionality but shows an opposite trend with respect to the linker’s length, that is, the longer the linker is, the lower the conductance. We attribute this behavior to weakening of van der Waals interactions between carbon nanotubes in the case of longer linkers as well as possible scattering of thermal vibrations that occur along the linker molecules.

Fe₃O₄/TiO₂ core/shell nanotubes are fabricated via a three-step process. α-Fe₂O₃ nanotubes are first obtained, and α-Fe₂O₃/TiO₂ core/shell nanotubes are subsequently fabricated using Ti(SO₄)₂ as a Ti source by a wet chemical process. The thickness of the amorphous TiO₂ shell is about 21 nm. After a H₂ deoxidation process, the amorphous TiO₂ layer changes into crystalline structures composed of TiO₂ nanoparticles with an average diameter of 2.5 nm, and its thickness is decreased to about 18 nm. At the same time, α-Fe₂O₃ transforms into cubic Fe₃O₄. Consequently, crystalline Fe₃O₄/TiO₂ core/shell nanotubes can be fabricated through the process above. The measurements of the magnetic properties demonstrate that the Fe₃O₄/TiO₂ core/shell nanotubes exhibit ferromagnetic behavior at room temperature, and the Verwey temperature is about 120 K. The eddy current effect is largely reduced and the anisotropy energy is improved significantly for the core/shell nanotubes due to the presence of the TiO₂ shells. The maximum reflection loss reaches −20.6 dB at 17.28 GHz for the absorber with thickness of 5 mm, and the absorption bandwidth with the reflection loss below −10 dB is up to 13.12 GHz for the absorber with a thickness of 2−5 mm. Our results demonstrate that the Fe₃O₄/TiO₂ core/shell nanotubes obtained in this work are attractive candidate materials for the magnetic and EM wave absorption applications.

Selective growth of boron nitride nanotubes (BNNTs) was demonstrated by plasma-enhanced pulsed laser deposition (PE-PLD). Although PLD is a physical vapor deposition technique for the growth of boron nitride (BN) thin films, ion sputtering induced by the plasma can eliminate the formation of BN thin films and lead to the so-called total resputtering region, in which, a pure phase of BNNTs can be grown at 600−700 °C using Fe catalyst. These BNNTs can be grown at desired locations and have high structural orders with diameter ∼10−20 nm. In addition, we found that effective catalysts for the growth of these BNNTs should have both significant solubility of boron and relatively low sputtering yield. All of these observations can be summarized into a phase selective growth model that combining the vapor−liquid−solid (VLS) mechanism and the effect of ion sputtering.

Covalent grafting of acrylate-functionalized single-walled carbon nanotubes (SWCNTs) with poly(methyl methacrylate) was accomplished by emulsion polymerization using sodium dodecylbenzene sulfonate (SDBS) as an emulsifying agent. The acrylate-functionalized SWCNTs with polymerizable vinyl groups on their surfaces were prepared by a reaction sequence involving oxidation, hydroxylation, and vinylation reactions. The as-prepared acrylate-functionalized SWCNTs were then dispersed in water in the presence of SDBS, resulting in the exfoliation of SWCNTs into small bundles of approximately 2−6 tubes and the simultaneous formation of SWCNT micelles. Subsequent addition of methyl methacrylate resulted in its absorption into the SWCNT micelles due to the interactions between the monomer and the nanotube surface. Grafting copolymerization of methyl methacrylate with the vinyl groups on the SWCNT surface was subsequently performed in the micelles to produce poly(methyl methacrylate)-functionalized SWCNTs. Thermogravimetric analysis indicated that the average polymer content in the functionalized SWCNTs ranged from 42 to 63 wt %, depending on the time of monomer pre-emulsion.

Arrays of nanoapertures have been demonstrated to realize efficient, robust, and reproducible substrates for surface-enhanced Raman scattering SERS spectroscopy. However, little attention has been devoted to single nanoapertures, although a thorough understanding of the SERS phenomenon in a single aperture is essential for the rationale optimization of nanoaperture arrays SERS. In this study, single nanoapertures milled in optically thick gold films are quantitatively evaluated for the first time to determine the SERS enhancement factors using para-mercaptoaniline as nonresonant analyte. We determine a peak enhancement factor of 2 × 10⁵ for a single 100 nm diameter aperture. Although this is a moderate enhancement factor, we believe that nanoapertures deserve special attention to highlight the physical and chemical phenomena leading to SERS enhancement and better understand the design of nanoaperture arrays for SERS substrates. The experimental data are supported by numerical simulations and argue for a careful consideration of aperture diameter, incident polarization, analyte deposition method, and nature of the gold adhesion layer while designing aperture-based SERS substrates and evaluating SERS enhancement factors.

Oleic acid capped lead sulfide (PbS) and lead selenide (PbSe) were synthesized, then subjected to a postsynthesis washing in a 1:1 ethanol/hexane solution. The relationship of third order nonlinear optical properties to nanocrystal surface chemistry as affected by washing was analyzed using nanosecond 532 nm Z-scan and measurement of near-IR radiative emission. The results indicated a significant change in optical nonlinearities which emerged only after the nanocrystals were washed in the ethanol/hexane mixture. Transmission electron microscopy of the oleic acid capped PbSe and PbS nanocrystals showed a cubic shape, narrow size distribution and an average size of ∼10 nm. Neither size nor shape of the nanocrystals were modified by the washing process, indicating that all optical differences were related to changes in surface chemistry and the formation of deep trap states. The “as grown” nanocrystals showed high emission efficiency, weak saturable absorption, and a self-defocusing refractive index, n₂, determined to be −(3.0 ± 0.9) × 10⁻¹⁴ and −(2.9 ± 0.6) × 10⁻¹⁴ cm²/W for PbS and PbSe nanocrystals, respectively. After post-synthesis washing, the nanocrystals were converted to a reverse saturable absorbing and strongly scattering media with a self-focusing refractive index of (11.4 ± 2.0) × 10⁻¹⁴ and (12.7 ± 0.9) × 10⁻¹⁴ cm²/W for PbS and PbSe nanocrystals, respectively. The fitted experimental Z-scan data for the samples after washing gave high values for the nonlinear absorption coefficient, β_eff, in the range of 130−150 cm/GW. The appearance of reverse saturable absorption in the nanocrystals was due to the presence of trap states at the nanocrystal surface that were not present in the as-grown nanocrystals and did not show similar optical nonlinearity.

Controlling the growth of nanoparticles (NP) in nanotechnology is crucial to produce high-quality particles with narrow size distribution. This simulation investigates the growth of colloidal semiconductor NPs in the presence of two distinctly sized NPs in the so-called “bimodal growth regime”. One of the sizes of the NPs is selected such that its radius falls below or close to the critical dissolution radius. These particles will act as sacrificial materials for a larger second size for the growth and size focusing. The bimodal distribution (or quantized Ostwald ripening) technique is found to be a slower process compared to the commonly used repeated injection technique to focus the size distribution of NPs. The slow growth condition could lead to a better reaction control over the NP synthesis. Slower growth will reduce the effect of inhomogeneous mixing in a scaled up production of NPs. The low monomer oversaturation over the growth could improve the overall quality of the NPs. The results presented here on colloidal NPs are potentially applicable to the size evolution of NPs on surfaces as well.

The photoemission enhancement with local surface plasmon resonance (LSPR) was studied by two-photon photoemission (2PPE) spectroscopy for size-selected silver (Ag) and gold (Au) metal nanoparticles (NPs) deposited on a hydrogen-terminated Si(111)-(1 × 1) [H−Si(111)] surface. At 0.0015 monolayer equivalents (MLE) of Ag NPs, the photoemission enhancement was observed at a photon energy of 3.10 eV, which corresponds to the peak energy for the LSPR of isolated Ag NPs. A surface with around 0.005 MLE LSPR of size-selected Ag NPs exhibited three- and four-photon photoemission processes, implying monodispersed Ag NPs on H−Si(111). This enhancement could not be observed for Au NP deposition, even at 1.0 MLE in the photon energy range of 2.90−3.23 eV. Taking into account the polarization and photoemission-angle dependences, the photoemission enhancement could be accounted for by a mechanism involving the near-fields induced by the LSPR of Ag NPs. This mechanism is consistent with an analysis based on the effect of the interparticle distance between Ag NPs on the near-field intensity and polarization.

In this work we study the far field optical properties of heterodimers composed of a silver and a gold nanosphere of the same size, by means of exact electrodynamics calculations based on the generalized multiparticle Mie theory. We analyze the effect of the incident polarization, nanosphere separation, radius and dielectric media on the optical response. The on resonance angular distribution of the scattered radiation is also analyzed. The nonsymmetrical features of this system allow us to evaluate and perform a careful examination of the contributions of absorption and scattering from each individual nanosphere to the total extinction of the system. At variance with the homodimer system, the heterodimer exhibits a simultaneous shift of two plasmonic resonances. This feature constitutes a very useful and accurate way to calibrate both interparticle distance and size at the same time for a given dielectric environment. In this way, we provide a general and complete description of the far field optical properties of this particular nanostructure, which may be valuable for the design and development of plasmonic devices and optical tools and could serve as benchmark calculations for future comparisons with experiments.

Stabilizing ligands play a major role in the synthesis and stabilization of metallic nanoparticles, allowing dispersibility in various solvents including gas-expanded liquids (GXLs). Interaction energy modeling has been used to predict the dispersibility of hydrophobically stabilized metal nanoparticles in GXLs but often overpredicts the mean particle size dispersed at a given solvent composition. More accurate and robust interaction energy models can be developed if the changes to both the ligand length and ligand solvation as a response to the composition of GXLs are better understood. Small-angle neutron scattering (SANS) is a unique technique for nanoparticle characterization where in-situ ligand solvation measurements can be obtained by contrasting hydrogenated nanoparticle ligands with deuterated solvent. This study presents the first in-depth SANS measurements of ligand length and ligand solvation variation during nanoparticle antisolvent precipitation. The focus of this investigation is dodecanethiol-stabilized silver nanoparticles in carbon dioxide (CO₂)-expanded hexane. Upon pressurization with CO₂ antisolvent, the ligand length and ligand solvation for dodecanethiol-capped silver nanoparticles decrease as a function CO₂ composition in the GXL prior to nanoparticle precipitation. This work discusses the dependence of nanoparticle dispersibility as a function of CO₂ composition in n-hexane-d₁₄ GXL and the competing roles of ligand surface coverage, ligand length, and ligand solvation for nanoparticles with varying surface curvature.

The ability to form single-walled carbon nanotube (SWNT) networks of known density and length distributions is of critical importance to the development of a wide variety of electronic materials that incorporate these molecular wires. Room temperature deposition methods are of great interest as they allow the use of heat-sensitive substrates like polymers and glass. Additionally, they allow greater control over the characteristics of the SWNTs in the network by facilitating physical and/or chemical modification steps prior to deposition. This manuscript describes how two-dimensional networks of SWNTs were formed from aqueous suspensions via spin-casting, a deposition method commonly used in the microelectronics industry due to its ability to deposit uniform thin films of polymers from organic solvents. In the current work, the low viscosity of aqueous suspensions and high spin rates used resulted in ultrathin layers of aqueous suspensions from which low densities of unbundled SWNTs were deposited in iterative deposition cycles. This process was repeated to grow networks exhibiting tunable macroscopic conductivity that could be described by percolation theory.

Tracer zero length column (TZLC) and pulsed field gradient (PFG) NMR techniques were used to study self-diffusion of toluene in two samples of SBA-15 silica. Analysis of the diffusion data allowed us to assign evaluated diffusivities to diffusion of toluene in pore systems of SBA-15 particles. It was observed that there is a large discrepancy between the values of the diffusivities obtained by the two techniques under very similar experimental conditions. The most likely reason of this discrepancy is related to the particular morphology of the SBA-15 particles, which form stringlike aggregates with lengths close to 20−30 μm. As a consequence of the formation of such aggregate structures some mesoporous channels can be as long as the length of these structures. These long channels are expected to have transport barriers at the points of intergrowth of primary particles. Other channels are much shorter and are not expected to exhibit any significant transport barriers. Under the experimental conditions used TZLC measurements are most sensitive to sorbate diffusion in the channels of the former type. At the same time, PFG NMR measurements are expected to be more sensitive to diffusion in the channels of the latter type where T₂ NMR relaxation times are not shortened by the presence of multiple transport resistances. As a result, these two techniques can provide complementary diffusion data on sorbate transport in SBA-15 materials.

A carbon-supported, dealloyed platinum−copper (Pt−Cu) oxygen reduction catalyst was prepared using a multistep synthetic procedure. Material produced at each step was characterized using high-angle annular dark-field scanning transmission electron microscopy, electron energy loss spectroscopy mapping, X-ray absorption spectroscopy, X-ray diffraction, and cyclic voltammetry, and its oxygen reduction reaction (ORR) activity was measured by a thin-film rotating disk electrode technique. The initial synthetic step, a coreduction of metal salts, produced a range of poorly crystalline Pt, Cu, and Pt−Cu alloy nanoparticles that nevertheless exhibited good ORR activity. Annealing this material alloyed the metals and increased particle size and crystallinity. Transmission electron microscopy shows the annealed catalyst to include particles of various sizes, large (>25 nm), medium (12−25 nm), and small (<12 nm). Most of the small and medium-sized particles exhibited a partial or complete core−shell (Cu-rich core and Pt shell) structure with the smaller particles typically having more complete shells. The appearance of Pt shells after annealing indicates that they are formed by a thermal diffusion mechanism. Although the specific activity of the catalyst material was more than doubled by annealing, the concomitant decrease in Pt surface area resulted in a drop in its mass activity. Subsequent dealloying of the catalyst by acid treatment to partially remove the copper increased the Pt surface area by changing the morphology of the large and some medium particles to a “Swiss cheese” type structure having many voids. The smaller particles retained their core−shell structure. The specific activity of the catalyst material was little reduced by dealloying, but its mass activity was more than doubled due to the increase in surface area. The possible origins of these results are discussed in this report.

Layered materials provide a two-dimensional interlayer space suitable for accommodating molecules with a designed functionality. In this study, inorganic−organic hybrids were prepared by intercalation of anionic porphyrin sensitizers into the host structure of layered zinc hydroxide salts. The inorganic host offers stabilization and protection, whereas the guest species provide the photofunction. The properties and arrangement of porphyrin molecules in the interlayer space were studied by a combination of experimental techniques and molecular simulations. Intercalation of porphyrins led to a gallery height that is comparable with the size of porphyrin molecules. Molecular simulations showed that the interlayer space is filled with disordered porphyrin units. The porphyrin sulfonate groups interact with the brucite-like layers via dominant electrostatic interactions similarly to layered double hydroxides. The photophysical experiments proved that intercalated anionic Pd porphyrins produce singlet oxygen, O₂(¹Δ_g), with long effective lifetimes, suggesting that layered zinc hydroxide salts are good carriers of porphyrin sensitizers.

We have developed a simple method for the selective colorimetric detection of aqueous mercuric (Hg²⁺), silver (Ag⁺), and lead (Pb²⁺) ions by using label-free gold nanoparticles (Au NPs) and alkanethiols. The degree of alkanethiol-induced aggregation of the Au NPs decreases in the order of 6-mercaptohexanol (6-MH) ∼ 4-mercaptobutanol (4-MB) > 11-mercaptoundecanol (11-MU) > 2-mercaptoethanol (2-ME). The specific and strong interactions of these alkanethiols with Au NPs and heavy metal ions enabled us to develop label-free assays for the sensitive and selective detection of Hg²⁺ ions using the 4-MB/Au NPs probe, as well as Ag⁺ and Pb²⁺ ions using the 2-ME/Au NPs probe. The presence of strong Hg²⁺-S bonds alleviated the extent of 4-MB-induced aggregation of the Au NPs, resulting in a declining ratio of the extinction coefficients at 650 to 520 nm (Ex_650/520, a measure of the molar ratio of the aggregated to the dispersed Au NPs) of the Au NP solution. In contrast, the presence of Ag⁺, Cu²⁺, and Pb²⁺ ions led to a severe aggregation of the Au NPs, mediated by the deposition of these ions on the surfaces of the Au NPs in the 2-ME/Au NPs system. In the presence of masking agents [ethylenediaminetetraacetic acid (EDTA), Na₂S], the 2-ME/Au NP-EDTA and 2-ME/Au NP-Na₂S sensors permitted the selective detection of Ag⁺ and Pb²⁺ ions, respectively, at concentrations down to the nanomolar range. This cost-effective process also allowed the rapid and simple determination of the concentrations of heavy metal ions in real environmental samples (river water and Montana soil). These alkanethiol/Au NP-based sensor probes enabled us to detect three different heavy metal ions, and we feel confident that, because of the simplicity, rapidity, and cost-effectiveness of these analyses, such systems demonstrate great potential for the practical detection of heavy metal ions in real samples.

Polypyrrole (PPy) nanocomposites reinforced with tungsten oxide (WO₃) nanoparticles (NPs) and nanorods (NRs) are fabricated by a surface-initiated polymerization method. The electrical conductivity is observed to depend strongly on the particle loadings, molar ratio of oxidant to pyrrole monomer, and the filler morphology. The electron transportation in the nanocomposites follows a quasi-three-dimensional variable range hopping (VRH) conduction mechanism as evidenced by the temperature-dependent conductivity function. Unique negative permittivity is observed in both pure PPy and its nanocomposites, and the switching frequency (frequency where the real permittivity switches from negative to positive) can be tuned by changing the particle loading, ratio of oxidant to pyrrole monomer, and the filler morphology. The extent of charge carrier localization calculated from the VRH mechanism is well-correlated to the dielectric properties of the nanocomposites. WO₃ NRs are observed to be more efficient in improving the electrical conductivity, dielectric permittivity, and thermal stability of the resulting nanocomposites as compared to those with WO₃ NPs. The microstructures of pure PPy and its nanocomposites are observed by scanning electron microscopy and transmission electron microscopy. Powder X-ray diffraction analysis demonstrates the crystalline structure of WO₃ nanostructures, as well as their corresponding nanocomposites. Thermogravimetric analysis reveals a significantly enhanced thermal stability with the addition of nanofillers.

In this work, we report a multifunctional inorganic nanocomposite which is composed of mesoporous silica coated ferrite core and numerous gold nanoparticles (NPs) support on the surface of mesoporous silica. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectra, Fourier transform infrared spectroscopy, UV−vis spectroscopy, N₂ adsorption/desorption, superconducting quantum interference device were used to characterize the samples. The results indicated that the nanocomposites show typical ordered mesoporous characteristics (2.4 nm) and high magnetization (46.3 emu/g), thus it is possible for drug targeting under a foreign magnetic field. In addition, the Au NPs’ shell, coated mesoporous silica containing ferrite cores, exhibits near-infrared absorption (suitable for photothermal therapy). A drug release test indicates that the multifunctional system shows drug-sustained properties with ibuprofen as the model drug. This multifunctional system has potential for targeting drug delivery and photothermal therapy based on all the properties they possess.

This paper reports the development of novel carbon nanotube immobilized composite membranes (CNIM) for pervaporative removal of organics from an aqueous matrix. The nanotubes were immobilized into the pores of a composite, where they served as sorption sites that provided additional pathways for enhanced solute transport, affecting both the partitioning and diffusion through the membrane. Depending upon the process conditions, the enhancement in organic removal and mass transfer rates were higher by 108 and 95%, respectively. The CNIM demonstrated several advantages including enhanced recovery at low concentrations, lower temperatures, and higher flow rates. Overall, these lead to more energy efficient processes.

We report polarized resonance Raman data of tetrakis(4-sulfonato)phenyl porphyrin (TSPP) aggregates in solution and deposited on Au(111) at wavelengths resonant with the red-shifted (J-band) and blue-shifted (H-band) components of the split Soret (B) band. We also report scanning tunneling microscopy (STM) images which reveal that the aggregate on Au(111) is a nanotube with a 2 nm wall thickness which tends to flatten on the substrate. Relative Raman intensities and their dependence on polarization of the incident and scattered light are found to vary greatly for H- and J-band excitation, revealing a much greater degree of coherence for the J-band, in agreement with the resonance light scattering spectrum. The J-band transition is found to have transition moment components both parallel and perpendicular to the long axis of the nanotube, consistent with a helical nanotube structure. The intensity increase of the Q-band on aggregation and the weak intensity of the H-band in both the absorption and the resonance light scattering spectra are explained by vibronic B-Q coupling, which is permitted in the lowered site symmetry of the aggregate. The resonance Raman data presented here provide insight into the molecular basis for the hierarchal structure of the aggregate.

Carbon nanowires made of long linear atomic chains have attracted considerable interest due to their potential applications in nanoelectronics. We report a theoretical characterization of assemblies with good prospects for chemical synthesis made of two coronene molecules (graphene-like pieces) bridged by carbon linear chains with distinct sizes and parities. Our calculations are performed within all-electron density functional theory. We examine the effects of two conformations (syn and anti) of the terminal anchor pieces, representing energy minima for these systems, on the properties of the carbon chains. The calculated electronic states reveal that simplified chemical models such as those based on cumulenes or polyynes are not appropriate to describe the linear chains with sp² terminations. For these types of atomic chains, we find that the electronic ground state of the odd-numbered chains is spin polarized. Vibrational properties of all these chains are studied by calculating Raman scattering and infrared spectra. We show that syn and anti conformations of the graphene-like terminations lead to important effects in the vibrational features of the chains, detectable by the Raman light-scattering depolarization.

The influence of the formulation process/pathway on the generation of electrostatic complexes made from polyelectrolyte-neutral copolymers and oppositely charged nanocolloids is investigated in this work. Under strong driving forces like electrostatic interaction and/or hydrogen bonding, the key factor controlling the polydispersity and the final size of the complexes is the competition between the reaction time of the components and the homogenization time of the mixed solution. The latter depends on the mixing pathway and was investigated in a previous publication by tuning the mixing order and/or speed (Qi, L.; Fresnais, J.; Berret, J.-F.; Castaing, J.-C.; Grillo, I.; Chapel, J.-P. J. Phys. Chem. C 2010, 114 (30), 12870−12877). The former depends on the initial concentration of the individual stock solutions and the strength of the interaction and is investigated here on a system composed of anionic cerium oxide functional nanoparticles (CeO₂-PAA) and cationic charged−neutral diblock copolymers (PTEA_11K-b-PAM_30K) or homopolyelectrolytes (PDADMAC_100K). The electrostatic interaction was screened off completely by adding a large amount of salts. Desalting kinetics was then controlled by slowly decreasing the ionic strength from I_b ≈ 0.5 M, the minimum ionic strength to totally prevent the complexation of the two components, to lower values where the electrostatically screened system undergoes an (abrupt) transition between an unassociated and a clustered state. Neutron scattering data evidenced differences in the nanostructure of complexes formed by either dilution or simple mixing. Furthermore, adsorption optical reflectometry experiments showed the impact of these different formulation processes on the wettability and antifouling properties of treated silica and polystyrene model surfaces. Better controlled mixing processes were put forward at the end to improve the productivity and reproducibility of the complexes generation. In particular, a microfluidic chip coupled with dynamic light scattering was used to better control the hydrodynamics of the complexation process.

Herein we developed a targeted anticancer drug delivery system based on folate-conjugated rattle-type Fe₃O₄@SiO₂ hollow mesoporous spheres combining receptor-mediated targeting and magnetic targeting. Folic acid (FA) ligands were successfully grafted onto rattle-type Fe₃O₄@SiO₂ hollow mesoporous spheres via amide reaction. The magnetization saturation value of folate-conjugated Fe₃O₄@SiO₂ spheres (Fe₃O₄@SiO₂−FA) was about 1.6 emu/g, and these spheres could be targeted under an external magnetic field. On the other hand, in vitro cytotoxicity and cell uptake of these Fe₃O₄@SiO₂−FA spheres to Hela cells were evaluated. These Fe₃O₄@SiO₂−FA spheres were nontoxic up to a concentration of 150 μg/mL, and further can be specifically taken up by Hela cells via FA receptor-mediated endocytosis. Doxorubicin hydrochloride (DOX), an anticancer drug, was introduced into Fe₃O₄@SiO₂−FA spheres. The release of DOX from Fe₃O₄@SiO₂−FA spheres had a sustained release pattern, and the DOX-loaded Fe₃O₄@SiO₂−FA spheres exhibited greater cytotoxicity than free DOX and DOX-loaded Fe₃O₄@SiO₂ spheres due to the increase of cell uptake of anticancer drug delivery vehicles mediated by the FA receptor. Therefore, we conclude that folate-conjugated Fe₃O₄@SiO₂ hollow mesoporous spheres have potential for targeted anticancer drug delivery for cancer therapy.

We report on the fabrication of three-dimensional colloidal crystal arrays (CCAs) on an underlying substrate via gravity sedimentation of TiO₂-coated polystyrene (PS) colloidal particles. The beauty of the described system lies in the fact that obtained CCAs, for the first time, display a photonic band gap in the near-infrared (NIR) region with as much bandwidth (Δλ/λ) as 54−61%. Interestingly, stop band position and bandwidth have been found to be modulated with structural parameters of building blocks such as particle size and thickness of TiO₂ shell, etc. Moreover, no significant change in stop band position was observed with the variation in incidence angle of the light. Theoretical calculations from the simulation studies have been found in agreement with the experimental findings.

An improved process to prepare MWNTs/polyester thin film nanocomposite membranes was initiated by interfacial polymerization of trimesoyl chloride (TMC) and triethanolamine (TEOA) solution containing MWNTs. The improved process was facilely done by immersing the support membrane into the organic phase before the conventional process of interfacial polymerization. The TEM images showed that the MWNTs were embedded throughout the polyester thin film layer. The MWNTs/polyester thin film nanocomposite membrane prepared via the improved process exhibited both high permeability and excellent selectivity when compared with the thin film composite membrane without MWNTs and the MWNTs/polyester thin film nanocomposite membrane prepared via the conventional process. The water permeability increased upon an increase of reaction time of TMC-saturated support membrane immersed into aqueous phase (step-1), reaching a maximum of 4.7 L/m² h at 25 min, while the membrane rejection rate kept increasing. The role of step-1 played a positive role in the performance and the morphology of the thin film composite membrane. It was found that the process of step-1 produced a low degree of cross-linking thin layer with high amount of hydrophilic and negatively charged carboxyl groups. This improved process of interfacial polymerization to prepare MWNTs/polymer thin film nanocomposite membranes provides a new approach to overcome the trade-off effect between permeability and selectivity.

Unsupported gold nanoparticles in solution are reported here for the first time to catalyze the oxidation of CO at ambient conditions. Gold was stabilized in solution by various polyamidoamine dendrimers. Dendrimer-encapsulated gold nanoparticles (DENs) 0.5−2.5 nm in diameter have low initial activity. With storage time, however, the activity of the aged DENs increased and became comparable to a reference Au−TiO₂ catalyst with the same gold loading and average gold particle size, which was tested under the same reaction conditions. The activation is attributed to partial hydrolysis of gold as followed by UV−vis spectroscopy.

White and green rusts are the active chemical reagents of buried scrap iron pollutant remediation. In this work, a comparison of the initial electron-transfer step for the reduction of CrO₄⁻² by Fe²⁺_(aq) and Fe(OH)_2(s) is presented. Using hybrid density functional theory and Hartree−Fock cluster calculations for the aqueous reaction, the rate constant for the homogeneous reduction of chromium by ferrous iron was determined to be 5 × 10⁻² M⁻¹ s⁻¹ for the initial electron transfer. Using a combination of Hartree−Fock slab and cluster calculations for the heterogeneous reaction, the initial electron transfer for the heterogeneous reduction of chromium by ferrous iron was determined to be 1 × 10² s⁻¹. The difference in rates is driven by the respective free energies of reaction: 33.4 vs −653.2 kJ/mol. This computational result is apparently the opposite of what has been observed experimentally, but further analysis suggests that these results are fully convergent with experiment. The experimental heterogeneous rate is limited by surface passivation from slow intersheet electron transfer, while the aqueous reaction may be an autocatalytic heterogeneous reaction involving the iron oxyhydroxide product. As a result, it is possible to produce a clear model of the pollutant reduction reaction sequence for these two reactants.

A cylindrical ultrasonic reactor was driven at eight discrete frequencies in the range 20−150 kHz. Imaging of multibubble sonoluminescence (MBSL) within this cell showed discrete modes of activity throughout this frequency range. This modal activity was compared to the pressure distribution through the cell and also to the erosion/corrosion activity. The erosion/corrosion was detected using an electrochemical method employing a passivated aluminum electrode (250 μm diameter). Each erosion/corrosion event was counted over a fixed time period (specifically 30 s) and used to map this phenomenon throughout a region of the cell. A strong spatial correlation was shown between the MBSL imaging, the acoustic pressure, and the erosion mapping at relatively low ultrasonic frequencies (here <50 kHz). However, at higher frequencies, although MBSL activity and relatively high acoustic amplitudes were detected, the rate of the erosion/corrosion activity of the system decreased. High-speed imaging (>100000 fps) of a bubble cloud near the electrode surface showed a region of bubble activity, the dynamics of which were correlated to the erosion/corrosion transients produced. These observations contribute to the growing body of knowledge which will allow the development of ultrasonic cleaning systems optimized for particular scenarios.

Synchrotron radiation photoemission spectroscopy (SRPES) has been used to study the electronic structure of the Au/CdZnTe(111)A for Au coverage ranging from about 0.3 up to 20 monolayers (ML). It is found that a Schottky barrier with a height of 0.82 eV is formed at the initial deposition of Au. This barrier decreases gradually with increasing Au coverage, which can be ascribed to band bending caused by charge redistribution at the interface and the formation of a positive interface dipole introduced by Cd diffusion. After an annealing process, a signal due to the formation of Au−Cd alloy caused by exquisite Cd diffusion into Au overlayer is observed, and simultaneously the Schottky barrier height (SBH) reduces to 0.32 eV. The present work indicates that cation diffusion into metal overlayer plays a critical role in controlling the SBH.

Periodic DFT (BLYP, B3LYP, and BHandHLYP) calculations have been used to study the properties of SiO^• radical defect on quartz, cristobalite, tridymite, and amorphous surface models. Crystalline orbitals are constructed by an expansion of Gaussian type orbitals in which all atoms are represented with a double-ζ plus polarization quality basis set. Starting from fully hydroxylated 2D slab models, the radical defect is constructed by removing a hydrogen atom from a silanol of the surface while conserving the other features of the crystalline polymorph. Among the different functionals used, the hybrid BHandHLYP is the one that better compares to the experimental EPR data and provides reaction energies in better agreement with CCSD(T). The GGA BLYP functional, however, tends to delocalize the spin density, which can have important consequences on the H-bonding at the surface, especially when it exhibits geminal silanols. Comparison between the hydroxylated and the radical slab shows that the radical defect at the surface does not induce significant tension at the crystalline structure, the Si−O bond distance associated to the radical defect being the only geometrical parameter that varies significantly (∼0.04 Å). The spin density analysis shows that, regardless of the surface, the unpaired electron is mainly localized on the radical defect and, thus, does not provide a clue to understanding the different behavior between crystalline and amorphous silica on the ≡SiO^• + H₂O → ≡SiOH + OH^• reaction. Instead, the ability of the surfaces to establish new H-bonds with the recovered silanol appears to be a relevant feature on the process that triggers OH^• formation from SiO^•.

Buckling in solid thin films supported by soft substrates has been well-studied. Many of those buckling features discovered, however, are monotonous without any hierarchical organizations. We report our finding of a substantial 2D hierarchical buckling atop a molecular type of multistacks or lamellae. This multistacked structure is a direct self-assembly from aminopropyltriethoxysilane, in which the polar amine groups promote the absorption of a large amount of water. We found that the resulting soft structures are good candidates to allow the formation of a complex buckling along the surface normal. Revealed cauliflower-like, hierarchical patterns are modeled by considering rigid columns standing on a soft substrate. In return, the hierarchical structures demonstrated could find applications in nanofabrication and enrich emerging fields, such as flexible electronics or optics.

The nanorod crystallites of ruthenium-grafted halogenous hydroxyapatite (RuXAp, X = F, Cl or Br) were newly developed through a facile method and identified as highly efficient catalysts for the aerobic oxidation of alcohols. Compared with RuHAp for selective oxidation of benzyl alcohol, the existence of F, Cl, and Br elements in hydroxyapatite dramatically enhanced the catalytic activity with a prominent selectivity of far more than 99%. In particular, the RuClAp and RuFAp catalysts, respectively, showed the excellent catalytic activity of TOF = ∼233 and 210 h⁻¹, which was nearly 3 times higher than that of RuHAp. The RuFAp catalyst was furthermore demonstrated to be recyclable and available to be applied for various alcohols. On the basis of the DRIFT and XAFS results, the enhanced activities could be preliminarily ascribed to the electron-withdrawing effect of halogens and the greater amounts of active species existing in the surface of RuXAp compared with that of RuHAp.

An oriented single-crystalline TiO₂ nanorod or wire array on transparent conductive substrates would be the most desirable nanostructure in preparing photoelectrochemical solar cells because of its efficient charge separation and transport properties as well as superior light harvesting efficiency. In this study, a TiO₂ nanorod array film grown directly on transparent conductive glass (FTO) was prepared by a simple hydrothermal method. The formation of CdS quantum dots (QDs) on the vertically aligned TiO₂ nanorods photoelectrode was carried out by chemical bath deposition. The as-prepared materials were characterized by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction. The results indicate that CdS QDs with a diameter smaller than 10 nm are uniformly covered on the surface of the single-crystalline TiO₂ nanorods. Under AM 1.5 G illumination, the photoelectrode was found with a photocurrent intensity of 5.778 mA/cm² at a potential of 0 V versus Ag/AgCl and an open-circuit photovoltage of 1.292 V versus Ag/AgCl. The photocurrent is 28.6 times higher than that of a bare TiO₂ nanorod array, and the photoelectrochemical properties are comparable to those of a CdS QDs-sensitized TiO₂ nanotube array, suggesting that the CdS QDs-sensitized TiO₂ nanorod array on FTO photoelectrodes has a potential application in solar cells.

A series of nanosized Co₃O₄ particles in which Cu was loaded on the surface were examined as robust catalysts for hydrogen evolution by ammonia borane hydrolysis. Their catalytic activity was dependent on the shape and size of nanosized Co₃O₄. The shape of nanosized Co₃O₄ was cube, hexagonal sheet, or uncontrolled. Among these, the Co₃O₄ in the shape of hexagonal sheet showed the highest catalytic activity. To investigate the size dependence of the catalytic reactivity, Co₃O₄ particles with the controlled size of about 4, 20, or 500 nm were examined, and it was found that the one in the size about 4 nm showed the highest activity although the size dependence was not remarkable compared with the shape dependence. The robustness of the catalyst was assured by no significant activity loss after 10 times repetitive reactions. The structural characterizations of Cu/Co₃O₄ composite in the fresh and used conditions were performed by X-ray photoelectron spectroscopy, Auger spectroscopy, and powder X-ray diffraction spectroscopy. The X-ray diffraction patterns assigned to Co₃O₄ were observed for both fresh and used catalysts, indicating that the Co₃O₄ form was maintained at the core part of each particle after the reaction. On the other hand, the XPS peaks or Auger peak for Cu 2p, Cu L₃M₄₅M₄₅, Co 2p, and O 1s of the used catalyst suggested that its surface was reduced or hydrolyzed to Cu₂O, Co metals, and Co(OH)₂ during the reaction. The observed Cu₂O and Co metals are regarded as active species for ammonia borane hydrolysis.

We used electrochemical testing and theoretical calculations based on density functional theory (DFT) to examine the oxygen reduction reaction (ORR) activity of platinum electrocatalyst supported on several forms of niobium oxide. Bilayer electrocatalysts were synthesized in the form of 5 nm thick Pt layers (ca. 0.01 mg/cm²), deposited on 5 or 10 nm thick niobium oxide and backed by glassy carbon (GC) electrodes. The NbO and NbO₂ supports enhance the specific electrochemical activity of Pt relative to the identically synthesized baseline system of Pt on GC but have no positive effect on the mass activity. The electrochemical stability of the Pt/NbO₂ bilayer system was investigated by potential cycling with up to 2500 cyclic voltammetry (CV) cycles. After 2500 cycles, data indicates minimal electrochemical area loss. With the use of DFT calculations, we have evaluated effects of oxygen incorporation on stability, electronic structure, and electrochemical activity of Pt|Nb_xO_y systems. Calculations predict a transfer of electronic charge density from Nb, NbO, and NbO₂ to Pt and a reverse case for Nb₂O₅. However, the experimental ORR activity does not follow the trends predicted by the d-band model.

The development of a high-efficiency TiO₂ photocatalyst is of great importance to a variety of solar light conversion and application fields; the desired high efficiency can be achieved by employing well-controlled TiO₂ nanoarchitectures. In this study, we have successfully synthesized well-ordered and aligned high surface area mesoporous TiO₂ nanofibers (TiO₂-NF) by electrospinning of TiO₂ powder dispersed in viscous polymer solution and subsequent calcination. For comparison, TiO₂ nanoparticles (TiO₂-NP) are also prepared from calcination of the same TiO₂ powder. The TiO₂-NF of ca. 500 nm in diameter and a few micrometers in length consist of compactly and densely packed spherical nanoparticles of ca. 20 nm in size and have mesopores of 3−4 nm in radius. Photocatalytic comparison between TiO₂-NF and TiO₂-NP indicated that the former had far higher photocatalytic activities in photocurrent generation by a factor of 3 and higher hydrogen production by a factor of 7. The photocatalytic superiority of TiO₂-NF is attributed to effects of mesoporosity and nanoparticle alignment, which could cause efficient charge separation through interparticle charge transfer along the nanofiber framework. Finally, various surface characterization experiments were conducted and included to understand the photocatalytic behaviors of TiO₂-NF and TiO₂-NP.

We have prepared a TiO₂-based novel visible-light-sensitive photocatalyst, in which Fe(III) species were grafted on a rutile TiO₂ surface (denoted as Fe(III)/TiO₂). With use of X-ray absorption fine structure analysis, the grafted iron species were determined to be in the 3+ state and adopt an amorphous FeO(OH)-like structure. Fe(III)/TiO₂ displayed optical absorption in the visible light range over 400 nm, which was assigned to the interfacial charge transfer from the valence band of TiO₂ to the surface Fe(III) species. Its photocatalytic activity was evaluated by the decomposition of gaseous 2-propanol under visible light (400−530 nm), which revealed a high quantum efficiency (QE) of 22%. Monochromatic light experiments indicated that the effective wavelength region was extended as far as 580 nm while maintaining a QE of greater than 10%. On the basis of the analogy to Cu(II)-grafted TiO₂ photocatalyst (Irie, H.; et al. Chem. Phys. Lett. 2008, 457, 202), we speculate that the high performance of the present photocatalyst is derived from the photoproduced holes that are generated in the valence band of TiO₂ and contribute to the oxidative decomposition of 2-propanol, and the catalytic reduction of oxygen (presumably multielectron reduction) by photoproduced Fe(II) species on TiO₂.

A simple-to-use method of carbon support surface activation using a PdCl₂−SnCl₂ solution (referred to as the Shipley solution) was developed, for improving the activity and durability of low Pt loading (0.1 mg cm⁻²) catalysts toward the oxygen reduction reaction (ORR). Three types of carbon supports were investigated: Denka, Graphitized Carbon (GC) and Vulcan XC-72R. Pt nanoparticles were synthesized by a modified polyol process and adsorbed on Shipley solution treated carbon supports. The resulting catalyst composition was Pt-SnO₂−Pd/C with beneficial atomic ratios of Pt/Sn ≥ 12 and Sn/Pd ≥ 2. Employing extensive potential cycling as accelerated degradation testing, we found that the Pt-SnO₂−Pd/C catalysts maintained excellent electrocatalytic activity for ORR with respect to control samples without carbon support treatment (both commercial and in-house prepared). The Pt area-specific oxygen reduction current density at 0.9 V_RHE and 25 °C was most improved in the case of the GC support. The activity of commercial Pt/GC after stability testing decreased by 21.5% to 0.055 A m⁻²_Pt while for Pt-SnO₂−Pd/GC, 0.078 A m⁻²_Pt was measured, identical to that of the fresh catalyst. The electrochemical results are supported by detailed surface analysis. Pt−Pd bimetallic nanoclusters were identified, and the kinetically beneficial role of the partially reduced SnO₂ surface for oxygen and water adsorption is discussed. The oxygen mass transfer limiting current densities in the porous rotating disk electrodes (PRDE) were qualitatively correlated with changes of the catalyst layer morphology during stability testing in terms of the Bonnecaze and Ahlberg models.

The enhancement in sensitivity of infrared reflection spectroscopy to adsorbates on multilayer structures (MEIRAS) is analyzed by using classical Fresnel’s expressions for reflection and transmission of electromagnetic radiation and the results are compared to experimental MEIRAS spectra of CO adsorbed on Pt/SiO₂/Au multilayer thin films. The analysis shows that the FTIR signal of adsorbed CO is significantly enhanced due to optical interference effects on the multilayer structures. The effect of different structural and optical parameters indicates that this sensitivity enhancement can be maximized by matching the interlayer thickness with the CO infrared absorption wavelength and the relative sensitivity to surface normal and tangential vibrational modes of adsorbates can be tuned. Practical considerations for designing a multilayer substrate and the potential application of MEIRAS technique in the study of adsorbates near metal−support boundary sites of model supported catalysts under reaction conditions are described.

Coadsorption of electrolyte ions can have a marked influence on the adsorption and hence interfacial reactivity of multicharged ions but has generally been overlooked in previous density functional theory (DFT) studies. The impact of this effect is demonstrated for the DFT-based interpretation of in situ FTIR spectra of the controversial binding form of weakly adsorbed carbonate on hydrated hematite nanoparticles and ferrihydrite. Using a new methodology, we show that addition of hydronium or sodium ions in the DFT models leads to assigning the weakly adsorbed carbonate to an inner-sphere monodentate mononuclear complex. FTIR data and the “bond length−vibrational frequency” correlations established by DFT suggest that the adsorption affinity of ferrihydrite toward carbonate is lower than that of 7 nm hematite NPs. As opposed to the case of carbonate, the outer-sphere adsorption form of sulfate is demonstrated to be stable in the presence of hydronium. These findings have important implications for DFT modeling of the solid−water interfaces, which has become a major complementary tool to interpret spectroscopic and macroscopic observations of adsorption phenomena.

Interstitial silicide-modified nickel, with high selectivity in some hydrogenation reactions, had been produced by dissolving silicon atoms into the nickel lattices. The metallic nickel was obtained by reducing the as-prepared high surface area NiO, followed by modification of the bulk nickel through silification of silane/H₂ at relatively low temperature and atmospheric pressure. The as-prepared materials were characterized by X-ray diffraction, magnetic measurements, X-ray photoelectron spectroscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and temperature-programmed reduction. The results show nickel silicide formation involves the following sequence as a function of increasing temperature: Ni (cubic) → Ni₂Si (orthorhombic) → NiSi (orthorhombic) → NiSi₂ (cubic). The insertion of Si atoms into the interstitial sites between Ni atoms resulted in a significant change in the unit cell lattice of nickel. All of the silicide-modified nickel materials were ferromagnetic at room temperature, and saturation magnetization values drastically decreased when Si is present. Silicide-modified nickel develops a thin silicon oxide layer during exposure to air, which can be removed by H₂-temperature programmed reduction. The as-prepared bulk silicide-modified nickel showed above 92% styrene selectivity in the hydrogenation of phenylacetylene under 0.41 MPa H₂ and at 50 °C for 5 h. In addition, only low conversions were obtained for styrene hydrogenation under the same hydrogen pressure and temperature for 50 min. These results indicate that these novel silicide-modified nickels are promising catalysts for the selective hydrogenation of unsaturated hydrocarbons.

Modification of metal oxides’ characteristics by decreasing the nanoparticles’ crystal size is usually interpreted in terms of increasing quantum size effects and/or oxygen vacancy concentration. However, some properties of TiO₂ nanoparticles, such as water adsorption strength on anatase or photoactivity for toluene mineralization in the gas phase, are optimized when the mean anatase crystal size is close to 6 nm, indicating the action of two opposed effects. Here, we show that these effects are originated by the increasing acidity of bridging hydroxyls with decreasing crystal size. Increasing acidity favors, first, water hydrogen bonding to bridging hydroxyls and, then, simultaneously to bridging and terminal hydroxyls of adjacent particles, favoring nanoparticle agglomeration and interfacial hydroxyls and water stability. A too strong acidic character of bridging hydroxyls favors proton exchange of stabilized hydronium ions with bridging O²⁻ and terminal hydroxyls, facilitating hydroxyl recombination and crystal growth.

We report a first-principles investigation aiming at controlling the stabilization and catalytic activity of metal nanoclusters supported on graphene via tuning the mechanical strain in graphene. We show that a relatively modest tensile strain (10%) applied in graphene greatly increases the adsorption energies of various kinds of metal clusters under study by at least 100%, suggesting the greatly strain-enhanced stabilization of these metal clusters on graphene, which is highly desired for graphene-based catalysis. Using Au₁₆ and Au₈ clusters on graphene as model catalysts for CO oxidation, we found that a small strain of 5% in graphene reverses the charge transfer between Au clusters and graphene, and reduces the reaction barrier of the catalyzed CO oxidation from around 3.0 eV (without strain) to less than 0.2 eV. These findings provide new opportunities for future development of graphene-based nanocatalysis.

Co-adsorption reactions between metal ions and anionic ligands play important roles in controlling availability and transport of chemical species in natural aquatic environments as well as in industrial processes. A molecular understanding of the properties of the surface species formed provides means to model these reactions in a predictive manner and to exploit them in synthetic routes of modified surfaces. In this study, we have used EXAFS and infrared spectroscopies in combination with quantitative adsorption measurements to investigate the coadsorption of Ga(III) and EDTA on α-FeOOH (goethite) as a function of pH. The quantitative results showed a 1:1 stoichiometry between adsorbed Ga(III) and EDTA and a maximum in total adsorption around pH 5. EXAFS and infrared data showed that the molecular structures displayed pH-dependent characteristics, and within the studied pH range, these results were concurrent and indicated that Ga(III)EDTA formed ternary surface complexes on goethite. The collective results were fully consistent with the occurrence of both outer sphere Ga(III)EDTA and inner sphere ternary surface complexes of type A (i.e., a surface−Ga(III)−EDTA structure), where the latter was favored by increasing pH. This study showed that despite a macroscopic adsorption behavior that was seemingly ligand-like, a substantial fraction of Ga(III) may bond directly to surface hydroxyl groups.

The physical adsorption of nanosized plastic beads onto a model cellulose film and two living algal species, Chlorella and Scenedesmus, has been studied. This adsorption has been found to ubiquitously favor positively charged over negatively charged plastic beads due to the electrostatic attraction between the beads and the cellulose constituent of the model and living systems. Such a charge preference is especially pronounced for Chlorella and Scenedesmus, whose binding with the plastic beads also depended upon algal morphology and motility, as characterized by the Freundlich coefficients. Using a CO₂ depletion assay, we show that the adsorption of plastic beads hindered algal photosynthesis, possibly through the physical blockage of light and air flow by the nanoparticles. Our ROS assay further indicated that plastic adsorption promoted algal ROS production. Such algal responses to plastic exposure may have implications on the sustainability of the aquatic food chain.

We investigate the effect of heat treatment on the structure of carbide-derived carbons (CDC) prepared by chlorination from nanosized βSiC particles and on their methane as well as hydrogen storage and delivery performance. Pore size and pore wall thickness distributions of the CDCs are obtained from interpretation of argon adsorption data using the finite wall thickness (FWT) model. The adequacy of the FWT model for adsorption modeling in the SiC-CDC samples is demonstrated by satisfactory prediction of subatmospheric and high pressure adsorption isotherms of CO₂ and CH₄ at 313 and 333 K. From the characterization results, it is observed that the SiC-CDC particles are predominantly amorphous with slight graphitization of the external surface. The degree of graphitization is more pronounced in the sample prepared at 1000 °C and increases slowly with heat treatment time. During this time the accessibility of methane molecules is found to increase, as a result of short-range ordering and opening up of pore entrances. Nevertheless, methane storage capacity is unsatisfactory, despite the high surface area and porosity, due to accessibility problems. On the other hand improvement in high pressure H₂ uptake (4.61 wt % at 77 K) is obtained for SiC-CDC chlorinated at 800 °C and heat treated for one day. The recently predicted optimal delivery temperature of 115 K for hydrogen storage is found to be appropriate for this material. It is demonstrated that accessibility is an important issue to be addressed for methane storage in carbons, but which has hitherto not received attention for this application.

Although theoretical analyses on electrophoresis are ample in the literature, most of them focused on the one- or two-dimensional problems for a simpler treatment; available results for the three-dimensional case, which may be closer to reality, are extremely limited. The electrophoresis of a soft, finite cylindrical particle positioned eccentrically along the axis of a narrow cylindrical pore is modeled in this study. The type of particle considered is capable of mimicking a wide class of nonrigid entities such as biocolloids and particles covered by an artificial polymer layer in practice. The electrophoretic behaviors of the particle under various conditions are simulated. We show that if the membrane layer of a particle is charged, then its electrophoretic behavior depends largely on its aspect ratio, eccentricity, and relative size, the thickness of double layer, and the thickness of the membrane layer, which might not be the case if that layer is uncharged. In addition, the electrophoretic mobility of a particle in the former may not increase with increasing thickness of the membrane layer, which has not been reported previously. The results gathered provide the theoretical basis for both the design of an electrophoresis apparatus and the interpretation of experimental data.

In an attempt to understand the single-molecule SERS of some small nonresonant molecules, such as adenine, it is inevitable to include the chemical enhancement mechanism to provide additional enhancement to the electromagnetic mechanism, although it may be much smaller than the electromagnetic field enhancement. We will report here the first experimental investigation of the charge-transfer (CT) enhancement of protonated adenine molecules on Rh and Pd by performing the potential-dependent SERS using one UV laser (325 nm) and two visible lasers (514.5 and 632.8 nm). A UV laser displays a significant role in the verification of the CT process due to its much larger photon energy and thus a much larger shift of potential of the maximum SERS intensity (E_max) than visible lasers. We find a well-discernible E_max and a linear relationship between E_max and the photon energy of the laser for adenine on both Rh and Pd surfaces. The E_max was found to shift positively with the increasing photon energy, which strongly indicates an electron transfer from the E_f of Rh and Pd to the lowest unoccupied orbital of adenine molecules. In addition, different contributions of CT enhancement to adenine Raman bands are also briefly discussed. By analyzing the wavelength-dependent intensity change and UV−vis absorption spectroscopy, we propose the contribution of preresonance Raman enhancement to the UV-SERS signal for the band at around 1330 cm⁻¹. The present study demonstrates that the use of a UV laser opens a promising way to understand the enhancement mechanism, especially the chemical enhancement mechanism.

¹H and ²⁷Al MAS NMR spectroscopies have been applied for studying the effect of water molecules, nitrogen bases, and o-xylene on the hydroxyl protons of bridging AlOH groups and framework aluminum atoms in the metal−organic framework (MOF) MIL-53. For water molecules adsorbed on the low-temperature form MIL-53lt, two ¹H MAS NMR signals were found indicating the formation of different O−H···O hydrogen bonds to neighboring oxygen atoms, such as to carboxylic oxygens. Upon adsorption of the nitrogen bases acetonitrile, ammonia, and pyridine, a linear increase of the quadrupole coupling constant, C_Q, of the framework aluminum atoms in dehydrated MIL-53 from C_Q = 8.5 MHz (unloaded material) to maximum 10.8 MHz (pyridine-loaded material) as a function of the proton affinity of the adsorbates was observed. Adsorption of o-xylene led to three stepwise changes of the quadrupole coupling constants, C_Q, of framework aluminum atoms in dehydrated MIL-53. While the first two stepwise changes of the C_Q values (C_Q = 8.0 and 8.7 MHz) occur for o-xylene loadings of lower than 4 molecules per unit cell and for all AlO₄(OH)₂ centers, the third change of the C_Q value to 9.4 MHz was observed for o-xylene loadings higher than 4 o-xylene molecules per unit cell and for maximum 50% of the framework aluminum atoms. This third adsorbate-induced change of the C_Q value of framework aluminum atoms in MIL-53 is accompanied by a significant decrease of the adsorbate mobility.

The adsorption of NO₂ onto oxygen vacancy sites, which naturally exist on the ZnO(21̅1̅0) surface, is widely believed to be one of the most important factors affecting gas sensor responses for this system. In this work we have examined surface reconstruction and relaxation, charge transfer, Bader charges, density of states, vibrational frequencies, and binding energies of the stable structures of NO₂ adsorbed on the defect ZnO(21̅1̅0) surface containing oxygen vacancies (V_O^••). Multiple minimum energy structures were found with binding energies of the order of ∼1 eV, indicating chemisorption on the surface. Significant post-adsorption reconstruction was observed, accompanied by minor surface relaxation. Adsorption in the most stable site gave rise to an impurity state within the band gap of the clean defect surface and was found to induce a magnetic moment on the most stable structure only. For all minimum energy structures, NO₂ behaves as a charge acceptor, withdrawing charge from the surface, which was calculated to be approximately six times greater on the ZnO(21̅1̅0)−V_O^•• surface than on the stoichiometric surface, suggesting that the defect surface may prove to be more sensitive. A comparison between theoretically obtained properties of defective and stoichiometrically balanced surfaces and experimental sensing observations is given.

In this work, a computational study is performed on CO₂ capture from various practical systems in a Li-modified metal−organic framework (MOF), chem-4Li MOF. The results demonstrate that this material shows exceptional CO₂ capture capability, due to the enhancement of the electrostatic potential in it by the presence of lithium. This study shows that not only the strength and gradient but also the distribution of the electrostatic potential can be controlled by metal doping, leading to more obvious heterogeneity in electrostatic potential in the material, resulting in the occurrence of molecular-level segregation for some systems. The present work observes for the first time that molecular-level segregation can occur in MOFs with simple cubic pores of different sizes and reveals that if the preferential adsorption sites of the less selective component can be shifted to its less preferential adsorption sites, the material may exhibit an exceptionally high selectivity, and such a shift can be achieved by various methods, for which metal doping is an effective way.

Growth characteristics of cadmium sulfide atomic layer deposition (ALD) from dimethylcadmium (DMCd) and hydrogen sulfide have been investigated by hybrid DFT and MP2 calculations. The steady-state film growth during one ALD cycle was modeled by studying dissociative chemisorption of the dimethylcadmium precursor on the sulfur-terminated (111) surface of zincblende CdS and then by investigating the chemisorption of hydrogen sulfide on the surface formed due to the treatment with the Cd reactant. The calculated reaction barriers for the ALD half reactions suggest that elevated temperatures are required for the film growth. Periodic calculations provide evidence for submonolayer growth per ALD cycle and suggest that steric factors prevent full monolayer formation during DMCd exposure, whereas all adsorption sites are likely to react during the hydrogen sulfide pulse.

This paper reports the template-induced formation of molecular corrals on the Si(111) surface by taking the advantage of the intrinsic property of the reconstructed (7 × 7) unit cell. Self-assembled molecular corrals have been formed on the Si(111)-(7 × 7) surface by binding pyrrole molecules chemically on the silicon center adatom through the breakage of the N−H bond. The dissociative adsorption of pyrrole on Si(111)-(7 × 7) leads to pyrroyl and H atom binding with an adatom and an adjacent rest atom, respectively. The molecular corral has dramatically modified the electronic property of the silicon surface, which leads to the formation of pyridine dative bonding to Si(111)-(7 × 7) surface at room temperature. The self-assembled molecular corral may provide a template for controlling the molecular binding configurations and quantum confinement effect of nanoclusters.

In the parent metal−organic framework Cu₃(btc)₂ material the Cu(II) pairs in the paddle wheel building blocks of the framework give rise to an antiferromagnetic spin state with an electron spin resonance (ESR) silent S = 0 ground state. The thermally excited S = 1 state of the Cu(II) pairs can be observed for temperatures above 80 K by ESR spectroscopy but give rise to an exchanged narrowed resonance line preventing the exploration of any structural details in the environment of the paddle wheel units. However, magnetically diluted paramagnetic binuclear Cu−Zn clusters can be formed by substitution of Cu(II) ions by Zn(II) at low doping levels, as already known for zinc-doped copper acetate monohydrate. Indeed, ESR, hyperfine sublevel correlation spectroscopy (HYSCORE) and pulsed electron nuclear double resonance (ENDOR) verify the successful incorporation of zinc ions at cupric ion sites into the framework of the resulting Cu_3−xZn_x(btc)₂ coordination polymer. The formation of such paramagnetic binuclear Cu−Zn paddle wheel building blocks allows the investigation of the interaction between the Cu(II) ions and various adsorbates by advanced pulsed ESR methods with high accuracy. As a first example we present the adsorption of methanol over Cu_3−xZn_x(btc)₂, which was found to coordinate directly to the Cu(II) ions via their open axial binding site.

This paper is an extension of previous work devoted to the characterization of platelet-like hydroxyapatite (HA) nanoparticles constituted by a crystalline core coated by an amorphous surface layer 1−2 nm thick (Bertinetti et al. J. Phys. Chem. C. 2007, 111, 4027−4035). By increasing the preparation temperature, the platelet morphology was retained but HA nanoparticles exhibited a higher degree of crystallinity (evaluated by X-ray diffractometry). High-resolution transmission electron microscopy revealed that, in this case, the crystalline order was extended up to the particles’ surfaces, which were of the (010), (100), and (001) types. IR spectroscopy was used to investigate the surface hydration of both materials, in terms of adsorbed H₂O molecules and surface hydroxy groups, as well as the Lewis acidity of surface cations, by removing water and adsorbing CO. For both features, strong similarities between amorphous and crystalline surfaces were found.

The chemisorption and surface diffusion/desorption of pyridine from TiO₂ powder (P25) have been measured as a function of temperature using transmission IR spectroscopy. Two classes of diffusion have been measured with activation energies of 36 kJ/mol (fast) and 90 kJ/mol (slow). By comparing density functional theory (DFT) calculations of bonding energies on TiO₂ rutile (110) and anatase (101), the dominant crystal planes expected in P25 TiO₂, it is found that fast diffusion would be expected on the rutile phase and that much slower diffusion would be expected on the anatase phase. In addition, the presence of oxygen defect sites will produce more strongly bound pyridine than either of the model crystal planes selected for investigation. To both types of TiO₂ surfaces, pyridine bonding occurs to coordinatively unsaturated Ti cation sites through the N lone pair of the pyridine molecule. More than 85% of the molecules exhibit slow surface diffusion, and this is attributed to diffusion on the dominant anatase crystallites as well as to diffusion on defective sites. Diffusing molecules exhibit a ν_19b ring-breathing mode, with the rapidly diffusing molecules exhibiting a mode frequency of ∼1438 cm⁻¹ and the slowly diffusing species exhibiting a mode frequency of ∼1445 cm⁻¹. Electron stimulated desorption ion angular distribution (ESDIAD) studies of the C−D bond directions for pyridine-d₅ on the rutile TiO₂(110)-1 × 1 surface show that the ring plane is rotated by 37 ± 1° with respect to the [001] azimuth on the crystal surface, in good agreement with the 39° rotational angle calculated by DFT. Several ring-breathing modes of pyridine are slightly broadened on rutile sites compared to anatase sites, and this may be due to more freedom for librational vibrations of the more weakly bound pyridine molecules.

The pressure and materials gaps in heterogeneous catalysis often complicate the extrapolation of results from surface science experiments over single crystals to real catalysis at elevated pressures and polycrystalline samples. Previous ammonia oxidation studies reported ca. 100% NO selectivity and the absence of N₂O on RuO₂(110) in ultrahigh vacuum (UHV) at 530 K, p(NH₃) = 10⁻⁷ mbar, and O₂/NH₃ = 20 (Wang, Y.; Jacobi, K.; Schone, W.-D.; Ertl, G. J. Phys. Chem. B 2005, 109, 7883). Differently, our steady-state and transient experiments over polycrystalline RuO₂ at ambient pressure reveal that N₂ is the predominant product. The NO selectivity was as low as 6% at O₂/NH₃ = 2 and reached a maximum of 65% at the highest temperature (773 K) and effective oxygen-to-ammonia ratio of 140, whereas the maximum N₂O selectivity was 25% at 100% NH₃ conversion. Density functional theory simulations of the competing paths leading to NO, N₂O, and N₂ over RuO₂(110) and RuO₂(101) at different coverages by O- and N-containing species provided insights into the selectivity differences between the extreme operation regimes. Comparison between the (101) and (110) facets reveals that the materials effect is not likely to explain the different product distribution. Instead, the pressure effect (8 orders of magnitude higher at ambient pressure than in UHV) does. Whereas NO is formed by the direct reaction of coadsorbed N and O atoms, N₂ can be formed through two different routes: direct N + N recombination or N₂O decomposition. The second path is only likely at high pressures because it implies more diffusion steps of surface species, which are highly unlikely at low coverage. Thus, the main pressure effect is to facilitate alternative routes for N₂ formation.

The role of a Co promoter in a water-gas-shift reaction on Co-MoS₂ has been investigated on the basis of density functional theory computation. On the basis of the computed adsorption energy of the reaction intermediates and H₂O dissociation barriers, the active catalyst is the Mo edge with 25% Co substitution and 25% sulfur coverage, while the S edge with 25% Co substitution and 50% sulfur coverage is not active. On the basis of the computed reaction barriers, the redox mechanism (CO + H₂O → CO + O + 2H; CO + O + 2H → CO₂ + H₂) is the preferable reaction path, and the rate-determining step is the second step dissociation of OH into surface O and H, while the reaction path from carboxy (CO + OH → COOH; COOH → CO₂ + H) is not favored due to its high dissociation barrier. In addition, formate (HCOO) is a side product from gas phase CO₂ and surface H and does not participate directly in the reaction mechanism. Detailed comparisons reveal that the Co promoter is not an active center in H₂O dissociation and CO oxidation but changes the adsorption configuration of the reaction intermediates and reduces the reaction barriers. The Co promoter plays the role of a textual promoter in creating more active sites and accelerating the reaction rate.

Supported palladium nanoparticles with different diameters were synthesized by the water-in-oil microemulsion method using TiO₂ as support. The materials were characterized by different physicochemical methods such as X-ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and H₂ chemisorption. The results confirmed that the microemulsion method permits well-dispersed palladium nanoparticles to be obtained. The size of the nanoparticles was estimated by XPS intensity ratios using models proposed by Davis and by Kerkhof and Moulijn and compared with XRD, TEM, and H₂ chemisorption analysis. Good accordance of the two models was found for very small Pd particles (smaller than 3 nm). The Kerkhof−Moulijn model seemed to be very sensitive to the small variation in the particle size distribution. The Davis model seemed to be more adequate to determine the size of small and biggest particles as compared with the Kerkhof−Moulijn model. A good accordance between TEM results and the Davis model was found. The results obtained using the Davis model permitted also understanding of the differences observed between XRD and TEM studies. XPS analysis could be a good and probably more accessible alternative to determine rapidly and with high accuracy nanosize particles of materials, in particular when others physicochemical techniques are not accessible or have a limited resolution.

This paper shows that it is possible to construct well-defined 2D structures at the air−water interface in which the lateral organization is controlled by means of the preparation of mixed films, and selecting the components so that there are attractive interactions between them. The goal here is to establish the lateral connection between components through self-aggregation of the dye. This can be achieved by selecting a suitable balance between the sizes of the hydrophobic and polar groups. In such a way, the domain structure depends on the ability of the tilt dye to fill the available area. Thus, the molecular organization and the domain morphology of mixed films containing dimyristoyl-phosphatidic acid (DMPA) and the hemicyanine dye, 4-[4-(dimethylamino)styryl]-1-docosylpyridinium bromide (SP), have been studied by using Grazing Incidence X-ray Diffraction (GIXD), Brewster angle microscopy (BAM), and reflection spectroscopy at the air−water interface. For this mixed system, the formation of circular domains with bright horizontal regions and dark vertical regions was observed. Furthermore, depending on the temperature, it is observed as branches grow from circular domains, whose brightness depends on the growth direction. Thus, BAM images allow us to observe some branches that, as their growth direction changes, their brightness also changes simultaneously. The GIXD experiment permits us to relate the circular domains with an orthorhombic phase and the branches grown from the circles with an Overbeck phase. In both cases, the formed structures are induced by the hemicyanine aggregation. Circular BAM domain textures have been simulated by using the Fresnel equations for biaxial anisotropic materials.

The molecular dynamics in nanometer thin films of glycerol was investigated upon thickness reduction by combining organic molecular deposition with in situ broadband dielectric spectroscopy. Changes in the cooperative dynamics with respect to bulk glycerol were observed for films of thicknesses down to 1.6 nm (corresponding to roughly three molecular layers). Systematic investigation revealed no pure size effects addressable merely to geometrical constraints. However, an increase in the glass transition temperature by 3.5 K was observed for the thinnest film, indicating the presence of a layer with reduced mobility in close proximity to the substrate. The impact of both the upper and lower interfaces has been disentangled by measurements performed during slow desorption. Moreover, proof is given for the existence of a layer with enhanced mobility in the vicinity of the free surface enslaved to the dynamics of the rest of the film.

In this work we present an absorbance investigation, mainly in the visible range, of two electrochromic devices (ECD), prepared with a viologen molecule and two different anodic substances (hydroquinone and ferrocene). The ethyl viologen has been used instead of other viologens because of its greater solubility into the selected plastic matrix. On the other hand the methyl viologen has been excluded due to its well-known high toxicity. Since, in view of practical applications, we are interested in the device behavior within the visible region, the ECD electrooptical properties were investigated with a spectrometer working in the 350−1200 nm range, which also extends into the NIR region. The measured spectra, as a function of time, have been registered while the coloration process was in progress during the application of a voltage supply across the film. The absorbance of each spectral transition was obtained by numerical integration and studied in its time evolution. The time evolution of the spectral data has been interpreted in the framework of a simple kinetic model. This model considers the two reactions involved in the chemical processes and the resulting kinetic equations have been numerically solved, without any approximation. The results of such analysis help to evaluate the assignment and correctness of various transitions. From the experimental data a value of 2.7 × 10⁷ cm² mol⁻¹ for the specific absorption has been estimated, which is in agreement with the corresponding evaluation available in the literature. Moreover a coherent peak attribution, to cation and neutral species of the viologen, is proposed. No transition due to anodic compounds inserted in the film is present, since the spectra of the two films, differing only for the used anodic species, exhibit the same transitions.

We investigated the electronic structure and transport properties of phosphorus- and arsenic-substituted Li₃N using first-principles methods. It is found that both P and As partial substitution reduce Li vacancy formation energy, without appreciable alteration of energy band gap, indicating an improvement in ionic conduction. But a full substitution of P and As results in variation of crystal structure from the space group P6/mmm to P6₃/mmc, and the energy band gaps of Li₃P and Li₃As are reduced to 0.72 and 0.65 eV, respectively, in comparison with 1.14 eV of Li₃N. A full substitution also brings about an increase of Li vacancy formation energies, suggesting degradation in ionic conduction. Our calculations suggest that it would be viable to achieve balanced electronic and ionic conduction of Li₃N by controlled P and As partial substitution.

Electronic structure calculations based on density functional theory in both optimized monoclinic (No. 14 P2₁/n) and rhombohedral (No. 148 R3̅) phases of La₂NiFeO₆ have been performed using full-potential linearized augmented plane wave method. The result indicates that La₂NiFeO₆ is a half-metallic ferromagnet within both crystal structures, and electronic correlation (U) plays a vital role in stabilizing the ferromagnetic ground state. Substitution of Mn⁴⁺ with Fe³⁺ induces a hole on Ni, making the transition of semiconducting La₂Ni²⁺Mn⁴⁺O₆ to half-metallic La₂Ni³⁺Fe³⁺O₆. Moreover, the half-metallicity is found to be robust under the compressive and tensile strains for both phases. The magnetic interaction constant is calculated according to the Heisenberg model, from which the Curie temperature is estimated within the mean field approximation. The Curie temperature is predicted to be as large as 495 and 474 K in P2₁/n and R3̅, respectively, making this system interesting candidates in spintronic devices.

We have conducted a theoretical investigation to model the mechanisms of photoinduced electron injection and energy transfer for a recent organic metal-free dye derived from the triphenylamine (2TPA-R) structure. The 2TPA-R system results from the fusion between two TPA moieties connected by a vinyl group, and the rhodanine-3-acetic acid is used as the electron acceptor group. In a first step, DFT and TDDFT approaches have been exploited to calculate the key parameters controlling the intramolecular charge transfer (ICT) injection and ET transfer rate constants in the classical Marcus formalism: (i) the electronic coupling; (ii) the reorganization energies; and (iii) the variation of the Gibbs energy. In a nice agreement with the experimental trends, the results have highlighted that (i) two excited states [EE⁽¹⁾, lower in energy, and EE⁽²⁾, higher in energy] have been calculated at 2.78 and 3.33 eV; (ii) the energy transfer (ET) between these two excited states is in competition with the electron injection from the EE⁽²⁾; (iii) when 2TPA-R is excited at 3.33 eV, the ET between the resulting relaxed excited states EE⁽²⁾ and EE⁽¹⁾ directly takes place, and the probability of injection from EE⁽²⁾ is weak; (iv) the ET remains governed by the Dexter mechanism. Indeed, the ratio between the Förster and Dexter rate constants (k^F/k^D) is evaluated at ∼10⁻⁴. Second, we propose structural modifications improving the electron injection efficiency of the TPA-based DSSCs, and we show that using the 1-CN,2-COOH-ethylene group as the acceptor unit combined with a functionalization of the TPA moieties by -OMe groups significantly improves the key parameters related to the electron injection.

Azo-phenol based receptors, having an azo core incorporated with naphthol and substituted (−H, −NO₂, −CH₃, and −OCH₃) benzothiazole units have been synthesized and their detailed optical properties have been investigated in different media. The nitro substituted azo derivative, 2, has shown, categorically, promising optical behavior in the absence as well as presence of different transition metal ions in aqueous-acetonitrile solution and has illustrated greater sensitivity, using the “naked-eye” for the detection of Hg²⁺ ion by enhanced fluorescence. The mechanism of metal−ion interaction has been established by absorption, emission, FT-IR, and ¹HNMR spectroscopic experiments that indicated favorable coordination of Hg²⁺ metal ion by the phenolic oxygen atom, the azo nitrogen atom adjacent to the naphthol ring, and the thiazole nitrogen of benzothiazole ring, obviously in a terdentate manner leading to the formation of a five-membered chelate ring. The 2:1 stoichiometry and association constants, K_assoc(abs.) = 1.04 ± 0.3 × 10⁵ M⁻² and K_assoc(em.) = 1.51 × 10⁵ M⁻² have been estimated with the help of Job’s plot and the Benesi−Hildebrand method. The cis−trans isomerism and azo-hydrazone type of tautomerism by the photoinduced proton transfer reaction and also metal induced (Hg²⁺ ion) proton transfer reaction from the hydrazone form in the present organic molecular systems have been confirmed by photoirradiation and fluorescence excitation experiments and by ¹H and ¹³C NMR spectral analysis.

Photoinduced isomerization in a bis(4,4′-dimethyl-2,2′-bipyridyl)(o-methylsulfinylbenzoate) ruthenium(II), (RuBzSO) complex is investigated using linear infrared absorption and dual-frequency two-dimensional infrared (2DIR) spectroscopies. The changes in the linear absorption spectrum associated with the photoisomerization were compared to the changes in the mode coupling pattern observed in the 2DIR spectra. The comparison indicates that the coupling of the SO and C═O stretching modes is much smaller in the photoisomerized compound compared to that in the ground-state isomer that has not been exposed to incident light (relaxed). Transition-dipole interaction estimations indicate a large decrease of the electric coupling contribution to the C═O/SO mode anharmonicity in the O-bonded versus S-bonded states thus supporting the formation of the O-bonded state upon photoisomerization of the RuBzSO compound.

Efficient simplified blue-emitting phosphorescent organic light-emitting diodes (OLEDs) were fabricated with a nickel oxide (Ni₂O₃) or molybdenum oxide (MoO₃) modified indium tin oxide (ITO) anode. The maximum current efficiency of device anode/bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium (FIrpic)/FIrpic:1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi)/LiF/Al was increased from 3.6 cd/A with ITO anode to 22.0 and 23.6 cd/A for Ni₂O₃ and MoO₃ modified ITO anodes, respectively. Moreover, the maximum current and power efficiencies of another bilayer device ITO/MoO₃/FIrpic:4,4′-N,N′-dicarbazole-biphenyl (CBP)/FIrpic:TPBi/LiF/Al were as high as 49 cd/A and 48 lm/W, respectively. Photoelectron spectroscopy measurements were employed to investigate the electronic structure of the anode/organic interfaces. Results show that the band alignment at the oxide/organic interface plays a critical role in these simplified blue devices.

Using synchrotron angle-dispersive X-ray diffraction and Raman spectroscopy techniques in a diamond anvil cell, we have examined the structural behaviors of the cubic (anti-C) Ca₃N₂ at high pressures and room temperature. Two first-order phase transformations were observed at 9.6 and 19.5 GPa accompanied by large volume collapses of 7 and 9%, respectively. The two high pressure phases were identified as monoclinic (anti-B) and hexagonal (anti-A) structures by Rietveld refinement. With the pressure derivatives fixed at 4, the bulk modulus of anti-C, anti-B, and anti-A type structures were determined as 53.1(2), 61.6(4), and 83.9(2) GPa, respectively, indicating the increased incompressibility of Ca₃N₂ under high pressure. The phase sequence observed in Ca₃N₂ is in accordance with the systematic behavior of C → B → A phase transitions occurring in most sesquioxides.

Radical pairs, polarons, and fullerene anion radicals photoinduced by photons with an energy of 1.98−2.73 eV in bulk heterojunctions formed by poly(3-hexylthiophene) (P3HT) and poly(3-dodecylthiophene) (P3DDT) with [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) and 2-(azahomo[60]fullereno)-5-nitropyrimidine (AFNP) fullerene derivatives were studied by a direct light-induced electron paramagnetic resonance (LEPR) method in a wide temperature range. LEPR spectra of the polymer/fullerene composites consist of contributions of mobile and trapped charge carriers. Concentration and magnetic resonance parameters of these charge carriers were found to depend on the energy of initiated photons. Spin−lattice and spin−spin relaxation times of polarons and fullerene anion radicals were determined by the steady-state saturation method. The interaction of most charge carriers with the lattice is characterized by monotonic temperature dependence, whereas the spin−lattice relaxation time of fullerene anion radicals trapped in the P3DDT matrix demonstrates sharper temperature dependence. Spin−spin interaction is shown to be nearly temperature independent and to be governed by structural properties of polymer/fullerene composites. Longitudinal diffusion of polarons and pseudorotation of fullerene derivatives was shown to follow the activation Elliot hopping model. The replacement of the P3HT matrix by P3DDT accelerates polaron dynamics and increases its anisotropy. The energetic barrier required for polaron interchain hopping mainly prevails upon that of its intrachain diffusion in all composites except P3DDT/AFNP one. Spin dynamics becomes easier when the PCBM fullerene derivative is replaced by the AFNP one.

The optical properties of photopolymer layers consisting of an acrylamide-based matrix and microporous aluminophosphate nanocrystals of AEI type are investigated. The compatibility of the photopolymer doped with the nanoparticles is studied. The surface and volume properties of the layers with different levels of doping with microporous nanocrystals are characterized. The effective refractive indices and absorption coefficients of the doped photopolymer layers are determined and used to calculate the refractive index and porosity of pure AEI nanoparticles used as dopants. Volume transmission gratings were recorded in the doped photopolymer layers at different spatial frequencies. By spatial monitoring of the characteristic Raman peak of the AEI particles across the grating vector, the optimal concentrations of the nanocrystals for obtaining the highest light induced redistribution of nanocrystals are determined. The optical properties of the photopolymer layers combined with the redistribution of the AEI nanoparticles during holographic recording are the parameters exploited for fabrication of optical sensors. An irreversible humidity sensor based on a transmission holographic grating is designed and fabricated. The diffraction efficiency of the sensor changes permanently after exposure to high humidity.