Photoelectrocatalytic Surfactant Pollutant Degradation and Simultaneous Green Hydrogen Generation

For the first time, we demonstrate a photoelectrocatalysis technique for simultaneous surfactant pollutant degradation and green hydrogen generation using mesoporous WO3/BiVO4 photoanode under simulated sunlight irradiation. The materials properties such as morphology, crystallite structure, chemical environment, optical absorbance, and bandgap energy of the WO3/BiVO4 films are examined and discussed. We have tested the anionic type (sodium 2-naphthalenesulfonate (S2NS)) and cationic type surfactants (benzyl alkyl dimethylammonium compounds (BAC-C12)) as model pollutants. A complete removal of S2NS and BAC-C12 surfactants at 60 and 90 min, respectively, by applying 1.75 V applied potential vs RHE to the circuit, under 1 sun was achieved. An interesting competitive phenomenon for photohole utilization was observed between surfactants and adsorbed water. This led to the formation of H2O2 from water alongside surfactant degradation (anode) and hydrogen evolution (cathode). No byproducts were observed after the direct photohole mediated degradation of surfactants, implying its advantage over other AOPs and biological processes. In the cathode compartment, 82.51 μmol/cm2 and 71.81 μmol/cm2 of hydrogen gas were generated during the BAC-C12 and S2NS surfactant degradation process, respectively, at 1.75 V RHE applied potential.

In the first step, a homogenous WO 3 paste was prepared using commercial WO 3 nanocrystalline powder (100 nm size).We adopted Regan's protocol where WO 3 nanopowder was utilised instead of TiO 2 1 .Briefly, the preparation involved the following stages, (a) grinding 5 g of WO 3 with 1 mL of acetic acid for 5 minutes using mortar and pestle, (b) adding 1 mL of deionised water and grinding for 1 minute (repeat this 6 times), (c) adding 1 mL of ethanol and grinding for 1 minute (repeat this 15 times), (d) adding 2.5 mL of ethanol and grinding for 1 minute (repeat 6 times).Then, the WO 3 colloid was transferred into a closed beaker using 100 mL of ethanol.The solution was then magnetically stirred (150 RPM) for 1 minute, sonicated for 10 minutes (10 seconds on/off) and magnetically stirred (150 RPM) for 1 minute again.Then 20 g of -terpineol was added to the above colloidal solution, and then it was magnetically stirred for 1 minute, sonicated for 10 minutes (10 seconds on/off) and magnetically stirred for 1 minute again.Once this step was completed, then 30g of 10% (w/w) ethyl cellulose in ethanol was added, and the solution was magnetically stirred for 1 minute, sonicated for 10 minutes (10 seconds on/off), and magnetically stirred for 1 minute again.The final step used a rotary evaporator to remove the ethanol from the paste.The setting was under vacuum, and the temperature ranged from 50 -70 °C, the speed of rotation was 90 -120 RPM, and it was conducted for 1 hour.Once the homogenous WO 3 paste was ready, it was applied on the pre-cleaned fluorine-doped tin oxide coated (FTO) glass The BiVO 4 solution was prepared by utilising the method reported by Choi et al. 2 .This was done by mixing 0.1462 g of ammonium metavanadate, 0.6061 g of bismuth deionised water together.The solution was then sonicated for 10 minutes.Once the solution was finished, it was spin-coated on top of the WO 3 surface by utilising a spin coater with a setting of 500 RPM for 5 seconds and 2000 RPM for 40 seconds.The From Figure S1 a the peaks exhibits around 18.9 °and 28.9° peaks correspond to the (011) and (013) reflections of monoclinic scheelite BiVO4 (PDF 01-075-1866) 3 .The other predominant peaks are attributed to FTO substrate.When BiVO 4 film coated onto WO 3 films, it exhibits a weaker crystallite peaks due to high crystalline nature of WO 3 film.

S5. Liquid chromatography results
Figure S4 The chromatogram obtained for a pure BAC-C12 standard after benchmarking.

(
Pilkington 12  sheet resistance) by utilising the doctor blade method.A hotplate was utilised to anneal the samples by utilising the following conditions: (a) Ramp Time = 1 hour, (b) Set temperature = 450 °C and (c) Annealing Time = 3 hours.This step was repeated twice to make a 2-layer WO 3 on the FTO glass.

Figure S5 .Figure S6 .
Figure S5.The chromatogram obtained for a pure S2NS standard after benchmarking.

Figure S7 .
Figure S7.PEC surfactant degradation (%) of BAC-C12 at dark and light irradiation conditions.The experiment was recorded at 1.75 V RHE applied potential.