Study Of Design And Synthesis Of Novel Photo/Electrodes And Their Self-sustaining Catalytic Wastewater Treatment And Water Splitting

The use of solar energy for degrading organic pollutants and splitting water into hydrogen is an important way to solve the problem of water pollution and energy.The key to realize the efficient use of solar energy is to develop highly active photoelectrocatalytic(PEC)systems.In the traditional PEC system,bias voltage is applied to promote the separation and transmission of photogenerated charges in the photoelectrode to improve the system performance,while the application of bias potential increases the consumption of energy.In addition,the traditional PEC system is not only energy consumption but also loses plenty of chemical energy of organic pollutants.Therefore,it is of great application value to develop high-active self-sustaining PEC system that can recover the chemical energy of organic matters.In this paper,series of novel visible-light-responsive photo/electrodes were designed and synthesized,and novel self-sustaining catalytic systems were constructed and successfully applied to the degradation of refractory organics and electricity recovery and water splitting.The main contents are as follows:1.Using a successive ion layer absorption and reaction technique,a 10 nm-thick Bi₂S₃layer was decorated on the Ti O2 nanotube array(TNA)to obtain the Bi₂S₃/TNA photoanode.The Bi₂S₃/TNA photoanode had an absorption edge of 900 nm,and showed a photocurrent density of 2.6 m A cm^-2 in the presence of hole-scavenger and under visible-light irradiation.It also exhibited highly efficient generation of hydrogen and electricity driven by visible-light in a dual-photoelectrode catalytic system using a Pt decorated Si photovoltaic cell(Pt/Si PVC)as photocathode,obtaining a solar-to-hydrogen(STH)efficiency of 1.9%and a photoelectric conversion efficiency of 0.718%,showing better technical effect than traditional system.2.A novel method based on the electrodeposition of uniform Fe film in ammonia condition and following an in-situ thermal oxidation process to prepare highly active?-Fe₂O₃ photoanode was developed,which avoided the microstructural defects arising from the traditional electrodeposition method and the unwanted phases of Fe O and Fe₃O₄produced by thermal oxidation of Fe foils.The?-Fe₂O₃ photoanode showed good PEC activity in alkali condition.The sample annealed at 500oC for 2 h exhibited the relatively highest(110)diffraction peak,and showed a photocurrent density of 1.35 m A cm^-2 in 1mol/L KOH under AM1.5 illumination,which was the highest value among the reported?-Fe₂O₃photoanodes prepared by electrodeposition method.The as-prepared?-Fe₂O₃ photoanode showed a photogenerated charge transport rate three times higher than the photoanode prepared by traditional electrodeposition method,exhibiting excellent PEC performance.3.A novel method based on peroxotungstate reduction reaction to prepare vertically aligned WO₃ nanoplate array(NPA)photoanode was developed,which is simple,controllable and suitable for large-scale preparation,overcoming the drawbacks of traditional methods such as hydrothermal process.In this method,a slow and controllable reduction of peroxotungstates by ethanol was used,which was the critical step to ensure the uniform and ordered synthesis of orthorhombic WO₃·H₂O NPA films which assembled directly on F-doped tin oxide substrates under the capping effect of oxalate,and subsequently WO₃·H₂O NPA films were converted into monoclinic WO₃ NPA films by calcination.C₂O₄^2-,an electron-rich organic ion,could form H-bonds with the interlayer H₂O molecules of orthorhombic WO₃·H₂O on the(010)facet which restricted the growth along[010],thus forming nanoplate structures.The WO₃ photoanode possessed preferentially exposed highly reactive(002)facets and showed excellent PEC performance.4.To enhance the absorption of visible-light of WO₃ photoanode(absorption band edge<470 nm),a novel method based on the reaction of bismuth nitrate with peroxovanadate to prepare BiVO₄ decorated WO₃(WO₃/BiVO₄)photoanode was developed,which prevented the introduction of structural defects in the WO₃ substrates from repeat heating-cooling process that occurs in conventional deposition-annealing(DA)methods.The as-prepared WO₃/BiVO₄ photoanode showed an increased absorption edge of 510 nm,and possessed a photocurrent density of 2.83 m A cm^-2.The Mo doped WO₃/BiVO₄ photoanode showed an increased photocurrent density of 3.78 m A cm^-2 because of the improved charge transport property of the BiVO₄ layer.The WO₃/BiVO₄ photoanode showed a photogenerated charge transport rate one times higher than the photoanode prepared by traditional DA method,showing excellent performance for PEC water splitting and organic degradation.5.To further improve the stability and resistance of acidic/alkaline conditions of WO₃photoanode,a novel method based on the energy-level match and lattice match between Ti O2and WO₃ to prepare nanobranched WO₃/Ti O2photoanode using epitaxial growth of Ti O2layer was developed.The epitaxial nanobranched layer composed of highly crystalline anatase Ti O2 with a thickness of 50 nm and 30 nm for the nanobranches with growth direction of[001].The epitaxial Ti O2 layer decreased the surface defect sites of WO₃,therefore reducing combination rate.The energy-level match between Ti O2 and WO₃facilitated the separation of photogenerated charges,therefore increasing their life-time.The pin-point structure of the Ti O2 nanobranches showed enhanced local electrical fields,which facilitated the degradation of organics and oxidation of water by photogenrated holes.The Ti O2 layer also inhibited the formation of peroxide species on the WO₃ surface,therefore improving the PEC stability of the photoanode.The of WO₃/Ti O2photoanode exhibited 80%improvement in photocurrent density compared with WO₃photoanode,which was excellent stable in 100 h operation while it was continuous decay for WO₃photoanode,showing high activity and stability for PEC water splitting and organic degradation.6.This paper constructed highly efficient self-sustaining catalytic system based on the WO₃/Ti O2photoanode,Si photovoltaic cell array(Si PVC)and Mo S₂ cathode.In this system,the front semitransparent WO₃/Ti O2photoanode could absorb short-wavelength photons of sunlight and generated electron/hole pairs,while the transmitting longer-wavelength photons were captured by the rear Si PVC to generate photovoltage,which facilitated the electrons from the photoanode to the Mo S₂ cathode.Using only sunlight,this self-sustaining system showed extremely efficient and stable performance for splitting water into hydrogen and oxygen with a solar-to-hydrogen(STH)efficiency of 3.4%,and had no obvious decay in 35-day simulated operation.When replacing Mo S₂ cathode with Ptblack/Pt cathode,the system was applied to solar-driven degradation of refractory organics and electricity recovery,successfully realizing the remove of refractory organics including phenol,Congo red and tetracycline hydrochloride,and a generating efficiency of 2.828%.Adding a small amount of Fe²⁺ion(2 mmol/L)into the self-sustaining system could improve the performance of degrading organics because the Fenton-like process introduced the radical reactions into the whole aqueous system,increasing the generation of·OH and facilitating the degradation of organics,which avoided the continuous addition of H₂O₂ in traditional Fenton method and the consumption of electricity in traditional electro-Fenton process,and additionally prevented the production of sludge because of the low concentration of Fe species.