Study On The Dual-functional Photocatalytic System With ZnIn₂S₄-based Photocatalyst For Simultaneous Hydrogen Evolution And Organic Pollutants Degradation

As a green and sustainable technology,photocatalytic technology has received widespread attention because of its ability to use solar energy to solve energy crises and environmental pollution.It is an ideal,pollution-free and green energy preparation technology to produce hydrogen by solar energy photocatalytic decomposition of water.Design and develop green treatment technologies for sewage treatment resources to completely degrade various toxic and harmful pollutants in sewage into H₂O and CO₂,and produce H₂ at the same time,so as to achieve efficient use of chemical energy in sewage and realize the transformation from solar energy to hydrogen energy.An important scientific topic that scholars at home and abroad are striving to make breakthroughs has broad application prospects in the field of water treatment technology research and development.In recent years,scientific researchers have devoted themselves to designing and developing photocatalytic materials with high efficiency of catalyzing the reaction of electrons and holes at the same time,high light utilization efficiency and light quantum efficiency.The ternary sulfide ZnIn₂S₄ has good visible light absorption,chemical stability and photoelectric properties,and is currently a new type of photocatalytic water splitting hydrogen production material with relatively promising development prospects.This thesis is dedicated to the design and preparation of a new type of ZnIn₂S₄-based bifunctional photocatalyst,by supporting co-catalysts,synthesizing heterojunction structure and other means to improve the photocatalytic activity of ZnIn₂S₄ and constructing a dual-functional photocatalytic system for degradation of organics and hydrogen production.The main research of this paper consists of the following two parts:（1）Using solvothermal method,ZnIn₂S₄ nanosheets were grown in situ on the surface of oxygen-doped MoS₂（OMS）nanospheres to prepare an urchin-like oxygen-doped MoS₂/ZnIn₂S₄（OMS/ZIS）composites.The activity test results showed that the hydrogen production rate of the OMS/ZIS composite with the best ratio under visible light irradiation was 12.8 mmol·g^-1·h^-1,which was 5 times that of ZnIn₂S₄,and the apparent quantum efficiency at a wavelength of 420 nm（AQE）was 14.9%.Experiments on photocatalytic hydrogen production and degradation of organic pollutants showed that resorcinol（RC）,tetracycline（TC）and bisphenol A（BPA）could be used as electron donors to promote the hydrogen production reaction.In the 4 h degradation process,the degradation efficiency of pollutants reached 41.5%,63.5%,and 53.0%,respectively.The rate of hydrogen production while degrading BPA was the highest,reaching 672.7μmol·g^-1·h^-1.The capture agent experiment confirmed that the main active species of the dual-functional degradation system is the hole.The structure-activity relationship between the degradation of organic pollutants and the activity of hydrogen production was further explored by using density functional theory calculations and other methods.The characterization results and mechanism studies showed that the unique microstructure of the catalyst could provide abundant active sites for catalytic reactions,shorten the charge transfer distance,thereby inhibit the recombination of electron-hole pairs,and reduce the charge transfer resistance and the overpotential of the hydrogen production reaction.（2）The ZnCo₂O₄/ZnIn2S4（ZCO/ZIS）composite material was prepared by a one-pot reflux wet chemical method.The ZnCo-ZIF-derived ZnCo₂O₄ material retains the dodecahedral structure of the metal organic framework material（MOFs）template,and at the same time forms a special hollow porous morphology after low-temperature annealing,and its special microstructure significantly improves the light utilization of the catalyst Rate,and shorten the migration and transmission distance of photogenerated carriers.In addition,the two-dimensional ZnIn₂S₄ nanosheets have a large specific surface area and abundant active sites,which can significantly improve the visible light catalytic performance of the catalyst.The activity test results showed that the hydrogen production rate of the ZCO/ZIS composite with the best ratio under visible light irradiation was 5713.4μmol·g^-1·h^-1,and the AQE at 420nm was 11.9%.Taking o-chlorophenol（2-CP）as the target pollutant,the photocatalytic organic degradation and hydrogen production performance test was carried out.The results showed that the degradation efficiency of the pollutants after 8 h of reaction was 100%,and the hydrogen production rate was 238.5μmol·g^-1·h^-1.Through the trapping agent experiment,it is determined that the main active substance in the dual-functional degradation system is the hole.Mechanism studies have shown that:an efficient heterojunction interface is formed between n-type ZnIn₂S₄ and p-type ZCO,and an efficient built-in electric field is formed at the heterojunction interface,which further accelerates the migration and migration of photogenerated electron-hole pairs.Transmission improves the separation efficiency of carriers.By designing two ZnIn₂S₄-based photocatalytic materials,hydrogen can be produced while degrading pollutants.It provides new methods and new strategies for the use of solar photocatalysis technology to solve wastewater treatment and energy recovery applications.It has important research value and practical significance for alleviating the current water environmental pollution and energy shortage problems.