Study On Photocatalytic Performance And Mechanism Of Environmental Catalytic Materials Based On Support Effect

The prevention of water and air pollution and the development and utilization of energy are important topics related to economic globalization and sustainable development.The over-exploitation and use of fossil energy have led to excessive emissions of CO₂ in addition to the depletion of energy resources,which has seriously affected the natural carbon cycle balance.Especially,the global warming caused by the greenhouse effect has brought severe environmental problems such as extreme weather.Photocatalytic technology has always had significant advantages in solving the problems of water pollution and energy regeneration.In particular,the utilization of photoreduction of CO₂ technology can reduce CO₂ to stable,efficient,and clean carbonaceous compound fuels such as carbon monoxide,methane,ethylene that are used in people’s daily life,which provides new ideas for alleviating the global energy crisis and maintaining the carbon balance in nature.However,the application of traditional semiconductor photocatalytic materials is severely restricted in the fields of photocatalytic degradation and reduction due to their low utilization rate of light energy,serious photoetching phenomenon,excessively fast photo-generated carrier recombination,and slow electron transfer rate.The problem of low efficiency of semiconductor catalysts caused by agglomeration can be effectively solved by introducing various types of carrier materials and compositing semiconductors with carriers that are compatible with their material properties.Moreover,some special excellent properties inherent in the carrier material itself is helpful to improve the composite semiconductor photocatalyst system,and can greatly promote the separation of photo-generated carrier and improve the utilization rate of light energy.Accordingly,different carriers were used to couple with semiconductor materials to construct the composite heterostructure photocatalytic system in this paper,aiming to take advantage of carrier materials’special effect to control semiconductor composite modes,interface behaviors and even energy band structures.The performance and physical and chemical properties of the composite photocatalyst were investigated and analyzed through a series of characterization and testing methods.Further,the enhancement mechanism of photocatalytic degradation/reduction in the composite material system was explored,aiming to truly realize the prevention and control of water pollution and the"carbon cycle".The main contents of this paper are as follows:1.Preparation of functional mineral carriers coupled composite materials and study of their enhanced photocatalytic behavior and mechanism（1）The two-dimensional network g-C₃N₄ modified ZnO/HNTs composite photocatalyst was prepared with a simple calcination method by using the unique double-layer functional group of high-quality natural mineral carrier HNTs to stabilize the tubular structure.HNTs perfectly solved the agglomeration phenomenon of nano-ZnO,and played the role of supporting framework in the composite system.The bulk phase g-C₃N₄ was successfully transformed into a two-dimensional network structure,which increased the contact area with pollutants and adsorption capacity.In addition,heterostructure g-C₃N₄-ZnO was formed,which effectively broadened the charge migration path,and improved the efficiency of separation photo-generated electron-hole pairs.Therefore,the carrier effect of HNTs was further exerted,and the degradation activity and stability of composite materials were improved.The optimal g-C₃N₄-ZnO/HNTs composite photocatalyst can degrade up to 89%of 20 mg/L tetracycline hydrochloride（TC）solution under visible light within 60 minutes,which is 3.35 times higher than that of ordinary ZnO monomer.（2）The functionalized rodlike natural clay mineral ATPs,which is more suitable for compounding with small-size semiconductor nanocrystals,were selected as carrier materials to construct a CeO₂-In₂O₃/HATP heterostructure composite photocatalyst containing oxygen vacancies with hydrothermal and calcination methods.HTAP effectively reduced the agglomeration of semiconductors while exposing more CeO₂oxygen vacancies and surface defects and active sites of the composite material,so that more CO₂ molecules were absorbed to accelerate the reaction rate.In addition,after load coupling,quantum bound effect between the small-size CeO₂ and In₂O₃ and the rodlike HATP was generated.The photoreduction yields of the prepared10In/Ce/HATP-20 heterostructure composite photocatalyst for CH₄ and CO could reach16.94μmol/g and 32.03μmol/g,respectively.2.The design of carbonaceous carrier coupled composite photocatalytic material and study of their performance and mechanism（1）The GO prepared with the modified Hummers method was selected as the carrier,and the quantum size effect of AgInS₂ QDs was used to promote the formation of the AgInS₂QDs homogenous heterojunction,which optimized the inherent defects of the AgInS₂ quantum dot material and improved the conductivity of Mo S₂.The interface contact effect between the carrier GO and the heterojunction effectively enhanced the transmission and separation rate of photogenerated carriers and optimized the performance of the photocatalyst by controlling its energy band structure.The results showed that AgInS₂-Mo S₂/GO composite had the best photocatalytic performance under 8%GO load.The degradation rate of TC solution under visible light irradiation was about 4.7 times（89.6%）of AgInS₂ monomer.In the 5h photocatalytic CO₂ reduction experiment under UV-Vis light,the yields of CO and CH₄ reached 52.4μmol/g and 26.2μmol/g,respectively,which were significantly improved compared with monomer materials.（2）In order to further utilize the advantages of carbon-based carriers in electron transport,SWNTs were selected to construct a new multi-dimensional CQDs@In₂S₃/SWNTs photocatalytic material with a C-S-C type composite heterostructure with cutting method.While improving the problem of low quantum yield caused by CQDs agglomeration,Shear-functionalized SWNTs successfully constructed a directional transfer channel of charges in the system,which promoted the plasma-like energy conversion and up-conversion effect of photo-excited CQDs,effectively improved the utilization rate of light energy,and inhibited the recombination of semiconductor photo-generated carriers.The degradation rate of CQDs@In₂S₃/SWNTs for ciprofloxacin（CIP）,TC and levofloxacin（LEV）antibiotic solutions in 60 min under visible light irradiation could reach 89%,93%and 78%,respectively.Through the sacrificial agent capture experiment and electron spin resonance（ESR）detection,it is concluded that superoxide radicals（·O₂^-）,holes and singlet oxygen（1O₂）were the main active species in the photocatalytic degradation reaction.3.Construction of a two-dimensional ultra-thin g-C₃N₄ carrier coupled photocatalytic system and study of its performance and mechanism（1）An Au@In₂O₃/g-C₃N₄ heterojunction composite photocatalyst with g-C₃N₄as a carrier was constructed based on the excellent photo-generated charge transfer bridge function of In₂O₃ and the ultra-thin two-dimensional structure of g-C₃N₄.The carrier effect based on ultra-thin two-dimensional g-C₃N₄ layer on the periphery of the multilayer heterostructure effectively inhibited the HER process.In addition,the LSPR effect of the thermionic donor Au NPs effectively adjusted the recombination potential,accelerated the electron migration and the separation of photo-generated carriers,and further improved the efficiency of light reduction of CO₂ to CO and CH₄.The yields of the prepared composite catalyst sample 2Au@CN-In₂O₃ for photoreduction of CH₄ and CO within 5 hours were 79.8μmol/g and 141.2μmol/g,respectively,which were about8.6 times and 8.1 times of the yield with In₂O₃ monomer.（2）Based on the above work,the precise temperature-controlled hydrothermal method was used to prepare single-crystal Zn In₂S₄ with different surface Zn vacancy defect concentrations.By loading ultra-thin g-C₃N₄ to form defect-state Zn In₂S₄-g-C₃N₄ heterojunctions,strong interface effects were more likely to be generated between zinc-rich defects r ZIS and the g-C₃N₄ containing surface active sites.In addition,the two-dimensional ultra-thin g-C₃N₄ provided a place for all redox reactions and directional electron migration,giving full play to its carrier-like effects.The SWNTs were introduced to construct multiple channels for charge transfer in the composite material system,which promoted the directional transfer of photo-generated charges and the efficient separation of carriers.Moreover,via adjusting the Zn defect concentration,the electron migration and reduction reaction path could be controlled,so as to achieve the effective adjustment and optimization of the selectivity and activity of CO₂ photoreduction.The yields of the prepared UCN@r ZIS/SWNT composite photocatalyst for photoreduction of CH₄ and CO within 2 hours were 40μmol/g and 32μmol/g,respectively,which improved the selectivity for reduction of CH₄.