Preparation of Carbon Nitride/Oxide Semiconductor Hierarchy Structure and Its Photocatalytic Performance

Author:Xiao Yu Zuo

Supervisor:fu hong gang

Database:Doctor

Degree Year:2019

Download:41

Pages:156

Size:13272K

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In recent years,the large consumption of fossil energy and the accompanying environmental problems has the seriously affected human life and development.Thus,it is urgent to find out a way to tackle energy crisis and environmental thesis.As a green strategy to convert low-density solar energy into high-density chemical fuels,semiconductor photocatalytic technology has shown great prospects in mitigating energy crisis and solving environmental pollution.Carbon nitride(C3N4)with suitable band structure,good thermal stability,low cost of raw materials and facile preparation method,which has been widely used in the fields of photocatalytic water splitting,degradation of pollutants,chemical synthesis.However,the bulk C3N4 suffers from the disadvantages of rapid recombination of electron-hole pairs,confined specific surface area,and poor conductivity,which hindered its practical applications.Therefore,it is necessary to improve the performance of C3N4 with proper modification.To date,many methods including element doping,construction of special morphology,establishment of heterostructures with other semiconductors,and exfoliation has been developed.Among various strategies,coupling C3N4 with other semiconductor photocatalyst to construct hiberarchy heterojunction structure is considered as a reliable and effective method to improve its performance.Based on the above analysis,the main contents include:1.Preparation of C3N4-based hiberarchy heterojunction photocatalysta).Combination of C3N4 nanosheets with metal oxide semiconductor photocatalystWe developed a simple and low-cost bottom-up method for production of porous few-layer C3N4,obtained by a sequential molecule self-assembly,alcohol molecules intercalation,thermal-induced exfoliation and polycondensation process.On the basis of the C3N4 exfoliation,we synthesized a series of C3N4/metal oxide heterojunction photocatalysts by utilizing layered-microrod precursor and metal salt as starting material and subsequent vacuum-assisted intercalation,solvothermal and thermal polycondensation process.The detailed procedure is as follows:the tetrabutyl titanate(TBOT)and cerium nitrate(Ce(NO3)3)were dispersed in the mixture of ethanol and glycerol,then with the help of vacuum-assisted intercalation,finally reticular C3N4nested with TiO2 nanoparticles(RCN/TiO2)and C3N4/CeO2 were obtained after thermal polycondensation process.b).Combination of tubular C3N4 with metal oxide semiconductor photocatalystHierarchical nitrogen-doped TiO2/C3N4 tubular heterostructure consisting of C3N4microtube trunks and TiO2 nanothorns on the outer surface of C3N4 microtube(N-TiO2/C3N4-O)was fabricated using hexagonal rod-like layered supramolecule as precursor by solvothermal and subsequent calcination process.2.Photocatalytic performanceThe obtained C3N4-based hiberarchy heterostructure photocatalysts were applied in the fields of photocatalytic hydrogen evolution,pollutants degradation,and organic synthesis.The results showed that the few-layer C3N4 nanosheets,RCN/TiO2 and N-TiO2/C3N4-O are beneficial for photocatalytic hydrogen production.The CeO2/C3N4heterojunction photocatalyst exhibited excellent performance in photocatalytic oxygen production and degradation of pollutants,it also has good stability.The remarkable improvement of the activity for C3N4-based heterojunction photocatalyst is mainly attributed to following reason:the construction of heterostructure can improve the absorption of visible light and promote the separation of photogenerated carriers;the special morphology can increase the specific surface area to provide more active site and shorten the diffusion distance of photogenerated electrons and the reactants.