Research On Photocatalysis And Photoelectrocatalysis Performance Of Semiconductor Heterojunction Materials

Degradation of pollutants and development of clean energy have become the key to dealing with environmental energy crises.Therefore,photocatalysis and photoelectrocatalysis technologies that use solar energy to solve the above challenges have been extensively studied.High efficiency,green and low cost are the key for photocatalysis and photocatalysis system.This thesis focuses on the construction and design of new type of semiconductor heterojunction to improve the performance of photocatalysis and photocatalysis.Novel two-dimensional black phosphorus nanosheets（BP）is used to construct heterojunction photocatalysts with graphite carbonitride（g-C₃N₄）and silver base compounds to improve photocatalytic activity and stability;precious metals（Ag nanoparticles）are deposited on titanium dioxide（TiO₂）nanorods/BP heterojunctions to construct composite photoanode materials to improve photocatalytic activity.The main research contents are as follows:（1）The BP/Ag₂CO₃ heterojunction photocatalyst was constructed by co-precipitation method using functionalized BP with polydiene dimethyl ammonium chloride（PDDA）solution.Through the systematic analysis of the BP/Ag₂CO₃ heterojunction photocatalyst,it is proved that the intervention of BP improves the transport efficiency of carriers in the BP/Ag₂CO₃ heterojunction material and inhibits the recombination of carriers,thereby inhibiting the photo-corrosion of Ag₂CO₃ and improving the stability of Ag₂CO₃and the degradation of methyl orange（MO）.After four cycles,the degradation rate of pure Ag₂CO₃material to MO is only 19.2%,while the degradation rate of BP/Ag₂CO₃ heterojunction material to MO is as high as 87.1%.Mott-Schottky and active species capture experiment analysis are used to obtain the band gap configuration of the BP/Ag₂CO₃ heterojunction.and the reaction mechanism of the direct Z-scheme was proposed.In situ X-ray photoelectron spectroscopy（in situ XPS）and density functional theory calculations verified the direct Z-scheme mechanism of the BP/Ag₂CO₃ heterojunction photocatalyst.The direct Z-scheme mechanism plays a decisive role in explaining the enhancement of the stability of BP/Ag₂CO₃ photocatalysis and the suppression of the photocorrosion of Ag₂CO₃.（2）A ternary CN/Ag Br/BP heterojunction composite photocatalyst was constructed by co-precipitation method to modify Ag Br with g-C₃N₄（CN）and PDDA functionalized BP.Compared with pure Ag Br,binary CN/Ag Br and binary Ag Br/BP,it was proved that the ternary CN/Ag Br/BP heterojunction photocatalyst effectively promotes the separation of electron-hole pairs and inhibits their recombination.The degradation efficiency of ternary CN/Ag Br/BP composites to MO is almost 8 times that of pure Ag Br,which is much higher than that of binary CN/Ag Br and Ag Br/BP composites.Through the capture experiment of active species,density functional theory calculation and energy band analysis,a dual S-scheme scheme is proposed to explain the carrier transport path in the ternary CN/Ag Br/BP composite.This double S-scheme mechanism can promote the transfer of electrons from the conduction band of Ag Br to the valence bands of CN and BP,which can overcome the photo-corrosion of Ag Br and enhance its stability.This new type of double S-scheme mechanism heterojunction photocatalytic material provides a more convenient way for efficient wastewater treatment.（3）By layer-by-layer self-assembly,PEI and BP（exfoliated in N-methylpyrrolidone（NMP）solution）were alternately loaded on the surface of TiO₂ nanorods to prepare TiO₂/BP heterojunction materials,and then Ag nanoparticles were loaded onto TiO₂/BP heterojunction materials to form the Ag-TiO₂/BP photoanode material.PEI plays a role for layering and increasing the load capacity.BP can promote charge separation and inhibit their recombination;Ag nanoparticles can promote the transport of surface carriers.The results show that,under the optimal conditions at 1.23 V vs.RHE,the photocurrent density of Ag-TiO₂/BP photoanode material increases from 0.52 m A·cm^-2 to 1.74 m A·cm^-2 under visible light irradiation compared to TiO₂ photoanode.From the above results,it can be seen that the Ag-TiO₂/BP composite material formed by loading Ag nanoparticles on the TiO₂/BP heterojunction can effectively improve the efficiency of the photoelectric catalytic reaction.