Study On Design,synthesis And Properties Of Bismuth-based Semiconductor Materials For Photocatalytic Degradation Of Tetracycline Hydrochloride

The development of social economy brings energy crisis and environmental pollution.With the consumption of a large number of non-renewable fossil energy in the process of social production and life,various chemical products,pesticides,fertilizers,antibiotics and other pollutants enters into the ecological system.Photocatalytic environmental treatment technology is a technology that converts renewable solar energy into chemical energy and eliminates harmful environmental pollutants.Thus semiconductor materials based photocatalysis attracts a lot of attention.Bismuth-based semiconductors possess inherent advantages,such as green and non-toxic,strong physical and chemical stability,and suitable band width,which become the hot research pots in photocatalytic field.However,the low photo-generated electron-separation efficiency,weak redox capacity and insufficient light absorption severely restrict the application of bismuth-based semiconductor materials in photocatalysis.In this study,carbon material doping,construction of Z-scheme heterojunctions and surface modification are adopted to modify bismuth-based semiconductor materials to improve their photo-generated electron-hole separation efficiency,redox capacity and light absorption efficiency.Furthermore,the performance and mechanism of photocatalytic degradation of tetracycline hydrochloride(TC)by bismuth-based semiconductor composites are investigated.It provides new ideas and theoretical basis for the design of bismuth-based semiconductor composite materials and the application of bismuth-based semiconductor materials in the photocatalytic degradation of antibiotic wastewater.The specific conclusions of this paper are as follows:1.Revealing the modification of Bi₂WO₆ with nitrogen-doped carbon quantum dots(N-CQDs),and the reasons for the improved photocatalytic performance of N-CQDs/Bi₂WO₆ was clarified.This study found that N-CQDs possessed good electron capture and transfer abilities and up-conversion ability,which improved the Bi₂WO₆ with inherent defects of low visible light absorption and carrier separation efficiency.Doping N-CQDs into Bi₂WO₆ via an one-step hydrothermal method can significantly improve the photocatalytic degradation of TC.The optimal ratio photocatalyst(N-CQDs/Bi₂WO₆-5)reached 97%efficiency for tetracycline hydrochloride(TC,10 mg L^-1)after 25 minutes of visible light irradiation,the efficiency rate was 2.2 times than pure Bi₂WO₆.2.A method for construction of N-CQDs mediated BiVO₄/Ag₃PO₄ Z-scheme heterojunctions was clarified.The formation of Z-scheme heterojunctions can achieve more efficient carrier separation and visible light absorption.BiVO₄/N-CQDs/Ag₃PO₄ Z-scheme photocatalyst was successfully synthesized by a hydrothermal-precipitation method.The morphology,chemical composition and physical and chemical properties of the composites were analyzed by means of SEM,TEM,XPS,XRD,FTIR and Raman.BiVO₄/N-CQDs/Ag₃PO₄ composites exhibited excellent TC photocatalytic degradation performance under visible light.The degradation efficiency of TC(10 mg L^-1)reached 88.9%in 30 minutes,and the mineralization rate reached 59.8%after 90 min irradiation.The N-CQDs with good electron transfer ability promote the formation of Z-shceme heterojunctions in composites.3.The study clarified the method of modification of band structure and molecular oxygen activation capacity of BiVO₄ by compunding with cuprous oxide(Cu₂O)with a relatively negative conduction band(CB)and N-CQDs.Cu₂O/BiVO₄ Z-scheme heterojunction photocatalyst with N-CQDs as electron mediators was synthesized by a hydrothermal-precipitation method,which exhibited good TC photocatalytic degradation performance under visible light.The BiVO₄/N-CQDs/Cu₂O Z-scheme heterojunction composites exhibited excellent photocatalytic performance and 99.1%TC removal efficiency under visible light irradiation for 60 min.N-CQDs provided a potential internal driving force to reconstruct the local electric field and promote the construction of Z-scheme heterojunction BiVO₄/N-CQDs/Cu₂O composites.The construction of Z-scheme heterojunction can simultaneously achieve the effective separation of photo-generated electron-hole pairs,improved the light absorption efficiency and maintain the maximum redox potential.4.This study clarified the feasible modification method of BiVO₄ by compounding with Ag@N-CQDs core-shell nanoparticles,which focused on improving the insufficient photocatalytic performance of BiVO₄ under long wavelength visible-near infrared(Vis-NIR)light.Ag@N-CQDs core-shell nanoparticles were synthesized by water bath method,and BiVO₄/Ag@N-CQDs photocatalyst was successfully synthesized by a self-assembly method.This photocatalyst exhibited a good photocatalytic degradation performance of TC under Vis-NIR light.After 60 min of visible light irradiation and 180 min of near-infrared light irradiation,the photocatalytic degradation efficiencies of the optimal ratio photocatalyst(BiVO₄/Ag@NCDs-2)were 80.70%and 65.80%,respectively.While the degradation efficiency of pure BiVO₄ under visible light is only 57.73%,and there is almost no degradation effect under near infrared light.The results showed that Ag@N-CQDs possessed the core-shell structure of N-CQDs wrapped Ag particles,which connected by chemical bonds.The study found that the Ag@N-CQDs core-shell structured nanoparticles possessed surface plasmon resonance(SPR)effect and strong up-conversion ability,resulting in an extended light absorption range in long wavelength Vis-NIR.Additionally,Ag@N-CQDs core-shell structured nanoparticles with good electron capture and transfer capabilities and photothermal conversion capabilities,which can promote the photo-generated electron-hole pair separation efficiency of BiVO₄/Ag@N-CQDs composites.Ag@N-CQDs core-shell structured nanoparticles exhibited strong molecular oxygen activation capability,thus^·O₂^-played a major role in the photocatalytic degradation of TC.In addition,the intermediate products of TC degradation by BiVO₄/Ag@N-CQDs were detected by LC-MS,the degradation pathways were proposed.