Preparation And Selective Removal Of Antibiotics And Heavy Metals By Molecularly Imprinted Photocatalytic Materials

With the rapid development of large-scale livestock and poultry farming,animal feed is often mixed with antibiotics and heavy metals.The animals’own restricted uptake often leads to residual antibiotics and heavy metals in excreta and wastewater,causing aquatic organisms to develop drug resistance and metal resistance,already posing a serious threat to the ecological environment.With the increase of environmental awareness,many new water pollution treatment technologies have emerged.Among them,photocatalysis is emerging as an effective water treatment technology due to its environmental friendliness and excellent redox properties.In recent years,bismuth-based photocatalysts have received increasing attention because of their excellent visible light response properties.However,they still suffer from some shortcomings,such as the difficulty of efficient separation of photogenerated electron-hole pairs and selectivity.The current research focuses on doping and surface modification to solve the problems of photocatalytic technology in water treatment.In this thesis,bismuth chlorate（Bi OCl）monomer photocatalysts and bismuth chlorate/bismuth niobate（Bi OCl/Bi₃Nb O₇）Z-type heterojunction composite photocatalysts were firstly prepared by the common hydrothermal method.Next,Bi OCl/Bi₃Nb O₇ was modified with molecular imprinting technique and carbon quantum dots（CQDs）,respectively,to construct MIP-BNO and CQDs-MIP-BNO bifunctional composite photocatalysts with selective removal ability for ceftriaxone sodium（CTRX）and hexavalent chromium（Cr（VI））.After the electron microscopy（SEM）,high-resolution transmission electron microscopy（TEM）,X-ray diffractometer and fluorescence spectrophotometer,finally a more comprehensive understanding of the photoelectrochemical properties and photocatalytic performance of the photocatalyst was obtained.This led to a better understanding of the reaction mechanism of heterojunction photocatalysts and possible pathways for photocatalytic degradation of CTRX.Details of the study are as follows:（1）Microspherical Bi OCl monomer photocatalysts and Z-type heterojunction Bi OCl/Bi₃Nb O₇ composite photocatalysts were prepared using the hydrothermal method with Bi（NO₃）₃·5H₂O,Nb₂O₅ and KCl as the bismuth,niobium and chloride sources,respectively.CTRX was used as the target pollutant and xenon lamp was used as a simulated solar light source for photocatalytic experiments.After 120 min of reaction,the Bi OCl/Bi₃Nb O₇heterojunction composite photocatalyst can degrade 80%of CTRX,which is 37%and 46%higher than the degradation efficiency of monomeric Bi OCl and Bi₃Nb O₇ photocatalysts,respectively.The main mechanism of the improved photocatalytic performance of Bi OCl/Bi₃Nb O₇ heterojunction was speculated by the results of UV-vis test and radical trapping experiments may be:The Z-type built-in electric field in the Bi OCl/Bi₃Nb O₇ heterojunction photocatalyst drives the rapid migration of photogenerated electrons from Bi OCl and photogenerated holes from Bi₃Nb O₇,which inhibits the photogenerated electron-hole complexation.At the same time,the Z-type heterojunction is constructed internally to provide better stability of the composite photocatalyst and finally achieve the photocatalytic degradation of CTRX.（2）Bi OCl/Bi₃Nb O₇ was used as the matrix photocatalyst,CTRX as the template molecule,α-methacrylic acid as the functional monomer,ethylene glycol dimethacrylate as the cross-linker,and azo diisobutyronitrile as the initiator.A molecularly imprinted photocatalyst with high efficiency and selectivity,MIP-BNO,was successfully prepared after a period of light exposure under UV lamp.Photocatalytic selective degradation experiments were conducted with CTRX as the target pollutant and chloramphenicol（CPL）as the competing pollutant under the irradiation of xenon lamp simulating sunlight as the light source.After 120 min of degradation,the molecularly imprinted photocatalyst MIP-BNO could degrade 92%of CTRX,with 12%higher degradation efficiency in the same time compared to non-molecularly imprinted Bi OCl/Bi₃Nb O₇,and showed excellent selectivity for CTRX.The mechanism of selective photocatalytic degradation of target pollutants by MIP-BNO molecularly imprinted photocatalysts is:The existence of pores on the surface of the substrate Bi OCl/Bi₃Nb O₇,which have specific recognition ability for CTRX,ensures that only the target pollutant can enter through the pores and undergo photocatalytic reaction.And non-target pollutants cannot be identified,which very much improves the specific adsorption and selective photocatalytic degradation of target pollutants by molecularly imprinted photocatalysts.（3）Doping modification of Bi OCl/Bi₃Nb O₇ photocatalyst with CQDs and construction of ternary composite molecularly imprinted photocatalyst CQDs-MIP-BNO by combining molecular imprinting technique.The experimental results revealed that the ternary composite photocatalysts of 10%CQDs-MIP-BNO had 94%and 81%photocatalytic removal efficiencies for the two pollutants in a single solution of CTRX and Cr（VI）,respectively.And the photocatalytic removal efficiency increased to 97%and 88%in the mixed pollutant mixture system of both.The improved photocatalytic performance was attributed to the incorporation of CQDs to further promote the rapid transfer of photogenerated electrons.In the selective photocatalytic experiments in the mixed solution of three pollutants,the ternary composite photocatalyst showed excellent selective performance for the target pollutants.Finally,a photocatalytic reactor was prepared,and the dual functional photocatalyst powder was loaded onto the surface of a sponge mesh covered with CS/PVA composite film to investigate the actual operation effect of the photocatalyst inside the reactor,providing strong support for the practical application of molecular imprinted photocatalysts.The above results show that the separation of photogenerated electron-hole pairs in bismuth-based composite photocatalysts can be improved by constructing internal Z-type heterojunctions and doping with CQDs.In addition,combining photocatalytic water treatment technology with surface molecular imprinting technology can further improve the specific adsorption and selective degradation of target pollutants by bismuth-based composite photocatalysts.The modified bismuth-based composite photocatalyst showed excellent removal effects for both CTRX and Cr（VI）in water,indicating its wide application prospects in practical wastewater treatment.