Synthesis Of CuBi₂O₄-based Composites And Study On Their Photocatalytic Activity For The Degradation Of Antibiotic In Aqueous Solution

The antibiotics is a double-edged sword,which saves a lot of human and animal lives.At the same time,due to the serious abuse and inappropriate treatment of the antibiotics,their residues in the environment has increased sharply,and greatly disrupted the ecological balance.In addition,it will be enriched through the food chain,enter the human body and pose a potential threat to human health.Therefore,it is of great significance to develop the research on antibiotic pollution control technology.The semiconductor-based photocatalytic technology,possess the advantages of cleanness,high efficiency,mild reaction conditions,etc.has stood out as a "dark horse" in recent years,and has been widely used in antibiotics wastewater treatment.The spinel-type compound CuBi₂O₄,as typical Bi-based semiconductor photocatalyst,exhibiting strong light absorption capacity due to its narrow band gap about 1.5-1.8 eV.It has excellent thermal and chemical stability,which is considered to be a promising metal oxide semiconductor photocatalyst.However,the low specific surface area and fast recombination of photogenerated carriers have limited the photocatalytic activity and the practical application in wastewater treatment.To solve the above problems,three different types of CuBi₂O₄ based composite photocatalysts were designed and prepared,including precious metal modification Au/CuBi₂O₄,p-n CuBi₂O₄/Bi₂MoO₆ and Z-Scheme Fe₂O₃/CuBi₂O₄.The synthesized CuBi₂O₄ based composite photocatalysts were used to degrade the antibiotics under visible light for investigating their photocatalytic performance.At the same time,the reaction mechanism and the charge migration path of diverse types of CuBi₂O₄ based composite photocatalysts were also discussed based on the active species trapping experiment.The main contents and results of this thesis are as follows:0D/1D,Au/CuBi₂O₄ composite photocatalysts were synthesized by a simple in situ thermal reduction-precipitation method.Due to the plasmon resonance effect of the Au nanoparticles,the visible-light absorption of the CuBi₂O₄ photocatalyst is enhanced.At the same time,the hot electrons excited by Au nanoparticles can be injected into the conduction band of CuBi₂O₄,thus increasing the photogenerated charge in the reaction process.In addition,in the 0D/1D structure the Au nanoparticles are dispersed more homogeneously on the surface of CuBi₂O₄ microrods,which results in a higher specific surface area and an increased number of active sites.Furthermore,the recombination of photogenerated carriers is further suppressed.The degradation test of tetracycline hydrochloride showed that the photocatalytic activity was significantly improved.The maximum photocatalytic degradation rate constant for Au/CBO composites with 2.5 wt.% Au NPs（120 min,93%）was 4.76 times as high as that of bare CBO microrods.The CuBi₂O₄/Bi₂MoO₆ p-n heterojunction photocatalyst was synthesized through a facile hydrothermal-solvothermal method.The representatives for two kinds of broad-spectrum antibiotics of tetracyclines（tetracycline,TC;oxytetracycline,OTC;chlortetracycline,CTC）and quinolones（ciprofloxacin,CIP）are used as the target pollutants to evaluate photocatalytic performance of the prepared photocatalysts.Compared with the pure p-type CuBi₂O₄ and n-type Bi₂MoO₆,the CuBi₂O₄/Bi₂MoO₆ p-n heterojunction photocatalyst exhibit the superior photocatalytic performance,which are mainly due to the following reasons:（i）the internal electric field established by p-n junction can further improve the separation efficiency of photogenerated electrons and holes in the CuBi₂O₄/Bi₂MoO₆ composite system;（ii）the unique 2D/1D hierarchical structure makes better use of the incident light by light reflections;（iii）the enhanced Specific surface area can provide rich reactive sites for photocatalysis.Notably,the 10 wt.% CuBi₂O₄/Bi₂MoO₆ photocatalyst displays the optimum photocatalytic performance in the degradation of tetracycline,oxytetracycline,chlortetracycline and ciprofloxacin（100 mL,20 mg/L）,72.8%,74.0%,74.4% and 36.7% degradation rates and 34.4%,52.4%,48.2% and 25.5% mineralization rates can be reached within 60 min under visible irradiation.Z-scheme core-shell Fe₂O₃/CuBi₂O₄heterojunction photocatalyst was synthesized by a simple hydrothermal method after Bi（NO₃）₃·5H₂O,Cu（NO₃）₃·3H₂O,NaOH and Fe₂O3 were mixed well in distilled water.The result of photocatalytic degradation experiment showed that 30 wt.% Fe₂O₃/CuBi₂O₄ composite exhibited the highest photoactivity for the degradation of TC（80% degradation within 120 min）under visible light irradiation.The results of capture experiment demonstrate that the electron transfer path in Fe₂O₃/CuBi₂O₄ composite photocatalyst followed the Z-scheme mechanism.The Z-scheme Fe₂O₃/CuBi₂O₄ heterojunction photocatalyst can effectively separate photogenerated carriers in the composite system.In addition,the strong redox potential can be retained to participate in the photocatalytic reaction.