Preparation Of Hydrotalcite-based Composite Photocatalytic Material And Its Application In Degradation Of Amoxicillin Wastewater

Antibiotic wastewater is a typical refractory organic wastewater.In addition,the unique property of antibiotic wastewater lies in its strong biological toxicity and antibacterial activity,which is a major difficulty in wastewater treatment.Amoxicillin（AMX）is a semi synthetic penicillin antibiotic withβ-lactam structure,which is the most commonly used antibiotic and one of the most detected antibiotics in surface water.Therefore,it is urgent to remove amoxicillin in water environment.Photocatalytic oxidation technology has significant advantages in environmental protection and thorough degradation of organic pollutants.However,the disadvantages of traditional catalysts are obvious.On the one hand,the lifetime of photo generated carriers is short,and the photo generated electrons and holes can not be effectively separated,resulting in the low efficiency of light quantum;on the other hand,they can only be excited by ultraviolet light（﹤380nm）,which only accounts for 4%of the sunlight,and the utilization rate of solar energy is low.Therefore,it is urgent to develop new photocatalysts with simple preparation process,high efficiency and response under visible light.Layered double hydroxides（LDHs）have unique layered structure,high thermal stability,large specific surface area and adjustable composition and structure.They are used in medicine,biomaterials,building materials,flame retardant materials,adsorption,catalysis and other fields,and also have great prospects in the field of water treatment.Based on this,in this study,different types of photocatalysts were constructed by using the layered material structure design theory,and a series of new composite photocatalysts were prepared by using different synthesis methods.Their photocatalytic properties were studied,and the research work is as follows:（1）New efficient quaternary LDHs photocatalysts were prepared by adjusting the types of metal cations.Two kinds of hydrotalcite like composite photocatalysts,quaternary Mg Al based（Cu Mg Al Ti system and Ni Mg Al Ti system）and Zn Al based（Cu Zn Al Ti system and Ni Zn Al Ti system）,were prepared by coprecipitation method.All quaternary LDHs photocatalysts can be excited by visible light,and cumgalti system has the strongest response to visible light and the widest range.The removal rate of amoxicillin（50mg/L）by all quaternary photocatalysts was more than 80%.The results show that the removal efficiency of Cu based catalysts are better than that of Ni based catalysts,and that of Mg Al based catalysts are better than that of Zn Al based catalysts.The removal efficiency of Cu Mg Al Ti-R400 is the most significant,under the reaction conditions of 2.0g/L dosage,60min dark adsorption and120min（500W,>380nm）xenon lamp illumination,the highest removal rate can reach 93%.（2）Mg Al-LDH/TiO₂ and Zn Al-LDH/TiO₂ photocatalysts were prepared by coprecipitation and hydrothermal methods using Mg Al hydrotalcite and Zn Al hydrotalcite as supports and TiO₂.The presence of hydrotalcite supports significantly improves the response of TiO₂ to visible light.The effect of Mg Al hydrotalcite is better than that of Zn Al hydrotalcite.The heterojunction formed at the interface hinders the recombination of photogenerated electrons and holes and enhances the photocatalytic activity.When the concentration of amoxicillin was 50mg/L and the dosage of catalyst was 2.0g/L,the highest removal rate of amoxicillin was 89.3%by Mg Al-LDH/TiO₂ and only 76.5%by Zn Al-LDH/TiO₂ after dark adsorption for 60min and illumination for 120min.（3）The mechanism of photocatalytic reaction was studied and verified by performance test and free radical quenching experiment,and the conclusion are as follows:In all amoxicillin degradation reaction systems,the main attacking active substances are holes（h+）and superoxide radicals （·O₂^-）.