Preparation Of ZnO-based Photocatalytic Materials And Its Application In The Treatment Of Antibiotic Pharmaceutical Wastewater

The production of antibiotics in China ranks among the top in the world,and a large amount of antibiotic waste water produced is discharged into nature,which seriously threatens the ecological environment and human health.Photocatalytic degradation technology has the characteristics of degrading multiple antibiotics,high efficiency,energy saving and no secondary pollution.It has a good application prospect in the treatment of antibiotic pharmaceutical wastewater.Semiconductor photocatalytic materials play a major role in Photocatalytic degradation technology.Among them,ZnO has the advantages of excellent physical and chemical properties and low production costs.It is always used as a catalytic material in photocatalytic degradation technology.However,the application is limited because of its wide bandgap width,low utilization of solar energy,high recombination probability of photo-generated carriers,and easy to be photocorroded.At present,there are few studies on the application of photocatalytic degradation technology in the treatment of practical pharmaceutical wastewater.In this paper,two kinds of functional composite photocatalytic materials,AgCl/ZnO/GO and AgCl/ZnO/g-C₃N₄,were prepared based on ZnO,which were characterized comprehensively,the performance of photocatalytic degradation of tetracycline hydrochloride simulated pharmaceutical wastewater were investigated,and the photocatalytic mechanism was analyzed.On this basis,the photocatalytic degradation effects of AgCl/ZnO/g-C₃N₄on the practical pharmaceutical wastewater containing two types of antibiotics were preliminarily studied.The composite photocatalytic materials,AgCl/ZnO,AgCl/ZnO/GO and AgCl/ZnO/g-C₃N₄,were prepared by hydrothermal method and chemical deposition method.The phase composition,micromorphology and optical properties of the materials were characterized by XRD,SEM,TEM,XPS and UV-Vis.The results show that compared with ZnO substrate,the absorption of visible light and the number of photo-generated electrons and holes generated under visible light irradiation are increased.Among them,AgCl/ZnO/GO（molar ratio of Ag Cl to ZnO is 1:1）and AgCl/ZnO/g-C₃N₄（molar ratio of Ag Cl to ZnO is 1:2）have the best photocatalytic performance and stability.At room temperature,the initial pH of11 and the dosage of 1.5 g/L,after visible light irradiation for 50 min,the degradation rates of the two composite materials for 20 mg/L tetracycline hydrochloride simulated pharmaceutical wastewater are 95.20%and 92.68%,respectively.After four reuses,the degradation rates of the two composite materials for the tetracycline hydrochloride simulated pharmaceutical wastewater can still reach 78.00%and 75.17%,respectively.Since the preparation cost of AgCl/ZnO/g-C₃N₄was lower,it was further used in the advanced treatment of practical pharmaceutical wastewater containing two types of antibiotics,tetracycline hydrochloride and cefoxitin.Using the removal rates of tetracycline hydrochloride,cefoxitin,COD and TOC as the indexes,the optimal reaction conditions of AgCl/ZnO/g-C₃N₄（molar ratio of Ag Cl to ZnO is 1:2）for the treatment of practical pharmaceutical wastewater were studied.The results show that the optimal reaction conditions for catalytic degradation of tetracycline hydrochloride pharmaceutical wastewater are:the dosage of AgCl/ZnO/g-C₃N₄is 1.5 g/L,the pH value is 9 and the illumination time is60 minutes.Under this condition,the removal rates of tetracycline hydrochloride,COD and TOC are 82.23%,73.72%and 75.59%,respectively.The optimal reaction conditions for catalytic degradation of cefoxitin pharmaceutical wastewater are:the dosage of AgCl/ZnO/g-C₃N₄is 1.5 g/L,the pH value is 9 and the illumination time is 90 minutes.Under this condition,the removal rates of cefoxitin,COD and TOC are 79.01%,75.42%,and77.81%,respectively.The research shows that the catalytic properties of the functionally modified ZnO composites have been significantly improved,and the advanced treatment of practical pharmaceutical wastewater containing two types of antibiotics has also achieved good application results.This research provides theoretical basis and technical support for the practical application of photocatalytic technology in the advanced treatment of antibiotic pharmaceutical wastewater.