The Removal Of Congo Red By Zero-Valent-Zinc And Photocatalytic Degradation Of Atrazine And Chloramphenicol By Znic Oxide

With the continuous progress in industrial,agricultural and medical field,a series of refractory environmental pollutants are gradually produced.Congo red(CR),atrazine(ATZ)and chloramphenicol(CAP)are representative pollutants in the industrial,agricultural,and medical fields,respectively.The chemical structures of these three pollutants are stable,and the biodegradability is poor.So the release of these contaminants poses a great harm to the environment,which threatens the ecological balance and human health seriously.The degradation of organic contaminants by enhanced zero-valent metal reduction technology and photocatalytic technology has drawn wide attention.In this study,the method of nano silica gel(nSG)enhanced zero-valent zinc(Zn0)method was adopted to degrade CR.and zinc oxide was selected as a photocatalyst to degrade ATZ and CAP under simulated sunlight.The influencing factors and the possible mechanism were investigated.This study is mainly consisted of three parts:In Part ?:Batch experiments have been conducted under different reaction conditions to investigate the influencing factors including the dosage of nso and Zn0,initial pH and CR concentration were studied.The results show that nSG plays the role of loading and dispersing Zn0 to avoid agglomeration,and silicic acid produced generally to prevent forming passive films of Zn(?)(hydr)oxides on the Zn0 surfaces.The optimum degradation condition for congo red is:pH=6,the dosage of nSG=2 g/L,the dosage of Zn0=0.5 g/L,approximately above 95%of the initial congo red was removed under this condition in 60 min.When the pH of the reaction system is above 6,the adsor:ption of CR by nSG could be ignored(3%).While pH<6,the removal of CR is accelerated,which is attributed to the adsorption of CR by nSG.Full wavelength scatning combined with the atomic absorption spectrometry was adopted to reveal the potential mechanism responsible for the enhanced reactivity of nSG.The degradation of CR by Zn0 enhanced by silica gel can be described by a pseudo-first-order kinetics.In Part ?:Zinc oxide synthesized by the co-precipitation method,analytical pure zinc oxide,nanoscale zinc oxide and industrial zinc oxide were compared as photocatalyst in the atrazine photocalalytic degradation under the irradiation of simulated sunlight offered by a 500-watt xenon lamp.The effects of temperature,pH,initial concentration of atrazine,and amount of ZnO were also studied.It is found that at temperature 25?,pH=6,ZnO loading=0.5 g/L,the concentration of 10 mg/L atrazine in the system was almost completely(98.4%)degraded within 60 min under a 500-watt xenon lamp irradation.And the kinetics obeys to pseudo-first-order pattern.Liquid chromatography-mass spectrometry(LC-MS)was used to explore the intermediate products of atrazine.And the electron paramagnetic resonance(EPR)technique was adopted to determine the free radicals generated during the photodegradation.In addition,the photodegradation experiments were carried out under real sunlight,which shows better efficiency than that under simulated sunlight,indicating that the ZnO photocatalytic system is promising in practical application of contamination treatment.In Part ?:The analytical pure ZnO was adopted as photocatalyst to decompose the emerging contaminant chloramphenicol under the irradiation of 500-watt xenon lamp.The optimum degradation condition was:T=25?,pH=6,ZnO loading is 0.5 g/L.The concentration of 10 mg/L chloramphenicol can be almost completely(96%)degraded within 90 minutes of reaction,the kinetics fits well with the pseudo-first-order kinetic model.The total organic carbon(TOC)results showed that the mineralization of chloramphenicol is much higher than atrazine in this ZnO photocatalytic system.