The Study On The Liquid Preparation And Photocatalytic Capability Of Nano Zinc Oxide And Zn-Cr Layered Double Hydroxides

Industrial wastewater contains a large amount of harmful organic compounds,which is challenging the quality of our life.Compared with traditional methods such as adsorption,filtration and sedimentation,semiconductor photocatalysis has attracted a great deal of attentions due to their wide application to environmental remediation,especially for organic pollutants removal.Photocatalytic degradation not only can eliminate the secondary pollution without further treatment,but also decrease the process cost.In this work,nano ZnO and Zn-Cr layered double hydroxides photocatalytic materials with great performance were explored to degradate pollutants.The results obtained in thesis could provide some guidelines for designing efficient photocatalyts.Firstly,pure ZnO was fabricated by hydrothermal method and homogeneous precipitation method.In the present work,zinc oxide nano-powder was prepared by hydrothermal method using zinc nitrate hexahydrate,sodium hydroxide and citric acid by altering the pH of the suspension.The results indicate that,the photocatalytic degradation reaction of methyl orange is first order reaction,when the pH=12?No citric acid?,excellent photocatalytic activity of the ZnO powders?2 h,degradation rate reach 99%?under 300 W high pressure mercury lamp.In the homogeneous precipitation method,the ratio of different zinc nitrate/urea was studied to obtain the best morphology with the best photocatalytic ratio of 1:2.ZnO prepared under these conditions had shown superior photocatalytic activity toward RhB and phenol degradation under UV light irradiation.The enhanced photocatalytic activity and favorable photostability could be attributed to the less agglomeration,good structure stability and the superior crystallinity of the ZnO.The results showed that ZnO prepared by the homogeneous precipitation method was higher photocatalytic activity than hydrothermal method in the UV degradation.Secondly,cerium-doped ZnO photocatalysts were successfully prepared by hydrothermal method and homogeneous precipitation method.The prepared Ce-ZnO morphology is consistent with that of pure ZnO,and the size of Ce-ZnO particles gradually decreases with the increase of cerium doping amount.The 4f level exists in the cerium ion,and the charge transfer occurs between the 4f level and the valence band/conduction band of ZnO,thereby reducing the bandgap of ZnO.Due to the doping of cerium,the recombination rate of electrons and holes of ZnO carrier is reduced,so cerium-doped ZnO shows more excellent catalytic performance than pure ZnO in photocatalytic degradation of RhB,The impurity is optimal at 0.5%,but excess cerium doping also counteracts the catalytic activity of ZnO.The reason for the higher catalytic activity exhibited by cerium-doped ZnO is due to their smaller grain size and lower band gap,more importantly,an effective reduction of the electron-hole recombination rate.Furthermore,Zn-Cr layered double hydroxides with Zn/Cr ratios of 2:1,3:1 and4:1 were successfully prepared by hydrothermal synthesis.This material has a high specific surface area and strong adsorption properties on the anionic dyes MO.The adsorption kinetics of Zn-Cr LDHs was studied by changing the adsorption time,the amount of adsorbent and the concentration of methyl orange,respectively.The experimental results showed that Zn-Cr LDHs with Zn/Cr ratio of 2:1 had the best adsorption capacity of 453 mg/g or more.The three proportions of Zn-Cr LDHs calcined at 800?are composed of ZnO and ZnCr₂O₄.The calcined products also have the photocatalytic activity of degrading methyl orange under ultraviolet light.Lastly,a facile anion-exchange precipitation method was explored to prepare a novel Ag/AgCl/Zn-Cr-NO₃ LDHs via the reaction of Zn-Cr-Cl LDHs with AgNO₃solution.Significantly,the obtained Ag/AgCl/Zn-Cr-NO₃ LDHs nanocomposite showed considerable efficiency visible-light photocatalytic activity for photodegradation of RhB.