Research On Preparation And Degradation Of Composite Photocatalysts Modified By Zinc Oxide

Nowadays,most oilfields in China are in the stage of tertiary oil recovery,and a large amount of oilfield wastewater is produced in the process of oil exploitation,storage,transportation,oil dehydration and reuse.Oilfield wastewater has complex components and high content of refractory pollutants,so it is difficult to treat.Photocatalytic oxidation technology is a new wastewater treatment method with high efficiency,short hydraulic retention time,simple reaction conditions and simple operation.It has strong practicality for treating refractory organic pollutants in oilfield wastewater.In this paper,zinc oxide was used as the basic photocatalyst,and in view of its wide band gap and easy recombination of photogenerated electron holes,zinc oxide was modified to treat refractory organic pollutants in oilfield wastewater.（1）Cu₂O@ZnO and RGO@Cu₂O@ZnO（reduced graphene oxide-copper-zinc complex oxide）photocatalysts were prepared by improved impregnation-reduction-air oxidation method and solvothermal method respectively.The photocatalysts were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）and fluorescence spectroscopy（PL）.（2）Two kinds of organic compounds with different chemical structures,p-nitrophenol（PNP）and polyacrylamide（PAM）,were used as characteristic pollutants in oilfield wastewater to investigate the treatment effect of composite photocatalysts.（3）The photocatalytic degradation mechanism and recycling performance of the composite photocatalyst were investigated by electrochemical characterization and repeatability test.The results showed that（1）Cu₂O@ZnO had high crystallinity and Cu₂O was grown on ZnO nanorods.compared with monomer ZnO,the photoresponse range of Cu₂O@ZnO was broadened,and the photocurrent response of Cu₂O@ZnO was enhanced,and the recombination rate of photogenerated electron-hole pairs was decreased.Under simulated sunlight,Cu₂O@ZnO composite photocatalyst has good photocatalytic degradation performance for p-nitrophenol and polyacrylamide simulated wastewater,and polyacrylamide was easier to degraded.The optimum treatment conditions for p-nitrophenol were as follows:the molar ratio of copper to zinc was 0.15,the concentration of Cu₂O@ZnO was 0.5 g/L,the initial concentration of p-nitrophenol was 10 mg/L,and the photocatalytic degradation rate was 98.2%.The optimal treatment conditions for polyacrylamide were as follows:copper-zinc molar ratio was 0.15,Cu₂O@ZnO concentration was 0.5 g/L,polyacrylamide initial concentration was 100 mg/L,and the photocatalytic degradation rate was 99.7%.Cu₂O and ZnO formed a type II heterojunction structure,which was suppressed the recombination of photogenerated electron-hole pairs effectively.At the same time,the composite had good stability and cycle regenerability.Cu₂O@ZnO still had high photocatalytic degradation rate after four cycles of reuse.（2）For RGO@Cu2O@ZnO,Cu2O@ZnO was uniformly distributed on the graphene carbon layer.Compared with Cu₂O@ZnO,the light absorption capacity of RGO@Cu₂O@ZnO was enhanced,and the photocurrent response of RGO@Cu₂O@ZnO was enhanced,and the recombination rate of photogenerated electron hole pairs was further reduced.Under simulated sunlight,RGO@Cu₂O@ZnO composite photocatalyst had good photocatalytic degradation performance for p-nitrophenol and polyacrylamide simulated wastewater,and accorded with the first-order reaction kinetics model.The optimal treatment conditions for p-nitrophenol was as follows:RGO loading was10%,RGO@Cu₂O@ZnO concentration was 0.3 g/L,p-nitrophenol initial concentration was20 mg/L,and photocatalytic degradation rate was up to 97%.The optimum treatment conditions for polyacrylamide were as follows:RGO loading was 10%,RGO@Cu₂O@ZnO concentration was 0.3 g/L,initial concentration of polyacrylamide was 20 mg/L,and photocatalytic degradation rate was 93%.By introducing RGO,electrons on the Cu₂O and ZnO conduction bands can be transferred to the planar carbon layer of RGO,which accelerated the electron transport speed,suppressed the recombination of electron-hole pairs effectively,and improved the photocatalytic degradation rate.And the composite material had good regenerability.