Synthesis Of ZnO Based Photocatalytic Materials For Efficient Photocatalytic Degrating Azo Dyes

Azo dye is one of the main pollutants in dye wastewater.It has the characteristics of high COD value,deep chroma,high salt content and low BOD₅/COD value,and it is not easy to be decolorized and biodegraded,causing very serious hazard to environment and human health.Therefore,it is of great significance to study how to efficiently remove azo dyes from water.Photocatalytic technology has the advantages of low energy consumption,high efficiency,complete degradation,etc.It is the most promising green treatment method.And,ZnO is widely used because it is non-toxic and harmless,cheap and easy to obtain,and has a good degradation effect on dyes.However,ZnO photocatalysts still have the disadvantages of low utilization of visible light,high electron-hole pair recombination rate,and difficulty in recovery,which limits their practical application.In this paper,we focus on the shortcomings of ZnO.Several photocatalysts were prepared by sol-gel method.The degradation rate of methyl orange was used to evaluate the photocatalytic performance of the photocatalyst.A series of characterizations and performance experiments were used to illustrate the degradation mechanism of photocatalytic degradation methyl orange.The results of the study are as follows:Zinc oxide?ZnO?photocatalysts were synthesized by sol–gel method using zinc acetate as precursor for degradation of azo dyes under UV irradiation.The resultant samples were characterized by different techniques,such as XRD,SEM,and EDX.The influence of preparation conditions such as calcination temperature and composite ratio on the degradation of methyl orange?MO?was investigated.ZnO prepared with a composite ratio of 4:1 and calcination temperature of 400°C exhibited 99.70%removal rate for MO.The effect of operation parameters on the degradation was also studied.Results showed that the removal rate of azo dyes increased with the increased dosage of catalyst and decreased initial concentration of azo dyes and the acidic condition is favorable for degradation.Furthermore,the kinetics and scavengers of the reactive species during the degradation were also investigated.It was found that the degradation of azo dyes fitted the first-order kinetics and superoxide ions were the main species during the degradation.The proposed photocatalyst can efficiently and rapidly degrade azo dyes;thus,this economical and environment-friendly photocatalyst can be applied to the treatment of wastewater contaminated with synthetic dyes.In order to enhance the photodegradation of methyl orange?MO?by ZnO under visible light irradiation,ZnO nanoparticles co-doped with Ag and N and supported on activated carbon?AC?with different properties were synthesized through the sol-gel method.The results shows that the photocatalytic activities of these photocatalysts followed the order:Ag-N-ZnO/ACs>Ag-N-ZnO>N,or Ag single-doped ZnO>ZnO.This result was attributed to the small particle size,large surface area,narrow band gap,and high charge separation of Ag-N-ZnO/ACs.The Ag-N-ZnO/coconut husk activated carbon?Ag-N-ZnO/CHAC?exhibited the highest degradation efficiency of 98.82%for MO under visible light irradiation.Moreover,the degradation of MO on photocatalysis followed first order kinetics.The reactive species·OH and·O₂^-played more important roles in the photocatalytic degradation of MO over composite photocatalyst.ZnO/Fe₃O₄/g-C₃N₄-x composite photocatalyst was synthesized using zinc acetate,oxalic acid and melamine as raw materials for the degradation of methyl orange.The structure and properties of the composite photocatalysts were characterized by TEM,EDX,PL,XPS,UV-Vis and photoelectrochemistry.The results show that the performance of the photocatalyst is improved,and the degradation rate of methyl orange can reach 97.87%under visible light.Superoxide radicals and hydroxyl radicals play a major role in the photocatalytic degradation of methyl orange.In addition,the addition of Fe₃O₄ greatly improves the stability and recyclability of the photocatalyst.