Preparation And Photocatalytic Properties Researchon M-BiVO₄/MFe₂O₄?M=Zn,Ca,Mg? Composite Photocatalytic Materials

Facing increasingly serious environmental pollution situation and manydefects in traditional water treatment technologies,semiconductor photocatalytic oxidation technology is being studied as an efficient pollution control technology.Monoclinic scheelite bismuth vanadat?m-BiVO₄?and spinel-ferrite?MFe₂O₄?M=Zn,Ca,Mg??are one of the research hotspots due to their unique photocatalytic performance.However,the photocatalytic activities of them are still low due to their narrow spectral response range and the rapid recombination rate of electron-hole pairs.Therefore,the development of photocatalytic materials with wide spectral response range and high light utilization becomes the focus of current research.The reasonable preparation parameters of MFe₂O₄?M=Zn,Ca,Mg?and m-BiVO₄ photocatalytic materials were discussed by sol-gel method in this paper.Using citric acid as a complexing agent and glycol as a dispersant.The samples were analyzed and characterized by means of TG-DSC,XRD,SEM,EDS,TEM,BET and UV-vis,including thermal stability,phase composition,microstructure,grain size and visible light absorption properties.Based on this,the degradation effect of m-BiVO₄/MFe₂O₄?M=Zn,Ca,Mg?composite photocatalyst on methyl orange solution was studied under visible light.Also,the reaction kinetics and the photocatalytic activity of the composite photocatalytic materials were discussed.the results indicated that:?1?when the spinel-ferrite powders of ZnFe₂O₄?CaFe₂O₄?MgFe₂O₄ prepared by sol-gel self-propagating combustion method,the reasonable technological parameters were as follows:the glycol to water ratio of precursor liquid solvent is 1:2,the pH value of the precursor liquid solvent was 4,2,2 and the calcination temperature was950?,850?and 900?respectively.Also,the reasonable holding time was 4h.The corresponding three crystal materials are spherical particles with good dispersion.Under these conditions,three materials have responsiveness to visible light and the corresponding band gap is 1.93eV,1.94 eV and 1.80eV,respectively.?2?The m-BiVO₄ powders prepared by ethylene glycol sol-gel method,the reasonable technological parameters were as follows:the pH value of the precursor liquid solvent was 9 and the calcination temperature was 550?.The sample showed a larger surface area of olive-like particles in this process.The specific surface area up to4.6573m²/g,corresponding to the narrowest band gap of 2.36eV.?3?The composite photocatalytic materials are prepared by the mass ratio of m[m-BiVO₄]:m[MFe₂O₄?M=Zn,Mg,Ca?]=?100-x?:x,?x=5%?10%?15%?20%?.The composite photocatalytic materials showed highest photocatalytic efficiency by photocatalytic degradation of methyl orange solution when the compound ratio was15%,20%,15%,respectively.?4?The degradation process of methyl orange solution by three kinds of composite catalysts is in accordance with the first order reaction kinetics equation,respectively,The fastest degradation rate constant is 0.5435min^-1,0.5218min^-1,0.5435min^-1 when the compound ratio of BiVO₄/ZnFe₂O₄,BiVO₄/CaFe₂O₄,Bi VO₄/MgFe₂O₄ is 15%,20%and 15%.Also,Corresponding to the shortest semi-reaction time is 25.50min,26.56min,25.50min.?5?The photocatalytic performance of m-BiVO₄/MFe₂O₄?M=Zn,Ca,Mg?composite photocatalyst is mainly due to the formation of p–n type hetero-junction with straddling alignmen.Broaden the range of light response,in the photocatalytic process can produce more active electron-hole pairs.As a result of broading the range of light response and producing more active electron-hole pairs,while effectively avoiding the photogenerated recombination probability.The ultimate result is produced more·O^2-?·OH?·HO₂,etc.to degrade the active constituents of the target pollutants and enhance the ability of photocatalytic reaction.