Preparation Of Cu₂O-based Photocatalysts And Its Photocatalytic

Dye wastewater with high organic content,deep color and complex composition makes the treatment of dye wastewater more and more difficult.Photocatalytic technology can realize degradation and mineralization of organic compounds,with the advantages of rapid reaction,low process cost,mild operating conditions and no secondary pollution.Cuprous oxide has forbidden band width about 2.17 eV and can be visible light excited with the energy conversion rate of12%in theory,making it good photocatalytic activity,adsorption and other catalytic activity.However cuprous oxide photocatalyst still has the disadvantages of insufficient catalytic activity and low light stability and high electrons and holes recombination,which restricts its application in actual environmental pollution control.In view of the increasingly serious harm to the environment of dye wastewater and insufficient catalytic activity,low light stability and high electrons and holes recombination of cuprous oxide photocatalyst,Cu₂O photocatalyst was prepared by low temperature liquid phase precipitation,using organic acid as ligand complexing agent and structure control agent and ascorbic acid as reducing agent,and then Cu₂O/rGO photocatalyst was prepared by in situ complex method.The effects of reaction parameters and photocatalytic conditions on photocatalytic degradation of methyl orange solution by Cu₂O and Cu₂O/rGO photocatalysts were investigated.Kinetics of photocatalytic dye degradation and recycling performance of Cu₂O and Cu₂O/rGO photocatalysts were studied.The photocatalytic mechanisms of Cu₂O and Cu₂O/rGO photocatalysts were preliminarily discussed.Structure and morphologies of Cu₂O and Cu₂O/rGO photocatalysts were characterized by way of a variety of modern analysis and test methods.Cu₂O and Cu₂O/rGO photocatalysts have high visible light photocatalytic dye degradation and good recycling performances.The main research work is as follows:1.XRD indicated that Cu₂O and Cu₂O/rGO photocatalysts had characteristics of diffraction peaks assigned to Cu₂O crystals without characteristics of diffraction peaks for CuO and zero-valent copper.Cu₂O photocatalysts prepared by reduction temperature of 20°C,copper ion/reductant molar ratio of 1:1 and copper ion/phthalic acid molar ratio of 1:1.1,respectively,had sharper and bigger diffraction peaks.Compared with the XRD spectra of Cu₂O photocatalyst prepared by organic acid assisted control method,the characteristic diffraction peaks of Cu₂O/rGO photocatalyst became wider and the intensity of diffraction peaks become lower.Field emission scanning electron microscopy?FESEM?showed that Cu₂O photocatalyst had spherical shape with porous structure,and particle size between20-40 nm.Cu₂O photocatalyst had uniform morphology,particle size distribution and good dispersion.Cu₂O/rGO photocatalyst has porous structure.Cu₂O particles with an average particle size of 50 nm were deposited on the surface of reduced graphene with layered or flaky structure.EDX energy spectra showed that Cu₂O photocatalyst has copper and oxygen atoms and the atomic ratio of copper atom and oxygen atom is 1.91:1,which is close to the atomic ratio of copper atom and oxygen atom 2:1 for Cu₂O photocatalyst.FT-IR spectrum indicated that Cu₂O/rGO photocatalyst had characteristic adsorption peaks of Cu₂O and rGO,which preliminarily indicated that the Cu₂O/rGO photocatalyst prepared in this paper has target structure.2.The effects of reaction parameters on photocatalytic degradation of methyl orange solution by Cu₂O and Cu₂O/rGO photocatalysts were investigated.he optimal synthesis conditions were as follows:Cu₂O photocatalyst in the condition of reduction reaction temperature of 20°C,reaction pH of 6 and reduction reaction time of 1.5 h,copper ion/reductants molar ratio of 1:1 and copper ion/organic molar ratio of 1:1.1,respectively,Cu₂O/rGO photocatalyst in the condition of GO content of 4%,reaction pH of 5,reduction reaction temperature of 20°C,reduction reaction time of 2 h,and copper ion/reductants molar ratio of 1:1,respectively.The effects of photocatalytic conditions on photocatalytic degradation of methyl orange solution by Cu₂O and Cu₂O/rGO photocatalysts were investigated.As the initial concentration of methyl orange dye increases,the degradation performance of methyl orange dye decreases.Photocatalytic degradation of dyes by Cu₂O and Cu₂O/rGO photocatalysts is suitable for neutral conditions.With the increase of the amount of photocatalyst,the photocatalytic degradation of dyes showed a trend of increasing but decreasing.Photocatalytic degradation of methyl orange dye processes for Cu₂O and Cu₂O/rGO photocatalysts were fitted using quasi first-order dynamic equation.Cu₂O and Cu₂O/rGO photocatalysts had correlation coefficients of 0.9615 and 0.9346,and rate constant k of 0.09427 min^-1 and 0.04868 min^-1,respectively.The results of recycling experiments showed that the photocatalytic degradation was still good after five cycles.3.The N₂ adsorption-desorption isotherms of Cu₂O and Cu₂O/rGO photocatalysts were type IV isotherms with typical hysteresis rings.Cu₂O photocatalyst had specific surface of 26.53 m²/g with the maximum pore size of 2.5nm,and the average pore size of 15.5 nm.Cu₂O/rGO photocatalyst had specific surface of 23.94 m²/g with the maximum pore size of 2.6 nm,and the average pore size of 17.28 nm.Cu₂O and Cu₂O/rGO photocatalysts had strong absorption in the visible and ultraviolet regions.Cu2O and Cu2O/rGO photocatalysts had energy gaps of 2.04 eV and 1.99 eV,and the corresponding absorption edges of 607.8 nm and623 nm,respectively.Cu₂O photocatalyst without organic acid and GO showed a strong emission band at 467 nm,while Cu₂O photocatalysts prepared by phthalic acid using as coordination complexing agent and structure control agent and Cu₂O/rGO photocatalysts prepared by in situ complex method showed reduced emission peaks strength at 467 nm.The contribution of the active species to Cu₂O and Cu₂O/rGO photocatalysts was in the order of hole?h⁺?>superoxide radical?O₂^-·?>hydroxyl radical.