Synthesis And Photocatalytic Properties Of CuO-ZnO-Ag And CuO-ZnCuO Nanocomposite Photocatalyst

Persistent organic pollutants are resistant to natural degradation of the environment and may not be completely removed by the self-cleaning process of the ecological environment.Their long-term existence will have a serious negative impact on the survival of wildlife and human beings.In this background,due to the characteristics of low cost and environment friendly,zinc oxide nanometer semiconductor has proven to be in the light catalytic degradation photocatalyst good candidates.However,in order to further development of application of ZnO,the weak spectral utilization and light absorption capacity,as well as the short life of photogenerated carriers need to be further improved.In this paper,an improved sol-gel method was used to synthesize CuO-ZnO-Ag and CuO-Zn CuO nanocomposite photocatalysts,which significantly reduce the photogenerated carrier recombination rate and optical band gap width of ZnO and improved the visible light absorption capacity.By using X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray photoelectron spectroscopy(XPS),ultraviolet-visible absorption spectra(UV-vis),photoluminescence(PL),surface photovoltage spectrum(SPV)and surface photocurrent spectrum(SPC)testing measure,the photoelectric properties and microstructure of the samples have been characterized,and discussed the effects of impurity level and surface heterojunction on photocatalytic performance,the influence of the main contents are as follows:(1)A kind of CuO-ZnO-Ag photocatalyst with multi-heterojunction structure was prepared by one-step sol-gel method.CuO-ZnO heterostructure was successfully obtained by introducing a high concentration of Cu ion(5 mol%8 mol%).The effect of Ag compound on the photocatalytic performance of CuO-ZnO system was studied.The XRD and SEM results show that the growth trend of ZnO crystal plane changes with the introduction of Ag,the area proportion of(0002)crystal plane with the stronger activity increases,and the morphology of the sample changes from nanoparticles to rod-like structure.XPS and PL measurements show that Cu ions coexist in the form of Cu²⁺and Cu⁺in the sample and affect the emission related to the defect level.UV-Vis,PL,SPV and SPC results confirm that the appropriate proportion of CuO-ZnO and Ag-ZnO heterojunction can synergically enhance the absorption capacity of ZnO to visible light and the separation effect of photogenerated carriers.The photocatalytic degradation results showed that the CuO-ZnO structure with low Ag loading(2 mol%)can achieve the best photocatalytic performance.The sample still maintains the good photocatalytic ability in the water environment with p H of 4-10,and the photocatalytic performance remains stable after five cycles of degradation.(2)A sol-gel two-step method was used to introduce an appropriate amount of defects into ZnO in the form of 0.2 mol%Cu ion doping,and then impregnated Zn CuO in a high concentration(5 mol%)Cu ion solution.The surface CuO-ZnO structure was formed after the surface Cu ions were annealed at high temperature.Finally,a CuO-ZnO nano-photocatalyst was synthesized based on the matching of surface and in-band energy levels.UV-vis shows that the absorption rate of ZnO system in the visible light region is improved and the optical bandgap is decreased to a certain extent.XRD,SPV and PL results show that the positively charged point defect levels match the surface CuO levels,and a large number of photogenerated holes on these defect levels can be transferred to the CuO conduction band rapidly through the CuO-ZnO interface electric field,thus further enhance the charge separation effect of CuO-ZnO heterojunction.Enhancing the charge separation effect of MOS-MOS heterojunction by means of energy level matching can effectively replace the synergistic effect brought by the formation of multiple heterojunction by constructing precious metals and MOS,which can improve the performance and reduce the preparation cost of the system.(3)The modified kinetic equation describing the photocatalytic performance of semiconductor photocatalysts was determined by the degradation of dyes under different irradiation intensities,which can be modeled as an exponential function,and the attenuation parameter is related to the illumination intensity.The band structure of ZnO-CuO used for effective charge separation shows obvious functionalization under low irradiation intensity,and the external in-band quantum yield gradually approach with the increasing of light intensity.In order to maximize the effective charge separation effect of CuO-ZnO structure under intense irradiation,the concentration of pollutants can be modified to the optimal value to achieve the max value of external in-band quantum yield.This method can explore the external conditions for maximizing the structural function in simple or complex band semiconductor photocatalytic material systems.