Preparation Of Zn_xCd_1-xS Based Catalysts And Its Performance In Photocatalytic H₂ Evolution Coupled With Microplastic Degradation

Solar photocatalytic hydrogen production from water decomposition is considered to be one of the important ways to solve the energy crisis and environmental problems.However,the slow kinetics of water oxidation has become one of the important factors limiting the efficiency of photocatalytic hydrogen production.In order to overcome the above difficulties,some researchers used sacrificial agents such as triethanolamine,lactic acid and methanol to replace H₂O oxidation to promote the oxidation half reaction kinetics,so as to improve the efficiency of photocatalytic hydrogen production by water decomposition.But the use of sacrificial agents will undoubtedly increase the cost of photocatalytic hydrogen production.Because triethanolamine,as a chemical with high added value,is finally oxidized into small molecular compounds.Therefore,it is more in line with the concept of sustainable development to find the other oxidation semi reactions coupling with water reduction hydrogen production.In recent years,plastics are widely used because of their convenience and low cost,but at the same time,the problem of"white pollution"is becoming more and more serious.Recycling waste plastics can not only solve the problem of environmental pollution,but also"turn waste into treasure"to realize resource utilization.Therefore,this paper mainly takes Zn_xCd_1-xS with strong light absorption capacity and controllable energy band structure as the research object,regulates the structural components,and studies the performance of photocatalytic water decomposition hydrogen production coupled with plastic degradation.The main contents of this paper are as follows:Firstly,we prepared Zn_xCd_1-xS nanosphere with different Zn/Cd ratios by hydrothermal method and tested their photocatalytic properties.The effects of morphology formation mechanism,energy band structure,valence band（VB）oxidation ability,light absorption ability and photogenerated carrier separation ability of Zn_xCd_1-xS on its photocatalytic performance were studied by means of X-ray Diffraction（XRD）,Scanning Electron Microscope（SEM）,Transmission Electron Microscope（TEM）,UV-vis and Electrochemical test.The results showed that Zn_0.6Cd_0.4S shows high photocatalytic activity.Under visible light irradiation,the activity in PET（polyethylene terephthalate）plastic substrate can reach 6.68 mmol·g^-1·h^-1,5.3times that of Zn S and 18.6 times that of Cd S.This is due to Zn_0.6Cd_0.4S having appropriate energy band structure,good light absorption capacity and enhanced carrier separation capacity.Secondly,in order to further promote the effective separation of electrons-holes and improve the photocatalytic activity,we constructed Zn_0.6Cd_0.4S/Mn O₂ photocatalyst.The results show that the load of Mn O₂ effectively improves the photocatalytic H₂ evolution activity.When the loading amount is 1 wt%,Zn_0.6Cd_0.4S/Mn O₂-1 has the highest activity,and its H₂evolution rate reaches 10.49 mmol·g^-1·h^-1.According to the ¹H NMR spectrum,it can be analyzed that the plastic is oxidized into many useful organic small molecules.According to the characterization of XRD,SEM and TEM,it can be seen that Mn O₂ uniformly wraps Zn_0.6Cd_0.4S nanosphere.The addition of Mn O₂ effectively enhanced Zn_0.6Cd_0.4S light absorption capacity provides more active sites.The VB position,and band gap width of Zn_0.6Cd_0.4S/Mn O₂ photocatalyst was analyzed by UV,Mott-Schottky（MS）and X-ray Photoelectron Spectroscopy（XPS）,indicating that Zn_0.6Cd_0.4S/Mn O₂ composite photocatalyst is a Z-type charge transfer mechanism,which promotes the separation of electrons and holes,improves the redox capacity of the catalyst,and improves the photocatalytic H₂ evolution coupling with plastic degradation activity.Finally,MXene/Zn_0.6Cd_0.4S was constructed by solvothermal method with MXene as co-catalyst.The degradation properties of PET plastics coupled with photocatalytic hydrogen production were studied.The results show that the load of 2wt%MXene/Zn_0.6Cd_0.4S showed an excellent H₂ evolution rate of 14.17 mmol·g^-1·h^-1 due to the catalyst has excellent synergy in charge separation,light absorption and oxidation potential.The products of photocatalytic oxidation of plastics were analyzed by ¹H-NMR,and small organic molecules such as methanol,acetic acid and ethanol were obtained.According to the results of UV and Photoluminescence spectra,it is proved that the introduction of MXene as a co-catalyst promotes the separation of electron-hole and inhibits the recombination of electron-hole,so as to remarkably improve the photocatalytic activity.Mxene/Zn_0.6Cd_0.4S photocatalytic hydrogen production coupled with plastic degradation mechanism was explained by Electron Paramagnetic Resonance（EPR）analysis and Fluorescence（FL）spectrum.The results show that the holes of VB on the surface of Zn_xCd_1-xS catalyst oxidize PET into organic small molecular compounds,and the electrons transferred from Zn_xCd_1-xS CB to MXene reduce H⁺to H₂.