Preparation Of Two-dimensional Ti₃C₂ Mxene Composite Photocatalyst And Photocatalytic Performance For CO₂ Reduction

The excessive combustion of fossil fuels has led to global issues such as energy shortages,climate change,and environmental pollution.CO₂ capture and storage provides a simple and effective solution for reducing CO₂ emissions.Scientists have developed hundreds of photocatalysts for CO₂ reduction.However,its safety,sustainability and economic feasibility are major issues for future large-scale implementation.MXenes is a kind of two-dimensional material with unique properties in optoelectronics,and has become an ideal catalyst in the field of photocatalysis.MXenes show some unique advantages:（1）Nanosheet morphology and metal conductivity ensure the rapid migration of charge carriers from the body to the surface;（2）The abundant hydrophilic surface functional groups on MXenes nanosheets facilitate the chemical bonding with semiconductors to enhance interfacial charge transfer;（3）Since MXenes usually contains a transition metal atomic layer as its top and bottom layers,these metal sites can provide strong redox activity.This paper focuses on the preparation of two-dimensional Ti₃C₂ MXene composite photocatalyst and its performance in photocatalytic CO₂ reduction.The research contents and conclusions of the experiment are as follows:（1）Using Ti₃AlC₂ as the raw material,the Al atomic layer was etched off by HCl and LiF,then centrifuged and layered to obtain Ti₃C₂ nanosheets.Ti O₂ with nanosheet morphology was prepared by solvothermal method using C16H36O4Ti as raw material.The metal Cu nanoparticles were loaded onto Ti O₂ by photodeposition,and different Cu-Ti O₂ photocatalysts were prepared by changing the quality of Cu nanoparticles.Finally,Cu-Ti O₂-Ti₃C₂ was obtained by combining Ti₃C₂ and Cu-Ti O₂ through electrostatic self-assembly.The experimental results show that 1%Cu-Ti O₂-Ti₃C₂ has the highest photocatalytic activity than other samples.The reduction products are CO and CH₄detected by gas chromatography.The production rates of CH₄ and CO are 12.93μmol h^-1 g^-1 and 6.81μmol h^-1 g^-1,respectively.The CH₄ production rate of 1%Cu-Ti O₂-Ti₃C₂is 9 times higher than that of Ti O₂.Schottky junctions have been formed between Ti₃C₂and Ti O₂,as well as between Ti O₂ and Cu,which is conducive to improving the separation efficiency of photogenerated carriers.（2）Using Ti₃AlC₂ as raw material,the Al atomic layer was etched by HCl and LiF,and then Ti₃C₂ nanosheets were obtained by centrifugal stratification.Then Ce-doped C₃N₄ photocatalyst was prepared by calcination method,and Ce-C₃N₄-Ti₃C₂ composite was synthesized by electrostatic self-assembly method.The results showed that 1%Ce-C₃N₄-Ti₃C₂ had the best photocatalytic activity,and the production rates of CH₄ and CO were 3.05μmol h^-1 g^-1 and 1.26μmol h^-1 g^-1,respectively.The CH₄ and CO production rates of C₃N₄ were 0.34μmol h^-1 g^-1 and 0.03μmol h^-1 g^-1,respectively.The CH₄production rate of 1%Ce-C₃N₄-Ti₃C₂ was 9 times higher than that of C₃N₄.The close contact between Ce-C₃N₄ and Ti₃C₂ form a Schottky junction,which prevents the recombination of photogenerated electron-hole pairs to a certain extent.（3）Using Ti₃AlC₂ as raw material,the Al atomic layer was etched by HCl and LiF,and then Ti₃C₂ nanosheets were obtained by centrifugal stratification.The Ag-Ti₃C₂composite photocatalyst was prepared by using the redox characteristics of Ti vacancies formed during etching to reduce Ag ions and form Ag nanoparticles.When the mass ratio of Ag added is 10%,the photocatalytic efficiency is the highest,the CO production rate is 1.36μmol h^-1 g^-1,and the CH₄ production rate is 10.85μmol h^-1 g^-1,which is 7.69 times that of CH₄ generated by pure Ti₃C₂.The combination of Ti₃C₂ and Ag nanoparticles improves the reactivity of the photocatalyst and provides more active sites.