The Preparation Of Ti₃C₂T_x-based Photocatalyst And Its Application For Photoreduction Of CO₂

Over-exploitation and utilization of fossil fuels leads to a global energy urgency,and the emission of carbon dioxide into the atomosphere from the combustion of fossil fuels caused a series of environment issues.Reduction of CO₂ to useful chemicals by solar energy is a potential research topic to solve the energy shortage and environmental problems simultaneously.However,the state-of-the-art situation of photocatalytic CO₂ reduction faces the common bottleneck of photocatalysis,i.e.low photocoversion efficiency and weak CO₂ adsorption on the catalyst surface.Thus,it was highly required to explore new high-efficiency catalysts.Recently,transition metal carbon compounds have attracted the attention of researchers owing to their special structure and excellent electronic conductivity.In this project,the preparation of layered Ti₃C₂T_X material and related Ti₃C₂T_X composite materials was studied,and the application of prepared materials in the direction of photoreduction of CO₂ to produce hydrocarbons was also explored.?1?Layered Ti₃C₂T_X materials were prepared by acid etching method,and layered Ti₃C₂T_X materials were applied to photoreduction of CO₂ for the first time.It was found that the morphology and transport rate of photogenerated carriers of the prepared materials were different when the conditions of synthesis were different.The characterization showed that the Ti₃C₂T_X materials prepared by acid etching method were loose multilayered structure.But,the layered Ti₃C₂T_X materials obtained by etching for 36 hours were homogeneous layered.The sheet was thin and the separation efficiency of photogenerated carriers was the highest.By comparing the photocatalytic reduction performance,the results showed that the layered Ti₃C₂T_X material after etching for 36 hours was the best.After 4 hours of photoreaction,the corresponding methanol and ethanol yields were 38.1?mol gcatal.^-1 and 22.9?mol gcatal.^-1,and the total yield was 61.0?mol gcatal.^-1.?2?Ag/Ag₂S/Ti₃C₂T_X composites were prepared by co-precipitation and photoreduction of Ag/Ag₂S nanoparticles onto layered Ti₃C₂T_X materials.The heterojunction can be formed when Ag/Ag₂S nanoparticles were loaded onto layered Ti₃C₂T_X material.Moreover,Ag acts as an electron acceptor and reactive site in composites because of the low Fermi energy level,which prevents the recombination of photogenerated electron-hole pairs.By comparing the photocatalytic reduction performance of Ag/Ag₂S/Ti₃C₂T_X composites,the yield of methanol and ethanol reached the highest when the addition amount of Ag₂S at 7.5 wt%.After 4 hours of photoreaction,the methanol yield was 107.4?mol gcatal.^-1,and the ethanol yield was17.9?mol gcatal.^-1.The total yield(125.3?mol gcatal.^-1)was 2.1 times higher than that of Ti₃C₂T_X(61.0?mol gcatal.^-1)and 5.1 times higher than that of Ag₂S(24.6?mol gcatal.^-1).?3?An alkaline CeO₂/Ti₃C₂T_X composite was successfully synthesized by hydrothermal growth of CeO₂ on the surface of the layered Ti₃C₂T_X.The resultant CeO₂/Ti₃C₂T_X composites can hinder the recombination of photogenerated electron-hole pairs,and the alkaline oxide CeO₂ endowed CeO₂/Ti₃C₂T_X composites with an enhanced CO₂ adsorption capability.Compared with the pure Ti₃C₂T_X and CeO₂ materials,the photocatalytic reduction ability of CeO₂/Ti₃C₂T_X composite material was improved significantly.The best photocatalytic reduction ability achieved when CeO₂/Ti₃C₂T_X composites loaded 12.5 wt%CeO₂.Methanol and ethanol yield were 76.2 and 33.7?mol gcatal.^-1 after 4 hour illumination,respectively.The total yield(109.9?mol gcatal.^-1)was 1.8 and 4.3 times higher than that of Ti₃C₂T_X material(61.0?mol gcatal.^-1)and CeO₂ material(25.8?mol gcatal.^-1).