Construction Of Non-noble Metal Modified Ti₃C₂T_x/g-C₃N₄ And Study On Photocatalytic CO₂ Reduction

Excessive using of fossil fuels will emit excessive CO₂,lead to global warming and affect human living environment.Generally,CO₂ is very stable,inspired by natural photosynthesis,using solar energy to convert CO₂ into CO,CH₄,CH₃OH and other clean fuels or chemical feedstock is an effective way to alleviate energy and environment problems.The development of semiconductor photocatalysts that can efficiently catalyze CO₂ conversion is the key to achieve efficient CO₂ conversion under mild conditions.Among them,due to the low cost,environmentally friendly,narrow band gap and high chemical stability and other advantages of g-C₃N₄,g-C₃N₄ was widely used in photocatalytic CO₂reduction reaction.However,the high recombination rate of photo-generated electrons and holes and fewer surface-active sites on g-C₃N₄ limits its application.The combination of g-C₃N₄ with co-catalyst is an effective strategy to inhibit the recombination of photo-generated electrons and holes.Due to the Fermi energy level of Ti₃C₂T_x is lower than the conduction band of g-C₃N₄,so the photo-generated electrons can transfer from g-C₃N₄ to Ti₃C₂T_x,thus the recombination of photo-generated electrons and holes can be inhibited.Moreover,the exposed metal atoms on Ti₃C₂T_x can be use as the adsorption and reaction sites of CO₂.Therefore,in this work,Ti₃C₂T_x/g-C₃N₄,Cu-Ti₃C₂T_x/g-C₃N₄ and Co-Ti₃C₂T_x/g-C₃N₄ composite photocatalysts were constructed,and the photocatalytic performance and reaction mechanism of CO₂reduction over these composite photocatalysts were studied.Firstly,Ti₃C₂T_x/g-C₃N₄ composites with different content of Ti₃C₂T_x was constructed by an electrostatic self-assembly method,and the Ti₃C₂T_x/g-C₃N₄was used for the reaction of photocatalytic CO₂ reduction.The results showed that Ti₃C₂T_x/g-C₃N₄ with 3 wt%Ti₃C₂T_x has the best performance for photocatalytic CO₂ reduction,after reaction for 4 h,the yield of CO and CH₄reached 23.87μmol·g^-1_cat and 1.89μmol·g^-1_cat,respectively,which were 4.4times and 4.8 times than that of g-C₃N₄.The study found that the larger specific surface area of two-dimension Ti₃C₂T_x and g-C₃N₄ nanosheets could provide more active sites,and the close contact interface between Ti₃C₂T_x and g-C₃N₄could shorten the migration distance of photo-generated carriers,thus enhanced the efficiency of photocatalytic CO₂ reduction over g-C₃N₄.Secondly,in the absence of reducing agent,Cu-Ti₃C₂T_x nanosheets with different content of Cu were prepared by spontaneously reduction of Cu ions on the Ti₃C₂T_x surface.The Cu-Ti₃C₂T_x/g-C₃N₄ composite photocatalyst was prepared by an electrostatic self-assembly method,and Cu-Ti₃C₂T_x/g-C₃N₄ was used for the reaction of photocatalytic CO₂ reduction.The results showed that Cu-Ti₃C₂T_x/g-C₃N₄ with 1 wt%Cu exhibited the best performance of photocatalytic CO₂ reduction,and the yield of CO and CH₄ were 49.02μmol·g^-1_cat and 3.6μmol·g^-1_cat,respectively,which were 9 times and 9.2 times than that og-C₃N₄.Combining the result of DFT simulated calculation,In situ infrared spectra,and ultraviolet photoelectron spectroscopy,it can be found that the Cu and the Ti₃C₂T_x can act as the fast transport channels for the photo-generated electrons in the Cu-Ti₃C₂T_x/g-C₃N₄ system.Moreover,the interface between the Cu and Ti₃C₂T_x can act as the active sites for the adsorption and activation of CO₂,thus enhanced the efficiency of photocatalytic CO₂ reduction over g-C₃N₄.Finally,Co-Ti₃C₂T_x nanosheets was prepared by reduction of Co ions on the surface of Ti₃C₂T_x with KBH₄ as the reducing agent,Co-Ti₃C₂T_x/g-C₃N₄composite photocatalyst was prepared by an electrostatic self-assembly method,and was used for the reaction of photocatalytic CO₂ reduction.The results showed that Co-Ti₃C₂T_x/g-C₃N₄ with 1 wt%Co exhibited the best performance of photocatalytic CO₂ reduction,and the yield of CO and CH₄ were 55.04μmol·g^-1_cat and 2.29μmol·g^-1_cat,respectively,which were 7.6 times and 5.9 times than that of g-C₃N₄.The catalyst characterization results showed that the 2D/2D compact interface between Co-Ti₃C₂T_x and g-C₃N₄ could accelerate the transfer of photo-generated carriers,inhibited the recombination of photogenerated electrons and holes,and improved the efficiency of photocatalytic CO₂ reduction over g-C₃N₄.