Boosting The Photocatalytic Activity Of P25 Using A 2D-like Ti₃C₂ Mxene As Co-catalyst

2D-like titanium carbide（Ti₃C₂）is a novel kind of noble-metal-free and semi-metallic inorganic material newly developed in recent years.It has been widely applied in energy conversion research areas due to its low cost,intrinsic stablility and versatile of physicochemical properties.However,the application of titanium carbide in photocatalysis has rarely been reported so far.Whether the titanium carbide has suitable band structure for photocatalytic reactions,and whether the surface modification could boost the dynamic process of reactions are still unknown.In this thesis,a systematic work was carried out on the fabrication,characterization of Ti₃C₂/P25 and its applications for photocatalytic H₂ evolution and CO₂ reduction.Particularly,the effect of surface hydroxyl-anchoring to Ti₃C₂ on the photocatalyitc activity of CO₂ reduction was investigated.The main results are as follows.We coupled the titanium carbide with the P25 by mechanical mixing.The Ti₃C₂/P25 hybrid showed an 18-fold enhancement of photocatalytic H₂ evolution（HER）compared to the pure P25.Meanwhile,the pure Ti₃C₂ showed no activity for photocatalytic HER.Various photoelectrochemical characteristics indicated the Ti₃C₂is an effective co-catalyst in HER,its Fermi level can be more negative than the H₂evolution level and positive than the conduction band of P25.Besides,after the coupling of Ti₃C₂ with different semiconductors（e.g.,C₃N₄,SrTiO₃）,the photocatalytic HER activities can be advanced in various degree,suggesting that the Ti₃C₂ can be a versatile co-catalyst in photocatalytic HER reactions.We performed the surface engineering on Ti₃C₂ by alkalinization.The anchoring of hydroxyl groups on Ti₃C₂ can be controlled effectively.After coupling of the hydroxyl-terminated Ti₃C₂ with P25,the photocatalytic CO₂ reduction（PCR）reactions can be boosted,i.e.,the evolution rates of CO(11.74 mol g^-1 h^-1)and CH₄(16.61 mol g^-1 h^-1)are equivalent to 3-fold and 277-fold increase,respectively,in comparison with the bare P25.Besides,the product selectivity for CH₄ can be enhanced to 58.5%,much higher than the catalytic efficiency of the noble metal platinum.To the best of our knowledge,the hydroxyl-terminated Ti₃C₂ can be the most effective noble-metal-free co-catalyst in PCR.The mechanism for such superior activity can be ascribed to three reasons:（1）suitable Fermi level of Ti₃C₂ facilitates the separation and transfer of photogenerated charge carriers;（2）excellent electron mobility helps constructing an electron-rich environment on Ti₃C₂ surface;（3）abundant hydroxyls are effective for the adsorption of acidic CO₂ molecules.This work,for the first time,evidenced the 2D-like Ti₃C₂ can be an effective co-catalyst in PCR.We provide a complete material system for the enhancement of PCR activity and selectivity for CH₄,moreover,our research has opened an new route for the low-cost,eco-friendly co-catalyst for photocatalytic CO₂ reduction.