Preparation Of TiO₂ Based Composite Photocatalyst With Ti₃C₂ MXene As Precursor And Its Hydrogen Production Performance

Two-dimensional materials have drawn much attention in the field of photocatalysis and electrocatalysis,due to their outstanding physical and chemical properties.Ti₃C₂MXene is a promising new two-dimensional material after graphene.Its unique accordion-like structure provides sufficient superficial area for physical adsorption and chemical reaction.Ti₃C₂chould be completely oxidized at high temperatures to form C-Ti O₂with photocatalytic hydrogen production.Moreover,the disordered carbon retained after calcination provided additional transport path of photogenerated electrons on Ti O₂surface for photocatalytic reaction.Furthermore,C-Ti O₂/Zn_0.5Cd_0.5S heterojunction was constructed with Zn_0.5Cd_0.5S,which improved the separation efficiency of photogenerated carriers and broadened the light absorption range.The photocatalytic water splitting rate increased greatly.C-Ti O₂photocatalyst was prepared by calcination method and molten salt method respectively.The effects of the two preparation methods on the microstructure,grain size,photocharge separation and migration rate of C-Ti O₂catalyst were compared.The XRD and XPS characterization proved the successful preparation of C-Ti O₂.The microscopic morphology characterization results showed that C-Ti O₂prepared by molten salt method retained the original Ti₃C₂structure.According to Schell formula calculation,the grain size of Ti O₂prepared by molten salt method was smaller than that by calcination method.The photocurrent response and electrochemical impedance spectra of C-Ti O₂indicated that the photocatalytic materials prepared by molten salt method had excellent electron-hole pair separation efficiency and low interfacial resistance.Under simulated sunlight,the hydrogen production capacity of T-400（Calcination temperature is 400°C,The T represents the Ti O₂）prepared by calcination method is 0.425 mmol/h/g,while the hydrogen production rate of T-Z-400（Calcination temperature is 400°C,The Z represents the Zn Cl₂）prepared by molten salt method is2.3 mmol/h/g,about 5.4 times that of T-400.C-Ti O₂/Zn_0.5Cd_0.5S heterojunction photocatalyst was prepared by hydrothermal method.SEM and TEM images showed that Zn_0.5Cd_0.5S nanoparticles were densely wrapped on the C-Ti O₂lamellar structure.The UV-vis diffuse reflectance test showed that the formation of C-Ti O₂/Zn_0.5Cd_0.5S heterojunction catalyst effectively reduced the band gap width and improved the visible light absorption.Combined with photoluminescence spectroscopy and electrochemical testing,it was further demonstrated that the heterojunction effectively reduced the internal resistance of charge transfer and enhanced the photogenerated electron-hole separation efficiency.Hydrogen production performance test under visible light showed that the composite ratio of Zn_0.5Cd_0.5S combined with 10 wt%C-Ti O₂（10T/ZCS）was the best of all experimental series.It reached 0.71 mmol/h/g,2.5 times that of the prepared Zn_0.5Cd_0.5S.After the addition of Pt,the performance of 10T/ZCS rose up to 4.9 mmol/h/g.