Preparation And Photocatalytic Properties Of MXene-Based Composites

The swiftness of industrialization and the ongoing surge in population have precipitated an unprecedented energy crisis and environmental pollution,thereby posing the most pressing survival challenges to humankind.Due to its high efficiency and eco-friendliness,photocatalytic technology is widely regarded as a principal approach for tackling these issues.Constructing efficient heterojunction structures and doping auxiliary catalysts with composite semiconductors are two effective means to improve the photocatalytic performance of materials.Ti₃C₂,one of the MXene materials,possesses unique physicochemical properties such as good conductivity,hydrophilicity and tunable structure,which make it possess great application potential as an auxiliary catalyst in the field of photocatalysis.This project designs three new types of Ti₃C₂-based composite photocatalysts,including Ti₃C₂/SrTiO₃ composites,Ti₃C₂/SrTiO₃/g-C₃N₄ composites and Ti₃C₂/TiO₂/SrTiO₃ composites.Various techniques were employed to characterize the microstructure,crystal structure,photoelectric effect and photocatalytic activities of the samples.These included field emission scanning electron microscopy（FESEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,Raman spectroscopy,X-ray photoelectron spectroscopy（XPS）,specific surface area testing（BET）,UV-visible diffuse reflectance spectroscopy（UV-Vis DRS）,photocurrent impedance and fluorescence spectroscopy（PL）.The specific research content is as follows:（1）Ti₃C₂/SrTiO₃ composites were prepared using TiO₂ as the Ti source by hydrothermal method.The effect of Ti₃C₂ content on the photocatalytic activity of the composite was probed.The results indicated that the introduction of Ti₃C₂ gradually enhances the visible light response of the composite material.The Ti₃C₂/SrTiO₃ composite exhibited a degradation rate of nearly100%for methylene blue（MB）solution after visible light irradiation for 90 min.The Ti₃C₂/SrTiO₃photocatalyst achieved optimal photocatalytic activity and the highest apparent rate constant when the weight percentage of Ti₃C₂ reached 60 wt%.The energy level difference between Ti₃C₂ and SrTiO₃ guided the migration of photo-generated carriers from SrTiO₃ to Ti₃C₂.The Schottky barrier formed at the interface between Ti₃C₂ and SrTiO₃ effectively inhibited the recombination of photoinduced electron/hole pairs（e^-/h⁺）,thereby enhancing the photocatalytic activity of the catalyst.（2）Ti₃C₂/SrTiO₃/g-C₃N₄ composites with a novel gradient heterojunction structure were prepared by a simple calcination method combining g-C₃N₄,Ti₃C₂ and SrTiO₃.The hydrogen evolution rate of Ti₃C₂/SrTiO₃/g-C₃N₄ under simulated solar illumination was investigated.The results showed that the composite material containing 60 wt%g-C₃N₄ exhibited the highest hydrogen evolution rate under simulated solar illumination for 4 h,reaching 1733.13μmol g^-1h^-1,which was approximately 3.3 times higher than that of Ti₃C₂/SrTiO₃(1346.3μmol g^-1h^-1).The gradient heterostructure extended the migration path of photogenerated charges,and the excellent conductivity of the Ti₃C₂ catalyst attracted electrons to Ti₃C₂,thereby improving the separation efficiency of e^-/h⁺.By utilizing the synergistic effect of the heterostructure and co-catalyst,the photocatalytic activity of the catalyst was further optimized.（3）Using the Ti source on Ti₃C₂ as the reaction site,TiO₂ nanosheets and thread-like SrTiO₃were grown successively on the Ti₃C₂ substrate through hydrothermal reaction,resulting in a network-structured Ti₃C₂/TiO₂/SrTiO₃ composite material.The results showed that the Ti₃C₂/TiO₂/SrTiO₃ composite material exhibited the best comprehensive photocatalytic activity when the doping amount of SrTiO₃ was 5 wt%.The hydrogen production rate reached 14322.6μmol g^-1h^-1 after 4 h of simulated solar light irradiation,which was 10.6 times that of Ti₃C₂/TiO₂.Moreover,the composite material also showed certain degradation effect on tetracycline（TC）solution,with the degradation rate of TC reaching 65.6%after 120 min of visible light irradiation.The synthetic method that excludes the use of additional Ti sources has significantly reinforced the interface binding between Ti₃C₂,TiO₂ and SrTiO₃,facilitated the migration of photoinduced charge carriers,and effectively enhanced the photocatalytic activity of the catalyst.