One-Step Preparation Of TiO₂@Ti₃C₂/Cd_xZn_1-xS Composite By Hydrothermal Method And Its Photocatalytic Performance

Energy shortage and environmental pollution have gradually become important factors restricting the national economic and social development.Photocatalytic technology can effectively solve above problems.To address the drawback of photocatalytic technology that include the commonly usage of single transition metal oxides with low utilization rate of sunlight,easy recombination of photogenerated electrons and holes,and long preparation cycle,this thesis selects MXene（Ti₃C₂）that has good electrical conductivity,hydrophilicity and rich surface functional groups,as a co-catalyst to modify the in-situ generated TiO₂,uses microwave hydrothermal method,through in-situ complex reaction and construction of semiconductor heterojunctions,finally achieving the rapid synthesis of MXene-based high-efficiency composite photocatalyst.The relationship among material composition-microstructure-performance is studied.Main research content and results of the thesis are as follows:（1）Using ternary MAX phase Ti₃AlC₂ as raw material,HF etching is used to obtain layered matrix material Ti₃C₂;the precursor Ti₃C₂ is treated by a simple hydrothermal method to synthesize TiO₂@Ti₃C₂ photocatalyst in situ;using XRD,FT-IR,XPS,UV-vis DRS,SEM,BET and other characterization methods to study the influence of hydrothermal temperature on phase composition,chemical composition,band gap width and micro morphology of the composite material,and test its photocatalytic degradation of rhodamine B（Rh B）performance.XRD and SEM results show that the size of TiO₂ nanoparticles generated by in-situ oxidation increases with the hydrothermal temperature.After 160℃hydrothermal treatment,anatase-type TiO₂nanoparticles grow in situ on the layered substrate Ti₃C₂ and the size is about 20 nm;the degradation rate constant of TiO₂@Ti₃C₂ on Rh B reaches 0.0065 min^-1,which is1.72 times as large as that of single TiO₂(0.0038 min^-1).（2）To further improve the photocatalytic performance of composite material,Ti₃C₂ was used as matrix and compounded with semiconductor Cd_xZn_1-xS（CZS）on the basis of the above results,and TiO₂@Ti₃C₂/Cd_xZn_1-xS（TO/CZS）multi-stage photocatalyst was synthesized in one step by hydrothermal method.Experimental results show that the synthesized sample TO/CZS-40 can degrade the Rh B solution by92.65%within 90 min of visible light irradiation when the CZS loading is 40 wt.%at160℃for 12 h,and its reaction rate constant is 0.0281 min^-1,which is 5.19 times as large as that of single TiO₂ and 23.42 times as large as that of substrate Ti₃C₂.Combing with the UV-vis DRS and the photocatalytic mechanism analysis,Ti₃C₂,TiO₂ and Cd_xZn_1-xS have matching band structures,and the Z-scheme semiconductor heterojunction that consists of three-phase composite enables the spatial separation of photogenerated electrons and holes,which can effectively reduce the carrier recombination opportunity and improve the catalytic activity.（3）Utilizing the excellent microwave absorbing performance of Ti₃C₂,TiO₂@Ti₃C₂/Cd_xZn_1-xS（MT-x C）photocatalyst is prepared by using microwave hydrothermal method in one step,and the effect of microwave hydrothermal process and CZS loading capacity on the microstructure phase composition and photocatalytic performance of the composite catalyst are investigated by various characterization methods.SEM and BET results show that microwave hydrothermal process accelerates the oxidation of MXene.The size of TiO₂ particles generated by in-situ oxidation in140°C microwave hydrothermal for 30 min is about 50 nm.This is because Ti₃C₂with the characteristics of wave absorption can absorb microwave in a very short time and quickly oxidize;at the same time,the dipole polarization generated by the water molecules under the action of microwaves makes them rapidly vaporize,increasing the interlayer spacing of the MXene matrix,which is beneficial to the absorption of visible light by the composite material.The photodegradation reaction shows that when the CZS loading is 30 wt.%,MT-3C sample can basically completely degrade Rh B,and the reaction rate constant is increased to 0.0374 min^-1,which is 33%higher than TO/CZS-40 prepared by the hydrothermal method.The semiconductor heterojunction that consists of Ti₃C₂,TiO₂ and Cd_xZn_1-xS is synergistic with the microwave effect to further improve the catalytic activity of the composite photocatalyst.