Synthesis Of Ti₃C₂ MXene-Based Catalysts For Degradation Of Organic Pollutants:Performances And Mchanism

Advanced oxidation processes（AOPs）have good application prospects in the treatment of refractory organic wastewater due to their high efficiency,environmental friendliness,and simple operation processes.Traditional transition metal oxide catalysts suffer from the disadvantages of few catalytic active sites,poor visible light absorption,and narrow p H applicable range,which limit their application in AOPs.Transition metal carbide Ti₃C₂ MXenes have been widely studied in the fields of energy storage,sensors and adsorption due to their unique two-dimensional layered structure,large surface area,abundant surface functional groups,and excellent optoelectronic properties.However,the metal-like properties of Ti₃C₂ MXenes restrict their application for catalytic oxidation removal of organic pollutants in water.Therefore,Ti₃C₂ MXene was taken as the research object in this study,and a series of Ti₃C₂MXene-based catalysts were prepared by various methods including self-doping and semiconductor combination to improve their catalytic performances for degradation of organic pollutants in Fenton-like reaction and photocatalytic systems.The main research contents and conclusions of this paper are as follows:（1）Multilayer Ti₃C₂ MXene nanosheets were prepared by a HF etching method,and their H₂O₂ activation performances under visible light irradiation for the degradation of cationic and anionic organic dyes were studied.The experimental results showed that Ti₃C₂ MXene nanosheets could selectively degrade cationic dyes（methylene blue,rhodamine B,basic fuchsin）in the visible light/H₂O₂ system with excellent p H work range（3.04-10.02）.Compared with the pristine Ti₃C₂ MXene,the recycled Ti₃C₂MXene after the photo-Fenton reaction had a significantly enhanced visible light absorption capability and possessed self-doped Ti³⁺-TiO₂,which was beneficial to improve the separation efficiency of photogenerated carriers.In addition,the photo-Fenton reaction processes boosted the content of hydroxyl groups on the surface of Ti₃C₂ MXene and increased the specific surface area by 19.48 times.The main reactive oxygen specie involved in the degradation of pollutants in the Ti₃C₂MXene/H₂O₂/visible light system was·OH_sur and·O₂^-.Density functional theory（DFT）calculations confirmed that electrons could migrate from TiO₂ to Ti₃C₂ in the TiO₂/Ti₃C₂ composite.（2）N-doped TiO₂/Ti₃C₂ catalysts were successfully prepared.N doping not only narrowed the band gap of TiO₂/Ti₃C₂,but also improved the separation efficiency of photogenerated carriers,which increased the specific surface area of TiO₂/Ti₃C₂ to35.86 m²/g.The experimental results showed that there was a synergistic effect between the photocatalysis and peroxymonosulfate（PMS）activation reactions in the N-TiO₂/Ti₃C₂-0.4/PMS/visible light system.In addition,the N-TiO₂/Ti₃C₂-0.4 sample had a wide p H applicable range（3.1-10.0）,good resistance to coexisting anions,and still exhibited excellent catalytic degradation performance after 5 cycles.Mechanism analyses showed that SO₄^·-and h⁺from the radical pathways and ¹O₂ from the non-radical pathways together participated in the Rh B degradation,while ¹O₂ was the main active species.（3）TiO₂@C modified Mg-Fe layered double metal oxides（TiO₂@C/Mg-Fe LDOs）were successfully prepared.The degradation rate of Rh B in 5%-TiO₂@C/Mg-Fe LDOs/PMS system reached 95.8%within 10 min,and its reaction kinetic rate(0.4537min^-1)was 2.5 times that of Mg-Fe LDOs/PMS system(0.1817 min^-1),and 15.7 times that of Mg-Fe LDH/PMS system（0.0290 min-1）.The 5%-TiO₂@C/Mg-Fe LDOs had a wide p H work range（3.1-11.0）,good stability and resistance to coexisting anions.Mechanism analyses showed that the introduction of TiO₂@C into Mg-Fe LDOs can promote the formation of electron-deficient≡Fe（III）-OH complexes and improve the electron transfer between≡Fe（III）-OH complexes and PMS,thereby enhancing their catalytic activation efficiency,promoting the degradation of organic pollutants.（4）Ag₂Zn Ge O₄/Ti₃C₂ Schottky heterojunction photocatalyst with hollow sphere structure was prepared via an electrostatic self-assembly process.Compared to the Ag₂Zn Ge O₄,the Ag₂Zn Ge O₄/Ti₃C₂ composite exhibited an enhanced photocatalytic performance for the degradation of acid red 1 under visible light irradiation owing to the larger surface area and more generated·O₂^-in the photocatalytic process.Photoluminescence spectroscopy and photoelectrochemical tests showed that the Ag₂Zn Ge O₄/Ti₃C₂ composite had higher separation efficiency of photogenerated electrons and holes.DFT calculation results show that the formed heterojunction between Ag₂Zn Ge O₄ and Ti₃C₂ is beneficial to transfer the electrons from Ag₂Zn Ge O₄to Ti₃C₂.In summary,this work not only provides a new method for the development and utilization of efficient environmental catalysts,but also provides a certain reference for the practical application of advanced oxidation technology.