Synthesis And Design Of Two-dimensional MXenes As Green Catalytic Materials

MXenes are a new type of two-dimensional material,which is one of the most concerned two-dimensional material families in the past decade.The current research around MXene materials mainly focuses on the fields of lithium-ion batteries,supercapacitors,electromagnetic shielding,tumor therapy,biosensing,strain sensing,photoelectric catalysis,etc.There are relatively few reports on traditional heterogeneous catalysis,and further exploration are needed.Therefore,through the innovation of etching process and intercalation scheme,this paper developed a new preparation scheme of MXenes materials,and expanded the application scope of MXenes materials.In particular,based on the research of MXenes materials,the construction of the metal self-reduction catalytic system is perfected,and its application prospects in the fields of heterogeneous catalysis are explored.This paper is divided into the following four parts:(1)A new surface microenvironment modification method(TMM)was developed,and organic bases were used as intercalation agents to intercalate and surface modify MXenes materials to achieve efficient exfoliation of MXenes materials in various organic solvents.The TMM scheme can achieve peeling of more than 30 g in one pot,and the dispersion concentration of organic solution up to 90mg/m L,superior to the previous report.This scheme breaks through the limitation of low concentration of organic solvent dispersion prepared by the traditional preparation scheme(less than 0.5 mg/m L),and expands the dispersion system of MXenes materials(from water solvent to organic solvent dispersion),it opens a new door for the wide application of MXenes materials.In this chapter,the preparation process of TMM method is described in detail,and the mechanism and application of dispersing MXenes materials by TMM method are discussed in depth.(2)The surface of the MAX phase material was etched with alkali as an environmentally friendly etching reagent,and the surface hydroxylated Ti₃C₂/Ti₃Al C₂(h-TC/TAC-x-y)composite catalyst was obtained.This solution avoids the use of hydrofluoric acid,is milder,safer and environmentally friendly,and a nanometer-thick layer of flocculent h-Ti₃C₂ was formed on the surface of Ti₃Al C₂ catalyst,exposing a large number of Ti-OH and Ti-O active centers,which was beneficial to the activation of the substrate and the occurrence of catalytic conversion.The catalyst exhibits excellent oxidative desulfurization activity against benzothiophene sulfides in diesel,and can achieve 99%removal within 3 hours,and can also be directly applied to the desulfurization of commercial diesel,and the catalyst can be reused 8 times without significant reduction in catalytic activity.More importantly,we only use cheap and easily available air as an oxidant in the process of oxidative desulfurization of diesel.More importantly,in the process of oxidative desulfurization of diesel,only cheap and easily available air is used as an oxidant.From catalyst preparation to application,it is in line with the advocacy value of green catalysis,that is,to maximize the rational use of resources and minimize environmental pollution.(3)The reduction process of metals on the surface of MXenes was systematically investigated,the mechanism was deeply analyzed,and the design theory of self-reducing metal catalysts based on MXenes materials was initially constructed.We can fully understand the principle of self-reduction and the phenomenon of electron transfer and element loss in the reduction process,and have a new understanding of the self-reduction process and the key structures and electronic properties of metals and MXenes at the interface.Based on this,the theoretical prediction and controllable preparation of the size,location and structure of metal self-reduction deposition were achieved.For example,by regulating the deposition amount of Rh,Pt,Ru,and Cu on the surface of Ti₃C₂T_x MXene,the controllable preparation of various metals from single atoms to nanoparticles has been realized;Controllable deposition of Au nanoparticles at the edge and surface sites of Ti₃C₂T_x MXene by tuning the surface charge properties of metals;And the deposition sequence of bimetallic Au and Ag can be controlled to achieve precise control of the deposition site and structure of the bimetallic.(4)Pt₁/Ti_3-xC_NT_y single-atom catalysts(SAC)were prepared using Ti_3-xCNT_yMXene material as catalyst carrier.The research shows that the Ti vacancies and the doped heteroatom N on the surface of Ti_3-xCNT_y MXene material are both beneficial to the anchoring of single atoms,which can achieve a high Pt single atom loading of0.5%.In addition,due to the introduction of N element,the Pt₁/Ti_3-xCNT_y SAC also exhibits a singular catalytic hydrogenation selectivity and excellent catalytic activity,which can precisely realize the selective addition of vinyl groups in the presence of the influence of nitro groups.The conversion and hydrogenation selectivity of hydrogen,selective hydrogenation of 3-nitrostyrene were all higher than 99%.