Construction And Room-Temperature Gas Sensing Properties Of Metal Oxide/Ti₃C₂T_x MXene Composite

With the advancement of modern society,the issue of air contamination has aggravated,seriously damaging the ecosystem on which humans rely for survival and greatly damaging mankind’s health.Hence,there is an urgent need to design a sensing device that can accurately monitor poisonous and hazardous gases in the environment in real time.To date,gas sensors have potential application value in fields such as environmental monitoring,industrial production,and medical diagnosis.Among them,typical metal oxide semiconductor（MOS）gas sensors such as Cu O,α-Fe₂O₃,and In₂O₃have caught high attention from researchers due to their high response value,low price,controllable preparation,and simple integration.However,pristine component metal oxides have low carrier mobility at room temperature and typically require operating temperatures in the range of 200 to 400°C,which hinders the progress of gas sensing.Therefore,developing new composite sensitive materials with large specific surface area,high carrier mobility,multiple gas sensitive active sites,and room temperature gas sensing properties is a feasible method to break through the bottleneck in the development of existing gas sensors.Ti₃C₂T_xMXene,as a newly introduced two-dimensional inorganic compound,including transition metal carbides,nitrides,carbonitrides,has proved to play a versatile role in electromagnetic interference shielding,energy storage,biomedicine,sensing and catalysis.Ti₃C₂T_xMXene is different from other two-dimensional materials.This material has high conductivity,excellent dispersibility,surface negative charge,and hydrophilic properties,which are expected to become an ideal substrate for constructing new composite sensitive materials.This article aims to develop a new type of high-performance,low-power gas sensor,based on the design and regulation of the composition and structure of new sensitive materials.A two-dimensional material（Ti₃C₂T_xMXene）is selected as the substrate material,and Cu O,α-Fe₂O₃,In₂O₃are active components,using simple hydrothermal methods and in situ reduction methods,a series of MOS/Ti₃C₂T_xMXene composites with different structures and Au nanoparticles modified MOS/Ti₃C₂T_xMXene ternary composites were constructed by simple hydrothermal method and in-situ reduction method.The morphology,crystal structure and surface chemical composition of the designed composite samples were analyzed through a series of characterization techniques,and theoretical simulation calculations were carried out based on density functional,the gas sensing mechanism of the composite material prepared was analyzed in depth.The main research results are as follows:（1）In order to obtain a two-dimensional Ti₃C₂T_xMXene material with controllable synthetic layers,using a ternary ceramic structure of Ti₃Al C₂MAX phase as a precursor material,an organ shaped Ti₃C₂T_xMXene was synthesized using hydrofluoric acid（HF）etching method to selectively remove Al atoms from the Ti₃Al C₂MAX phase,with a relatively open structure at one end and a small layer spacing at the other end.In addition,the organ shaped Ti₃C₂T_xMXene was intercalated with dimethyl sulfoxide（DMSO）and ultrasonically peeled to obtain a layered Ti₃C₂T_xMXene.The fully peeled Ti₃C₂T_xMXene nanosheet had a single layer thickness of 3.1 nm,and the layer spacing was measured to be between 1-1.5 nm.（2）To explore the impact of multi-layer Ti₃C₂T_xMXene and p-p heterojunction on gas sensing performance,a sandwich structure Cu O/Ti₃C₂T_xMXene composite material was prepared using multi-layer Ti₃C₂T_xMXene as the substrate and Cu O as the gas sensing active material,and simple hydrothermal technology was used to attach Cu O to the surface and interlayer of multi-layer Ti₃C₂T_xMXene.The composition and morphology of the prepared composite materials were analyzed through various characterization techniques,and the interrelationships between gas sensor pollution detection and the chemical composition,crystal structure,and sensing performance of Cu O/Ti₃C₂T_xMXene sensitive materials were elucidated.（3）To explore the influence of micromorphology and p-n heterojunction on gas sensing performance,Ti₃C₂T_xMXene nanoflakes were used as the substrate,α-Fe₂O₃with controllable morphology was used as the sensitive material,and the hydrothermal high-temperature calcination method was utilized to optimize reaction conditions.α-Fe₂O₃was anchored on Ti₃C₂T_xMXene nanoflakes,and different configurations ofα-Fe₂O₃/Ti₃C₂T_xMXene composite materials were prepared.The mechanism of the influence of reaction conditions on the morphology and structure of the composite was explored,thus achieving controllable construction and functional regulation.The adsorption capacity of composite based sensors was discussed by density functional theory（DFT）simulation.（4）To explore the effects of the number of piles and porosity of the sensing material Ti₃C₂T_xMXene on the gas sensing behaviors,the In₂O₃/Ti₃C₂T_xMXene composite materials were prepared using hydrothermal technology using multi-layer Ti₃C₂T_xMXene and single-layer Ti₃C₂T_xMXene as the substrate materials,and In₂O₃as the gas sensing active site.Considering the number of layers,as the number of Ti₃C₂T_xMXene layers increases,the possibility of gas molecules adsorbing between layers increases.From the surface adsorption analysis,single layer Ti₃C₂T_xMXene is the best material for adsorbing gas molecules,and single layer Ti₃C₂T_xMXene can form more vacancies and expose more surface active adsorption sites.（5）To explore the catalytic effect of small layers of Ti₃C₂T_xMXene and Au nanoparticles on gas sensing performance,Au-Cu O/Ti₃C₂T_xMXene,Au-α-Fe₂O₃/Ti₃C₂T_xMXene and Au-In₂O₃/Ti₃C₂T_xMXene composites were designed and synthesized,respectively.Combined with structural characterization,gas sensing performance testing,and sensitivity theoretical analysis,the synergistic effects of electron and chemical sensitization of precious metal Au nanoparticles were revealed,which was beneficial to the adsorption of oxygen and the surface catalytic dissociation of oxygen species,thereby improving room temperature sensitivity characteristics.