Controllable Preparation Of MOF-derived Nanostructural In₂O₃ And Their Gas-sensing Properties

The rapid development of science and technology has enriched people’s food,clothing,housing and transportation and promoted the progress of human civilization,but the toxic and harmful gases produced by it have seriously harmed the living environment,thus reducing people’s quality of life.In order to avoid harm to people’s life and property safety,gas sensor comes into being.The metal oxide semiconductor gas sensor has been widely studied and applied in the field of gas sensing due to its advantages of simple manufacture,low cost and sensitive detection.Among them,N-type metal oxide semiconductor Indium oxide（In₂O₃）with cubic phase structure has become one of the most promising gas-sensitive materials in the field of gas detection due to its high catalytic activity and special band gap（3.55-3.75 e V）.In recent years,in order to avoid the poor gas-sensitive performance of metal oxides caused by the shortcomings of the traditional preparation methods,such as uneven grain size and large morphological difference,researchers have selected MOFs with uniform morphology and structure,large specific surface area and high porosity as the precursor,and then derived and synthesized nanostructured metal oxide semiconductor gas-sensitive materials.In this paper,1,3,5-homophenic acid（H₃BTC）was selected as the organic ligand and solvothermal/oil bath method was adopted to synthesize the In-BTC precursor with two-dimensional（2D）nanosheets and three-dimensional（3D）hierarchical structure by adjusting experimental parameters.In₂O₃nanosheets and nests of In₂O₃were synthesized by high temperature calcination.In order to further improve the sensitivity,Au-In₂O₃nanosheets,Au-In₂O₃nest-shaped hierarchical structure,Sn O₂/In₂O₃nanocomposites,and Au-Sn O₂/In₂O₃nanocomposites were constructed,and their microstructure and gas-sensitive properties were analyzed and studied to explore the gas-sensitive mechanism.The main contents of this paper are as follows:1.2D In-BTC hexagonal nanosheets containing In³⁺and 3D In-BTC nested hierarchical structure precursor were prepared by solvothermal method and oil bath method using H₃BTC as organic ligands,and then 2D In₂O₃hexagonal nanosheets and 3D In₂O₃nested hierarchical structure were successfully derived by removing the organic ligands by calcination.It can be seen from the characterization that In₂O₃nanosheets have a hexagonal structure,a thickness of about 35 nm,and an obvious porous structure.The gas sensitivity test shows that In₂O₃nanosheets have good gas sensitivity to trimethylamine gas,and the best working temperature is 160°C.The nest-like hierarchical structure of In₂O₃assembled by nanosheet is complete in morphology and uniform in size,which effectively reduces the agglomeration of nano-sheet and is conducive to the diffusion and desorption of gas.The optimal working temperature of formaldehyde gas is reduced to 140°C,and the detection limit is as low as 1 ppm.2.Au-In₂O₃nanosheets and Au-In₂O₃nanocomposites with nested hierarchical structure were synthesized by liquid phase reduction method.The microstructure analysis confirmed that Au nanoparticles with the size of about 20～30 nm were uniformly distributed on the surface of the In₂O₃nanosheets.Au nanoparticles have electron sensitization and chemical sensitization,which can activate more active sites,increase the adsorption of oxygen molecules and the reaction of the gas to be measured,thus improving the gas response value at room temperature.The gas-sensitive test results show that 1wt%Au-In₂O₃nanosheets have excellent response and recovery to low concentration ammonia gas at RT,and the response value is 21.42.The response of 0.5wt%Au-In₂O₃nested hierarchical structure to 50 ppm ethanol gas at RT is 18.96,and the response recovery time is 7 s and 12 s.3.In order to further improve the response recovery rate of In₂O₃nanosheets,Sn O₂/In₂O₃nanocomposites with N-N heterojunctions were prepared by hydrothermal method,and Au-Sn O₂/In₂O₃nanocomposites were further synthesized by loading Au nanoparticles.By characterization analysis,it was found that both of them were composed of In₂O₃nanosheets and Sn O₂nanorods,and the specific surface area was greatly improved.In addition,Au nanoparticles effectively increased the content of chemisorbed oxygen.The gas-sensitive test showed that both of them had good gas-sensitive properties to formaldehyde gas,and the optimal working temperature was reduced.The reaction recovery time of Sn O₂was reduced to 5 s and 10 s due to the effect of N-N heterojunction.In addition,the gas-sensitive response value of the nanocomposite was effectively improved by loading Au nanoparticles.Its response value is 10.98,which provides experimental basis and theoretical basis for the study of fast and highly sensitive gas-sensitive materials at low temperature or even room temperature in the future.