Preparation And Gas Sensing Properties Of MOF Derived Indium Oxide Semiconductor Nanomaterials

Various toxic and harmful gases in production and life can often cause environmental pollution or safety accidents,which will affect human health.Therefore,it is necessary to detect these gases in time and quickly.There are many kinds of sensors that can be used for gas detection.Semiconductor gas sensor is widely used because of its high response,good selectivity,fast response and recovery,high repeatability,high stability and low cost.In semiconductor gas sensors,gas sensing material is one of the main factors to determine its performance.Just for this reason,improving the gas sensing performance of the materials is a main research direction in this field.Among all the semiconductor gas sensing materials,n-type semiconductor material In₂O₃ has high gas sensing performance because of its wide band gap and low resistivity,which is worthy of further study.Generally speaking,the structure,morphology and composition of the materials have an important impact on their properties.The metal organic frameworks(MOFs)derived oxides can inherit the specific structure and morphology of MOFs,so they have higher properties than the materials prepared by conventional methods.In order to improve the gas sensing properties of In₂O₃,a novel MIL-68(In)derivative In₂O₃ with terephthalic acid as ligand was prepared.The preparation method was also optimized and In₂O₃was modified by aluminum doping.The research contents and main achievements are as follows:1.The precursor was prepared by solvothermal method,using In³⁺as the central ion,pyromellitic acid or terephthalic acid as the ligand,2,4?-bipyridine or 2,2?-bipyridine as additive to regulate its morphology.Four different morphologies of In₂O₃,including nanospheres,micro frustum of prisms,nanowires and micro hexagonal prisms,were obtained by annealing the precursors.The results show that the gas sensitivity of In-MIL-68 derived porous morphology In₂O₃ with terephthalic acid ligand is the best.The response to 10 ppm n-butanol is 14.7 at 200?,and the response/recovery time is 28 s/19 s,which is significantly higher than that of In₂O₃ with other morphology,the main reason is that the porous structure accelerates the internal diffusion and provides more active sites for n-butanol gas adsorption and reaction.2.The preparation method of In-MIL-68 derived porous hexagonal In₂O₃ was optimized,and the effect of annealing temperature on its structure and gas sensing properties was studied.The results show that the response of In₂O₃-500 annealed at 500?to n-butanol is higher than that of In₂O₃-550 annealed at 550?,but the increase is not significant.However,the material has better sensitivity to 5 ppm triethylamine gas at120?.The response value is 226,the response and recovery time are 9 s and 36 s respectively,the linear response correlation coefficient is 0.9969 in the range of 0.1-5ppm,and the detection limit is 0.1 ppm.In addition,the material also showed good selectivity,stability(no obvious change in response within 40 days)and moisture resistance.The good crystallinity,large specific surface area,loose and porous structure and more oxygen vacancies of In₂O₃-500 are the reasons for its good gas sensitivity.3.In-MIL-68 precursors doped with different amounts of Al³⁺were prepared and annealed in air to obtain x mol%Al-In₂O₃(x=2,5,8,11 and 14)products,the effect of Al³⁺doping on the properties of In-MIL-68 derived In₂O₃ was studied.The results show that Al³⁺enters into the lattice of In₂O₃ and occupies some In³⁺position.Due to the appropriate amount of Al³⁺doping,5 mol%Al-In₂O₃ forms a hollow structure.Compared with pure In₂O₃,the sensitivity of the material to triethylamine is better,and the response value increases from 34.7 to 92.8 at 120?,the response/recovery time was reduced from 67 s/85 s to 38 s/64 s,and the detection limit was as low as 0.1 ppm.The main reason for the improvement of gas sensitivity of 5 mol%Al-In₂O₃ is the formation of unique hollow structure,the change of the energy band structure of In₂O₃after doping with Al³⁺and the increase of adsorption oxygen and oxygen vacancy.