| In the case of metal oxide semiconductor gas sensors,the performance of gas sensing mainly depends on the changes in the electrical properties such as the electrical resistance caused by the oxidation-reduction reaction on the surface of the sensing materials.However,the current gas sensors still show low response,poor selectivity,and other problems.Therefore,the composition between metal oxide semiconductor and noble metal materials can solve the above-mentioned problems to a certain extent.In the past research process of gas sensing materials,the noble metals are usually doped into crystal to improve the gas sensing performance of the materials,while other existing forms of noble metals are rarely studied.Therefore,In2O3 nanorods prepared on the kaolin substrate and catalyst layer of the kaolin substrate were investigated,and the influences of the catalyst layer of noble metal on the structure and gas sensing properties of In2O3 nanomaterials were also discussed.In2O3 nanorods were prepared on the surface of the kaolin substrate by hydrothermal method by using indium nitrate hydrate as the source of indium,urea as the alkali source,and glucose as the template.The microstructure,crystallization and other structural properties were characterized by XRD,SEM,EDS,FTIR and other characterization methods.By optimizing the condition parameters in the hydrothermal synthesis process,it is determined that the favorable preparation conditions for obtaining In2O3 nanorods are the indium source ratio of 1.5:2.5:4,the hydrothermal temperature of 120℃,the hydrothermal time of 12 h,the heat treatment temperature of 500℃ and the heat treatment time of 3 h.The diameter and length of In2O3 nanorods obtained under such conditions are 30 nm and 200～800 nm,respectively,with a large specific surface area,uniform distribution,and good crystallinity.The catalyst layers of noble metal were deposited on the kaolin substrate by vacuum sputtering method,and then In2O3 nanomaterials were optimally synthesiezed on the surface of the catalyst layer on the kaolin substrate by hydrothermal method.The structure and morphology were characterized by SEM,EDS,XRD and other characterization methods.The catalyst layer of noble metal prepared under the same conditions presents different existence states on the surface of the substrate.The yield of In2O3 nanorods synthesized based on the gold nanoparticle catalyst layer is significantly higher than that of platinum nanofilms or palladium nanofilms.These nanorods tend to be vertically distributed,providing more adsorption sites for subsequent gas sensing detection.In2O3 nanomaterials based on kaolin substrate,kaolin substrate with gold catalyst layer,kaolin substrate with platinum catalyst layer and kaolin substrate with palladium catalyst layer were used to fabricate the gas sensors.The gas sensing performance of these materials obtained under four conditions to NO2 gas was investigated by a static gas distribution method.The results show that these sensing materials show good response,selectivity and stability to NO2 gas,and the highest response can be obtained at 150℃.Especially,the gas sensing properties of In2O3 nanomaterials obtained on the gold catalyst layer of the kaolin substrate are significantly higher than those of the other three samples with higher response,selectivity and stability.Based on the results of structural characterization and corresponding growth mechanism,the growth mechanism of In2O3 nanomaterials obtained based on kaolin substrate and catalyst layer of kaolin substrate was explored.In2O3 nanomaterials obtained based on different surfaces are affected by the characteristics and existence of the catalyst with the mutual influence of multiple growth models.The sensing reaction mechanism between NO2 gas and In2O3 nanomaterials obtained based on kaolin substrates and different catalyst layers is clarified according to the large specific surface area of the materials and the catalytic effect of noble metals. |
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