A Highly Sensitive Colorimetric Gas Sensor Based on Indium Oxide Nnnostructures for H2S Detection at Room Temperature

Metal oxides are an attractive choice in the gas sensor industry due to their physical and chemical properties. Here, we have developed a highly sensitive colorimetric gas sensor for H2S gas based on indium oxide (In2O3) nanostructures. The In2O3 nanostructures were prepared by the modified sol-gel method. The optical darkness ratio (ODR) of H2S gas-exposed In2O3 nanostructured samples was determined by using a smartphone-based application. The change in color of H2S exposed In2O3 nanostructured films was found to be due to sulfurization of top of In2O3 nanostructured film and formation of In2S3 layer. The oxygen vacancies (V-o) defects were observed to be the promising factor that boosts the formation of the In2S3 layer. The photoluminescence and X-ray photoelectron spectroscopy measurements revealed that the V-o defects get annihilated when the In2O3 nanostructured film was exposed to H2S gas for a longer time. At room temperature, In2O3 nanostructured film has exhibited a lower detection limit of 10 ppm in 30 seconds for H2S gas. A mechanism based on V-o defects in In2O3 nanostructured film is invoked to explain the colorimetric detection of H2S gas.