A Highly Sensitive Colorimetric Gas Sensor Based on Indium Oxide Nanostructures 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 H
₂
S gas based on indium oxide (In
₂
O
₃
) nanostructures. The In
₂
O
₃
nanostructures were prepared by the modified sol-gel method. The optical darkness ratio (ODR) of H
₂
S gas-exposed In
₂
O
₃
nanostructured samples was determined by using a smartphone-based application. The change in color of H
₂
S exposed In
₂
O
₃
nanostructured films was found to be due to sulfurization of top of In
₂
O
₃
nanostructured film and formation of In
₂
S
₃
layer. The oxygen vacancies (V
_o
) defects were observed to be the promising factor that boosts the formation of the In
₂
S
₃
layer. The photoluminescence and X-ray photoelectron spectroscopy measurements revealed that the V
_o
defects get annihilated when the In
₂
O
₃
nanostructured film was exposed to H
₂
S gas for a longer time. At room temperature, In
₂
O
₃
nanostructured film has exhibited a lower detection limit of 10 ppm in 30 seconds for H
₂
S gas. A mechanism based on V
_o
defects in In
₂
O
₃
nanostructured film is invoked to explain the colorimetric detection of H
₂
S gas.