High-performance photoactivated gas sensor with Au-loaded In₂O₃ 2D nanosheet for low-temperature applications

Semiconductor metal oxide (SMO) gas sensors generally require high operating temperatures (250–400 °C) for adequate sensitivity. This leads to high power consumption, safety hazards, and shortened device lifetimes. To address these limitations, Au-loaded In₂O₃ two-dimensional (2D) nanosheets were synthesized by reducing Au ions using HAuCl₄ and spray-coated on interdigitated electrode chips. The fabricated sensors were tested against various gases (formaldehyde, ethanol, toluene, benzene, ammonia, and acetone) from room temperature (RT) to 250 °C under dark and visible-light illumination conditions. Notably, formaldehyde, which was initially unresponsive at RT in the dark, exhibited a clear sensing response (R_a/R_g = 1.58 at 1 ppm) and complete recovery when illuminated with a 445 nm LED. In addition, ethanol sensing significantly improved at low temperatures; a 102-fold enhancement was achieved at 150 °C with Au loading and 445 nm illumination, compared with the bare In₂O₃ 2D sensor under dark conditions. Moreover, the sensor successfully detected typically high-temperature-dependent nonpolar gases (toluene and benzene) at 100 °C. These findings suggest that Au-loaded In₂O₃ 2D nanosheets, coupled with 445 nm light, significantly reduce the operating temperature required for sensing. This approach reduces energy consumption and leverages an inexpensive and safe light source.