Enhancing room-temperature gas sensing performance of metal oxide semiconductor chemiresistors through 400 nm UV photoexcitation

One of the most significant drawbacks of metal oxide (MOS) based chemiresistive gas sensors is the requirement of high operating temperature (250–450 °C), which results in significant power consumption and shorter lifetime. To develop room temperature (21±2 °C) MOS chemiresistive gas sensors, the sensing performance of different MOS nanostructures (i.e., tin (IV) oxide (SnO₂) nanoparticles (NPs), indium (III) oxide (In₂O₃) NPs, zinc oxide (ZnO) NPs, tungsten trioxide (WO₃) NPs, copper oxide (CuO) nanotubes (NTs), and indium tin oxide (In₉₀Sn₁₀O₃ (ITO)) NPs) were systematically investigated toward different toxic industrial chemicals (TICs) (i.e., nitrogen dioxide (NO₂), ammonia (NH₃), hydrogen sulfide (H₂S), carbon monoxide (CO), sulfur dioxide (SO₂) and volatile organic compounds (VOCs) (i.e., acetone (C₃H₆O), toluene (C₆H₅CH₃), ethylbenzene (C₆H₅CH₂CH₃), and p-xylene (C₆H₄(CH₃)₂)) in the presence and absence of 400 nm UV light illumination.

Sensing performance enhancement through photoexcitation is strongly dependent on the target analytes. Under 400 nm UV photoexcitation at 76.0 mW/cm² intensity, room temperature (21±2 °C) NO₂ sensing was readily achieved where SnO₂ NPs exhibited the highest sensor response (S = 474.4 toward 10 ppm_m (parts per million by mass)) with good recovery followed by ZnO NPs > In₂O₃ NPs > ITO NPs. Meanwhile, indirect bandgap n-type WO₃ NPs showed limited NO₂ sensing performance under illumination, whereas p-type CuO NTs showed relatively good sensing response. The most significant improvements in SnO₂ compared to other MOS nanoparticles might be attributed to the highest number of photogeneration electrons, which rapidly reacted with adsorbed $N{O}_2^{-}$ species to enhance the reaction kinetics. WO₃ NPs showed a unique sensing response toward aromatic compounds (e.g., ethylbenzene and p-xylene) under UV illumination, where maximum sensitivity was achieved under 36 mW/cm² irradiation. Changing light intensity from 0.0 to 36.4 mW/cm², WO₃ showed 15.4-fold and 6.3-fold enhancement in sensing response toward 25 ppm_m ethylbenzene and 100 ppm_m p-xylene, respectively. 400 nm optical excitation has a limited effect on the sensing performance toward CO, SO_2, toluene, and acetone.