Highly selective detection of ppb-level formaldehyde realized by regulating the surface chemisorbed oxygen of Ga-doped In2O3 microspheres

Formaldehyde is a ubiquitous indoor pollutant. Developing metal oxide semiconductors gas sensors for selective ppb-level formaldehyde detection is challenging. Therefore, developing gas sensors that can selectively detect indoor formaldehyde at ppb levels is important. In this study, outer-walled thin sheet-like microspheres of Ga-doped In ₂O ₃ (Ga _xIn _2-xO ₃, x = 0, 0.1, 0.2, 0.3, and 0.4) were fabricated using a facile two-step synthetic method. The Ga _0.3In _1.7O ₃ based sensor shows the response (556 ± 25) to 100 ppm formaldehyde at 80 °C, which is around 6.5 times that of the pure In ₂O ₃ based sensor at 90 °C. Furthermore, it has fast response time (< 3 s), excellent selectivity (S _Formaldehyde/S _Ethanol = 160, S _Formaldehyde/S _Acetone = 267), good stability (at least 60 days), and ultra-low limit of detection (10 ppb) for formaldehyde at 80 °C. The improved formaldehyde sensing performance of Ga _0.3In _1.7O ₃ microspheres is attributed to the optimization of surface chemisorbed oxygen, which is caused by Ga doping regulating the Fermi level of In ₂O ₃ as well as an increase in the specific surface area.