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

Abstract

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 In₂O₃ (Ga_xIn_2-xO₃, x = 0, 0.1, 0.2, 0.3, and 0.4) were fabricated using a facile two-step synthetic method. The Ga_0.3In_1.7O₃ based sensor shows the response (556 ± 25) to 100 ppm formaldehyde at 80°C, which is around 6.5 times that of the pure In₂O₃ 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_1.7O₃ microspheres is attributed to the optimization of surface chemisorbed oxygen, which is caused by Ga doping regulating the Fermi level of In₂O₃ as well as an increase in the specific surface area.