Rare-earth-doped indium oxide nanosphere-based gas sensor for highly sensitive formaldehyde detection at a low temperature.

Formaldehyde (HCHO) is widely viewed as a carcinogenic volatile organic compound in indoor air pollution that can seriously threaten human health and life. Thus, there is a critical need to develop gas sensors with improved sensing performance, including outstanding selectivity, low operating temperature, high responsiveness, and short recovery time, for HCHO detection. Currently, doping is considered an effective strategy to raise the sensing performance of gas sensors. Herein, various rare earth elements-doped indium oxide (RE-InO) nanospheres were fabricated as gas sensors for improved HCHO detection a facile and environmentally solvothermal method. Such RE-InO nanosphere-based sensors exhibited remarkable gas-sensing performance, including a high selectivity and stability in air. Compared with pure, Yb-, Dy-doped InO and different La ratios doped into InO, 6% La-doped InO (La-InO) nanosphere-based sensors demonstrated a high response value of 210 to 100 ppm at 170 °C, which was around 16 times higher than that of the pure InO sensor, and also exhibited a detection limit of 10.9 ppb, and a response time of 30 s to 100 ppm HCHO with a recovery time of 160 s. Finally, such superior sensing performance of the 6% La-InO sensors was proposed to be attributed to the synergistic effect of the large specific surface area and enhanced surface oxygen vacancies on the surface of InO nanospheres, which produced chemisorbed oxygen species to release electrons and provided abundant reaction sites for HCHO gas. This study sheds new light on designing nanomaterials to build gas sensors for HCHO detection.