Microstructure-controlled preparation of monodisperse In2O3 for excellent HCHO sensing with high selectivity, good anti-humidity and low detection limit

Abstract

Morphology control significantly improves the microstructure, increases the number of defects, tailors porosity, and optimizes the band gap of gas-sensing materials, profoundly affecting the adsorption and desorption capabilities for gas molecules. Herein, we prepared In(OH)₃ precursors via a hydrothermal method and rationally controlled the microstructure of In₂O₃ by varying annealing temperatures (400°C, 500°C, 600°C). Characterizations revealed that the porous cubic In₂O₃-500 (500°C) exhibited superior properties, including more balanced grain size and crystallinity, superior pore structure, more oxygen vacancies and adsorbed oxygen, and a narrower band gap compared to the surface-dense cubic In₂O₃-400 (400°C) and the porous spherical In₂O₃-600 (600°C). Gas-sensing tests demonstrated that three sensors displayed exceptional selectivity towards formaldehyde (HCHO), with rapid response times (1 s) to 100 ppm HCHO. Notably, In₂O₃-500, operating at a lower temperature (175°C), achieved the highest response (R_a/R_g = 200), good humidity resistance, and the lowest detection limit (30 ppb). The gas-sensing performance at 60 RH% showed that In₂O₃-500 still exhibited the highest response (161) to 100 ppm HCHO at 175℃, a decrease of less than 20 %. This study offers insights into the cost-effective and facile fabrication of high-performance HCHO gas sensors based on In₂O₃ materials.