Nanoporous Mixed-Phase In₂O₃ Nanoparticle Homojunctions for Formaldehyde Sensing

Designing a reliable sensor for indoor formaldehyde (HCHO) with high sensitivity and selectivity is crucial for environmental and health protection. This study reported HCHO sensors based on a nanoporous mixed-phase In 2 O 3 nanoparticle. A combined cubic and orthorhombic phase In(OH) 3 /InOOH [c-In(OH) 3 /o-InOOH] precursor, synthesized through a facile solvothermal route at different temperatures, was annealed to prepare the In 2 O 3 nanoparticle homojunction. The obtained In 2 O 3, calcined at 350 °C, exhibited a porous structure and a large specific surface area of 81.46 cm 3 ·g –1, facilitating more number of active sites’ exposure for HCHO-sensing reactions. Results showed that the In 2 O 3 calcined at 350 °C exhibited the best HCHO-sensing performances at 120 °C with a large response value (330–50 ppm), good selectivity, and a short response time (12 s). Additionally, its detection limit could reach 11 ppb. This HCHO gas sensing behavior was owing to the mixed-phase homojunction structure formed between cubic and rhombohedral In 2 O 3, the large specific surface area, and the porous structure with abundant oxygen vacancies. This study indicated that the nanoporous mixed-phase In 2 O 3 nanoparticles could be the potential candidates for rapidly detecting HCHO at low concentration levels under low power consumption.