In2O3 nanoparticles and nanoaggregates for formaldehyde recognition and mechanism insight: Enabled by engineering multi-crystal facets.

The toxic and carcinogenic formaldehyde necessitate developing high-performance sensing material for its monitoring. Herein, we provided feasible strategy to prepare and integrated multiple crystal planes of In2O3 to enhance sensing performance for formaldehyde recognition. As-prepared In2O3 nanoparticles and cubic nanoaggregates with hollow structures and controlled oxygen vacancy provides plentiful diffusion space and adsorption sites for gas molecules, and accelerates electron transport by coupling with different crystal boundaries. The findings of research show that as-optimized In2O3 exhibits high sensitivity, selectivity and fast response/recovery to less than 100 ppm formaldehyde at low temperature of 120 °C, and practical stability during 14-day record. Notably, the linear relationships of concentration-dependent response endow In2O3 quantitative monitoring formaldehyde and limit of detection reaches 312 ppb, and sensing performance of In2O3 are superior to that of reported materials significantly. The sensing mechanism have been expounded by in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy, and the gas sensing involves formaldehyde adsorption and nucleophilic addition, intermediate oxidation, dehydrogenation and oxidation. DFT calculations further confirm that low adsorption energy and electron transition of crystal planes are conductive to HCHO sensing performance. The portable device of microelectron mechanical systems integrated with In2O3 can be employed to monitoring formaldehyde efficiently, which drives the deployment of oxides sensing materials for intelligent sensor in environmental monitoring and life science applications.