Impact of Surface Faceting on Gas Sensing Selectivity of NiO: Revealing the Adsorption Sites of Organic Vapors on the {111} Facet

Air pollution by volatile organic compounds (VOCs) has been responsible for the decline of human health and environmental quality. NiO-based materials hold great promise as high-performance sensing materials to monitor the VOC concentration in air. The present research focuses on the design of NiO nanocrystals and the investigation of the effect of surface-terminated facets on their VOC gas sensing selectivity. NiO nanoparticles (NPs) with no specific surface facet exhibited a poor responsivity and selectivity toward VOC detection at all observed working temperatures, while the octahedral morphology of NiO exposed to the {111} facet demonstrated a better VOC sensing responsivity (R-g/R-a = 6.2) and high selectivity toward toluene at 250 degrees C. Owing to the terminated Ni metal as the highly reactive adsorption site, the octahedral morphology of NiO with the {111} facet exhibited an improved sensing and selectivity performance. Based on the experimental evidence, an ab initio DFT calculation is performed to investigate the analyte adsorption on the {111} facet of NiO and explain the high toluene selectivity on this facet. It is revealed that the {111} facet is energetically favorable for toluene adsorption, with an energy adsorption (E-ads) of -3.927 eV at the hollow HCP site. This study has a significant potentiality to be extended to many surface phenomena such as sensors, catalysis, and energy storage.

Automated summary

This research focuses on the design of NiO nanocrystals and investigates the effect of surface-terminated facets on their VOC gas sensing selectivity. Experimental results show that the octahedral morphology of NiO exposed to the {111} facet exhibits good VOC sensing responsivity and high selectivity towards toluene.