Nickel-doped indium oxide ultrafine nanoparticles for ppb-level nitrogen dioxide detection

Metal oxide semiconductor sensors were designed utilizing 0.17 mol% Ni:In 2 O 3 nanoparticles for detecting ppb-level NO 2 in the air. Synthesized using the carbon template hydrothermal method, our Ni:In 2 O 3 nanoparticles achieved a monodispersion of Ni atoms in the crystal structure of In 2 O 3 , with indistinguishable XRD patterns but a slightly different lattice spacing and an average particle size of 35.3 nm. Concerning NO 2 -sensing capacity, our Ni:In 2 O 3 -based sensors outperformed those from similar doped In 2 O 3 nanomaterials regarding higher sensitivity and selectivity. Our maximum dimensionless response values achieved 377 for 500 ppb and 21.7 for 10 ppb at an operational temperature of 100 °C, ∼ 50 times greater than 10 ppm of other gases, and our response and recovery times were comparable to state-of-the-art technology under similar circumstances. Combining the electron depletion layer model and density functional theory, electronic origins of the NO 2 -sensing mechanism on the Ni:In 2 O 3 surface were deciphered based on redox-based chemisorptions of NO 2 . The significantly enhanced response of Ni:In 2 O 3 compared to In 2 O 3 was attributed to the reduced fundamental band gap and the increased number of NO 2 -attracting oxygen vacancy sites on the surface. Our study set the stage for promising applications of Ni:In 2 O 3 and similar metal oxide semiconductor nanoparticles for ppb-level gas detection.