Room temperature detection and modelling of sub-ppm NO2 by low-cost nanoporous NiO film

NiO-based NO2 sensors operating at room temperature are attracting great attentions due to their promising energy and cost saving performances. However, only a few reports showed high sensitivity and selectivity in the sub-ppm concentration range and low limit of detection (LoD). In this work, we designed and fabricated by a low-cost chemical bath deposition (CBD) and thermal annealing a nanostructured and porous NiO thin film (nanoporous NiO film) composed of NiO nanoparticles (30−50 nm). The nanoporous NiO film was then applied as sensing element for the NO2 detection at room temperature, demonstrating a high response to sub-ppm level NO 2 (140 ppb), excellent selectivity and stability, and a very low LoD of 20 ppb. The NO 2 sensing mechanism was investigated and satisfactorily modelled by two energetically different and independent adsorption sites at room temperature. Both sites contribute to the NO 2 detection at room temperature while only one site contributes at higher temperatures. The described low-cost fabrication method and the discussed superior NO 2 sensing performances at room temperature make the nanoporous NiO film a promising NO 2 sensor for environmental monitoring.