A selective resistive CO gas sensor based on bio-waste derived 2D-CaO nanoplates

This study marks the inaugural documentation of the synthesis of fine calcium oxide (CaO) nanoplates (NPs) with an average length of ≈97 nm and a breadth of ≈50 nm derived from eggshell bio-waste, without using additional chemical agents. This environment friendly approach not only exemplifies sustainable materials science but also paves the way for the development of a highly specific sensor capable of detecting minute concentrations of CO gas, offering both ecological and economic benefits. The fabricated CaO NPs showed a cubic crystal phase and a band gap of ≈3.65 eV, a lattice constant of ≈0.485 nm with semiconducting nature having an activation energy of ≈0.21 eV. Prominent defects of oxygen vacancies and calcium interstitials were observed. The resistive gas sensor made with CaO NPs showed selective detection of CO among different gases (CO₂, NH₃, CO, and NO₂) and VOCs (acetone and ethanol). The device showed the highest response ≈3.45 ± 0.17 at an operating temperature of 300 °C for 150 ppm of CO gas. The device response time varies from 75 ± 3.75 s to 140 ± 7 s, whereas the recovery time varies between 80 ± 4.1 s and 255 ± 12.75 s. The device showed a sensitivity of 0.43 ± 0.094 ppm^-1 with LOD ≈ 14.4 ± 1.15 ppm. The sensor showed long time stability along with good anti-humidity responsive nature.