Temperature-driven n- to p-type transition of a chemiresistive NiO/ CdS-CdO NO₂ gas sensor

A new NiO/CdS-CdO composite-based chemiresistive gas sensor for NO2 detection exhibits temperature-driven adsorption switching. In-situ CdS nanoparticle growth on Ni-based metal-organic framework (MOF) spheres produced Ni-MOF/CdS, and then calcinating the Ni-MOF/CdS in air yielded NiO/CdS-CdO composite. The composite's NO2 sensing characteristics were examined at 25-350 degrees C, demonstrating that the NiO/CdS-CdO composite switches from n- to p-type above 200 degrees C with strong NO2 sensitivity and selectivity. Adsorption switching allows the NiO/CdS-CdO composite to serve as a dual-mode sensor, where NiO and CdS-CdO dominate at higher temperatures (>200 degrees C) and lower temperatures (<= 200 degrees C) with realistic detection ability, respectively. This switching is mainly caused by variations in charge carrier concentration and NO2 adsorption/desorption behavior on the composite surface. At 150 degrees C, NiO/CdS-CdO sensors have a low detection limit of 100 ppb, high response (R-g/R-a, similar to 215), quick response time (similar to 47 s), and recovery time (similar to 66 s) at 100 ppm. FTIR analysis, estimation of activation energies, and a qualitative comparison of n- to p-type transition with a typical full-wave rectification process explain the adsorption switching phenomenon. Adsorption switching in NiO/CdS-CdO-based gas sensors with great repeatability, stability, and fast response may be a promising route for high-performance gas sensing applications.