Highly sensitive and selective sensing of H2S gas based on CuO–SnO2 nanocomposite

This study investigates the influence of Cu/Sn atomic ratio on the structural, microstructural, electrical, and gas sensing properties of CuO–SnO 2 nanocomposite thin films synthesized via air-assisted spray pyrolysis. X-ray diffraction (XRD) analysis confirmed the formation of a tetragonal SnO 2 phase and monoclinic CuO phase, with dominant diffraction peaks corresponding to (110), (101), (200), and (211) planes of SnO 2 , along with (110) and (111) planes of CuO. The average crystallite sizes, calculated using the Scherrer formula, were found to be 26 nm, 30 nm, and 38 nm for samples with Cu/Sn atomic ratios of 0.54, 0.63, and 1.41 respectively. Scanning electron microscopy (SEM) revealed a direct correlation between Cu/Sn ratio and surface morphology. At a lower Cu/Sn ratio of 0.54, the films exhibited a dense structure with small, uniformly distributed grains, enhancing surface area and active sites for gas adsorption. At 0.63, grain growth increased moderately, balancing surface area and electrical conductivity. At the highest Cu/Sn ratio of 1.41, SEM images showed larger faceted grains with increased crystallinity and porosity, improving charge carrier mobility but reducing gas sensitivity due to a decreased active surface area. Elemental analysis (EDAX) confirmed the composition of Cu, Sn, and O in the films, with Cu (at%) increasing from 13.26 % to 16.69 % as the Cu/Sn ratio increased. Electrical conductivity measurements confirmed the semiconducting behavior of the films, with conductivity increasing with temperature. Gas sensing studies demonstrated that the Cu/Sn 50:50 composition exhibited the highest sensitivity to H 2 S gas at 350°C, with a maximum response of 4590 at 50 ppm concentration. Response and recovery times were recorded as ∼60 s and ∼110 s, respectively. The enhanced gas sensing performance is attributed to optimized heterojunction formation between p-type CuO and n-type SnO 2 , leading to improved charge carrier separation and sensor response. These findings underscore the crucial role of Cu/Sn ratio in tailoring film morphology and optimizing gas sensing performance. The study provides a foundation for developing high-performance metal oxide-based gas sensors with improved selectivity and response characteristics. • CuO–SnO 2 thin films were studied for structural, electrical and gas sensing properties • Prepared via air-assisted spray pyrolysis; characterized using XRD, SEM, and EDAX. • Particle size increased with higher Cu/Sn ratio • Cu/Sn ratios shows that composition significantly impacts morphology and gas sensing performance • Cu/Sn (50:50) thin film showed the best H 2 S gas response at 350 °C with quick response and recovery times