pH-Dependent growth and gas sensing properties of hydrothermally synthesized SnO2 nanostructured films

This study investigates the growth of tin dioxide (SnO 2 ) nanostructures for NO 2 gas sensing applications. SnO 2 nanoparticle seed layers were deposited upon glass substrates employing chemical spray pyrolysis, followed by the synthesis of various nanostructured films through the hydrothermal technique. The structural, electrical, optical, and sensing characteristics of the SnO 2 films were examined. The polycrystalline tetragonal SnO 2 phase was confirmed by X-Ray Diffraction (XRD) measurements. The Field Emission-Scanning Electron Microscope (FE-SEM) images revealed a transition in morphology as the pH increased from 3 to 11. At lower pH, the nanoparticles appeared spherical. With increasing pH, the morphology changed to cubic forms and finally to cauliflower-like aggregates. The optical energy gap values were found to be 3.13, 3.31, and 3.00 eV, for pH 3, 9, and 11, respectively. Hall measurements confirmed the n-type conductivity for all films. Gas sensing tests were performed at different operating temperatures, and the sample prepared at pH 9 showed the highest NO 2 response at 150 °C. These findings demonstrate that optimizing the pH and seed-assisted hydrothermal synthesis significantly enhances the structural behavior and the gas sensing performance of the SnO 2 films, making them promising candidates for low-cost NO 2 detection.