Nanometer-Thick ZnO/SnO₂ Heterostructures Grown on Alumina for H₂S Sensing

Designing heterostructure materials at the nanoscale is a well-known method to enhance gas sensing performance. In this study, a mixed solution of zinc chloride and tin (II) chloride dihydrate, dissolved in ethanol solvent, was used as the initial precursor for depositing the sensing layer on alumina substrates using the ultrasonic spray pyrolysis (USP) method. Several ZnO/SnO₂ heterostructures were grown by applying different ratios in the initial precursors. These heterostructures were used as active materials for the sensing of H₂S gas molecules. The results revealed that an increase in the zinc chloride in the USP precursor alters the H₂S sensitivity of the sensor. The optimal working temperature was found to be 450 °C. The sensor, containing 5:1 (ZnCl₂: SnCl₂·2H₂O) ratio in the USP precursor, demonstrates a higher response than the pure SnO₂ (∼95 times) sample and other heterostructures. Later, the selectivity of the ZnO/SnO₂ heterostructures toward 5 ppm NO₂, 200 ppm methanol, and 100 ppm of CH₄, acetone, and ethanol was also examined. The gas sensing mechanism of the ZnO/SnO₂ was analyzed and the remarkably enhanced gas-sensing performance was mainly attributed to the heterostructure formation between ZnO and SnO₂. The synthesized materials were also analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, and X-ray photoelectron spectra to investigate the material distribution, grain size, and material quality of ZnO/SnO₂ heterostructures.