Although single-nozzle electrospraying seems a versatile technique in the synthesis of spherical semiconducting metal oxide structures, the synthesized structures find limited use in gas-sensing applications because of their thick and dense morphology, which minimizes the accessibility of their inner surfaces. Herein, unprecedented spherical SiO2@SnO2 core-shell structures are synthesized upon calcination of single-nozzle as-electrosprayed spheres (SPs) containing tin (Sn) and silicon (Si) precursors. Subsequent etching of SiO2 in NaOH (pH 12) affords meso/macroporous SnO2 hollow spheres (HSPs) with short diffusion length (31.4 ± 3.1 nm), small crystallites (15.5 nm), and large Brunauer-Emmett-Teller surface area (124.8 m2 g-1). Apart from surface meso/macropores, diffusion of gases into porous SnO2 sensing layers is realized through inner interconnection of voids of the SnO2 HSPs into a three-dimensional network. Functionalization of the postetched SnO2 HSPs with platinum (Pt) nanoparticles at 0.08 wt % yields gas-sensing materials with outstanding response ( Ra/ Rg = 1.6, 10.8, and 105.1-0.1, 1, and 5 ppm of H2S, respectively) and selectivity toward H2S against interfering gas molecules at 250 °C. The SiO2 phase in the postcalcined SiO2@SnO2 SPs acts as a sacrificial template for pore creation and crystal growth inhibition, whereas the small amount of SiO2 residues in HSPs enhances the selectivity.
Keywords: SnO2 hollow spheres; core−shell; electrospraying; etching; gas sensor.