Facile Synthesis of Pt-Functionalized Meso/Macroporous SnO 2 Hollow Spheres through in Situ Templating with SiO 2 for H 2 S Sensors.

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 SiO ₂ @SnO ₂ core-shell structures are synthesized upon calcination of single-nozzle as-electrosprayed spheres (SPs) containing tin (Sn) and silicon (Si) precursors. Subsequent etching of SiO ₂ in NaOH (pH 12) affords meso/macroporous SnO ₂ 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 m ² g ^-1 ). Apart from surface meso/macropores, diffusion of gases into porous SnO ₂ sensing layers is realized through inner interconnection of voids of the SnO ₂ HSPs into a three-dimensional network. Functionalization of the postetched SnO ₂ HSPs with platinum (Pt) nanoparticles at 0.08 wt % yields gas-sensing materials with outstanding response ( R _a / R _g = 1.6, 10.8, and 105.1-0.1, 1, and 5 ppm of H ₂ S, respectively) and selectivity toward H ₂ S against interfering gas molecules at 250 °C. The SiO ₂ phase in the postcalcined SiO ₂ @SnO ₂ SPs acts as a sacrificial template for pore creation and crystal growth inhibition, whereas the small amount of SiO ₂ residues in HSPs enhances the selectivity.