We report the facile synthesis of thin-walled SnO nanotubes (NTs) with numerous clustered pores (pore radius 6.56 nm) and high surface area (125.63 m/g) via selective etching of core (SiO) region in SiO-SnO composite nanofibers (NFs), in which SnO phase preferentially occupies the shell while SiO is concentrated in the center of the composite NFs. The SiO-etched SnO NTs are composed of ultrasmall crystallites (∼6 nm in size) originating from crystal growth inhibition by small SiO domains, which are partially segregated in the polycrystalline SnO shell during calcination. These features account for efficacious diffusion and innumerable active sites, which maximize interaction between background gas (air) and analyte gas (HS). Evaluation of gas-sensing performance of the porous SnO NTs before and after decorating the exterior and interior walls with Pt nanoparticles (NPs) reveals exceptional selectivity and superior response (R/R) of 154.8 and 89.3 to 5 and 1 ppm of HS, respectively. Excellent gas-sensing characteristics are attributed to the porous topography, nanosized crystallites, high surface area, and the catalytic activity of Pt/PtO NPs.
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@SnO 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 in NaOH (pH 12) affords meso/macroporous SnO 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 g). Apart from surface meso/macropores, diffusion of gases into porous SnO sensing layers is realized through inner interconnection of voids of the SnO HSPs into a three-dimensional network. Functionalization of the postetched SnO HSPs with platinum (Pt) nanoparticles at 0.08 wt % yields gas-sensing materials with outstanding response ( R/ R = 1.6, 10.8, and 105.1-0.1, 1, and 5 ppm of HS, respectively) and selectivity toward HS against interfering gas molecules at 250 °C. The SiO phase in the postcalcined SiO@SnO SPs acts as a sacrificial template for pore creation and crystal growth inhibition, whereas the small amount of SiO residues in HSPs enhances the selectivity.
Perovskite-type oxides with general stoichiometry ABO 3 (A is a lanthanide or alkali earth metal, and B is transition metal) constitute a rich material playground for application as resistive-type gas-sensing layers. Immense interest is triggered by, among other factors, stability of abundant elements (≈ 90% in the periodic table) in this stoichiometry, relatively easy tunability of structure and chemical composition, and their off-stoichiometry stability upon doping. Moreover, their capability to host cationic and abundant oxygen vacancies renders them with excellent electrical and redox properties, and synergistic functions that influence their performance. Herein, we present an overview of recent development in the use of ABO 3 perovskites as resistive-type gas sensors, clearly elucidating current experimental strategies, and sensing mechanisms involved in realization of enhanced sensing performance. Finally, we provide a brief overview of limitations that hamper their potential utilization in gas sensors and suggest new pathways for novel applications of ABO 3 materials.
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