One-step synthesis of micro-/mesoporous SnO₂ spheres by solvothermal method for toluene gas sensor

A facile solvothermal synthesis in an ethanol/acetic acid mixture for the fabrication of SnO₂ with a controllable hierarchical spherical size and micro-/mesoporosity is presented. SEM, TEM and N₂ adsorption/desorption investigation unveiled that the obtained SnO₂ spheres exhibited a particle size in the range of 0.6–1.6 μm and a pore size of about 1.4–1.9 nm depending on the volume ratio of acetic acid to ethanol in the reaction mixture, and the spheres were constructed by nanoscale particles. Due to its micro-/mesoporous structure, the SnO₂ spheres exhibited large specific surface areas over 100 m²/g. When 10 vol. % of acetic acid at 200 °C for 20 h was used for the reaction, the obtained SnO₂ possessed a higher specific surface area of 145 m²/g (SnO₂_10). The gas sensing property of SnO₂_10 without an additional noble metal co-catalyst exhibited a large toluene sensing response (R_a/R_g) of 20.2 at 400 °C, which was about 6 times higher and acceptable selectivity compared to those of other samples. The study found that the sensing performance in the SnO₂ hierarchical spheres was influenced by several factors e.g. particle morphology, pore size and specific surface area rather than only a single parameter. Therefore, a precise control of those influencing parameters may lead to the optimum sensing property. These findings are important for the further development of the micro-/mesoporous metal-based oxide as an alternative successor for toluene gas sensor material.