The growth behavior of brain-like SnO2 microspheres under a solvothermal reaction with tetrahydrofuran as a solvent and their gas sensitivity

Abstract

In this paper, the growth behavior of brain-like SnO₂ microspheres synthesized by a tetrahydrofuran (THF) solvothermal method was studied. Unlike water or ethanol as the solvent, THF is a medium polar and aprotic solvent. Compared with other common polar solvents, the THF has no strong irregular effects on the growth process of SnO₂. In addition, the viscosity of THF also helps the SnO₂ to form a regular microstructure. The growth behavior of the brain-like SnO₂ microspheres is controlled by changing the synthesis temperature of the reaction. The SEM and TEM results reveal that the SnO₂ forms particles first (125 °C/3 h), and then these nanoparticles connect to each other forming nanowires and microspheres (diameter ≈ 1–2 μm) at 135 °C for 3 h; finally the microspheres further aggregate to form double or multi-sphere structures at 180 °C for 3 h. In this paper, the brain-like SnO₂ microspheres obtained at 125 °C for 3 h were selected as sensitive materials to test their gas sensing performance at different operating temperature (50 °C and 350 °C). The H₂S was tested at 50 °C which is the lowest operating temperature for the sensor. The combustible gas (H₂/CH₄/CO) was measured at 350 °C which is the highest temperature for the sensor. They all have extremely high sensitivity, but only H₂S has excellent selectivity.