Superior ethanol-sensing behavior based on SnO2 mesocrystals incorporating orthorhombic and tetragonal phases

Abstract

SnO₂ mesocrystals with mixed phases (i.e., tetragonal and orthorhombic phases) and nanoporous structures have been successfully synthesized via a facile annealing topotactic transformation from SnO precursors under ambient-pressure and a moderate temperature range of 400–600 °C. The morphology of the mesocrystal precursor possesses a hydrangea ball or multilayer pancake structure, which is determined by a novel ionothermal strategy using choline chloride/urea based deep eutectic solvent (DES) as the reaction medium and water as the morphology controlling agent. The self-assembly of SnO mesocrystals is based on a “non-classical crystallization” process involving an oriented attachment mechanism. The polarity dependent self-assembly of SnO mesocrystals in the reaction system is also highlighted. Significantly, the mixed phase and nanoporous SnO₂ mesocrystal exhibits superior ethanol sensitivity compared with that of the SnO₂ with a single tetragonal phase or a solid structure. The sensitivity of the SnO₂ sample obtained at 400 °C is as high as 28.06 under 100 ppm ethanol and an optimum operation temperature of 300 °C, standing out from most of the state-of-the-art SnO₂ nanomaterials, which is due to the incorporation of orthorhombic and tetragonal phases and the porous structure. Furthermore, the SnO₂ mesocrystal with the mixed phases is also demonstrated to be a good selective ethanol sensor to effectively discriminate ethanol from acetone, methanol, and benzene.