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

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 degrees 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 degrees C is as high as 28.06 under 100 ppm ethanol and an optimum operation temperature of 300 degrees 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.