Sub-2 nm SnO2 nanocrystals: A reduction/oxidation chemical reaction synthesis and optical properties

A simple reduction/oxidation chemical solution approach at room temperature has been developed to synthesize ultrafine SnO2 nanocrystals, in which NaBH4 is used as a reducing agent instead of mineralizers such as sodium hydroxide, ammonia, and alcohol. The morphology, structure, and optical property of the ultrafine SnO2 nanocrystals have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), differential scanning calorimetry and thermogravimetric analysis (DSC–TGA), X-ray photoelectron spectroscopy (XPS) and UV–vis absorption spectroscopy. It is indicated that the uniform tetragonal ultrafine SnO2 nanocrystals with the size below 2 nm have been fabricated at room temperature. The band gap of the ultrafine SnO2 nanocrystals is about 4.1 eV, exhibiting 0.5 eV blue shift from that of the bulk SnO2 (3.6 eV). Furthermore, the mechanism for the reduction/oxidation chemical reaction synthesis of the ultrafine SnO2 nanocrystals has been preliminary presented.