Controlled Synthesis of Monodisperse Sub-100 nm Hollow SnO2 Nanospheres: A Template- and Surfactant-Free Solution-Phase Route, the Growth Mechanism, Optical Properties, and Application as a Photocatalyst

Graphical Shape and size control of sub-100 nm SnO 2 hollow nanostructures, such as the depicted hollow nanospheres, was achieved by a mild template- and surfactant-free hydrothermal route starting from potassium stannate and urea in ethylene glycol/water. Precise control of morphology and size is possible by varying reaction parameters, such as reaction time, urea concentration, and reaction temperature. Controlled synthesis of low-dimensional materials, such as nanoparticles, nanorods, and hollow nanospheres, is vitally important for achieving desired properties and fabricating functional devices. We report a systematic investigation of the growth of low-dimensional sub-100 nm SnO 2 hollow nanostructures by a mild template- and surfactant-free hydrothermal route, aiming to achieve precise control of morphology and size. The starting materials are potassium stannate and urea in an ethylene glycol (EG)/H 2 O system. We found the size of the SnO 2 hollow nanospheres can be controlled by simply adjusting the urea concentration. Investigation of the mechanism of formation of the SnO 2 hollow nanospheres revealed that reaction time, urea concentration, and reaction temperature make significant contributions to the growth of hollow nanospheres. On switching the solvent from EG/H 2 O to H 2 O or ethanol, the SnO 2 nanostructures changed from nanospheres to ultrafine nanorods and nanoparticles. On the basis of reaction parameter dependent experiments, oriented self-assembly and subsequent evacuation through Ostwald ripening are proposed to explain the formation of hollow nanostructures. Their size-dependent optical properties, including UV/Vis absorption spectra and room-temperature fluorescence spectra, were also studied. Moreover, the studies on the photocatalytic property demonstrate that the fabricated hollow structures have slightly enhanced photocatalytic degradation activity for rhodamine B when exposed to mercury light irradiation compared to solid SnO 2 nanospheres under the same conditions. The synthesized tin oxide nanoparticles display high photocatalytic efficiency and have potential applications for cleaning polluted water in the textile industry.