Thorn-ball shaped TiO2 nanostructures: Influence of Sn2+ doping on the morphology and enhanced visible light photocatalytic activity

Abstract

A novel solution based route to synthesize thorn-ball shaped Sn2+ doped TiO2 nanostructures in a large scale without the use of any reducing agents is demonstrated. White precipitates are formed instantaneously when a solution of cetyltrimethylammonium bromide with milli-molar quantities of stannous chloride dihydrate (SnCl2·2H2O) is mixed to a solution of titanium isopropoxide in hydrochloric acid. The morphology of the precipitates analyzed using scanning electron microscope and transmission electron microscope reveal a complex morphology with crystalline nanorods grown uniformly over the balls. When the precipitates were treated hydrothermally by suspending in ethylene glycol (EG), further reduction takes place and “Thorn-ball shaped nanostructures” with very thin and long nanorods are formed. The thorn-ball samples (ST2-HTB) showed a large surface area of ∼244m2g−1 and the band-gap was ∼0.3eV narrower than that of pure TiO2, P25 (∼3.2eV), enhancing its visible light absorption. The samples exhibited a superior efficiency in the photocatalytic degradation of Rhodamine B (RhB) under visible light irradiation to P25, and the efficiency was comparable to P25 under UV irradiation despite of their polycrystalline nature. Under visible light irradiation the degradation of RhB using thorn-ball nanostructure photocatalysts was accompanied by a gradual shift in the absorption peak owing to formation of several N-de-ethylated intermediates of RhB. Photodegradation reaction mechanism of RhB under visible light irradiation, was proposed to be initiated by the valence band holes or through the conduction band electrons. The novel strategy demonstrated here for preparing thorn-ball nanostructures opens a new horizon to design complex structures of TiO2 for various applications.