Influence of Surface Defects and Size on Photochemical Properties of SnO₂ Nanoparticles.

We report the successful synthesis of surface defective small size (SS) SnO₂ nanoparticles (NPs) by adopting a low temperature surfactant free solution method. The structural properties of the NPs were analyzed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The presence of surface defects, especially oxygen vacancies, in the sample were characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence emission. The Brunauer⁻Emmet⁻Teller (BET) nitrogen adsorption⁻desorption isotherms demonstrated the superior textural properties (high surface area and uniform pore size) of SS SnO₂ compared to large size (LS) SnO₂. A comparable study was drawn between SS SnO₂ and LS SnO₂ NPs and a significant decrease in the concentration of surface defects was observed for the LS sample. The results showed that surface defects significantly depend upon the size of the NPs. The surface defects formed within the band gap energy level of SnO₂ significantly participated in the recombination process of photogenerated charge carriers, improving photochemical properties. Moreover, the SS SnO₂ showed superior photoelectrochemical (PEC) and photocatalytic activities compared to the LS SnO₂. The presence of a comparatively large number of surface defects due to its high surface area may enhance the photochemical activity by reducing the recombination rate of the photogenerated charges.