Optical investigation of the size effects on NO2 adsorption in SnO2 nanoparticles

The size effects on adsorption of NO2 in SnO2 nanoparticles have been investigated by means of Raman and UV–Vis spectroscopy in the size range of 3–44 nm. It is found that the intrinsic and superficial Raman modes for SnO2 exhibit an intensity decrease and increase notably by reducing the particle size, respectively, suggesting the domination of the surface state in SnO2 nanoparticles. We further find that the intensities of the NO2-related modes show significant increases as the size decreases, which can be ascribed to the enhanced adsorption of NO2 due to the domination of the surface state in SnO2 nanoparticles. In addition, we also find the evident enhancement of the surface state absorption due to decrease of the size, which is consistent with the Raman investigation.