Tuning the “O” vacancies density in SnO2 nanocrystals during and after humid air plasma synthesis: implications on the photocatalytic performances under UV light

Abstract

Tin(IV) oxide is a very attractive material with promising applications in new-generation devices. In this work, we reported a powerful but cheap and sustainable approach for preparing SnO2 nanocrystals based on the use of a non-thermal plasma burning in humid air. Physicochemical characterizations by Raman, Infrared and X-ray photoelectron spectroscopies revealed the presence of few hydroxyl groups and few oxygen vacancy (Ov) defects in the material obtained after 30 min under plasma (hereafter called NC-Sn30). By increasing the synthesis duration up to 120 min, the number of Ov decreased while the material became more hydroxylated. Furthermore, the material obtained after 120 min under plasma (i.e. NC-Sn120) was more crystallized. When tested as photocatalyst in iodide oxidation, NC-Sn120 showed lowest activity compared to NC-Sn30. After further calcination under air or nitrogen atmosphere at 550 °C, the crystallites size of pristine materials increased and their specific surface area values which were 190 and 206 m2 g−1 for NC-Sn30 and NC-Sn120, respectively, dropped to about 30 m2 g−1. Meanwhile, the Ov density increased leading to the rise of the valence band maximum and the decrease of the band gap energy of materials. The calcined samples with higher Ov density showed better photocatalytic performances, as the rate of formation of reactive iodine species (i.e. I3−, I2) normalized with the surface area of calcined photocatalysts was about 4 times higher than that of their corresponding pristine SnO2. These results open the door to a new route synthesis of SnO2 nanocrystals with tunable “O” vacancies density and photocatalytic performances.