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

• Published in: Journal of materials science 2020-04, Vol.55 (11), p.4792-4807
• Main Authors: Tiya-Djowe, Antoine, Dourges, Marie-Anne, Deleuze, Hervé
• Format: Article
• Language: English
• Subjects: Air plasma; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystal defects; Crystallites; Crystallization; Crystallography and Scattering Methods; Density; Energy gap; Energy Materials; Hydroxyl groups; Iodine; Materials Science; Nanocrystals; Oxidation; Photocatalysis; Photocatalysts; Photoelectrons; Plasma; Polymer Sciences; Roasting; Solid Mechanics; Surface area; Synthesis; Thermal plasmas; Tin dioxide; Ultraviolet radiation; Vacancies; Valence band
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-019-04335-5

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 SnO 2 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 (O v ) 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 O v 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 m 2  g −1 for NC-Sn30 and NC-Sn120, respectively, dropped to about 30 m 2  g −1 . Meanwhile, the O v 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. I 3 − , I 2 ) normalized with the surface area of calcined photocatalysts was about 4 times higher than that of their corresponding pristine SnO 2 . These results open the door to a new route synthesis of SnO 2 nanocrystals with tunable “O” vacancies density and photocatalytic performances.