Charge separation and ROS generation on tubular sodium titanates exposed to simulated solar light

• Published in: Applied surface science 2019-03, Vol.470, p.1053-1063
• Main Authors: Preda, Silviu, Anastasescu, Crina, Balint, Ioan, Umek, Polona, Sluban, Melita, Negrila, Catalin C., Angelescu, Daniel G., Bratan, Veronica, Rusu, Adriana, Zaharescu, Maria
• Format: Article
• Language: English
• Subjects: Charge separation; Photocatalysis; Reactive oxygen species; Simulated solar light; Titanate nanotubes
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2018.11.194

•High surface area tubular morphology lead to enhanced photocatalytic performances.•Density of surface hydroxyls decreases with development of tubular sodium titanate.•ROS (OH and O2−) yield depends on concentration of surface hydroxyls.•Rate of solar H2 and CO2 output declines with decrease in density of surface OH.•Charge separation at anatase-sodium titanate interfaces boosts efficiency. The research focuses on a few key points concerning the light-driven processes taking place on TiO2 anatase and sodium titanates with tubular morphology, such as the relationship between the morphology and activity for H2 and CO2 production, density of surface hydroxyl groups, ROS (OH and O2−) production and photocatalytic activity, and charge separation at the interface of semiconducting domains and enhancement of activity. One key point discussed is whether the materials with peculiar morphologies (i.e. tubular) are superior to the conventional ones. The experimental evidences show that the main advantage of the tubular morphology of sodium titanate is given by its significantly higher surface area compared to parental anatase. FTIR and XPS progressive analyses evidence that the density of surface hydroxyl groups decreases with the development of the tubular morphology. The radical trapping experiments show that the variation of surface hydroxyl density is, generally, followed by activities for OH and O2− generation, as well as by the photocatalytic production of H2 and CO2 from water/methanol mixture. Consequently, the ROS, formed by action of photogenerated electrons and holes on adsorbed O2 and hydroxyl groups, respectively, play an important role in determining the photocatalytic activity of titania-based materials. The other major aspect revealed by this research is that the charge separation at the interfaces formed between anatase and sodium titanate crystalline phases has remarkable effect on the activity formation rates of H2 and CO2.