A Combined Photoelectrochemical and Theoretical Study to Understand Adsorption Properties of Organic Molecules on TiO2 Surfaces

T. Sun
Yunnan University,
China

Keywords: TiO2, surface adsorption, photoelectrochemical measurement, DFT

Summary:

Titanium dioxide (TiO2) applications in clean energy generation and environmental remediation involve interactions between organic species and TiO2 materials. Such interactions not only depend on the intrinsic properties of TiO2, but also on its surfaces structure and adsorption properties. Understanding the adsorption properties of organic compounds on various crystalline TiO2 surfaces is essential for further technological development. In this project, theoretical studies initially demonstrated that TiO2 is the most photoactive all Ti-O based materials. A combined photoelectrochemical (PEC) and theoretical study was conducted to understand the adsorption properties of organic molecules on anatase (001) and rutile (111) TiO2 surfaces.[1] PEC measurements can provide quantitative thermodynamic and kinetic information on the adsorption properties of organic species on the TiO2 surface under operational, practical conditions. The theoretical studies provide further information on interactions at the atomic level. To perform PEC measurements, an anatase photoanode with a double-layer structure dominated by {001} facets was designed, synthesized and immobilized onto conductive FTO glass by combined sol-gel and hydrothermal synthesis methods. The comparative results confirm the high reactivity of the anatase (001) surface.[2,3] Theoretical analysis of the adsorption properties of oxalic acid on the anatase TiO2 (001) surface identified the adsorption configurations and oxidation mechanism at the atomic level. Results demonstrated that the adsorption of oxalic acid on the anatase (001) surface generally occurs in a dissociative state. [4] The adsorption of organic molecules on the rutile (111) surface was studied also because of the specific visible light activity of rutile photoanodes capped by {111} facets at the solid/liquid interface.[5] The geometrical surface structure of rutile (111), which was previously unknown, was theoretically modelled. Results demonstrate that the bulk-truncated and reconstructed TiO2 (111) surfaces possess high surface energies. Further in-situ PEC measurements on the adsorption properties of organic molecules with different functional groups demonstrated a highly selective adsorption behaviour for aldehydes on {111} faceted rutile photoanodes.[6] The adsorption strength of aldehyde on the rutile (111) surface was investigated through analysis of the thermodynamic and kinetic properties of photo-degradation processes using ex-situ PEC measurements. The high capacity of the rutile (111) surface to selectively adsorb aldehyde can be utilized as a new approach to separate and purify aldehyde in industry. The combination of these experimental measurements and theoretical analyses can be used to investigate the adsorption properties of molecules with different functional groups on the various photocatalyst surfaces, which may benefit the development of photocatalysts with improved solar conversion efficiencies.