Photocatalytic reactivity of {121} and {211} facets of brookite TiO₂ crystals

Abstract

For the facet engineering of brookite TiO 2 , the surface atomic structure is known but the electronic structure has been rarely studied to date. Herein, we investigated both the surface atomic and electronic structure of brookite TiO 2 with various facets exposed. Theoretical calculations reveal that the {121} surface contains more undercoordinated Ti atoms and a higher surface energy than that of the {211} surface, and the experimental results show that brookite TiO 2 nanorods exposed with majority {121} facets (T 121 ) have a lower valence band (VB) potential; those above-mentioned superior properties enable T 121 to show excellent performance in RhB photodegradation. Nevertheless, the electronic structure analyzed from the Density of State (DOS) plots revealed that the electron density is dispersed in the bulk for TiO 2 covered with a {121} surface, indicating that the electrons might be more reluctant to migrate from bulk to surface, which might be the reason for the poor H 2 productivity of T 121 . In contrast, brookite TiO 2 nanosheets exposed with dominant {211} facets (T 211 ) exhibited a much higher conduction band (CB) potential resulting in a much higher H 2 evolution rate (801 mmol h À1 ) in photocatalytic water splitting. Accordingly, combining the analyses of the surface atomic structure and electronic band structure, it is suggested that, for brookite TiO 2 , the {121} surface is beneficial for photocatalytic oxidation reactions while the {211} surface can facilitate the photocatalytic reduction process.

Photocatalytic degradation of alprazolam in water suspension of brookite type TiO2 nanopowders prepared using hydrothermal route

“…Several authors have pointed out an optimum ratios between anatase and brookite corresponding to the highest photoactivity in particular degradation processes [7,44]. On the other side, the nature of brookite-based photocatalysts is still matter of discussion, as pure brookite samples of different structures have been reported as both more and less active than other titania polymorphs or mixtures of brookite with other titania phases [5,14,15]. In photocatalytic degradation of alprazolam, presented in this work, the samples consisted of brookite-anatase mixed phase have shown increasing efficiency with decreasing of anatase in favor of brookite content.…”

Influences of Doping on Photocatalytic Properties of TiO2 Photocatalyst

“…That is, the purpose of doping is relatively straightforward: modifying its large bandgap and electronic structure to optimize its optical properties for visible light harvest, improving each step in the charge kinetics to reduce the massive recombination of photogenerated carriers, and improving the interface and surface characteristics [16]. On the contrary, the photocatalytic activity depends strongly on the exposed crystalline faces [17,18]. Given that different crystal surfaces have different surface energy levels for the conduction band (CB) and valence band (VB), such differences in the energy levels will drive the electrons and holes to different crystal faces.…”

Brookite: Nothing New under the Sun?

“…The sequence of surface energies of ten stoichiometric 1 × 1 low-index surfaces of brookite was calculated by first-principle density functional theory (DFT) simulations, showing that the electronic and chemical properties of brookite and the other TiO 2 phases can be significantly different [67]. Recently, combined theoretical and experimental studies of brookite nanomaterials demonstrated that preferential exposure of {121} faces, with under-coordinated atoms and lower VB potential, led to higher performance in photodegradation, while preferential exposure of {211} surface, with higher CB potential, resulted in enhanced H 2 productivity [71,72]. Such calculations also suggested that electrons struggle to migrate from bulk to {121} faces, in accordance for their poor H 2 production efficiency.…”