Brookite: Nothing New under the Sun?

Matteo Monai,Paolo Fornasiero,Tiziano Montini

doi:10.3390/catal7100304

Matteo Monai, Paolo Fornasiero + Show 1 more

Open Access

https://doi.org/10.3390/catal7100304

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Abstract

Advances in the synthesis of pure brookite and brookite-based TiO2 materials have opened the way to fundamental and applicative studies of the once least known TiO2 polymorph. Brookite is now recognized as an active phase, in some cases showing enhanced performance with respect to anatase, rutile or their mixture. The peculiar structure of brookite determines its distinct electronic properties, such as band gap, charge–carrier lifetime and mobility, trapping sites, surface energetics, surface atom arrangements and adsorption sites. Understanding the relationship between these properties and the photocatalytic performances of brookite compared to other TiO2 polymorphs is still a formidable challenge, because of the interplay of many factors contributing to the observed efficiency of a given photocatalyst. Here, the most recent advances in brookite TiO2 material synthesis and applications are summarized, focusing on structure/activity relation studies of phase and morphology-controlled materials. Many questions remain unanswered regarding brookite, but one answer is clear: Is it still worth studying such a hard-to-synthesize, elusive TiO2 polymorph? Yes.

Highlights

Polymorphism—the ability of a solid material to exist in more than one crystal structure—is a common property of metal oxides [1]
Anatase-rich/brookite mixture (75:25) was shown to be much more active for CO2 photoreduction than Degussa P25, an anatase-rich/rutile mixture with similar anatase fraction [45]. These results suggest that electron transfer may take pace in brookite-based TiO2 composites, which may be a new direction for the development of efficient photocatalysts
The activity normalized to the surface area continuously increased with the brookite content, indicating that the surely worthy extensive investigation, terms higher of the development new synthetic routes exposed facets of of more brookite nanorods possess an in intrinsic activity in H2 of production than that of and of in-depth characterization

Summary

Introduction

Polymorphism—the ability of a solid material to exist in more than one crystal structure—is a common property of metal oxides [1]. Rationalizing the effect of crystal structure on the performance of a photocatalytic material is a pivotal research goal, since both Fe2 O3 and TiO2 , the most investigated and widely used photocatalysts, may exist in different crystal structures [7,8]. Studying such a relation is not a trivial task, because of the many interconnected factors which influence the rate of photochemical reactions (e.g., particle size, shape, crystallinity, number/type of defects, electron–hole recombination, surface area, reactant and intermediate species adsorption on the catalyst surface) and the difficulty of synthesizing materials with a single crystal structure. Structure/activity relations are summarized and a perspective on the future development of brookite nanostructured materials is given

Characterization

Synthesis

Photocatalytic Studies

Conclusions and Perspectives

Results