Brookite: Nothing New under the Sun?

Abstract

Advances in the synthesis of pure brookite and brookite-based TiO 2 materials have opened the way to fundamental and applicative studies of the once least known TiO 2 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 TiO 2 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 TiO 2 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 TiO 2 polymorph? Yes.

Template-Free Preparation and Photocatalytic and Photoluminescent Properties of Brookite TiO2 Hollow Spheres

“…The corresponding bandgap energy is estimated as follows: where α is absorbance, hν represents the energy of incident photons, K is a constant, and n equals to 2 for direct transition and 1/2 for indirect transition [24]. As displayed in the insert of Figure 3(c), the bandgap energy E g was 3.13 eV for the prepared hollow-structure brookite TiO 2 , in good agreement with previously reported results [25]. The surface chemical property of the sample was determined by the XPS technique.…”

A Review on Catalytic Nanomaterials for Volatile Organic Compounds VOC Removal and Their Applications for Healthy Buildings

“…TiO 2 primarily exists in three crystal phases: anatase, brookite and rutile. Among them, the anatase form appears to be the most photoactive and the most practical for widespread environmental applications [25]; the brookite was once regarded to not be suitable as a photocatalyst [25,61], and later the successful synthesis of nanostructured brookite was showed to greatly enhance the photocatalytic performance [62]. Wu et al [38] investigated the synergetic effect between anatase and rutile nanoparticles in gas-phase photocatalytic oxidations of hexane and methanol.…”

Titanium Dioxide Photocatalysis

“…Monai et al [9] provides a comprehensive review of the advancement in the applications of brookite as a photocatalyst. First, the most advanced synthetic methodologies to produce pure brookite and well-defined brookite-containing composites are presented, together with some guidelines for thorough characterization of the materials.…”