Brookite, a sometimes under evaluated TiO2 polymorph

Some of the advancements concerning the study of phase-pure brookite and, especially, brookitecontaining
TiO2 mixed phases are reviewed. Relevance is given to their prospective photocatalytic
applications, where the (positive) effect of the presence of brookite has been demonstrated, especially
when solar light is concerned. From the literature, it emerges that, besides the band gap determination,
which still requires more detailed studies (band gap values in a wide range are reported), the roles of
brookite-containing heterojunctions, of the surface properties (i.e. acidity, redox behaviour, and the
presence of coordinatively unsaturated sites), of the particular crystalline structure and of brookite
influence on the anatase to rutile transition are crucial for its applications in the field of (solar)
photocatalysis and electrocatalysis, but also electrochemical applications (i.e. Li batteries). The need
emerges for a deeper understanding of the physico-chemical phenomena underlying their (recently
demonstrated) capacity of stabilizing photogenerated electron/hole pairs. In perspective, the
development of green synthesis methods to tailor the surface and structural properties of phase-pure
brookite and brookite-containing mixed phases could extend their photo- and electrochemical
applications.