The synergistic effect of anatase and brookite for photocatalytic generation of hydrogen and diclofenac degradation

The development of promising technologies (eco-friendly, cost-effective and simple) for fuel generation and removal of organic pollutants has attracted extensive attention in recent years worldwide. Accordingly, heterogeneous photocatalysis has been considered as most recommended since various chemical reactions could be carried out on the surface of recyclable photocatalysts under sole irradiation (preferably solar). This paper presents the crucial role of the synergistic effect between brookite and anatase titania photocatalysts for their potential application in H2 generation and removal of organic pollutants. Here, a facile hydrothermal treatment of an alkaline solution of Ti2(SO4)3, containing Na+, NH4+, and glycine/Na+ was used to prepare titania photocatalysts in the form of brookite (B), anatase (A), and binary phase (BA), respectively. The comparative photocatalytic activities of obtained photocatalysts and the “standard” P25-TiO2 have been evaluated by the photocatalytic hydrogen evolution (with in situ platinum deposition as a co-catalyst), and photodegradation and mineralization of diclofenac under UV/vis and UV-A, respectively. It has been found that the most active photocatalyst contains 38.2% brookite and 61.8% anatase, has the highest specific surface area (62.3 m2 g-1), and the highest light harvesting ability (absorption edge at 399 nm). The synergistic effect has been confirmed for both tested reactions in comparison to the activities of single-phase photocatalysts. Moreover, the obtained activities are around two times higher than that by famous P25 of similar surface properties. Based on the scavenger tests’ study, the new mechanism for brookite-anatase composites has been proposed, i.e., interparticle charge transfer excitation (ICTE), in which electrons are excited from the valence band (VB) of anatase to the conduction band (CB) of brookite, with simultaneous charge migration according to the heterojunction type II.