Photocatalytic Performance of Highly Active Brookite in the Degradation of Hazardous Organic Compounds Compared to Anatase and Rutile

The photocatalytic activity of brookite was studied and compared with anatase, rutile, and commercial titania P25 (Degussa). Brookite exhibited relatively high activity in the degradation of different hazardous compounds under sunlight equivalent conditions. Brookite and other titania polymorphs anatase and rutile were hydrothermally synthesized under the similar reaction conditions starting with the same amorphous titania precursor. The highly crystalline titania polymorphs were characterized by XRD, SEM, TG-DSC, Raman-and diffuse reflectance UV-vis spectroscopy. Brookite (B) and anatase (A) crystallized in form of agglomerated spherical-shaped nanoparticles of ca. 10 nm in size. Rutile (R) formed up to 500 nm large rod-like nanocrystals. The band gaps of the titania polymorphs were about 3.25-3.34 eV. The aromatic ring opening in different hazardous compounds was monitored by UV-vis absorption spectroscopy and the mineralization was determined by total organic carbon (TOC) measurements. Additionally, the formation of intermediates was studied by electrospray ionization time-of-flight mass spectra (ESI-TOF-MS). The recalcitrance of organic compounds against the photocatalytic degradation increases in the following order: cinnamic acid < ibuprofen < phenol. The general order of photocatalytic activity was B approximate to A > R. (C) 2016 Elsevier B.V. All rights reserved.