Periodic mesoporous titania with anatase and bronze phases – the new generation photocatalyst: synthesis, characterisation, and application in environmental remediation

Abstract

High-quality 2D-hexagonal ordered mesoporous titania with a well-crystallized framework structure and a high surface area was successfully synthesized, in a reproducible way, using Pluronic F127, Pluronic P123, Synperonic F108 and CTAB as structure-directing agents, and the resulting nanostructured matrix is designed as TMF-127, TMP-123, TMF-108 and TMC-016/TMC-036, respectively. The periodic array of the pore structure of these mesoporous materials is described by combining small-angle X-ray diffraction, high-resolution transmission electron microscopy and nitrogen sorption techniques. All these materials show significant amounts of intrinsic defects, viz., electrons trapped in oxygen vacancy and/or Ti³⁺ centres, by tuning the pore structure. These defects in-turn promote the charge separation of photogenerated excitons, and therefore exhibit excellent photocatalytic activity for the degradation of famotidine (TMP-123: DE₁₀₀ = 75 min; P-25: DE₁₀₀ = 120 min), and 4-chlorophenol (TMP-123: DE₉₅ = 180 min; P-25: DE₆₀ = 180 min). The superior activity of the mesoporous titania over the fumed titania (P-25) is ascribed to: (i) light absorption extending into the visible region, (ii) low charge-transfer resistance and high carrier density, and (iii) intrinsic Ti³⁺ defects, as deduced from DRUV-Visible, photo-electrochemical (Nyquist and Mott–Schottky) and EPR studies, respectively.