Photocatalytic Active Titania Thin Films through Oxidation of Metallic Ti in Aqueous H2O2 Solutions Containing Various Block Copolymers

Various nanostructured titania thin films were fabricated by direct oxidation of metallic Ti substrates in hydrogen peroxide solutions with the additives of nitric acid and block copolymers of P123 or F127. X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) were utilized to analyze the morphology and structure of the titania films. Photocatalytic properties of the thin films were evaluated by the degradation of rhodamine B in water under the illumination of a high-pressure mercury lamp. The film only with the block copolymer additive consists of rod-like titania; while flower-like titania aggregates are achieved when both block copolymers and nitric acid are added to the hydrogen peroxide solution. After a subsequent calcination at 450 °C, all the titania films are crystallized further to a mixture of anatase and rutile with a similar average grain size. An indirect bandgap of 2.65–2.85 eV is estimated for the present films, which is significantly lower that of the bulk titania. The titania film derived with the P123 additive shows higher photocatalytic activity than that with the F127 additive, either with or without the additive of nitric acid.