State of doped phosphorus and its influence on the physicochemical and photocatalytic properties of P-doped titania

A series of phosphorus-doped titania samples with different phosphorus contents have been prepared by a simple, modified sol-gel method. The obtained samples were characterized by X-ray diffraction spectrometry, Brunauer-Emmett-Teller surface area, differential thermal analysis-thermogravimetry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and UV-vis diffuse reflectance spectroscopy, and the photodegradation of methylene blue (MB) on the samples was tested under both UV and visible light irradiation. It was found that the doped phosphorus existed in a pentavalent oxidation state, replacing part of Ti4+ in the anatase lattice in the form of Ti-O-P bonds. Increased calcination temperature gave an enrichment of P species on the titania surface. The P species in the titania lattice should be the dominant group responsive to visible light, whereas the P species on the surface could retard the phase transition of anatase to rutile and increase the surface area and adsorption capability. The photocatalytic activity of P-doped titania with the optimal P content was 4-fold higher than that of pure TiO2 and was 41% higher than that of commercial Degussa P-25 under UV irradiation. Furthermore, P-doped titania presented significant photocatalytic activity under visible light (>400 nm) irradiation.