Nanocrystalline Co2+/F− codoped TiO2–SiO2 composite films for environmental applications

Abstract

The band gap of pure TiO 2 , TiO 2 –SiO 2 , Co 2+ doped TiO 2 –SiO 2 , and Co 2+ /F − codoped TiO 2 –SiO 2 films are 3.36, 3.34, 2.99, 2.34 eV, respectively. • We synthesize nanocrystalline Co 2+ /F − codoped TiO 2 –SiO 2 composite film. • The film shows strong visible light adsorption and diminished e − /h + recombination. • The film is effective in oxidizing organic dyes and emerging contaminants. • The mechanism of enhanced photocatalytic activity is explained. A simple and novel process was developed for preparation of highly photoactive nanocrystalline Co 2+ /F − codoped TiO 2 –SiO 2 composite film with anatase phase and narrowed band gap (2.34 eV). The X-ray diffraction (XRD) and differential thermal analysis–thermogravimetry (DTA–TG) results indicated that the crystallinity of anatase not only improved but also effectively prevented the formation of brookite and the transition of anatase to rutile upon SiO 2 composite with Co 2+ /F − codoping. The field emission scanning electron microscopy (FE-SEM) results showed that the multi-modified film was composed of smaller nanoparticles or aggregates compared to pure TiO 2 film. The X-ray photoelectron spectroscopy (XPS) was carried out to determine the chemical composition of the multi-modified TiO 2 film. The Brunauer–Emmett–Teller (BET) surface area results revealed that the specific surface area of pure TiO 2 , TiO 2 –SiO 2 , and Co 2+ /F − codoped TiO 2 –SiO 2 is 103.4 m 2 g −1 , 388.2 m 2 g −1 , and 394.2 m 2 g −1 , respectively. The photoluminescence (PL) spectra results showed that the recombination rate of the photo-generated species was effectively prohibited by the multi-modification. The photocatalytic properties of the films were evaluated by degradation of organic dyes including acid naphthol red (ANR) and methyl green (MG), emerging contaminants including oxytetracycline and formaldehyde. Experimental results indicated that the multi-modified TiO 2 film exhibited the best photocatalytic activity compared to a pure TiO 2 film and singly-modified TiO 2 film.