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

• We synthesize nanocrystalline Co2+/F− codoped TiO2–SiO2 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 Co2+/F− codoped TiO2–SiO2 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 SiO2 composite with Co2+/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 TiO2 film. The X-ray photoelectron spectroscopy (XPS) was carried out to determine the chemical composition of the multi-modified TiO2 film. The Brunauer–Emmett–Teller (BET) surface area results revealed that the specific surface area of pure TiO2, TiO2–SiO2, and Co2+/F− codoped TiO2–SiO2 is 103.4 m2 g−1, 388.2 m2 g−1, and 394.2 m2 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 TiO2 film exhibited the best photocatalytic activity compared to a pure TiO2 film and singly-modified TiO2 film.

The band gap of pure TiO2, TiO2–SiO2, Co2+ doped TiO2–SiO2, and Co2+/F− codoped TiO2–SiO2 films are 3.36, 3.34, 2.99, 2.34 eV, respectively.Figure optionsDownload as PowerPoint slide