Photocatalytic reduction of 4-nitrophenol on in situ fluorinated sol-gel TiO2 under UV irradiation using Na2SO3 as reducing agent

The in situ fluorination of the TiO2 semiconductor was performed via sol-gel method. Photocatalysts with different fluoride percentage were synthesized using ammonium fluoride as hydrolysis catalyst and as anionic precursor. For comparison, sol-gel TiO2 was also studied as a reference material. The solids were characterized using several techniques in order to analyze their structural, textural and optical properties. The fluorination of the TiO2 favored the preferential formation of the anatase phase and an increase in the crystallinity; in contrast, a decrease in the specific surface area was observed. The photocatalytic activity of the materials was evaluated in the 4-nitrophenol photoreduction to 4-aminophenol using Na2SO3 as reducing agent under UV light irradiation. It was found that the generation of the aeTi-F surface species increased the photocatalytic properties of the semiconductor; thus, the 4-nitrophenol photoreduction rate using the fluorinated solids was higher compared with the sol-gel TiO2 and Degussa P-25. Favorable efficiency in the photoreduction of the 4-NP molecule after the recycling experiments of the photocatalyst was observed.