Enhanced photocatalytic degradation of 4-chlorophenol and 2,4-dichlorophenol on in situ phosphated sol-gel TiO2.

BACKGROUND Phosphated TiO₂ photocatalysts with different phosphate content were synthesized by in situ phosphatation of sol-gel TiO₂. H₃PO₄ was used as a hydrolysis catalyst and as an anionic precursor. The solids were analyzed by several techniques to determine the structural, textural and optical characteristics. The photoactivity of the materials was tested in the degradation of 4-chlorophenol and 2,4-dichlorophenol, under UV irradiation. RESULTS XRD patterns showed that the presence of phosphate anions decreases the crystallite size without modification of the anatase phase. Specific surface areas higher than the pristine TiO₂ were obtained on the phosphated samples. The presence of bidentate phosphates attached to the surface was identified by FTIR. The photoactivity of the materials tested in the degradation of 4-chloropehol and 2,4-dichlorophenol showed notable improvement on phosphated TiO₂. The degradation rate of the chlorophenolic compounds increases with the degree of substitution in the aromatic ring. Thus, the degradation rate of 2,4-dichlorophenol is higher than that of 4-chlorophenol. High efficiency in the degradation of the molecules after the recycling of the photocatalysts was observed. CONCLUSION The modification in situ of TiO₂ with low phosphate content promotes higher photocatalytic activity than that of unmodified TiO₂ and Degussa P-25 in the photodegradation of the chlorophenolic compounds. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]