An approach on the comparative behavior of chloro / nitro substituted phenols photocatalytic degradation in water

The study of position and number of substituents on the photocatalytic removal of some mono-, di- and tri-, chloro- and nitrophenols, as well as more known initial TOC concentration effect, has revealed the noteworthy impact on the process efficiency. Despite the complex effect of multiple substituents directing the HO center dot attack to their preferential positions, Hammett constant could be used to predict photocatalytic degradation performance. TiO2 P25 was able to mineralize initial TOC concentrations up to 25-50 mg.L-1. Higher TOC concentrations constitute a drawback and drive to residual parent pollutants and organic by-products, which become more important when raising the starting TOC loading. Increasing the number of chloro- or nitro- groups in the aromatic ring does not imply higher ecotoxiticy values; contrarily, the position of the substituent can lead to significant differences. TOC conversion values are hardly affected by the substituent position, but by the number of groups in the organic molecule, probably due to steric hindrance. The formation of chloride and nitrogen inorganic ions, inherent to photocatalytic degradation, fulfills the Cl and N mass balances. Finally, the effect of number, position and electronic nature of substituents on contaminant initial photocatalytic degradation rates was studied by corresponding Hammett constant correlations.