Mechanism investigation on the enhanced photocatalytic oxidation of nonylphenol on hydrophobic TiO₂ nanotubes

Enhanced and selective photocatalytic oxidation of nonylphenol (NP), a typical hydrophobic endocrine disrupting chemicals (EDCs), was realized on hydrophobic titanium dioxide nanotubes (H-TiO₂NTs), which was fabricated by an electrochemical anodization method, followed by grafting of perfluorooctyl groups. The water contact angle of catalyst surface changed from 21.1° to 128.4° after hydrophobic modification. H-TiO₂NTs showed excellent photocatalytic oxidation performance for NP, that it was completely converted in 40 min under irradiation, which was improved for about 17% compared with the hydrophilic TiO₂NTs. The enhanced photocatalytic performance of H-TiO₂NTs was attributed to the stronger adsorption ability toward NP identified by ATR-FTIR, with an initial adsorption rate of 4 times as higher as that of bare TiO₂NTs. Meanwhile, the hydrophobic surface of H-TiO₂NTs was beneficial for generation of more hydroxyl radicals. The apparent rate constant of hydroxyl radicals' generation on H-TiO₂NTs, which was the main oxidizing species, could reach 1.83 times that of the hydrophilic TiO₂NTs. Both the two factors contributed to the successful competition of NP against the coexistent hydrophilic contaminates in the adsorption and oxidation on the catalyst surface, leading to the selective removal of NP in mixed systems finally.