The widespread persistent organic pollutants including the polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and alkylphenols etc. are always with very low concentration in the waters owing to their high hydrophobicity, but posed significant risk to human health due to the bioaccumulation through the food chains. Meanwhile, these highly toxic contaminants can only be partially removed in the conventional water treatment systems resulted from the low concentration and poor biodegradability. The TiO2 based photocatalytic oxidation technique has been extensively investigated for the efficient removal of the trace amount of pollutants in the waters. To facilitate efficient electron-transfer (ET) and high oxidation efficiency, the pollutants are highly required to be adsorbed on the catalyst surface. However, the surface of TiO2 is always hydrophilic in the water, which makes against the efficient adsorption of these hydrophobic pollutants, leading to the lower photocatalytic oxidation efficiency. In this work, hydrophobic TiO2 nanotube arrays (NTs) with the contact angle of about 128° was obtained by the modification of perfluorinated silane. Nonyl phenol (NP) was selected as the model hydrophobic pollutants owing to the wide presence in the Huangpu River in Shanghai of China. The investigation results found that enhanced photocatalytic oxidation of NP could be achieved on the hydrophobic TiO2 NTs compared with the hydrophilic pollutants such as paraquat and xanthonate, which were oxidized more easily on the hydrophilic TiO2 NTs. It could be explained from the following two aspects. Firstly, by hydrophobic modification, the apparent rate constant of hydroxyl radicals’generation could reach 2.3 times that of the hydrophilic TiO2 NTs, leading to the fast and enhanced oxidation ability to NP. Secondly, the enhanced adsorption kinetics of NP on the hydrophobic TiO2 NTs was monitored by in situ ATR-IR. It indicated NP could be adsorbed more efficiently on the hydrophobic TiO2 NTs by hydrophobic interactions, which was beneficial for the efficient ET and oxidation. Both the two aspects made the complete photocatalytic removal of NP in 40 min on the hydrophobic TiO2 NTs, whereas the removal rate was only about 85.5% on the hydrophilic TiO2 NTs surface. These findings indicated that the hydrophobic TiO2 NTs had the potential to be applied in the selective and enhanced photocatalytic oxidation of hydrophobic pollutants in complex waste waters.

Mechanism investigation of the enhanced photocatalytic oxidation of nonyl phenol on hydrophobic TiO2 nanotubes

256th National Meeting (2018)

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