Synergistic effect of nickel ions on the coupled dechlorination of trichloroethylene and 2,4-dichlorophenol by Fe/TiO2 nanocomposites in the presence of UV light under anoxic conditions

The coupled removal of priority pollutants by nanocomposite materials has recently been receiving much attention. In this study, trichloroethylene (TCE) and 2,4-dichlorophenol (DCP) in aqueous solutions were simultaneously removed by Fe/TiO2 nanocomposites under anoxic conditions in the presence of nickel ions and UV light at 365 nm. Both TCE and DCP were effectively dechlorinated by Fe/TiO2 nanocomposites, and the pseudo-first-order rate constants (kobs) for TCE and DCP dechlorination were (1.39 ± 0.05)×10−2 and (1.08 ± 0.05)×10−2 h−1, respectively, which were higher than that by nanoscale zerovalent iron alone. In addition, the kobs for DCP dechlorination was enhanced by a factor of 77 when Fe/TiO2 was illuminated with UV light for 2 h. Hydrodechlorination was found to be the major reaction pathway for TCE dechlorination, while DCP could undergo reductive dechlorination or react with hydroxyl radicals to produce 1,4-benzoquinone and phenol. TCE was a stronger electron acceptor than DCP, which could inhibit the dechlorination efficiency and rate of DCP during simultaneous removal processes. The addition of nickel ions significantly enhanced the simultaneous photodechlorination efficiency of TCE and DCP under the illumination of UV light. The kobs values for DCP and TCE photodechlorination by Fe/TiO2 in the presence of 20–100 μM Ni(II) were 30.4–136 and 13.2–192 times greater, respectively, when compared with those in the dark. Electron spin resonance analysis showed that the photo-generated electron-hole pairs could be effectively separated through Ni ions cycling, leading to the improvement of electron transfer efficiency of TCE and DCP by Fe/TiO2.

Figure optionsDownload high-quality image (95 K)Download as PowerPoint slideHighlights
► Hydrodechlorination was the major reaction mechanism for TCE dechlorination by Fe/TiO2 nanocomposites.
► Reductive dechlorination as well as hydroxyl radical reaction were the major reaction mechanisms for DCP photodechlorination.
► The photodechlorination efficiency and rate of TCE and DCP was significantly enhanced in the presence of nickel ions.
► The Ni2+ ions behaved as the hole trap to produce Ni3+ ions and oxygen-center radicals in the presence of UV light.