Unveiling the intermediates/pathways towards photocatalytic dechlorination of 3,3′,4,4′-trtrachlorobiphenyl over Pd /TiO2(B) nanosheets

Abstract

This work reports the rapid and effective photocatalytic dechlorination of 3,3′,4,4′-trtrachlorobiphenyl (PCB77) with highly dispersed Pd nanoclusters loaded two-dimensional (2D) TiO2(B) nanosheets (Pd/TiO2(B)) under visible light irradiation, achieving a dechlorination efficiency of 100 % with H2O used as an H-donor source. The ultra-thin TiO2(B) nanosheets provide a good platform for studying the dechlorination intermediates/pathways of PCB77 at the molecular level. It is proved that the dechlorination of PCB77 is a stepwise process, in which chlorines at the para positions are much more susceptible than those at the meta positions due to the activation of the CCl bond in the presence of Pd nanoclusters. Furthermore, in-situ FTIR results of D2O absorption suggest that the TiO2(B) nanosheets with abundant surface defects greatly promote the activation of water molecules via the formation of surficial complexes by hydrogen bonds. Finally, a synergistic mechanism is proposed for photocatalytic dechlorination of PCB77 over Pd/TiO2(B). The study provides an efficient method for complete dechlorination of PCB77 and an in-depth understanding photocatalyzed dechlorination reaction mechanism at the molecular level, which may extend to other photocatalytic dehalogenation reactions of halogenated pollutants.