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

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) TiO 2 (B) nanosheets (Pd/TiO 2 (B)) under visible light irradiation, achieving a dechlorination efficiency of 100 % with H 2 O used as an H-donor source. The ultra-thin TiO 2 (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 C Cl bond in the presence of Pd nanoclusters. Furthermore, in-situ FTIR results of D 2 O absorption suggest that the TiO 2 (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/TiO 2 (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.