Optimizing the d-band center of sub-nanometer Pd–Pt alloy clusters for improved photocatalytic dehalogenation of polyhalogenated biphenyls

The efficient removal of highly toxic polyhalogenated biphenyls is rather challenging, mainly due to the difficulties in splitting C-X (X = Cl or Br) bond with high bond energy, as well as the transfer of active hydrogen species during the reduction dehalogenation process. In this work, sub-nanometer Pd–Pt alloy clusters (ca. 1 nm) supported on defect-containing TiO2(B) nanosheets (PdPt/TB), on absorption of visible light illumination (λ > 400 nm), were prepared and served as an efficient photocatalysts for dehalogenation of polyhalogenated biphenyls with H2O as the hydrogen source. An optimal sample (Pd0.7Pt0.3/TB) shows the highest photocatalytic dehalogenation efficiency for 3,3′,4,4′-trtrachlorobiphenyl (PCB77) within 30 mins, which is 12.5, 3.5 and 3 times higher than that of Pt1/TB, Pd1/TB, and Pd0.7 + Pt0.3/TB samples, respectively. Besides, 4,4′-dibromobiphenyl (PBB15) was also completely removed within 10 mins by using Pd0.7Pt0.3/TB photocatalyst, demonstrating its potential applications. Experiments and d-band theory calculations revealed that the introduction of Pt can regulate the d-band center of Pd to strength the interaction between active hydrogen with alloy and promote the transfer of hydrogen species. Meanwhile, Pd–Pt alloy is conducive to activate the C-X bond of polyhalogenated biphenyls. Finally, a mechanism based on Pd–Pt alloy clusters synergistic interaction is proposed at the molecular level. This work demonstrates the successful synthesis of sub-nanometer Pd–Pt alloy nanoclusters and elucidates the effect of interaction among Pd, Pt and supports, providing an efficient method for the removal of polyhalogenated compounds by photocatalytic technology.