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Ligand-Triggered Tunable Charge Transfer toward Multifarious Photoreduction Catalysis

Li, Tao, Li, Yu-Bing, Dai, Xiao-Cheng, Huang, Ming-Hui, He, Yunhui, Xiao, Guangcan, Xiao, Fang-Xing
Journal of physical chemistry 2019 v.123 no.8 pp. 4701-4714
active sites, electrons, energy conversion, heavy metals, hydrogen production, irradiation, ligands, metal ions, motivation, nanocrystals, nanowires, nitroaromatic compounds, photocatalysis, semiconductors, solar energy
Metal/semiconductor heterostructures have been arousing persistent interest on account of prominent roles of metal nanocrystals (NCs) in modulating charge transfer in photocatalysis. It has been generally accepted that ligands capped on the tailor-made metal NC surfaces should be removed for exposing more active sites, and the interface between the metal and semiconductor should be clean enough to facilitate charge flow. Would the ligands of metal NCs definitely deteriorate charge separation/transfer and what is its correlation with photoactivity? Inspired by this motivation, herein, interface configuration between the metal and semiconductor was exquisitely designed by a ligand-triggered electrostatic self-assembly strategy, wherein tailor-made intrinsically positively charged Pd NCs capped with hierarchically branched ligand 4-dimethylaminopyridine (DMAP) and negatively charged surface-modified CdS nanowires (NWs) were judiciously utilized as the building blocks. Significantly, spontaneous and monodispersed immobilization of Pd@DMAP on CdS NWs was readily initiated by DMAP ligands, which endows self-assembled Pd@DMAP/CdS NW heterostructures with conspicuously enhanced and versatile photoreduction performances in comparison with CdS NWs toward anaerobic photoreduction of aromatic nitro compounds, photocatalytic hydrogen generation, and photoreduction of heavy metal ions under visible light irradiation, owing to the crucial role of Pd@DMAP for efficaciously capturing electrons without the inhibition of the hierarchical ligand structure and interfacial integration mode. More intriguingly, the interfacial distance between Pd@DMAP and CdS NWs was finely mediated to achieve tunable charge transport. Finally, the ligand-involved photocatalytic mechanism was elucidated. It is anticipated that our work could shed new insights on the role of ligands in modulating the directional charge transfer over metal/semiconductor photocatalytic systems for substantial solar energy conversion.