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Mechanistic insights into the photocatalytic properties of metal nanoclusters/graphene ensembles. Examining the role of visible light on the reduction of 4-nitrophenol

Abstract

Metal nanoclusters (MNCs) based on silver and gold, abbreviated as AgNCs and AuNCs, respectively, were synthesized and combined with functionalized graphene, abbreviated as f-G, forming novel MNCs/f-G ensembles. The preparation of MNCs/f-G was achieved by employing attractive electrostatic interactions developed between negatively charged MNCs, owed to the presence of carboxylates due to α-lipoic acid employed as stabilizer, and positively charged f-G, owed to the presence of ammonium units as addends. The realization of MNCs/f-G ensembles was established via titration assays as evidenced by electronic absorption and photoluminescence spectroscopy as well as scanning transmission electron microscopy (STEM) and energy-dispersive X-ray (EDX) spectroscopy analysis. Photoinduced charge-transfer phenomena were inferred within MNCs/f-G, attributed to the suppression of MNCs photoluminescence by the presence of f-G. Next, the MNCs/f-G ensembles were successfully employed as proficient catalysts for the model reduction of 4-nitrophenol to the corresponding 4-aminophenol as proof for the photoinduced hydrogen production. Particularly, the reduction kinetics decelerated by half when bare MNCs were employed vs the MNCs/f-G ensembles, highlighting the beneficial role of MNCs/f-G to catalyse the process. Furthermore, AuNCs/f-G displayed exceptionally higher catalytic activity both in dark and under visible light illumination conditions, which is ascribed to three synergistic mechanisms, namely, (a) hydride transfer from Au-H, (b) hydride transfer from photogenerated Au-H species, and (c) hydrogen produced by the photoreduction of water. Finally, recycling and re-employing MNCs/f-G in successive catalytic cycles without loss of activity toward the reduction of 4-nitrophenol was achieved, thereby highlighting their wider applicability.

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Publication details

The article was received on 25 Apr 2017, accepted on 09 Jun 2017 and first published on 14 Jun 2017


Article type: Paper
DOI: 10.1039/C7NR02944F
Citation: Nanoscale, 2017, Accepted Manuscript
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    Mechanistic insights into the photocatalytic properties of metal nanoclusters/graphene ensembles. Examining the role of visible light on the reduction of 4-nitrophenol

    M. Koklioti, T. Skaltsas, Y. Sato, K. Suenaga, A. Stergiou and N. Tagmatarchis, Nanoscale, 2017, Accepted Manuscript , DOI: 10.1039/C7NR02944F

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