Inferring the Interfacial Reactivity of Gold Nanoparticles by Surface Plasmon Resonance Measurements

Romain, Mélanie; Roman, Phoölan; Saviot, Lucien; Millot, Nadine; Boireau, Wilfrid

doi:10.1021/acs.langmuir.3c01365

Cited by 2 publications

(1 citation statement)

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“…SPR energies are well-known to shift upon the formation of surface Au–S or Au–halogen bonds. ,, The redshift from added thiolate ligands has been suggested to be due to electron donation to the gold core (again, opposite to the simple Drude model prediction) . In one study, the appearance of an SPR band for very small (1.2 nm) AuNPs treated with BH 4 – was attributed to “electron doping to the Au sp band by the adsorbed H atoms”a rare prior example invoking surface H.…”

Section: Discussionmentioning

confidence: 99%

Hydrogen on Colloidal Gold Nanoparticles

Gentry,

Kurimoto,

Cui

et al. 2024

J. Am. Chem. Soc.

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Colloidal gold nanoparticles (AuNPs) have myriad scientific and technological applications, but their fundamental redox chemistry is underexplored. Reported here are titration studies of oxidation and reduction reactions of aqueous AuNP colloids, which show that the AuNPs bind substantial hydrogen (electrons + protons) under mild conditions. The 5 nm AuNPs are reduced to a similar extent with reductants from borohydrides to H2 and are reoxidized back essentially to their original state by oxidants, including O2. The reactions were monitored via surface plasmon resonance (SPR) optical absorption, which was shown to be much more sensitive to surface H than to changes in solution conditions. Reductions with H2 occurred without pH changes, demonstrating that hydrogenation forms surface H rather than releasing H+. Computational studies suggested that an SPR blueshift was expected for H atom addition, while just electron addition likely would have caused a redshift. Titrations consistently showed a maximum redox change of the 5 nm NPs, independent of the reagent, corresponding to 9% of the total gold or ∼30% hydrogen surface coverage (∼370 H per AuNP). Larger AuNPs showed smaller maximum fractional surface coverages. We conclude that H binds to the edge, corner, and defect sites of the AuNPs, which explains the stoichiometric limitation and the size effect. The finding of substantial and stable hydrogen on the AuNP surface under mild reducing conditions has potential implications for various applications of AuNPs in reducing environments, from catalysis to biomedicine. This finding contrasts with the behavior of bulk gold and with the typical electron-focused perspective in this field.

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