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Chen Liang, Jun Young Cheong, Gabriel Sitaru, Sabine Rosenfeldt, Anna S. Schenk, Stephan Gekle, II-Doo Kim, Andreas Greiner

Adv. Materials, 2022, 9, 4, https://doi.org/10.1002/admi.202100867

Gold nanoparticles (AuNP) are widely used for reaction catalysis. The common understanding is that the smaller the particles, the more reactive they are. It is reported here that this is not always the case for citrate (Ct) or polyvinylpyrrolidone (PVP) stabilized AuNP in the catalytic reduction of 4-nitrophenol with sodium borohydride (NaBH4), when the total surface area is kept constant. The results prove that for AuNP in the size range of 10–58 nm, the reactivity increases with increasing particle diameter for the investigated model reaction. The trend of catalytic activity is independent of the conjugated ligands for citrate and PVP ligands. Purely based on size and resulting surface area, the trend in catalytic activity is unexpected. Only a more detailed structural investigation revealed that internal structure parameters like defect tendency also play a strong role. Larger AuNP possess more defects between crystalline domains. Further, the influence of the ligand density on the surface of AuNP and the diffusion effect of reactants are excluded for the nitrophenol reduction.