We report a citrate-free synthesis of Ag nanoplates with an edge length of 50 nm that involved the reduction of AgNO3 by poly(vinyl pyrrolidone) (PVP) in ethanol at 80 oC under a solvothermal condition. Within a period of 4 hours, >99% of the initially added AgNO3 could be converted into Ag nanoplates with excellent stability. To understand this remarkably simple and efficient process, we systematically investigated the roles played by various reaction parameters, which include the type of precursor, the reducing powers of PVP and ethanol, the molar ratio of PVP to AgNO3, the solvent, the involvement of O2, and the effects of pressure and temperature. Our results suggest a plausible mechanism that involves i) fast reduction of AgNO3 to generate Ag multiple twinned particles (MTPs) via a thermodynamically controlled process, ii) kinetically controlled formation of plate-like seeds and their further growth into small nanoplates in the presence of Ag+ ions at a low concentration, and iii) complete transfer of Ag atoms from the MPTs to nanoplates via O2-mediated Ostwald ripening. We demonstrated that the molar ratio of PVP to AgNO3 in ethanol plays an essential role in controlling the reduction rate for the formation of MTPs and plate-like seeds under the solvothermal condition, the transformation kinetics, and the final morphology taken by the Ag nanoplates. In particular, when the reaction temperatures were above the boiling point of ethanol, the pressure induced by a solvothermal process accelerated the oxidative etching of Ag MTPs to facilitate their complete conversion into nanoplates. The mechanistic insight could serve as a guideline to optimize the experimental parameters of a solvothermal synthesis to control the reduction kinetics and thus the formation of metallic nanocrystals with controlled shapes, and in high yields and large quantities.

Citrate-free synthesis of Ag nanoplates and the mechanistic study

247th National Meeting (2014)

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