Department of Chemical Engineering , Pennsylvania State University , University Park , Pennsylvania 16802 , United States.
Department of Chemical Engineering , Kumoh National Institute of Technology , Gumi-si , Gyeongsangbuk-do 39177 , South Korea.
J Am Chem Soc. 2019 Mar 13;141(10):4328-4337. doi: 10.1021/jacs.8b11295. Epub 2019 Feb 4.
Polyvinylpyrrolidone (PVP) is used in the synthesis of Ag nanoparticles (NPs) with controlled shape, most commonly producing cubes. The mechanism for shape control is unclear but believed by many to be caused by preferential binding of PVP to Ag(100) facets compared to Ag(111) facets and assumed by most to be the result of thermodynamic control, whereby facets with lower interfacial free energy predominate. To investigate this mechanism, we measured adsorption isotherms of PVP on different-shaped Ag NPs, to determine the thermodynamics of PVP adsorption to Ag(100) and Ag(111) facets. The equilibrium adsorption constant is independent of PVP molecular weight and depends only weakly on NP shape (and thus Ag facet). The equilibrium adsorption constant for PVP on Ag(111) (2.8 M) is about half that on Ag(100) (5 M). From a Wulff construction, this difference is not nearly enough to produce cubes via thermodynamic control. This result indicates the importance of kinetic control of the Ag nanoparticle shape by PVP, as has recently been proposed.
聚乙烯吡咯烷酮（PVP）用于合成具有可控形状的银纳米颗粒（NPs），最常见的形状是立方体。形状控制的机制尚不清楚，但许多人认为是由于 PVP 优先与 Ag(100)面结合，而不是与 Ag(111)面结合，并且大多数人认为这是热力学控制的结果，其中具有较低界面自由能的面占主导地位。为了研究这种机制，我们测量了 PVP 在不同形状的 Ag NPs 上的吸附等温线，以确定 PVP 在 Ag(100)和 Ag(111)面上的吸附热力学。吸附平衡常数与 PVP 分子量无关，仅与 NP 形状（因此 Ag 面）弱相关。PVP 在 Ag(111)（2.8 M）上的吸附平衡常数约为在 Ag(100)（5 M）上的一半。从 Wulff 构造来看，这一差异远远不足以通过热力学控制来产生立方体。这一结果表明 PVP 对 Ag 纳米颗粒形状的动力学控制的重要性，正如最近所提出的。
