Size Modulation of Colloidal Au Nanoparticles via Digestive Ripening in Conjunction with a Solvated Metal Atom Dispersion Method: An Insight Into Mechanism

Abstract

Digestive ripening, a postsynthetic treatment of colloidal nanoparticles, is a versatile method to produce monodisperse nanoparticles and to prepare various bimetallic nanostructures. The mechanism of this process is largely unknown. Herein, we present a systematic study conducted using Au nanoparticles prepared by a solvated metal atom dispersion method to probe the mechanistic aspects of digestive ripening. In our study, experimental conditions such as concentration of capping agent, reaction time, and temperature, were found to influence the course of the digestive ripening process. Here it is shown that, during digestive ripening under reflux, nanoparticles within an optimum size window are conserved, and surface etching facilitated mass transfer resulted in monodisperse nanoparticles. Overall, digestive ripening can be considered as a kinetically controlled thermodynamic process.

Understanding Digestive Ripening of Ligand-Stabilized, Charged Metal Nanoparticles

“…4,24,32 Moreover, the effect of the binding energy described in Figure 3b also helps to understand the observations for dodecanethiol-stabilized Ag, Au, and Pd NPs. Thiol possess the strongest attraction for Ag, intermediate for Au and the weakest for Pd.…”

“…58 With typical parameter values used in the experiments (i.e., no fitting parameters), the thermodynamic equilibrium for ligand-stabilized NPs predicts that the average size increases with temperature for constant metal:ligand ratio (Figure 3c inset), in agreement with the experimental observations. 21,26,32 ■ CONCLUSIONS In spite of the experimental efforts to provide insights on DR, 5,21,24 many authors stress that the DR process is still poorly understood. 4,10,18,22−25,27−31 The DR studies often cite the theory proposed by Lee et al 41 which considers the electrostatic energy of charged NPs as one of the key contributions.…”

“…4 The DR process is often carried out in toluene or other organic solvents, but aqueous media have also been used. 5,13 In spite of the experimental efforts to provide insights, 5,21,24 most authors stress that the mechanisms of the DR process are not yet known. 4,10,18,22−25,27−31 Hence, there is a pressing need for thermodynamic studies that identify the factors determining the size distribution.…”

A facile one step conversion of the sub-micrometer to uniform nanopowder in tetragonal BaTiO3 via a surface active etching salt

“…These processes need to meet the industrial requirements based on geopolitical uncertainty, reproducibility, scarcity and cost. A recent method allowed for highly desirable properties for obtaining metals, metal sulfides, and even magnetic fine nanoparticles by using a digestive ripening process [26][27][28][29][30], which involved refluxing the poly-dispersed bulk precursor within the excess solution of complex capping agents, such as hexadecylamine (HDA), tetraoctyl-ammonium bromide (TOAB), hexadecyl-trimethyl-ammonium bromide (CTAB), etc. During the reflux process at over the melting point of the capping agent, larger particles were etched out as clusters, resulting in size reduction.…”

“…During the reflux process at over the melting point of the capping agent, larger particles were etched out as clusters, resulting in size reduction. These clusters were deposited simultaneously on another smaller particle, which preferred to grow by Ostwald ripening or other mechanisms in order to attain equilibrium of a specific size [26][27][28][29][30]. The final size and size distribution of nanoproducts are influenced mainly by the capping agent used [30].…”