Growth Mechanisms of Metal Nanoparticles via First Principles

Despite the important applications of nanoparticles (NPs), their mechanisms of growth still remain elusive. Herein we elucidate the growth mechanisms of silver NPs via first-principle calculations to elucidate anisotropic growth and shape selectivity by a symmetry-break mechanism. The capping agent (citrate) can play a multifunctional action: under certain conditions, it blocks NP growth via an electrostatic or a van der Waals stabilization mechanism, and under others, it induces NP growth.

Figure 1

Acetate’s binding interaction with different coordinated surface silver atoms of neutral ${\mathrm{Ag}}_{55}$ NPs (filled symbols) and reduced by one electron ${\mathrm{Ag}}_{55}$ NPs (open symbols) of Ico (triangles), Tdec (squares), and Cubo (turned triangles) symmetry. The coordination number is the mean value of the coordination number of the two silver atoms. The insets show the three ${\mathrm{Ag}}_{55}$ structures: (a) (Ico), Cubo (b), and Tdec (c).

Figure 2

(a) ${\mathrm{Ag}}_{55}$-Tdec interaction with citrate relaxed on its (100) plane. ${\mathrm{Ag}}_{40}$ cluster having two citrates on its (100) plane interacting via hydrogen bonds, when the third carboxyl is monoprotonated (b), and noninteracting via hydrogen bonds, when the third carboxyl is deprotonated (c). Front and side view of a ${\mathrm{Ag}}_4$ cluster approaching the surface of the ${\mathrm{Ag}}_{40}(\mathrm{\text{citrate}}{)}_2$ complex (d).

Figure 3

Potential energy surface (PES) scan of the ${\mathrm{Ag}}_4$ and citrate-complexed ${\mathrm{Ag}}_4$ cluster approaching the ${\mathrm{Ag}}_{40}(\mathrm{\text{citrate}}{)}_2$ colloid as shown in Fig. 2d. The third carboxyl group of the citrate can be either deprotonated or protonated according to the solution $p\mathrm{H}$.

Figure 4

Proposed mechanism for NP growth in citrate.