Understanding the Role of Poly(vinylpyrrolidone) in Stabilizing and Capping Colloidal Silver Nanocrystals

Abstract

The ligands anchored to the surface of metal nanocrystals play an important role in controlling their colloidal synthesis for a broad spectrum of applications, but it remains a daunting challenge to investigate the ligand−surface and ligand−solvent interactions at the molecular level. Here, we report the use of surface-enhanced Raman scattering (SERS) to extract structural information about the binding of poly-(vinylpyrrolidone) (PVP) to Ag nanocubes as well as its conformational changes in response to solvent quality. When a PVP chain binds to the surface of a Ag nanocube through some of its carbonyl groups, the segments between adjacent binding sites are expelled into the solvent as loops. As a result, the carbonyl peak (ν CO ) resolved in the SERS spectrum includes the contributions from those anchored to the surface and those residing on the loops, with their frequencies located at ν CO(Ag) and ν CO(free) , respectively. While ν CO(Ag) remains at a fixed frequency due to the coordination between the carbonyl groups with Ag surface, the spectral position of ν CO(free) is dependent on the solvent. As the strength of hydrogen bonding between PVP and solvent increases, the peak position of ν CO(free) shifts toward lower frequencies. When exposed to bad and good solvents in an alternating manner, the PVP loops undergo conformational changes between collapsed and extended states, altering the separation between the free carbonyl groups and the Ag surface and thereby the intensity of the ν CO peak.

Bromide‐Mediated Reduction Kinetics and Oxidative Etching for Manipulating the Twin Structure and Facet of Pd Nanocrystals for Catalysis

“…When the electron beam was aligned perpendicular to the bottom side of a penta‐twinned Pd nanorod, the continuous {111} fringes with a lattice spacing of 0.23 nm could be identified (Figure 3G,H), which is consistent with the previous experimental observations in the cases of penta‐twinned Pd, Au, Ag, and Cu rods/wires. [ 16,21 ] When the reaction time was prolonged to the later stage of synthesis ( t = 180 min), the multiply twinned nanocrystals almost disappeared, and the products consisted mostly of single‐crystal nanocubes and singly twinned bipyramids, as shown in Figure 3I,J. The Pd nanocubes with sharp corners and their side faces enclosed by a (200) plane with a lattice spacing of 0.19 nm were observed (Figure 3K,L).…”

“…[9,15] It is generally accepted that the formation of a seed with a certain internal structure is determined by thermodynamics or kinetics in the nucleation stage, which then dictates the shape evolution of a nanocrystal with symmetries as same as or similar to the seed in the growth stage. [4,16,17] The significant progress has been made to manipulate the internal twin structures of seeds by controlling the reduction kinetics of salt precursor under kinetic control. [8,[18][19][20][21][22][23][24][25][26][27] For example, tiny Pd seeds with single-crystal, multiply twinned, and stacking-fault-lined structures can be obtained by manipulating the initial reduction rate of Pd(II) precursor.…”

Precise and Controllable Assembly of Silver Nanolines under the Dual-Energy Irradiation of Ultraviolet and Heat

“…Here, we creatively proposed the assembly mechanism of the precise and controllable AgNLs forming different structures (Figure c). For the crystal facets of AgNPs, their free energy increases in the order of {111} < {100} < {110}. , PVP is a structural guiding agent that can strongly bind to {100} facets of Ag nanocrystals to limit their growth. − …”

Operando electrochemical SERS monitors nanoparticle reactions by capping agent fingerprints

“…Nanomaterials show physical properties that may strongly differ from the corresponding bulk material [17]. For instance, their high surface-to-volume ratio makes them ideal candidates as highly active heterogeneous catalysts or sensitive sensor components [18,19]. However, nanoparticle engineering usually requires the use of capping agents to adjust their sizes and shapes to prevent agglomeration [20].…”