Plasmon-Mediated Synthesis of Hybrid Silver–Platinum Nanostructures

Abstract

Fine-tuning of metal ion reduction kinetics is crucial to the successful synthesis of designer bimetallic nanomaterials with well-defined morphologies and tailored localization of the constituent elements for use in catalysis, sensing, and other applications. However, achieving desired reduction kinetics can be challenging within the restrictions of available reducing agents, seed particle stability, metal ion solubility, and competing chemical processes such as galvanic exchange. Herein, we report the plasmon-assisted reduction of Pt ions onto Ag cores by using visible light illumination to accelerate the oxidation kinetics of a weak reducing agent, trisodium citrate. Using this approach, we are able to synthesize both core–shell and core–satellite structures composed of a plasmonic Ag core and a poorly plasmonic Pt shell or satellites. The controlled formation of these hybrid structures relies on the plasmon-mediated enhancement of the Pt ion reduction rate into a range where, under standard thermal conditions, reduction with citrate is too slow and reduction using even low concentrations of a slightly stronger reducing agent is too fast. This work expands the scope of citrate-assisted plasmon-mediated synthesis to metals other than Ag, opening possibilities for using plasmon-enhanced reduction by citrate as a more generalizable synthetic tool.

Bridging Colloidal and Electrochemical Nanoparticle Growth with In Situ Electrochemical Measurements

“…Just as an electrochemical synthesis of Au nanorods inspired the development of some of the first colloidal syntheses for shaped nanoparticles, the now well-established field of colloidal synthesis is ideally positioned to inspire advances in electrochemical nanoparticle growth. Many research groups, including our own, have contributed to the development of a broad range of techniques for controlling colloidal nanoparticle shape using reaction kinetics, molecular and ionic additives, secondary metals, seed structure, and other means. ,,,,− For example, surfactants and their corresponding counterions are common components of colloidal growth solutions because of their ability to modify crystal growth pathways through preferential adsorption onto particular facets in addition to their primary role of stabilizing particles against aggregation. ,− However, while additives are often present in electrochemical plating solutions, they are not used deliberately to define particle morphology. Using strategies from colloidal approaches in combination with the ability to facilely tune applied current or potential in electrodeposition opens exciting pathways for moving well beyond the existing limitations of both synthetic methods.…”

Plasmonics: A Versatile Toolbox for Heterogeneous Photocatalysis

“…Reproduced with permission. [ 171 ] Copyright 2020, American Chemical Society. d) SEM images (left panel) and g‐factor spectra (right panel) of different photogrowth stages towards the formation of chiral Au NPs from achiral seeds in the presence of an L‐peptide and using left‐handed circularly polarized light.…”

“…[ 170 ] The same objects have been used in a subsequent work as scaffolds for the growth of a catalytic metal following the same citrate‐mediated mechanism. [ 171 ] Herein, the localization of Pt deposition onto the Ag triangular bipyramids, either covering the entire surface or just at the vertices of the NPs, can be easily modified by changing the concentrations of citrate and Pt 2+ , while the intensity and excitation wavelength of the irradiation source also play a role (Figure 6c). Importantly, the authors demonstrate the minor importance of temperature, leaving plasmon‐induced catalysis as the major mechanism.…”

“…STEM image and corresponding EDS mappings of Ag bipyramids functionalized with Pt onto their tips. Reproduced with permission [171]. Copyright 2020, American Chemical Society.…”

Single-Particle Investigation of Plexcitons in Bimetallic Nanorods

“…Bimetallic nanostructure-based plasmonic systems have a significant advantage over their monometallic counterparts due to the spectral tunability of the localized plasmon resonances arising from the compositional difference. − Herein, we investigate the strong plasmon-exciton coupling interactions of bimetallic gold-silver core-shell NRs with the J -aggregate of the cationic cyanine dye, 1,1′-diethyl-2,2′-cyanine iodide (Cy). The nanostructure with Au NRs as the core and silver as the shell (hereafter referred as Au@Ag NRs) is employed as an effective plasmonic material where the Ag shell thickness is used as the parameter for fine-tuning the plasmon resonance to establish a perfect resonance with the excitonic counterparts. , The ensemble-level plasmon-exciton coupling is monitored using UV–vis absorption spectroscopy, whereas DFM is adopted to monitor these interactions at the single-particle level.…”