Palladium-rich plasmonic nanorattles with enhanced LSPRs via successive galvanic replacement mediated by co-reduction.

Mariia Ivanchenko,Hao Jing,Andrew J Evangelista

doi:10.1039/d1ra06109g

Abstract

Catalytic transformations under light irradiation have been extensively demonstrated by the excitation of the localized surface plasmon resonances (LSPRs) in noble metal-based nanoparticles. To fully harness the potential of noble metal-based nanocatalysts, it is fundamentally imperative to explore hybrid nano-systems with the most desirable enhanced LSPRs and intrinsic catalytic activities. Pd-containing hollow multimetallic nanostructures transformed from the sacrificial template of Ag via galvanic replacement reaction (GRR) offer such ideal platforms to gain quantitative insights into nanoparticle-catalyzed reactions. In this work, we successfully fabricated Pd-rich plasmonic nanorattles by means of co-reduction mediated GRR using CTAC-stabilized Au@Ag nanocuboids as templates and H2PdCl4 as a Pd precursor in the presence of ascorbic acid (AA) acting as a mild reducing agent. Successive titration of Au@Ag nanocuboids with the Pd precursor in the presence of AA modulates the rate of the galvanic replacement reaction as well as effective diffusion of Pd into the Ag matrix, resulting in increased dimensions and enlarged cavity sizes. Reduction of oxidized Ag+ back to Ag0 by AA, along with the deposition of Pd to form homogeneously mixed bimetallic layers not only prevents LSPRs peak from damping with increasing Pd content but also ensures the enhanced catalytic activities. Through precise control of added H2PdCl4 titrant, an unconventional steep increase in extinction intensity accompanied by tunable plasmon resonances shifted towards the NIR spectral region was experimentally observed due to the increasing physical cross-sections and plasmon hybridization in hollow nanorattles. Four colloids of Pd-rich nanorattles obtained by addition of different amounts of the H2PdCl4 titrant were used as catalysts for reduction of 4-nitrothiophenol in the presence of NaBH4 monitored by SERS.

Highlights

Plasmonic nanocatalysts generally based on noble metal nanoparticles, such as gold (Au),[1,2,3] silver (Ag),[4,5] and copper (Cu),[6] have been widely studied in chemical transformations owing to the geometrically tunable optical properties dominated by the collective oscillations of free electrons referred to as localized surface plasmon resonances (LSPRs).[7,8]
To fully harness the potential of noble metal-based nanocatalysts, it is fundamentally imperative to explore other hybrid hollow nano-systems with most desirable enhanced LSPRs and intrinsic catalytic activities besides traditional Au–Ag hollow particles, such as Pd-containing hollow nanostructures transformed from the sacri cial template of Ag
We have synthesized Au@Ag nanocuboids and used a facile galvanic replacement reaction (GRR) mediated by co-reduction for their transformation into Pd-rich nanorattles to modify their structural, optical, and catalytic properties

Summary

Introduction

Due to the strong plasmon damping when incorporating Pd into the nanoparticles.[51] Such robustness in the optical behaviors, especially with enhanced plasmon resonances, has only been experimentally observed in Au–Ag hollow nanostructures so far.[52,53] To fully harness the potential of noble metal-based nanocatalysts, it is fundamentally imperative to explore other hybrid hollow nano-systems with most desirable enhanced LSPRs and intrinsic catalytic activities besides traditional Au–Ag hollow particles, such as Pd-containing hollow nanostructures transformed from the sacri cial template of Ag. Taking into account of the catalytically active characteristics of Pd and the fact Ag nanocrystals exhibiting the strongest plasmon resonances with least damping, greatest optical tunability, and most intense near- eld enhancements among all other noble metal counterparts,[54] the resultant Ag–Pd hollow nanostructures will open new opportunities in various plasmon-enabled applications, such as photocatalysis,[55] surface-enhanced Raman scattering,[56] optics,[57] sensing,[58] imaging,[59] photothermal therapies,[60] and drug delivery.[61] In our work, we successfully obtained Pd-rich plasmonic nanorattles with enhanced LSPRs via successive galvanic replacement reactions mediated by coreduction in the presence of a mild reducing agent, ascorbic acid (AA). The detailed understanding will enrich the versatility of current synthetic approaches for rational design of multimetallic hollow nanostructures with unprecedented tunability in compositions, optical, and catalytic properties

Results and discussion

Synthetic procedures

Conclusions