In Situ Electron Microscopy of Transformations of Copper Nanoparticles under Plasmonic Excitation

Mapping the local stoichiometry in Cu nanoparticles during controlled oxidation by STEM-EELS spectral imaging

Copper nanoparticles (NPs) can be coupled with cuprous oxide, combining photoelectrocatalytic properties with a broad-range optical absorption. In the present study, we aimed to correlate changes in morphology, electronic structure and plasmonic properties of Cu NPs at different stages of oxidation. We demonstrated the ability to monitor the oxidation of NPs at the nanometric level using STEM-EELS spectral maps, which were analyzed with machine learning algorithms. The oxidation process was explored by exposing Cu NPs to air plasma, revealing systematic changes in their morphology and composition. Initial plasma exposure created a Cu2O shell, while prolonged exposure resulted in hollow structures with a CuO shell. This study identified procedures to obtain a material with Cu2O surface stoichiometry and absorption extended into the near-infrared range. Moreover, this study introduced a novel application of machine learning clustering techniques to analyze the morphological and chemical evolution of a nanostructured sample.

Noble Metal Plasmon-Molecular Catalyst Hybrids for Renewable Energy Relevant Small Molecule Activation

Significant endeavors have been dedicated to the advancement of materials for artificial photosynthesis, aimed at efficiently harvesting light and catalyzing reactions such as hydrogen production and CO2 conversion. The application of plasmonic nanomaterials emerges as a promising option for this purpose, owing to their excellent light absorption properties and ability to confine solar energy at the nanoscale. In this regard, coupling plasmonic particles with molecular catalysts offers a pathway to create high-performance hybrid catalysts. In this review, we discuss the plasmonic-molecular complex hybrid catalysts where the plasmonic nanoparticles serve as the light-harvesting unit and promote interfacial charge transfer in tandem with the molecular catalyst which drives chemical transformation. In the initial section, we provide a concise overview of plasmonic nanomaterials and their photophysical properties. We then explore recent breakthroughs, highlighting examples from literature reports involving plasmonic-molecular complex hybrids in various catalytic processes. The utilization of plasmonic materials in conjunction with molecular catalysts represents a relatively unexplored area with substantial potential yet to be realized. This review sets a strong basis and motivation to explore the plasmon-induced hot-electron mediated photelectrochemical small molecule activation reactions. Utilizing in situ spectroscopic investigations and ultrafast transient absorption spectroscopy, it presents a comprehensive template for scalable and sustainable antenna-reactor systems.

Switching of electrochemical selectivity due to plasmonic field-induced dissociation

Electrochemical reactivity is known to be dictated by the structure and composition of the electrocatalyst-electrolyte interface. Here, we show that optically generated electric fields at this interface can influence electrochemical reactivity insofar as to completely switch reaction selectivity. We study an electrocatalyst composed of gold-copper alloy nanoparticles known to be active toward the reduction of CO2 to CO. However, under the action of highly localized electric fields generated by plasmonic excitation of the gold-copper alloy nanoparticles, water splitting becomes favored at the expense of CO2 reduction. Real-time time-dependent density functional tight binding calculations indicate that optically generated electric fields promote transient-hole-transfer-driven dissociation of the O─H bond of water preferentially over transient-electron-driven dissociation of the C─O bond of CO2. These results highlight the potential of optically generated electric fields for modulating pathways, switching reactivity on/off, and even directing outcomes.

Plasmon-powered chemistry with visible-light active copper nanoparticles

In the quest for affordable materials for performing visible-light driven chemistry, we report here intriguing optical and photothermal properties of plasmonic copper nanoparticles (CuNPs). Precise tuning of reaction conditions and surface functionalization yield stable and monodisperse CuNPs, with a strong localized surface plasmon absorption at ∼580 nm. The molar extinction coefficient is estimated to be ∼7.7 × 107 M-1 cm-1 at 580 nm, which signifies their suitability for various light-harnessing studies. The characteristic wine-red colour and crystallography studies confirm the presence of mainly Cu(0) atoms in CuNPs, which showed excellent long-term colloidal and compositional stability under ambient conditions (at least 50 days). The as-synthesized oleylamine-capped CuNPs are ligand-exchanged with charged thiolate ligands of both polarities to form stable dispersions in water, with complete retention of their plasmonic properties and structural integrity (for ∼2 days and ∼6 h under inert and ambient conditions, respectively). Photothermal-conversion efficiency of CuNPs is estimated to be ∼80%, raising the surrounding temperature to ∼170 °C within ∼30 s of irradiation with a 1 W 532 nm diode laser, which is 'hot' enough to perform useful solar-vapor generation and high-temperature crystal-to-crystal phase transformation. Our work projects plasmonic CuNPs as an affordable and effective alternative to conventional metal NPs to harness light-matter interactions for future plasmon-powered chemistry.

Atomic Au3Cu Palisade Interlayer in Core@Shell Nanostructures for Efficient Kirkendall Effect Mediation

Plasmonic Cu@semiconductor heteronanocrystals (HNCs) have many favorable properties, but the synthesis of solid structures is often hindered by the nanoscale Kirkendall effect. Herein, we present the use of an atomically thin Au3Cu palisade interlayer to reduce lattice mismatch and mediate the Kirkendall effect, enabling the successive topological synthesis of Cu@Au3Cu@Ag, Cu@Au3Cu@Ag2S, and further transformed solid Cu@Au3Cu@CdS core-shell HNCs via cation exchange. The atomically thin and intact Au3Cu palisade interlayer effectively modulates the diffusion kinetics of Cu atoms as demonstrated by experimental and theoretical investigations and simultaneously alleviates the lattice mismatch between Cu and Ag as well as Cu and CdS. The Cu@Au3Cu@CdS HNCs feature exceptional crystallinity and atomically organized heterointerfaces between the plasmonic metal and the semiconductor. This results in the efficient plasmon-induced injection of hot electrons from Cu@Au3Cu into the CdS shell, enabling the Cu@Au3Cu@CdS HNCs to achieve high activity and selectivity for the photocatalytic reduction of CO2 to CO.