Intrinsic Visible Plasmonic Properties of Colloidal PtIn2 Intermetallic Nanoparticles

Materials that intrinsically exhibit localized surface plasmon resonance (LSPR) in the visible region have been predominantly researched on nanoparticles (NPs) composed of coinage metals, namely Au, Ag, and Cu. Here, as a coinage metal-free intermetallic NPs, colloidal PtIn2 NPs with a C1 (CaF2 -type) crystal structure are synthesized by the liquid phase method, which evidently exhibit LSPR at wavelengths similar to face-centered cubic (fcc)-Au NPs. Computational simulations pointed out differences in the electronic structure and photo-excited electron dynamics between C1-PtIn2 and fcc-Au NPs; reduces interband transition and stronger screening with smaller number of bound d-electrons compare with fcc-Au are unique origins of the visible plasmonic nature of C1-PtIn2 NPs. These results strongly indicate that the intermetallic NPs are expected to address the development of alternative plasmonic materials by tuning their crystal structure and composition.

Interfacial States in Au/Reduced TiO2 Plasmonic Photocatalysts Quench Hot-Carrier Photoactivity

Understanding the interface of plasmonic nanostructures is essential for improving the performance of photocatalysts. Surface defects in semiconductors modify the dynamics of charge carriers, which are not well understood yet. Here, we take advantage of scanning photoelectrochemical microscopy (SPECM) as a fast and effective tool for detecting the impact of surface defects on the photoactivity of plasmonic hybrid nanostructures. We evidenced a significant photoactivity activation of TiO2 ultrathin films under visible light upon mild reduction treatment. Through Au nanoparticle (NP) arrays deposited on different reduced TiO2 films, the plasmonic photoactivity mapping revealed the effect of interfacial defects on hot charge carriers, which quenched the plasmonic activity by (i) increasing the recombination rate between hot charge carriers and (ii) leaking electrons (injected and generated in TiO2) into the Au NPs. Our results show that the catalyst's photoactivity depends on the concentration of surface defects and the population distribution of Au NPs. The present study unlocks the fast and simple detection of the surface engineering effect on the photocatalytic activity of plasmonic semiconductor systems.

Opportunities and Challenges for Alternative Nanoplasmonic Metals: Magnesium and Beyond

Materials that sustain localized surface plasmon resonances have a broad technology potential as attractive platforms for surface-enhanced spectroscopies, chemical and biological sensing, light-driven catalysis, hyperthermal cancer therapy, waveguides, and so on. Most plasmonic nanoparticles studied to date are composed of either Ag or Au, for which a vast array of synthetic approaches are available, leading to controllable size and shape. However, recently, alternative materials capable of generating plasmonically enhanced light-matter interactions have gained prominence, notably Cu, Al, In, and Mg. In this Perspective, we give an overview of the attributes of plasmonic nanostructures that lead to their potential use and how their performance is dictated by the choice of plasmonic material, emphasizing the similarities and differences between traditional and emerging plasmonic compositions. First, we discuss the materials limitation encapsulated by the dielectric function. Then, we evaluate how size and shape maneuver localized surface plasmon resonance (LSPR) energy and field distribution and address how this impacts applications. Next, biocompatibility, reactivity, and cost, all key differences underlying the potential of non-noble metals, are highlighted. We find that metals beyond Ag and Au are of competitive plasmonic quality. We argue that by thinking outside of the box, i.e., by looking at nonconventional materials such as Mg, one can broaden the frequency range and, more importantly, combine the plasmonic response with other properties essential for the implementation of plasmonic technologies.

Plasmonic catalysis with designer nanoparticles

Catalysis is central to a more sustainable future and a circular economy. If the energy required to drive catalytic processes could be harvested directly from sunlight, the possibility of replacing contemporary processes based on terrestrial fuels by the conversion of light into chemical energy could become a step closer to reality. Plasmonic catalysis is currently at the forefront of photocatalysis, enabling one to overcome the limitations of "classical" wide bandgap semiconductors for solar-driven chemistry. Plasmonic catalysis enables the acceleration and control of a variety of molecular transformations due to the localized surface plasmon resonance (LSPR) excitation. Studies in this area have often focused on the fundamental understanding of plasmonic catalysis and the demonstration of plasmonic catalytic activities towards different reactions. In this feature article, we discuss recent contributions from our group in this field by employing plasmonic nanoparticles (NPs) with controllable features as model systems to gain insights into structure-performance relationships in plasmonic catalysis. We start by discussing the effect of size, shape, and composition in plasmonic NPs over their activities towards LSPR-mediated molecular transformations. Then, we focus on the effect of metal support interactions over activities, reaction selectivity, and reaction pathways. Next, we shift to the control over the structure in hollow NPs and nanorattles. Inspired by the findings from these model systems, we demonstrate a design-driven strategy for the development of plasmonic catalysts based on plasmonic-catalytic multicomponent NPs for two types of molecular transformations: the selective hydrogenation of phenylacetylene and the oxygen evolution reaction. Finally, future directions, challenges, and perspectives in the field of plasmonic catalysis with designer NPs are discussed. We believe that the examples and concepts presented herein may inspire work and progress in plasmonic catalysis encompassing the design of plasmonic multicomponent materials, new strategies to control reaction selectivity, and the unraveling of stability and reaction mechanisms.

Plasmon-Catalysed Decarboxylation of Dicarboxybipyridine Ligands in Ru(II) Complexes Chemisorbed on Ag Nanoparticles: Conditions, Proposed Mechanism and Role of Ag(0) Adsorption Sites

Plasmon-catalyzed decarboxylation reactions of Ru(II) bis(2,2‘-bipyridine)(4,4‘-dicarboxy-bipyridine) denoted as Ru(bpy)2(dcbpy) and Ru(II) tris(4,4‘-dicarboxy-bipyridine) denoted as Ru(dcbpy)3 complexes in hydrosol systems with Ag nanoparticles (NPs) conditioned by the presence of Ag(0) adsorption...

Cost-effective large-area Ag nanotube arrays for SERS detections: effects of nanotube geometry

This study demonstrated highly-ordered metallic nanotube arrays (MeNTAs) with a precisely controlled geometric shape to promote surface-enhanced Raman scattering (SERS). Using both simulation and experimental methods, we designed and fabricated MeNTAs with nanotube geometries that possess a large surface area to absorb probe molecules as well as geometric features capable of inducing hot spots for SERS enhancement. The proposed top-down wafer-scale lithographic and sputter-deposition process is a simple and cost-effective approach to the fabrication of 1 mm × 1 mm MeNTA at room temperature. Simulation results of nanotubes with various materials (Au, Ag, and Cu), diameters (100-1500 nm), geometric shapes (circle, equilateral triangle and square) and triangle corner curvatures (ranging from 0 to 300 nm) identified Ag triangles with sharp tips as the geometry best suited to SERS enhancement. The SERS spectra of crystal violet molecules generated from the Ag MeNTAs verified the patterns observed in computational simulations, wherein the effects of MeNTA on SERS decreased with an increase in the size of the nanotubes. Enhancement factor of 1.06 × 10⁹was obtained from our triangular Ag MeNTA, confirming its efficacy as an ultrahigh sensitivity SERS-active substrate.

Visible light plasmon excitation of silver nanoparticles against antibiotic-resistant Pseudomonas aeruginosa

The interaction of metallic nanoparticles with light excites a local surface plasmon resonance (LSPR). This phenomenon enables the transfer of hot electrons to substrates that release Reactive Oxygen Species (ROS). In this context, the present study aimed at enhancing the antibacterial effect of citrate-covered silver nanoparticles (AgNPs) by LSPR excitation with visible LED. AgNPs possess excellent antimicrobial properties against Pseudomonas aeruginosa, one of the most refractory organisms to antibiotic treatment. The Minimum Inhibitory Concentration (MIC) of the AgNPs was 10 μg/ml under dark conditions and 5 μg/ml under light conditions. The combination of light and AgNPs led to 100% cell death after 60 min. Flow cytometry quantification showed that bacteria treated with LSPR-stimulated AgNPs displayed 4.8 times more ROS. This significant increase in ROS possibly accounts for most of the antimicrobial effect of the AgNPs. In addition, light exposition caused a small release of silver ions (0.4%) suggesting that silver ions may play a secondary role in P. aeruginosa death. Overall, the results presented here show that LSPR stimulation of AgNPs by visible light enhances the antimicrobial activity of silver nanoparticles and can be an alternative for the treatment of topic infections caused by antibiotic-resistant bacteria such as P. aeruginosa.

Efficient Plasmon-Mediated Energy Funneling to the Surface of Au@Pt Core-Shell Nanocrystals

The structure and ultrafast photodynamics of ∼8 nm Au@Pt core-shell nanocrystals with ultrathin (<3 atomic layers) Pt-Au alloy shells are investigated to show that they meet the design principles for efficient bimetallic plasmonic photocatalysis. Photoelectron spectra recorded at two different photon energies are used to determine the radial concentration profile of the Pt-Au shell and the electron density near the Fermi energy, which play a key role in plasmon damping and electronic and thermal conductivity. Transient absorption measurements track the flow of energy from the plasmonic core to the electronic manifold of the Pt shell and back to the lattice of the core in the form of heat. We show that strong coupling to the high density of Pt(d) electrons at the Fermi level leads to accelerated dephasing of the Au plasmon on the femtosecond time scale, electron-electron energy transfer from Au(sp) core electrons to Pt(d) shell electrons on the sub-picosecond time scale, and enhanced thermal resistance on the 50 ps time scale. Electron-electron scattering efficiently funnels hot carriers into the ultrathin catalytically active shell at the nanocrystal surface, making them available to drive chemical reactions before losing energy to the lattice via electron-phonon scattering on the 2 ps time scale. The combination of strong broadband light absorption, enhanced electromagnetic fields at the catalytic metal sites, and efficient delivery of hot carriers to the catalyst surface makes core-shell nanocrystals with plasmonic metal cores and ultrathin catalytic metal shells promising nanostructures for the realization of high-efficiency plasmonic catalysts.