Plasmonic nanoreactors regulating selective oxidation by energetic electrons and nanoconfined thermal fields

The plasmonic effect of Cu on tuning CO2 reduction activity and selectivity

Copper (Cu) has been widely used for catalyzing the CO2 reduction reaction (CO2RR), but the plasmonic effect of Cu has rarely been explored for tuning the activity and selectivity of the CO2RR. Herein, we conducted a quantitative analysis on the plasmon-generated photopotential (Ehv) of a Cu nanowire array (NA) photocathode and found that Ehv exclusively reduced the apparent activation energy (Ea) of reducing CO2 to CO without affecting the competitive hydrogen evolution reaction (HER). As a result, the CO production rate was enhanced by 52.6% under plasmon excitation when compared with that under dark conditions. On further incorporation with a polycrystalline Si photovoltaic device, the Cu NA photocathode exhibits good stability in terms of photocurrent and syngas production (CO : H2 = 2 : 1) within 10 h. This work validates the crucial role of the plasmonic effect of Cu on modulating the activity and selectivity of the CO2RR.

Theory of Hot-Carrier Generation in Bimetallic Plasmonic Catalysts

Bimetallic nanoreactors in which a plasmonic metal is used to funnel solar energy toward a catalytic metal have recently been studied experimentally, but a detailed theoretical understanding of these systems is lacking. Here, we present theoretical results of hot-carrier generation rates of different Au-Pd nanoarchitectures. In particular, we study spherical core-shell nanoparticles with a Au core and a Pd shell as well as antenna-reactor systems consisting of a large Au nanoparticle that acts as an antenna and a smaller Pd satellite nanoparticle separated by a gap. In addition, we investigate an antenna-reactor system in which the satellite is a core-shell nanoparticle. Hot-carrier generation rates are obtained from an atomistic quantum-mechanical modeling technique which combines a solution of Maxwell's equation with a tight-binding description of the nanoparticle electronic structure. We find that antenna-reactor systems exhibit significantly higher hot-carrier generation rates in the catalytic material than the core-shell system as a result of strong electric field enhancements associated with the gap between the antenna and the satellite. For these systems, we also study the dependence of the hot-carrier generation rate on the size of the gap, the radius of the antenna nanoparticle, and the direction of light polarization. Overall, we find a strong correlation between the calculated hot-carrier generation rates and the experimentally measured chemical activity for the different Au-Pd photocatalysts. Our insights pave the way toward a microscopic understanding of hot-carrier generation in heterogeneous nanostructures for photocatalysis and other energy-conversion applications.

Geometric Control and Optical Properties of Intrinsically Chiral Plasmonic Nanomaterials

Intrinsically chiral plasmonic nanomaterials exhibit intriguing geometry-dependent chiroptical properties, which is due to the combination of plasmonic features with geometric chirality. Thus, chiral plasmonic nanomaterials have become promising candidates for applications in biosensing, asymmetric catalysis, biomedicine, photonics, etc. Recent advances in geometric control and optical tuning of intrinsically chiral plasmonic nanomaterials have further opened up a unique opportunity for their widespread applications in many emerging technological areas. Here, the recent developments in the geometric control of chiral plasmonic nanomaterials are reviewed with special attention given to the quantitative understanding of the chiroptical structure-property relationship. Several important optical spectroscopic tools for characterizing the optical chirality of plasmonic nanomaterials at both ensemble and single-particle levels are also discussed. Three emerging applications of chiral plasmonic nanomaterials, including enantioselective sensing, enantioselective catalysis, and biomedicine, are further highlighted. It is envisioned that these advanced studies in chiral plasmonic nanomaterials will pave the way toward the rational design of chiral nanomaterials with desired optical properties for diverse emerging technological applications.

Thermoplasmonic In Situ Fabrication of Nanohybrid Electrocatalysts over Gas Diffusion Electrodes for Enhanced H2O2 Electrosynthesis

Large-scale development of electrochemical cells is currently hindered by the lack of Earth-abundant electrocatalysts with high catalytic activity, product selectivity, and interfacial mass transfer. Herein, we developed an electrocatalyst fabrication approach which responds to these requirements by irradiating plasmonic titanium nitride (TiN) nanocubes self-assembled on a carbon gas diffusion layer in the presence of polymeric binders. The localized heating produced upon illumination creates unique conditions for the formation of TiN/F-doped carbon hybrids that show up to nearly 20 times the activity of the pristine electrodes. In alkaline conditions, they exhibit enhanced stability, a maximum H2O2 selectivity of 90%, and achieve a H2O2 productivity of 207 mmol gTiN-1 h-1 at 0.2 V vs RHE. A detailed electrochemical investigation with different electrode arrangements demonstrated the key role of nanocomposite formation to achieve high currents. In particular, an increased TiOxNy surface content promoted a higher H2O2 selectivity, and fluorinated nanocarbons imparted good stability to the electrodes due to their superhydrophobic properties.

Promises of Plasmonic Antenna-Reactor Systems in Gas-Phase CO2 Photocatalysis

Sunlight-driven photocatalytic CO2 reduction provides intriguing opportunities for addressing the energy and environmental crises faced by humans. The rational combination of plasmonic antennas and active transition metal-based catalysts, known as "antenna-reactor" (AR) nanostructures, allows the simultaneous optimization of optical and catalytic performances of photocatalysts, and thus holds great promise for CO2 photocatalysis. Such design combines the favorable absorption, radiative, and photochemical properties of the plasmonic components with the great catalytic potentials and conductivities of the reactor components. In this review, recent developments of photocatalysts based on plasmonic AR systems for various gas-phase CO2 reduction reactions with emphasis on the electronic structure of plasmonic and catalytic metals, plasmon-driven catalytic pathways, and the role of AR complex in photocatalytic processes are summarized. Perspectives in terms of challenges and future research in this area are also highlighted.

Impact of bimetallic interface design on heat generation in plasmonic Au/Pd nanostructures studied by single-particle thermometry

Localized surface plasmons are lossy and generate heat. However, accurate measurement of the temperature of metallic nanoparticles under illumination remains an open challenge, creating difficulties in the interpretation of results across plasmonic applications. Particularly, there is a quest for understanding the role of temperature in plasmon-assisted catalysis. Bimetallic nanoparticles combining plasmonic with catalytic metals are raising increasing interest in artificial photosynthesis and the production of solar fuels. Here, we perform single-particle thermometry measurements to investigate the link between morphology and light-to-heat conversion of colloidal Au/Pd nanoparticles with two different configurations: core-shell and core-satellite. It is observed that the inclusion of Pd as a shell strongly reduces the photothermal response in comparison to the bare cores, while the inclusion of Pd as satellites keeps photothermal properties almost unaffected. These results contribute to a better understanding of energy conversion processes in plasmon-assisted catalysis.

Near-Infrared Trapping by Surface Plasmons in Randomized Platinum-Ceramic Metamaterial for Thermal Barrier Coatings

As the operation temperature of next generation gas turbine is targeted to be 1800 °C toward a higher efficiency and lower carbon emission, the near-infrared (NIR) thermal radiation becomes a major concern for the durability of the metallic turbine blades. Although thermal barrier coatings (TBCs) are applied to provide thermal insulations, they are translucent to the NIR radiation. It is a major challenge for TBCs to achieve optically thick with limited physical thickness (usually < 1 mm) for effectively shielding the NIR radiation damage. Here, an NIR metamaterial is reported, where a Gd₂ Zr₂ O₇ ceramic matrix is randomly dispersed with microscale Pt (0.53 vol%) nanoparticles with a size of 100-500 nm. Attenuated by the Gd₂ Zr₂ O₇ matrix, a broadband NIR extinction is achieved through the red-shifted plasmon resonance frequencies and higher-order multipole resonances of the Pt nanoparticles. A very high absorption coefficient of ≈3 × 10⁴ m^-1 , approaching the Rosseland diffusion limit for a typical coating thickness, minimizes the radiative thermal conductivity to ≈10^-2  W m^-1 K^-1 and successfully shields the radiative heat transfer. This work suggests that constructing a conductor/ceramic metamaterial with tunable plasmonics could be a strategy to shield NIR thermal radiation for high temperature applications.

Intrinsic Optical Properties and Emerging Applications of Gold Nanostructures

The collective oscillation of free electrons at the nanoscale surface of gold nanostructures is closely modulated by tuning the size, shape/morphology, phase, composition, hybridization, assembly, and nanopatterning, along with the surroundings of the plasmonic surface located at a dielectric interface with air, liquid, and solid. This review first introduces the physical origin of the intrinsic optical properties of gold nanostructures and further summarizes stimuli-responsive changes in optical properties, metal-field-enhanced optical signals, luminescence spectral shaping, chiroptical response, and photogenerated hot carriers. The current success in the landscape of nanoscience and nanotechnology mainly originates from the abundant optical properties of gold nanostructures in the thermodynamically stable face-centered cubic (fcc) phase. It has been further extended by crystal phase engineering to prepare thermodynamically unfavorable phases (e.g., kinetically stable) and heterophases to modulate their intriguing phase-dependent optical properties. A broad range of promising applications, including but not limited to full-color displays, solar energy harvesting, photochemical reactions, optical sensing, and microscopic/biomedical imaging, have fostered parallel research on the multitude of physical effects occurring in gold nanostructures.

Ultrafast Laser Plasmonic Fabrication of Nanocrystals by Molecule Modulation for Photoresponse Multifunctional Structures

Nanotechnology has attracted wide research attention in constructing functional devices, including integrated circuits, transparent electrodes, and flexible actuators. Bottom-up fabrication is an important approach for functional structure manufacture, however, the controllable fabrication of complex architectures for practical applications has long been a challenge. Here, a novel strategy of laser plasmonic fabrication based on glue molecule modulation is proposed that can assemble metal nanocrystals into interconnected pattern networks. The plasmonic response of nanocrystals is adjustable with molecule modulation, which is a benefit for the effective formation of laser-induced localized oscillating electrons. The further decomposition of molecules and the movement of nanocrystal surface atoms can achieve the coalescence of assembled nanocrystals. It demonstrates that complex architectures can be controllably constructed by molecule level modulation. Through molecule-assisted laser plasmonic fabrication, the functional nanocrystals with enhanced photothermal capacity can be used for information encryption and soft machinery. This work expands the knowledge of bottom-up fabrication and provides a method for designing functional nanocrystals for a wide range of applications.

Active Site Engineering on Plasmonic Nanostructures for Efficient Photocatalysis

Plasmonic nanostructures have shown immense potential in photocatalysis because of their distinct photochemical properties associated with tunable photoresponses and strong light-matter interactions. The introduction of highly active sites is essential to fully exploit the potential of plasmonic nanostructures in photocatalysis, considering the inferior intrinsic activities of typical plasmonic metals. This review focuses on active site-engineered plasmonic nanostructures with enhanced photocatalytic performance, wherein the active sites are classified into four types (i.e., metallic sites, defect sites, ligand-grafted sites, and interface sites). The synergy between active sites and plasmonic nanostructures in photocatalysis is discussed in detail after briefly introducing the material synthesis and characterization methods. Active sites can promote the coupling of solar energy harvested by plasmonic metal to catalytic reactions in the form of local electromagnetic fields, hot carriers, and photothermal heating. Moreover, efficient energy coupling potentially regulates the reaction pathway by facilitating the excited state formation of reactants, changing the status of active sites, and creating additional active sites using photoexcited plasmonic metals. Afterward, the application of active site-engineered plasmonic nanostructures in emerging photocatalytic reactions is summarized. Finally, a summary and perspective of the existing challenges and future opportunities are presented. This review aims to deliver some insights into plasmonic photocatalysis from the perspective of active sites, expediting the discovery of high-performance plasmonic photocatalysts.

Dichalcogenide and Metal Oxide Semiconductor-Based Composite to Support Plasmonic Catalysis

Nanocomposites comprising plasmon active metal nanostructures and semiconductors have been used to control the charge states in the metal to support catalytic activity. In this context dichalcogenides when combined with metal oxides offer the potential to control charge states in plasmonic nanomaterials. Using a model plasmonic mediated oxidation reaction p-amino thiophenol ↔ p-nitrophenol, we show that through the introduction of transition metal dichalcogenide nanomaterial, reaction outcomes can be influenced, achieved through controlling the occurrence of the reaction intermediate dimercaptoazobenzene by opening new electron transfer routes in a semiconductor-plasmonic system. This study demonstrates the ability to control plasmonic reactions by carefully controlling the choice of semiconductors.

Magnetic-Plasmonic Multimodular Hollow Nanoreactors for Compartmentalized Orthogonal Tandem Catalysis

In tandem catalytic systems, controlling the reaction steps and side reactions is extremely challenging. Here, we demonstrate a nanoreactor platform comprising magnetic- and plasmonic-coupled catalytic modules that synchronizes reaction steps at unconnected neighboring reaction sites via decoupled nanolocalized energy harvested using distinct antennae reactors while minimizing the interconflicting effects. As was desired, the course of the reaction and product yields can be controlled by a convenient remote operation of alternating magnetic field (AMF) and near-infrared light (NIR). Following this strategy, a tandem reaction involving [Pd]-catalyzed Suzuki-Miyaura C-C cross-coupling and [Pt]-catalyzed aerobic alcohol oxidation enabled an excellent yield of cinnamaldehyde (ca. 95%) by overcoming the risk of side reactions. The customization scope for using different catalytic metals (Pt, Pd, Ru, and Rh) with in situ control over product release through remotely operable benign energy sources opens avenues for designing diverse catalytic schemes for targeted applications.

Thermo-photo catalysis: a whole greater than the sum of its parts

Thermo-photo catalysis, which is the catalysis with the participation of both thermal and photo energies, not only reduces the large energy consumption of thermal catalysis but also addresses the low efficiency of photocatalysis. As a whole greater than the sum of its parts, thermo-photo catalysis has been proven as an effective and promising technology to drive chemical reactions. In this review, we first clarify the definition (beyond photo-thermal catalysis and plasmonic catalysis), classification, and principles of thermo-photo catalysis and then reveal its superiority over individual thermal catalysis and photocatalysis. After elucidating the design principles and strategies toward highly efficient thermo-photo catalytic systems, an ample discussion on the synergetic effects of thermal and photo energies is provided from two perspectives, namely, the promotion of photocatalysis by thermal energy and the promotion of thermal catalysis by photo energy. Subsequently, state-of-the-art techniques applied to explore thermo-photo catalytic mechanisms are reviewed, followed by a summary on the broad applications of thermo-photo catalysis and its energy management toward industrialization. In the end, current challenges and potential research directions related to thermo-photo catalysis are outlined.

Precursor Heterogeneity Driven Mo-Te Nanoparticle Structural Diversification for Cancer Photo-Theranostics

Chemical reactions between homogeneous precursors are typically used to synthesize monodisperse nanoparticles with well-controlled size and morphology. It is difficult to predict the evolved nanostructures when using two heterogeneous precursors. In this study, three types of Mo-Te nanoparticles shaped like leaves, spindles, and rice grains (denoted respectively as nanoleaf, nanospindle, and nanorice) were obtained from dextrose-mediated proton-coupled electron transfer reaction between the solid polyoxomolybdate (POM) and the ionic tellurite anion as precursors. All produced nanoparticles had excellent optical absorption in the ultraviolet(UV)-visible(Vis)-near-infrared(NIR) regions, with only slight deviations among them. After confirming nanoparticles' photothermal conversion and photocatalytic activity at multiple wavelengths, the Mo-Te nanorice was tested as a potential agent for cancer treatment due to its minimum toxicity, excellent colloidal stability, and intrinsic anticancer effect. Excellent treatment efficacy and clearance were confirmed in vitro and in vivo. Due to their photoacoustic imaging capability, the injection of pristine nanoparticles could also realize phototheranostics without using additional drugs, probes, or photosensitizers.

Enhancement of Ti3C2 MXene on Au@Ag/TiO2 for the visible-light-driven photoreduction of nitroaromatics

Au@Ag/TiO2/Ti3C2 exhibits outstanding photoreduction activity at 0 °C because of the combination of efficient hot carrier generation and separation ability in one system.

Selective Enhancement of Surface and Bulk E-Field within Porous AuRh and AuRu Nanorods

A variety of multisegmented nanorods (NRs) composed of dense Au and porous Rh and Ru segments with lengths controlled down to ca. 10 nm are synthesized within porous anodic aluminum oxide membranes. Despite the high Rh and Ru porosity (i.e., ∼40%), the porous metal segments are able to efficiently couple with the longitudinal localized surface plasmon resonance (LSPR) of Au NRs. Finite-difference time-domain simulations show that the LSPR wavelength can be precisely tuned by adjusting the Rh and Ru porosity. Additionally, light absorption inside Rh and Ru segments and the surface electric field (E-field) at Rh and Ru can be independently and selectively enhanced by varying the position of the Rh and Ru segment within the Au NR. The ability to selectively control and decouple the generation of high-energy, surface hot electrons and low-energy, bulk hot electrons within photocatalytic metals such as Rh and Ru makes these bimetallic structures great platforms for fundamental studies in plasmonics and hot-electron science.