Plasmonic Metal Nanoparticles Research Articles

Prospects of Utilizing Quantum Emitters to Control the Absorption of Non‐Noble Plasmonic Metal Nanoparticles

AbstractProspects of controlling the absorption of the cost‐effective plasmonic metal nanoparticles (MNPs) Cu and Al using quantum emitters (QEs) are demonstrated semi‐analytically. The resulting spectra are compared with the absorption of commonly used noble plasmonic metal nanoparticles Au and Ag under similar conditions. It is observed that Cu and Au based plasmonic nanoparticles exhibit largely similar exciton–plasmon Fano interaction signatures in addition to their similar spectral regions of operation (lower end of the visible range). Furthermore, the QE‐enhanced maximum absorption (Fano maximum) of Cu based nanohybrids are seen to approach the maximum absorption level of isolated Au MNPs, with decreasing QE‐Cu separation, increasing QE dipole element magnitude, and increasing medium permittivity, in the parameter region considered. This renders Cu based exciton–plasmon nanohybrids as more economical alternatives for Au MNPs and Au‐based nanohybrids in absorption‐based applications (such as thermoplasmonic), when stabilized in protective embedding media such as poly (methyl methacrylate) (PMMA).

Plasmonic Silver‐Nanoparticle‐Catalysed Hydrogen Abstraction from the C(sp3)−H Bond of the Benzylic Cαatom for Cleavage of Alkyl Aryl Ether Bonds

AbstractSelective activation of the C(sp3)−H bond is an important process in organic synthesis, where efficiently activating a specific C(sp3)−H bond without causing side reactions remains one of chemistry's great challenges. Here we report that illuminated plasmonic silver metal nanoparticles (NPs) can abstract hydrogen from the C(sp3)−H bond of the Cαatom of an alkyl aryl etherβ‐O‐4 linkage. The intense electromagnetic near‐field generated at the illuminated plasmonic NPs promotes chemisorption of theβ‐O‐4 compound and the transfer of photo‐generated hot electrons from the NPs to the adsorbed molecules leads to hydrogen abstraction and direct cleavage of the unreactive ether Cβ−O bond under moderate reaction conditions (≈90 °C). The plasmon‐driven process has certain exceptional features: enabling hydrogen abstraction from a specific C(sp3)−H bond, along with precise scission of the targeted C−O bond to form aromatic compounds containing unsaturated, substituted groups in excellent yields.

Plasmonic Silver-Nanoparticle-Catalysed Hydrogen Abstraction from the C(sp3 )-H Bond of the Benzylic Cα atom for Cleavage of Alkyl Aryl Ether Bonds.

Selective activation of the C(sp3 )-H bond is an important process in organic synthesis, where efficiently activating a specific C(sp3 )-H bond without causing side reactions remains one of chemistry's great challenges. Here we report that illuminated plasmonic silver metal nanoparticles (NPs) can abstract hydrogen from the C(sp3 )-H bond of the Cα atom of an alkyl aryl ether β-O-4 linkage. The intense electromagnetic near-field generated at the illuminated plasmonic NPs promotes chemisorption of the β-O-4 compound and the transfer of photo-generated hot electrons from the NPs to the adsorbed molecules leads to hydrogen abstraction and direct cleavage of the unreactive ether Cβ -O bond under moderate reaction conditions (≈90 °C). The plasmon-driven process has certain exceptional features: enabling hydrogen abstraction from a specific C(sp3 )-H bond, along with precise scission of the targeted C-O bond to form aromatic compounds containing unsaturated, substituted groups in excellent yields.

Investigation of the Plasmon-Activated C-C Coupling Reactions by Liquid-State SERS Measurement.

The implementation of plasmonic materials in heterogeneous catalysis was limited due to the lack of experimental access in managing the plasmonic hot carriers. Herein, we propose a liquid-state surface-enhanced Raman scattering (SERS) technique to manipulate and visualize heterogeneous photocatalysis with transparent plasmonic chips. The liquid-state measurement conquers the difficulties that arise from the plasmon-induced thermal effects, and thus the plasmon based strategies can be extended to investigate a wider range of catalytic reactions. We demonstrated the selection of reaction products by modulating the plasmonic hot carriers and explored the mechanisms in several typical C-C coupling reactions with 4-bromothiophenol (4-BTP) as reactants. The real-time experimental results suggest brand new mechanisms of the formation of C-C bonds on plasmonic metal nanoparticles (NPs): the residue of 4-BTP, but not thiophenol (TP), is responsible for the C-C coupling. Furthermore, this technique was extended to study the evolution of the Suzuki-Miyaura reaction on nonplasmonic palladium metals by establishing the charge transfer channels between palladium and Au NPs. The cleavage and formation of chemical bonds in each individual reaction step were discerned, and the corresponding working mechanisms were clarified.

Regioselective Plasmon-Driven Decarboxylation of Mercaptobenzoic Acids Triggered by Distinct Reactive Oxygen Species

The non-radiative decay of surface plasmon resonance (SPR) in plasmonic metal nanoparticles (NPs) opens up unique hot-carrier-driven chemical transformation mechanisms. Here, the hot-carrier generation of reactive oxygen species was demonstrated to trigger the regioselective plasmon-driven decarboxylation of mercaptobenzoic acid (MBA) isomers over Ag (AgNPs) and Au nanoparticles (AuNPs). Controlled catalytic experiments indicated that the catalytic C–C bond cleavage over AgNPs and AuNPs is primarily initiated by photogenerated singlet oxygen (1O2) and hydroxyl radical (•OH), respectively. Energetic hot electrons on AgNPs can successfully generate 1O2 from 3O2 via Dexter energy transfer, while hot holes generated under the Fermi level of AuNPs have sufficient energy to oxidize OH– and promote the formation of reactive •OH. The catalytic activity trend was evaluated considering the known ortho-substituent effect. The data discussed herein shed light on how the intrinsic differences in electronic energy levels and metal–molecule interactions precisely tune the regioselectivity of plasmon-driven transformations and may guide the rational design of plasmonic catalysts for distinct desired reactions.

Novel Heterostructures of Noble Plasmonic Metals/Ga-Substituted Hydrotalcite for Solar Light Driven Photocatalysis toward Water Purification

Heterostructures formed by close conjunctions of plasmonic metal nanoparticles and non-plasmonic (2D) lamellar nanostructures are receiving extensive interest as solar-light-driven photocatalysts for environmental pollutant remediation. Herein, the conjunction of plasmonic Au or Ag and Ga-substituted hydrotalcite are obtained by exploiting the manifestation of the structural “memory effect” of Ga-substituted hydrotalcite in the aqueous solutions of Au(CH3COO)3 and Ag2SO4, respectively. The 2D layered matrix of MgGaAl plays a dual function; it is involved in the synthesis of the plasmonic metal nanoparticles, and further, is acting as a support. The compressive investigations using X-ray diffraction (XRD), UV-diffuse reflectance spectroscopy (UVDR), infrared spectroscopy (FT-IR), transmission electron microscopy (TEM/HRTEM), high-angle annular dark-field imaging/scanning transmittance electron microscopy (HAADF/STEM) and X-ray photoelectron spectroscopy (XPS) describe structural, composition and nano/micromorphology characteristics of the novel heterostructures, while UVDR analysis afforded to study the features of their plasmonic responses. Results reveal that the catalysts are formed by close conjunction of small nanoparticles of Au or Ag (with a mean size less than 20 nm) that are formed on the larger particles of MgGaAl and own plasmonic features within the visible range. The catalysts performances were tested towards photocatalytic degradation of p-dichlorobenzene and 4-nitrophenol under solar light irradiation. Results revealed that the degradation of the pollutants is entangled to the plasmonic response of the heterostructured catalysts that is the key functionality in promoting photocatalysis and degrading the pollutants, under solar light irradiation. MgGaAl showed a very low photocatalytic activity when irradiated by UV or solar light. Notably, the heterostructured catalysts proceeded in good to excellent yield to remove the tested pollutants, under solar light irradiation. The sustainability of the novel catalysts was assessed through the kinetic analysis of the degradation processes of the tested pollutants and their mixture.

Elucidating the Roles of Local and Nonlocal Rate Enhancement Mechanisms in Plasmonic Catalysis.

Plasmonic metal nanoparticles (e.g., Ag, Au, and Cu) constitute a class of materials that interact with light via the excitation of localized surface plasmon resonance (LSPR). Numerous studies have reported substantial enhancements in the rates of chemical reactions on illuminated plasmonic nanoparticle catalysts compared to corresponding systems in the absence of illumination. There are two mechanisms that have been proposed to explain the LSPR-induced chemical reactivity. One mechanism assumes a local plasmon-induced hot charge-carrier-mediated activation of the reactants, while the other assumes an LSPR-induced equilibrium heating of the catalyst, which leads to energy transfer to and chemical reaction of the adsorbed reactants. In this contribution, we developed a setup amenable to accurate in situ catalyst temperature and kinetic reaction rate measurements. We employed this setup to study the LSPR-induced rate enhancement in a case study of the CO oxidation reaction on plasmonic, monometallic Ag nanoparticle catalysts supported on α-Al2O3. We explored various Ag loadings and clustering levels. Our data show that the equilibrium heating of the catalyst cannot fully explain the illumination-induced plasmonic rate enhancements. This is the case even for high loading and clustering of Ag nanoparticles, where the equilibrium heating significantly increases. Based on the analysis, we propose that local effects, related to the plasmon-induced activation of adsorbates (reactants) via electronic excitation of the reactant or photothermal heating of the reactants that is highly localized to the individual nanoparticles, play a critical role in driving LSPR-induced chemical reactions.

Engineering Heterostructures of Layered Double Hydroxides and Metal Nanoparticles for Plasmon-Enhanced Catalysis

Artificially designed heterostructures formed by close conjunctions of plasmonic metal nanoparticles (PNPs) and non-plasmonic (2D) lamellar nanostructures are receiving extensive interest. The synergistic interactions of the nanounits induce the manifestation of localized surface plasmon resonance (LSPR) in plasmonic metals in the specific environment of the 2D-light absorbing matrix, impacting their potential in plasmon enhanced catalysis. Specifically, layered double hydroxides (LDH) with the advantages of their unique 2D-layered structure, tuned optical absorption, ease of preparation, composition diversity, and high surface area, have emerged as very promising candidates for obtaining versatile and robust catalysts. In this review, we cover the available PNPs/LDH heterostructures, from the most used noble-metals plasmonic of Au and Ag to the novel non-noble-metals plasmonic of Cu and Ni, mainly focusing on their synthesis strategies toward establishing a synergistic response in the coupled nanounits and relevant applications in plasmonic catalysis. First, the structure–properties relationship in LDH, establishing the desirable features of the 2D-layered matrix facilitating photocatalysis, is shortly described. Then, we address the recent research interests toward fabrication strategies for PNPs/support heterostructures as plasmonic catalysts. Next, we highlight the synthesis strategies for available PNPs/LDH heterostructures, how these are entangled with characteristics that enable the manifestation of the plasmon-induced charge separation effect (PICS), co-catalytic effect, or nanoantenna effect in plasmonic catalysis with applications in energy related and environmental photocatalysis. Finally, some perspectives on the challenges and future directions of PNPs/LDHs heterostructures to improve their performance as plasmonic catalysts are discussed.

(Digital Presentation) Plasmonic Enhanced CuBi2O4 Photocathode for Solar Driven Water Splitting

Hydrogen is a fuel for sustainable and renewable energy development that emits no carbon dioxide when compared to traditional fossil fuels. Photoelectrochemical (PEC) water splitting is a sustainable method of converting solar energy that falls on earth into useful chemical fuels. However, the sluggish surface reaction kinetics, high cost, and low natural abundance limit the use of photoelectrodes for practical application. It is critical to developing effective and resilient photoelectrodes that provide high efficiency with good stability. Copper based oxides like CuO, Cu2O, CuBi2O4, CuFeO2, and Cu3VO4 are some of the most well-known low-cost materials with apt band gap and band edges for proton reduction reaction. Among them, CuO is one of the most extensively researched photocathodic materials for PEC water splitting owing to its natural abundance and facile synthesis. However, the photocorrosion problem at CuO limits its use in practical application. The conduction band of CuO is contributed by Cu 3d bands which easily get reduced to Cu0 on photoexcited electron diffuse to conduction band. On the other hand, CuBi2O4 is ternary metal oxide which is more resistant and forbids photocorrosion owing to it conduction band contributed by Bi atom orbitals rather than Cu orbitals1.Metal sulfides like Sb2S3 is good photo-absorber material for solar cells consists of non-toxic and low-cost metal. It has favorable band gap and conduction band and valence band alignment for proton reduction reaction. The type II heterojunction between CuBi2O4 and Sb2S3 can present effective strategy of charge separation and enhanced photoconversion. The plasmon behavior of metal NPs is widely studied in PEC to further improve the photoelectrochemical performance of the photoelectrodes. Plasmonic metal nanoparticles (NPs) absorb light of a threshold wavelength and vibrate emitting out the hot electrons2. Adding Au plasmonic NPs to the photoelectrode might increase the charge carrier concentration, enhance the PEC efficiency, and boost hydrogen production.The objectives of this study are to investigate fabrication of CuBi2O4/Sb2S3 heterojunction and investigate the dual role of plasmonic Au NPs sandwiched between CuBi2O4/Sb2S3 heterojunction. This heterojunction is developed through three synthesis process: synthesis of CuBi2O4 microrods (MRs) through co-precipitation, Sb2S3 plates via a hybrid chemical bath deposition, and Au NPs via seed-assisted synthesis. XRD, SEM, TEM, and XPS are used to examine the CuBi2O4/Au/Sb2S3, CuBi2O4/Sb2S3, and CuBi2O4/Au heterostructures that were synthesized. At 0 VRHE, the photocurrent of CuBi2O4/Au/Sb2S3 (-3.12 mA.cm-2) was > 200 percent greater than that of pristine CuBi2O4 (-1.45 mA.cm-2), Sb2S3 (-1.02 mA.cm-2), and CuBi2O4/Sb2S3 (-2.15 mA.cm-2). Impedance spectroscopy revealed that CuBi2O4/Au/Sb2S3 has the lowest charge transfer resistance value when compared to the pristines. Stability tests revealed the superior stability of CuBi2O4/Au/Sb2S3 compared to their counterparts3. The increase in photoelectrode PEC activity can be attributed to: (i) effective heterojunction formation for facile charge transfer, (ii) increased light absorption, (iii) incorporation of plasmonic Au NPs increased charge carrier concentration, and (iv) Au NPs also served as a relay for charge transfer between CuBi2O4 and Sb2S3 due to their metallic properties, which increased photoelectrode conductivity. The synergistic effect of fabricated CuBi2O4/Sb2S3 heterojunction and dual role of Au NPs sandwiched resulted in improved PEC conversion and boosted hydrogen evolution. The findings of this study will pave the way for photoelectrodes to be sandwiched between plasmonic NPs through a heterojunction interface that boosts hydrogen production. References (1) Li, C.; He, J.; Xiao, Y.; Li, Y.; Delaunay, J. J. Earth-Abundant Cu-Based Metal Oxide Photocathodes for Photoelectrochemical Water Splitting. Energy Environ. Sci. 2020, 13 (10), 3269–3306. https://doi.org/10.1039/d0ee02397c.(2) Subramanyam, P.; Meena, B.; Biju, V.; Misawa, H.; Challapalli, S. Emerging Materials for Plasmon-Assisted Photoelectrochemical Water Splitting. J. Photochem. Photobiol. C Photochem. Rev. 2022, 51 (November 2021), 100472. https://doi.org/10.1016/j.jphotochemrev.2021.100472.(3) Kumar, M.; Ghosh, C. C.; Meena, B.; Ma, T.; Subrahmanyam, C. Plasmonic Au Nanoparticle Sandwiched CuBi2O4 /Sb2S3 Photocathode with Multi-Mediated Electron Transfer for Efficient Solar Water Splitting. Sustain. Energy Fuels 2022. https://doi.org/10.1039/D2SE00600F. Figure 1

Hot Carrier Lifetimes and Electrochemical Water Dissociation Enhanced by Nickel Doping of a Plasmonic Electrocatalyst

Hot carriers generated by localized surface plasmon resonance (LSPR) excitation of plasmonic metal nanoparticles are known to enhance electrocatalytic reactions. However, the participation of plasmonically generated carriers in interfacial electrochemical reactions is often limited by fast relaxation of these carriers. Herein, we address this challenge by tuning the electronic structure of a plasmonic electrocatalyst. Specifically, we design an electrocatalyst for alkaline hydrogen evolution reaction (HER) that consists of nanoparticles of a ternary Cu-Pt-Ni ternary alloy. The CuPt alloy has both plasmonic attributes and electrocatalytic HER activity. Ni doping contributes an electron-deficient 3d band and fully filled 4s band, which promotes water adsorption and prolongs the lifetimes of excited carriers generated by plasmonic excitation. As an outcome, the Cu-Pt-Ni nanoparticles exhibit boosted activity for electrochemical water dissociation and HER under LSPR excitation.

Metallic nanoparticles loaded Al–SrTiO3 supported with RhCr2O3 and CoOOH cocatalysts for overall water splitting

Developing new renewable, carbon-neutral fuels to diminish the amount of released CO2 in the atmosphere and to solve global challenges such as global warming and climate change is significant. Among them, hydrogen (H2) is attracting much attention due to its high energy density, ease of transportation, and multiple means of production. To meet the global demand of H2, photocatalytic water splitting is one of the most promising methods for large scale production. Herein, Al-doped SrTiO3 photocatalyst (Al–SrTiO3) was prepared by a molten flux method. Then, plasmonic metal nanoparticles (Au, Cu, Pt), and cocatalysts Rh/Cr2O3 and CoOOH were selectively deposited onto the reductive and oxidative active sites of Al–SrTiO3 using multi-step photodeposition-impregnation methods for water splitting and H2 production under UV-rays, UV–Vis. Light, and visible light (λ ≥ 400 nm). Our results showed that, compared with Pt and Cu loaded Al–SrTiO3 photocatalyst supported with Rh/Cr2O3 and CoOOH cocatalysts, Au-loaded samples showed the highest H2 production efficiency under both UV (920 μmol/h - EQE = 41% at 365 nm) and UV–Vis (100.5 μmol/h) rays. In addition, the amount of evolved H2 decreased by increasing the weight ratio of Au nanoparticles (NPs) due to the overlap between Au NPs and Rh/Cr2O3 cocatalyst. Although Au 0.3 wt%-loaded sample showed high activity under both UV and UV–Vis. Rays, it exhibited almost no efficiency under visible light because of the large bandgap of Al–SrTiO3 (3.1 eV) and the poor absorption in the visible region. Visible light absorption was then enhanced by increasing the loaded amount of Au NPs and by separating Au NPs and Rh/Cr2O3 cocatalyst responsible for H2 evolution by combining both photodeposition and impregnation methods. Under visible light, Rh/Cr2O3-loaded Al–SrTiO3 with 4 wt % Au NPs showed the highest H2 evolution efficiency (41 μmol/3 h). This was attributed to the efficient hot electron transfer from Au NPs to Al–SrTiO3 then to RhCr2O3, resulting in charge separation needed for efficient H2 generation.

A physicochemical and spectroscopic characterization of novel erlotinib conjugates with platinum nanoparticles

Anticancer drug conjugates with metal nanoparticles are in the center of research interest due to the promising application potential in modern medicine. It was proved that plasmonic metal nanoparticles are not only drug carriers and amplifiers of biological effect but also sensors for tracking the fate of the drug in organisms and cells. The formation of drug conjugates with gold (AuNPs) and silver nanoparticles (AgNPs) are widely described in the literature whereas less attention was paid on the formation of anticancer drug conjugates with platinum nanoparticles (PtNPs). These studies were conducted to verify the main hypothesis that conjugates of erlotinib (ERL), belonging to drugs used in non-small cell lung cancer (NSCLCs) treatment, with PtNPs can be formed in electrostatically-driven self-organization process. PtNPs were prepared using a seed-mediated growth method. The micrographs obtained from transmission (TEM) and scanning (SEM) electron microscopy revealed that PtNPs exhibited quasi-spherical shape and an average size equal to 108 ± 11 nm. The stability of PtNPs under controlled pH and ionic strength was determined by dynamic (DLS) and electrophoretic (ELS) light scattering. The formation of ERL-PtNP conjugates was carried out under mild acidic conditions, at pH 4.9 and ionic strength 7 × 10−3 M. The spectroscopic analysis of formed conjugates was performed with the use of surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared adsorption spectroscopy (SEIRA). The spectroscopic investigation was carried out for positively charged conjugates. The performed SERS and SEIRA studies indicate that the prepared PtNPs provide effective surface enhancement in visible and infrared regions, respectively, ensuring the possibility to perform detailed characterization of the adsorption process on these metal nanostructures. The considered ERL indicates strong interaction with the PtNPs mainly through the quinazoline and the amino moieties. Also, the ethylene bridge takes part in the conjugates formation, while methoxy moiety and phenylacetylene ring remain at a certain distance from the metal surface. The comparison of obtained results with available literature data showed that the adsorption pattern of ERL strongly depends on the type of plasmonic nanoparticles because the phenylacetylene ring of ERL plays a crucial role in the formation of conjugates with AuNPs and AgNPs. Based on these findings, the chemical structure of ERL in the formed conjugates was proposed. It was concluded that the stable ERL-PtNP conjugates can exhibit comparable electrokinetic properties with ERL conjugates with AuNPs and AgNPs while the chemical structure of ERL layer on nanoparticle surface strongly depends on the plasmonic metal type.

Front Cover: Metal‐Organic‐Frameworks and Their Derived Materials in Photo‐Thermal Catalysis (Eur. J. Inorg. Chem. 28/2022)

The Front Cover shows the two routes in which metal-organic frameworks (MOFs) can participate in photo-thermal reactions. In the case of MOF-based composites, MOFs can act as hosts for plasmonic metal nanoparticles that, upon irradiation, are able to drive chemical reactions through high-energy electrons and/or thermal enhancement. In the case of MOF-derived materials, MOFs play a role as sacrificial templates to create new materials based on highly dispersed metal nanoparticles embedded into a carbon matrix. These latter materials benefit from the outstanding light-to-heat conversion and broadband absorption of carbon structures. Both approaches mentioned above represent promising pathways for the implementation of MOFs as photo-thermal catalysts for the production of solar fuels and chemicals. More information can be found in the Review by J. Gascon and co-workers.

Hierarchical mesoporous plasmonic Pd-Fe3O4/NiFe-LDH composites: Characterization, and kinetic study of a photodegradation catalyst for aqueous metoclopramide

With the primary objective to develop efficient, environmentally benign, visible-light-driven heterogeneous catalysts for the degradation of metoclopramide (MCP), a waste-water pollutant, a newly prepared heterogeneous composite Pd-Fe 3 O 4 /NiFe-LDH catalyst is reported. This material has been characterized with a wide range of analysis methods (i.e. XRD, SEM-EDS, BET, FTIR, TG-DTG, DTA, DRUV and TEM analysis). When applied to aqueous solutions of MCP, Pd-Fe 3 O 4 /NiFe-LDH displayed a photocatalytic degradation of MCP with an efficiency of 95.2% in 80 min. The photocatalytic degradation rate for this composite material was higher than that of pure NiFe-LDH or Fe 3 O 4 /NiFe-LDH. The best photocatalytic activity was obtained at pH 6.5, with 0.4 g/L of the catalyst. Application of the Arrhenius equation yielded an activation energy for this process of 13.4 kJ/mol. A negative activation Δ S ‡ (-0.25 kJ/mol) with the positive Δ H ‡ and Δ G ‡ values were obtained for this MCP photodegradation. • Environmentally friendly photocatalysts for degradation of aqueous pharmaceutical pollutants. • Higher photocatalytic activity of Pd-Fe 3 O 4 /NiFe-LDH composite compared to components. • Magnetic semiconductor nanomaterial (Fe 3 O 4 ) and a plasmonic metal (Pd) nanoparticle. • Composite catalyst maintained good photocatalytic recyclability.

Fundamentals and applications of metal nanoparticle- enhanced singlet oxygen generation for improved cancer photodynamic therapy.

The introduction of nanotechnology in the field of Photodynamic Therapy (PDT) has proven to have great potential to overcome some of the challenges associated with traditional organic photosensitizers (PS) with respect to their solubility, drug delivery, distribution and site-specific targeting. Other focused areas in PDT involve high singlet oxygen production capability and excitability of PS by deep tissue penetrating light wavelengths. Owing to their very promising optical and surface plasmon resonance properties, combination of traditional PSs with plasmonic metallic nanoparticles like gold and silver nanoparticles results in remarkably high singlet oxygen production and extended excitation property from visible and near-infrared lights. This review summarizes the importance, fundamentals and applications of on plasmonic metallic nanoparticles in PDT. Lastly, we highlight the future prospects of these plasmonic nanoengineering strategies with or without PS combination, to have a significant impact in improving the therapeutic efficacy of cancer PDT.

Light responsive plasmonic silicone elastomer/hydrogel soft actuator.

Soft robots offer unique advantages in their ability to interact with fragile organisms. Light responsive soft actuators are promising for the development of the untethered soft robots. However, this requires a mechanism for converting the externally applied light into mechanical actuation. We designed, fabricated, and tested a light responsive soft actuator consist of silicone elastomer with plasmonic metal nanoparticle embedment and temperature sensitive hydrogel. We found that the selection of the carrier solvent for the metal nanoparticle embedment in silicone elastomer to be crucial. The fabricated soft actuator showed a relatively fast response time (< 5 min) under light illumination.

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

(Digital Presentation) Characterization of Ultrafast Dynamics of Refractory Metal Nanoparticles of Interest as Photocatalysts

Plasmonic noble metal nanoparticles are of interest as photocatalysts for several reasons, including a very large absorption cross section and the creation of a greatly enhanced evanescent electromagnetic field at the surface of the nanoparticles when excited at the plasmon resonance. Furthermore, the plasmon resonance is tunable over a wide wavelength range as a function of the size, shape, and composition of the nanoparticles. When these properties are combined with the known photocatalytic activity of noble metals for technologically important targets such as solar fuels, it is not surprising that these nanoparticle systems are widely studied. Noble metals do, however, possess a weakness in that they can be easily melted upon photoexcitation, due to the fact that noble metals dissipate absorbed photon energy efficiently through ultrafast electron-phonon coupling, in roughly one picosecond, to produce heat. As a result, the study of new classes of plasmonic materials, such as refractory metals, with much higher melting points than noble metals is growing rapidly. While there are still challenges in the size-selective synthesis of refractory metal nanoparticles, characterization efforts on these materials are of strong interest. We report here a study on the time-resolved spectroscopy of electron-phonon coupling in refractory metal nanoparticles. There are very significant variations in the efficiency and time-scales of electron-phonon coupling in refractory metal nanoparticles as compared to noble metal nanoparticles. Furthermore, due to the fact that many refractory metals are oxidized under ambient conditions to create a thin oxide layer on the surface of the nanoparticles, these materials also demonstrate dynamics related to electron injection from the metal to the oxide layer that noble metals do not show. Far from being a negative, the added electron injection dynamics offer new opportunities for photocatalysis that we discuss. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

(Invited) Photoelectrochemical Fabrication of Chiral Plasmonic Nanostructures By Circularly Polarized Light

Chiral plasmonic nanostructures attracts attention because they are potentially applicable to optical materials such as enantioselective sensors and metamaterials, as well as photoelectrochemical devices. Chiral nanostructures are often prepared by electron beam lithography or synthesis based on DNA templates. We have recently developed a photoelectrochemical method, in which handedness of the chiral nanostructure can be controlled by right- or left- circularly polarized light.The photoelectrochemical method is based on plasmon-induced charge separation (PICS),1,2 in which electrons are injected from a plasmonic metal nanoparticle to a semiconductor such as titania in direct contact. In PICS, anodic reactions often occur at the resonance sites of the plasmonic nanoparticle, at which electron oscillation is localized.3,4 Energetic electron-hole pairs generate at the resonance site, and holes are used for the local anodic reaction, probably via trap sites. On the basis of the mechanisms, we have demonstrated site-selective etching of silver nanoparticles and site-selective deposition of lead oxide on gold nanoparticles.Under right-circularly polarized light (CPL), distribution of the resonance sites could be the mirror image of that under left-CPL.5 Therefore, we performed site-selective deposition of lead oxide on gold nanocuboids on titania under right- or left-CPL.6 As a result, lead oxide was deposited on the gold nanocuboids in a chiral geometry. The nanostructures thus obtained exhibited circular dichroism (CD), and the CD spectrum obtained for the structure prepared under right-CPL was opposite to that obtained for the structure prepared under left-CPL. Reversible switching of the handedness of the chiral plasmonic nanostructures can also be possible.7 This method also allows us to fabricate spiral nanostructures. 1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005). 2. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review]. 3. I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012). 4. T. Tatsuma and H. Nishi, Nanoscale Horiz., 5, 597 (2020) [review]. 5. S. Hashiyada, T. Narushima, and H. Okamoto, J. Phys. Chem. C, 118, 22229 (2014). 6. K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018). 7. K. Morisawa, T. Ishida, and T. Tatsuma, ACS Nano, 14, 3603 (2020).

Plasmon Mediated Electron Transfer and Temperature Dependent Electron-Phonon Scattering in Gold Nanoparticles Embedded in Dielectric Films.

Excitation of localized surface plasmon resonance in metal nanoparticles (NPs) embedded in a glassy matrix generates hot electrons, which can be extracted for different optoelectronic applications. The insights of plasmon relaxation dynamics with varying surrounding dielectric environments and temperature dependence electron-phonon scattering process in gold (Au) NPs are still not very clear. Here, we have employed ultrafast transient absorption (TA) spectroscopy to explore the hot plasmon mediated electron transfer (PMET) and electron-phonon dynamics of photo-excited Au NPs in glassy film matrix with variable SiO2 /TiO2 compositions at cryogenic (5 K) to room temperature (300 K). Herein, we have chosen two pump excitation wavelengths (400 and 700 nm). The 400 nm excitation (d→sp) generates hot electron and the 700 nm excitation (sp→sp) provide information of direct plasmon relaxation. Drastic reduction of the transient signal of Au NPs in the high TiO2 content film as compared to pure SiO2 confirm hot electron transfer (HET) from Au plasmon to TiO2 . Electron-phonon scattering time constant (τe-ph ) of Au NPs in the glassy film is found to be faster in presence of TiO2 due to facile electron transfer/injection. Temperature dependent TA studies suggest that electron-phonon scattering time decreases with temperature. These findings would assist to develop more advanced photo-voltaic, opto-electronic and quantum optic-based devices using the plasmonic metal NPs.