Plasmon-driven Reactions Research Articles

Manipulating the surface-enhanced Raman spectroscopy (SERS) activity and plasmon-driven catalytic efficiency by the control of Ag NP/graphene layers under optical excitation

Abstract Highly efficient plasmon-driven catalysis and excellent surface-enhanced Raman spectroscopy (SERS) performance are proportional to the square of the local electromagnetic field (hot spot). However, a proven way to realize the enhancement in intensity and density of “hot spot” still needs to be investigated. Here, we report on multilayered Ag nanoparticle (Ag NP)/graphene coupled to an underlying Cu film system (MAgNP-CuF) which can be used as an effective SERS substrates realizing ultra-sensitive detection for toxic molecules and in situ monitoring the plasmon-driven reaction for p-nitrothiophenol (PNTP) to p,p′-dimercaptobenzene (DMAB) conversion. The mechanism of ultra-sensitive SERS response and catalytic reaction is investigated via Ag NP/graphene layer-dependent experiments combined with theoretical simulations. The research found that the intensity and density of “hot spot” can be effectively manipulated by the number of plasmonic layers, and the bottom Cu film could also reflect the scattered and excitation beam and would further enhance the Raman signals. Moreover, the MAgNP-CuF exhibits outstanding performance in stability and reproducibility. We believe that this concept of multilayered plasmonic structures would be widely used not only in the field of SERS but also in the wider research in photocatalysis.

Super-Resolution Mapping of a Chemical Reaction Driven by Plasmonic Near-Fields.

Plasmonic nanoparticles have recently emerged as promising photocatalysts for light-driven chemical conversions. Their illumination results in the generation of highly energetic charge carriers, elevated surface temperatures, and enhanced electromagnetic fields. Distinguishing between these often-overlapping processes is of paramount importance for the rational design of future plasmonic photocatalysts. However, the study of plasmon-driven chemical reactions is typically performed at the ensemble level and, therefore, is limited by the intrinsic heterogeneity of the catalysts. Here, we report an in situ single-particle study of a fluorogenic chemical reaction driven solely by plasmonic near-fields. Using super-resolution fluorescence microscopy, we map the position of individual product molecules with an ∼30 nm spatial resolution and demonstrate a clear correlation between the electric field distribution around individual nanoparticles and their super-resolved catalytic activity maps. Our results can be extended to systems with more complex electric field distributions, thereby guiding the design of future advanced photocatalysts.

Nanoscale structural characterization of plasmon-driven reactions

Abstract Illumination of noble metal nanostructures by electromagnetic radiation induces coherent oscillations of conductive electrons on their surfaces. These coherent oscillations of electrons, also known as localized surface plasmon resonances (LSPR), are the underlying physical cause of the electromagnetic enhancement of Raman scattering from analytes located in a close proximity to the metal surface. This physical phenomenon is broadly known as surface-enhanced Raman scattering (SERS). LSPR can decay via direct interband, phonon-assisted intraband, and geometry-assisted transitions forming hot carriers, highly energetic species that are responsible for a large variety of chemical transformations. This review critically discusses the most recent progress in mechanistic elucidation of hot carrier-driven chemistry and catalytic processes at the nanoscale. The review provides a brief description of tip-enhanced Raman spectroscopy (TERS), modern analytical technique that possesses single-molecule sensitivity and angstrom spatial resolution, showing the advantage of this technique for spatiotemporal characterization of plasmon-driven reactions. The review also discusses experimental and theoretical findings that reported novel plasmon-driven reactivity which can be used to catalyze redox, coupling, elimination and scissoring reactions. Lastly, the review discusses the impact of the most recently reported findings on both plasmonic catalysis and TERS imaging.

Challenges in Plasmonic Catalysis.

The use of nanoplasmonics to control light and heat close to the thermodynamic limit enables exciting opportunities in the field of plasmonic catalysis. The decay of plasmonic excitations creates highly nonequilibrium distributions of hot carriers that can initiate or catalyze reactions through both thermal and nonthermal pathways. In this Perspective, we present the current understanding in the field of plasmonic catalysis, capturing vibrant debates in the literature, and discuss future avenues of exploration to overcome critical bottlenecks. Our Perspective spans first-principles theory and computation of correlated and far-from-equilibrium light-matter interactions, synthesis of new nanoplasmonic hybrids, and new steady-state and ultrafast spectroscopic probes of interactions in plasmonic catalysis, recognizing the key contributions of each discipline in realizing the promise of plasmonic catalysis. We conclude with our vision for fundamental and technological advances in the field of plasmon-driven chemical reactions in the coming years.

Core–Shell Bimetallic Nanoparticle Trimers for Efficient Light-to-Chemical Energy Conversion

Incorporation of catalytically active materials into plasmonic metal nanostructures can efficiently merge the reactivity and energy harvesting abilities of both types of materials for visible light photocatalysis. Here we explore the influence of electromagnetic hotspots in the ability of plasmonic core-shell colloidal structures to induce chemical transformations. For this study, we developed a synthetic strategy for the fabrication of Au nanoparticle (NP) trimers in aqueous solution through fine controlled galvanic replacement between Ag nanoprisms and Au precursors. Core-shell Au@M NP trimers with catalytically active metals (M = Pd, Pt) were subsequently synthesized using Au NP trimers as templates. Our experimental and computational results highlight the synergy of geometry and composition in plasmonic catalysts for plasmon-driven chemical reactions.

Switching a Plasmon-Driven Reaction Mechanism from Charge Transfer to Adsorbate Electronic Excitation Using Surface Ligands

Understanding a photocatalytic reaction conditions that selectively leads to a desired product on metal surfaces is a longstanding research problem in heterogeneous catalysis. Here, using plasmon e...

Plasmon catalytic PATP coupling reaction on Ag-NPs/graphite studied via in situ electrochemical surface-enhanced Raman spectroscopy.

The p-aminothiophenol (PATP) coupling reaction on plasmon substrates such as Ag and Au nanoparticles has received extensive attention since the catalytic effect of the surface plasmon was found. Currently, in situ kinetic studies of this reaction are rare, especially those focusing on the specific role of the hot electron-hole carriers. Here, in situ electrochemical surface-enhanced Raman spectroscopy (SERS) is developed to study the plasmon catalytic reaction of PATP in a controlled aqueous environment involving the factors of O2, electron and hole carriers, and solution pH. Ag nanoparticles supported on graphite serve as a SERS substrate, which could separate hot electron-hole pairs effectively and is beneficial to study the effects of hot carriers on plasmon-driven reactions. In situ electrochemical SERS measurements reveal two reaction paths for the PATP coupling reaction. One is that plasmon-induced hot holes activate the dehydrogenation of PATP and then the radical coupling reaction to form p,p'-dimercaptoazobenzene (DMAB) under O2-free conditions. Another is likely to be that the surface Ag2O/AgOH, which is generated from Ag and 1O2/O2-, catalyzes the oxidation of PATP and then the coupling process under O2-rich conditions. Benefitting from the potential/atmosphere controlled measurements in situ, the intermediate species of PATP(NH)/PATP(N) are observed with vibrational bands at around 1056, 1202, 1253, 1395, 1514 and 1540 cm-1.

Plasmon-driven protodeboronation reactions in nanogaps.

Boronic acids are the key compounds in Suzuki coupling reactions and in the detection of monosaccharides. The C-B bond cleavage deboronation is an important side reaction that lowers the Suzuki coupling reaction yield and even disables saccharide detection. Here, we report that protodeboronation occurs for 4-mercaptophenylboronic acid (MPBA) within narrow nanogaps between gold nanoparticles (AuNPs) and planar gold substrates. The irradiation of such nanoparticle-on-mirror (NPoM) systems at 785 nm drives the protodeboronation reaction to form benzenethiol (BT). Wavelength-dependence experiments, combined with dark-field single-particle scattering spectroscopy, reveal that excitation of the bonding dipole plasmon mode of the NPoM leads to the best efficiency. Among the excited plasmon decay pathways, the generation of hot charge carriers induces the protodeboronation of MPBA. The possibility of plasmonic thermal reactions is ruled out because external heating of the substrates does not cause the reaction to take place. A comparison of the reaction yield under ambient, Ar, and oxygen gas conditions reveals that hot charge carriers directly transfer to MPBA, which subsequently produces BT, but the presence of oxygen promotes the reaction by opening another hot-electron transfer channel. The protodeboronation reaction of MPBA is an important addition to the catalog of plasmon-driven chemical reactions, not only because the reaction is relevant to organic and analytical chemistry but also because it deepens our understanding of the hot carrier dynamics at the interface between plasmonic nanoparticles and molecules.

Plasmon-Driven C–N Bond Cleavage Across a Series of Viologen Derivatives

The optical excitation of surface plasmons leads to the generation of highly enhanced nanoscale local fields and an abundance of harvestable hot carriers. When certain analytes are positioned within these unique environments, surface plasmons may be able to induce chemical reactions that are energetically unfavorable under standard conditions. Sometimes, the plasmonic environments can initiate entirely new reaction pathways for the chemical adsorbates. Here, we investigate the nature of plasmon-driven reactions on three viologen derivatives: methyl viologen, ethyl viologen, and benzyl viologen. Viologens have traditionally been employed as excellent redox agents due to their ability to reversibly stabilize additional electrons in their molecular structures. However, by using surface-enhanced Raman spectroscopy, we were able to directly observe a C–N bond cleavage on benzyl and ethyl viologen to form 4,4′-bipyridine on the surface of gold film-over-nanosphere substrates. Surprisingly, methyl viologen does ...

How Does a Plasmon-Induced Hot Charge Carrier Break a C-C Bond?

Hot-electron chemistry at gold nanoparticle (AuNP) surfaces has received much attention recently because its understanding provides a basis for plasmonic photocatalysis and photovoltaics. Nonradiative decay of excited surface plasmons produces energetic hot charge carriers that transfer to adsorbate molecules and induce chemical reactions. Such plasmon-driven reactions, however, have been limited to a few systems, notably the dimerization of 4-aminobenzenethiol to 4,4'-dimercaptoazobenzene. In this work, we explore a new class of plasmon-driven reactions associated with a unimolecular bond cleavage process. We unveil the mechanism of the decarboxylation reaction of 4-mercaptobenzoic acid and extend the mechanism to account for the β-cleavage reaction of 4-mercaptobenzyl alcohol. Combining the construction of well-controlled nanogap systems and sensitive Raman spectroscopy with methodical changes of experimental conditions (laser wavelengths, interface materials, pH, ambient gases, etc.), we track the hot charge carriers from the formation to the transfer to reactants, which provides insights into how plasmon excitation eventually leads to the C-C bond cleavage of the molecules in the nanogap.

Nano-scale image rendering via surface plasmon-driven reaction controlled by tip-enhanced Raman spectroscopy

Plasmon-driven selective oxidation reaction of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) can be realized in a local electromagnetic field (hot spot) because of surface plasmon resonance (SPR). To a remarkable extent, the size and movement of the hot spot can be freely controlled, via tip-enhanced Raman scattering (TERS) spectroscopy. In a particular TERS system, the hot spot can move by following the TERS tip, and the PATP molecules located in the trajectory of the TERS tip, but not in other areas, can be transformed into DMAB molecules. Through this feature, we can realize artificially drawn DMAB molecular graphics on a flat surface equably covered by PATP molecules at the micronano scale using TERS. We analyzed the range and effect of the instant hot spot according to the results of simulation using the finite-difference time-domain (FDTD) method for the TERS system and surface-enhanced Raman scattering (SERS) mapping. The selectivity and controllability of catalysis in the TERS system provides a new technique for marking, with this work contributing to the field of nanotechnology by providing a new method to obtain nanoscale patterns.

Plasmon-Driven Reaction Mechanisms: Hot Electron Transfer versus Plasmon-Pumped Adsorbate Excitation

Photochemistry that can be driven at low incident photon flux on optically excited plasmonic nanoparticles is attracting increasing research interest because of the fundamental need to combine surface reaction and in situ spectroscopy as well as the opportunity that plasmon-driven reactions may offer a pathway for efficient conversion of solar energy into fuel. In mechanistic studies of plasmon-driven reactions to date, a great deal of emphasis is given to hot electron transfer. The results summarized in this Feature Article indicate that photochemistry on plasmonic nanoparticles can be induced by hot electron transfer from the nanoparticle to an unoccupied orbital of the adsorbate and/or by plasmon-pumped electron transition from an occupied molecular orbital to an unoccupied molecular orbital of the adsorbate. The branching photochemical reaction of para-aminothiophenol on the plasmonic gold surface depending on the presence of a cetyltrimethylammonium bromide surface ligand that influences the hot elec...

Tuning the SERS activity and plasmon-driven reduction of p-nitrothiophenol on a Ag@MoS2 film.

The combination of plasmonic metal nanostructures with semiconductors has been widely applied in plasmon-driven photocatalysis. Here, a uniform Ag@MoS2 hybrid film is fabricated by depositing MoS2 onto a thin Ag film via the pulsed laser deposition (PLD) technique. The thickness and crystallinity of MoS2 can be adjusted by controlling the PLD deposition time and temperature, respectively. With the assistance of surface-enhanced Raman scattering (SERS) analysis, the Raman enhancement uniformity of the substrate and plasmon-driven reaction of p-nitrothiophenol (PNTP) dimerizing into p,p'-dimercaptobenzene (DMAB) are carefully studied on Ag@MoS2 film substrates with different MoS2 crystallinities. The Raman enhancement decreases with increased MoS2 thickness, due to the weakened electromagnetic field enhancement as suggested by finite-difference time-domain (FDTD) simulations. The increased crystallinity of MoS2 can efficiently accelerate the hot electron transfer process, resulting in the enhancement of SERS activity and the improved efficiency of the plasmon-driven reaction. This study may pave the way for the design of other uniform metal-semiconductor hybrids for use as SERS substrates and photocatalysts.

Au Tip-Enhanced Raman Spectroscopy for Catalysis

Plasmon-driven chemical reactions have been a prospective field for surface plasmon resonance and tip-enhanced Raman scattering. In this review, the principles of tip-enhanced Raman spectroscopy (TERS) are first introduced. Following this, the use of Au TERS for plasmon-driven synthesis catalysis is introduced. Finally, the use of Au TERS for catalysis of dissociation reactions is discussed. This review can provide a deeper understanding of Au TERS for plasmon-driven catalysis.

SERS‐Based Plasmon‐Driven Reaction and Molecule Detection on a Single Ag@MoS2 Microsphere: Effect of Thickness and Crystallinity of MoS2

AbstractPlasmon‐driven catalysis on a single particle has attracted great attention in recent years, while the relationship between reaction efficiency and substrate remains to be deeply studied. Here, we demonstrate the fabrication of a novel Ag@MoS2 core‐shell single particle SERS substrate by coating MoS2 film on Ag microspheres through the pulsed laser deposition (PLD) technique, where the thickness and crystallinity of MoS2 can be effectively controlled by the PLD time and temperature. It is revealed that both the thickness and crystallinity of MoS2 can greatly influence the hot electron transfer process, and thus the plasmon‐driven reaction (4‐NTP into DMAB) efficiency and Raman enhancement of dye molecules on Ag@MoS2 substrates. Generally, high crystallinity and thin thickness of MoS2 can lead to accelerated plasmon‐driven reaction efficiency and greatly enhanced Raman signals of target molecules. This study opens up a new avenue for broadening the research area of the plasmon‐driven catalysis and Raman enhancement on the hybrid system of two‐dimensional materials and metal nanostructures.

Principle and Application of Tip-enhanced Raman Scattering

Tip-enhanced Raman scattering (TERS), as a combination of scanning probe microscopy (SPM) and surface-enhanced Raman spectroscopy (SERS) makes a huge progress in high sensitive optical and spectral analysis field by plasmon and plasmonic gradient enhancement. We introduce the mechanisms and setup of TERS with several experimental cases. Among them, high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) is introduced in detail by describing the plasmon-driven reactions.

Plasmon-Driven Diazo Coupling Reactions of p-Nitroaniline via −NH2 or −NO2 in Atmosphere Environment

Plasmon-driven diazo coupling reaction of p-nitroaniline (PNA), containing both an amine group (−NH2) and a nitro group (−NO2), in ambient atmosphere environments remains unknown in experiments, on both metal nanoparticles and graphene-mediated metal nanostructures. Using the surface-enhanced Raman scattering (SERS) technique, we presented the surface coupling reactions of PNA under atmospheric environment, adsorbed on the Ag nanoparticle (AgNP) arrays, graphene-coated Ag nanoparticle (G/AgNPs) hybrids, and graphene-covered Ag nanowire (G/AgNW) composites, respectively. It was found that PNAs were converted into 4,4′-diaminoazobenzene (DAAB) through a selective reduction reaction, rather than oxidized into 4,4′-dinitroazobenzene (DNAB). These results may be useful for understanding the reaction mechanism for plasmon-driven chemical reactions of the molecules containing both amine groups and nitro groups under ambient conditions.

Ultrafast Dynamics of Plasmon-Exciton Interaction of Ag Nanowire- Graphene Hybrids for Surface Catalytic Reactions.

Using the ultrafast pump-probe transient absorption spectroscopy, the femtosecond-resolved plasmon-exciton interaction of graphene-Ag nanowire hybrids is experimentally investigated, in the VIS-NIR region. The plasmonic lifetime of Ag nanowire is about 150 ± 7 femtosecond (fs). For a single layer of graphene, the fast dynamic process at 275 ± 77 fs is due to the excitation of graphene excitons, and the slow process at 1.4 ± 0.3 picosecond (ps) is due to the plasmonic hot electron interaction with phonons of graphene. For the graphene-Ag nanowire hybrids, the time scale of the plasmon-induced hot electron transferring to graphene is 534 ± 108 fs, and the metal plasmon enhanced graphene plasmon is about 3.2 ± 0.8 ps in the VIS region. The graphene-Ag nanowire hybrids can be used for plasmon-driven chemical reactions. This graphene-mediated surface-enhanced Raman scattering substrate significantly increases the probability and efficiency of surface catalytic reactions co-driven by graphene-Ag nanowire hybridization, in comparison with reactions individually driven by monolayer graphene or single Ag nanowire. This implies that the graphene-Ag nanowire hybrids can not only lead to a significant accumulation of high-density hot electrons, but also significantly increase the plasmon-to-electron conversion efficiency, due to strong plasmon-exciton coupling.

Plasmon-driven reaction controlled by the number of graphene layers and localized surface plasmon distribution during optical excitation

Graphene-plasmonic hybrid platforms have attracted an enormous amount of interest in surface-enhanced Raman scattering (SERS); however, the mechanism of employing graphene is still ambiguous, so clarification about the complex interaction among molecules, graphene, and plasmon processes is urgently needed. We report that the number of graphene layers controlled the plasmon-driven, surface-catalyzed reaction that converts para-aminothiophenol (PATP)-to-p,p′-dimercaptoazobenzene (DMAB) on chemically inert, graphene-coated, silver bowtie nanoantenna arrays. The catalytic reaction was monitored by SERS, which revealed that the catalytic reaction occurred on the chemical inertness monolayer graphene (1G)-coated silver nanostructures. The introduction of 1G enhances the plasmon-driven surface-catalyzed reaction of the conversion of PATP-to-p,p′-DMAB. The chemical reaction is suppressed by bilayer graphene. In the process of the catalytic reaction, the electron transfer from the PATP molecule to 1G-coated silver nanostructures. Subsequently, the transferred electrons on the graphene recombine with the hot-hole produced by the localized surface plasmon resonance of silver nanostructures. Then, a couple of PATP molecules lost electrons are catalyzed into the p,p′-DMAB molecule on the graphene surface. The experimental results were further supported by the finite-difference time-domain method and quantum chemical calculations. The introduction of a graphene coating on metal nanostructures can help control the efficiency of plasmon-driven chemical reactions. Xiang-heng Xiao and co-workers from China used an array of silver bowtie nanoantennas to perform a surface-enhanced photocatalytic reaction and convert para-aminothiophenol (PATP) into p,p′-dimercaptoazobenzene under optical excitation. The conversion was enhanced when the nanoantennas were coated with monolayer graphene, whereas it was suppressed when they were coated with bilayer graphene. The reaction was monitored in situ by capturing and analysing surface-enhanced Raman spectra. The enhanced reaction rate is thought to stem from the efficient transport of electrons from the PATP molecules to the nanoantennas coated with monolayer graphene and their subsequent recombination with hot-holes. Quantum chemical calculations and finite-difference time-domain modelling confirmed this scenario.

PH-Dependent plasmonic catalysis of 4-nitrobenzenethiol in aqueous environment

Plasmon-driven chemical reaction of 4-nitrobenzenethiol (4-NBT) dimerizing to p,p′-dimercaptoazobenzene (DMAB) has been successfully monitored under different pH solutions. The experimental results indicated that the chemical reactions were dependent on the pH values, and they proceeded more completely under acidic conditions than those under neutral and alkaline conditions. Furthermore, the rate of the chemical reactions was effectively controlled by exposure time and incident laser power. The stable pH dependence demonstrated the plasmon-driven chemical reactions of 4-NBT to DMAB are sensitive to the surrounding environment, and have wider applications.