Plasmon-driven Catalysis Research Articles

Role of Plasmonic Antenna in Hot Carrier-Driven Reactions on Bimetallic Nanostructures.

Noble metal nanostructures can efficiently harvest electromagnetic radiation, which, in turn, is used to generate localized surface plasmon resonances. Surface plasmons decay, producing hot carriers, that is, short-lived species that can trigger chemical reactions on metallic surfaces. However, noble metal nanostructures catalyze only a very small number of chemical reactions. This limitation can be overcome by coupling such nanostructures with catalytic-active metals. Although the role of such catalytically active metals in plasmon-driven catalysis is well-understood, the mechanistics of a noble metal antenna in such chemistry remains unclear. In this study, we utilize tip-enhanced Raman spectroscopy, an innovative nanoscale imaging technique, to investigate the rates and yields of plasmon-driven reactions on mono- and bimetallic gold- and silver-based nanostructures. We found that silver nanoplates (AgNPs) demonstrate a significantly higher yield of 4-nitrobenzenehtiol to p,p'-dimercaptoazobisbenzene (DMAB) reduction than gold nanoplates (AuNPs). We also observed substantially greater yields of DMAB on silver-platinum and silver-palladium nanoplates (Ag@PtNPs and Ag@PdNPs) compared to their gold analogues, Au@PtNPs and Au@PdNPs. Furthermore, Ag@PtNPs exhibited enhanced reactivity in 4-mercatophenylmethanol to 4-mercaptobenzoic acid oxidation compared to Au@PtNPs. These results showed that silver-based bimetallic nanostructures feature much greater reactivity compared to their gold-based analogues.

(Invited) Ultrafast Reducing Power of a Plasmonic Photocatalyst

Plasmonic nanomaterials are promising catalysts for selective, green, and efficient photo-driven processes, however currently the mechanisms involved in plasmon-driven catalysis are under debate. Contributions from processes such as vibrational and electronic energy transfer, electron transfer, or electromagnetic field enhancement could all lead to modified potential energy landscapes in the plasmon-molecule system. We have developed ultrafast and electrochemical surface-enhanced Raman spectroscopic (SERS) techniques to probe the contribution of these processes on the nanometer length scale and femtosecond timescale. This talk will highlight the use of these approaches in quantifying the rate, yield, and lifetime of plasmon-to-molecule charge transfer. We monitor changes in the vibrational spectra of adsorbed molecular species following plasmon excitation with picosecond time resolution, and quantify how many molecules are reduced and how quickly they undergo back electron transfer. Overall, these methods allow for quantification of the ultrafast reducing power of a plasmonic surface, and suggest routes for optimizing plasmonic systems for efficient and selective photochemistry.

Plasmonic Hot-Electron-Painted Au@Pt Nanoparticles as Efficient Electrocatalysts for Detection of H2O2.

Plasmon-driven catalysis of metal nanostructures has garnered wide interest. Here, a photogenerated plasmonic hot-electron painting strategy was reported to form Au@Pt composite nanoparticles (Au@Pt NPs) with high catalytic reactivity without using reducing agents. Au nanoparticles, including Au nanospheres (Au NSs), Au nanorods (Au NRs), and Au nanobipyramids (Au NBPs), generated hot electrons under localized surface plasmon resonance (LSPR) excitation, which made the platinum precursor reduced as a consequence that Pt(0) atoms were painted on the surface of Au NPs to form an asymmetric Pt shell outside the plasmonic Au core. Compared with bare Au NPs, Au@Pt NPs exhibited significantly enhanced electrocatalytic activity toward reduction of H2O2 due to the bimetallic synergistic effect and great dispersion of Au@Pt NP-modified indium tin oxide (Au@Pt NPs/ITO). It exhibited a linear detection of H2O2 in a wide concentration range from 0.5 to 1000 μM with a low detection limit of 0.11 μM (S/N = 3). Therefore, the plasmonic hot-electron-painted Au@Pt NPs represent a novel and simple method for the design of advanced noble asymmetric metal nanomaterials.

Highly ordered arrays of hat-shaped hierarchical nanostructures with different curvatures for sensitive SERS and plasmon-driven catalysis

Abstract Regulation of hot spots exhibits excellent potential in many applications including nanolasers, energy harvesting, sensing, and subwavelength imaging. Here, hat-shaped hierarchical nanostructures with different space curvatures have been proposed to enhance hot spots for facilitating surface-enhanced Raman scattering (SERS) and plasmon-driven catalysis applications. These novel nanostructures comprise two layers of metal nanoparticles separated by hat-shaped MoS2 films. The fabrication of this hybrid structure is based on the thermal annealing and thermal evaporation of self-assembled polystyrene spheres, which are convenient to control the metal particle size and the curvature of hat-shaped nanostructures. Based on the narrow gaps produced by the MoS2 films and the curvature of space, the constructed platform exhibits superior SERS capability and achieves ultrasensitive detection for toxic molecules. Furthermore, the surface catalytic conversion of p-nitrothiophenol (PNTP) to p, p′-dimercaptobenzene (DMAB) was in situ monitored by the SERS substrate. The mechanism governing this regulation of hot spots is also investigated via theoretical simulations.

Plasmon-Driven Catalytic Chemotherapy Augments Cancer Immunotherapy through Induction of Immunogenic Cell Death and Blockage of IDO Pathway.

Clinical trials confirm the combination of indoleamine 2,3-dioxygenase (IDO) blockade and immunogenic chemotherapy represents a brilliant future in cancer therapy. However, it remains challenging to precisely activate chemo-immunotherapy in situ to avoid side effects from the systemic administrations and reverse the poor immunogenicity and immunosuppressive microenvironment in tumor sites. Herein, a hybrid nanomedicine ("RPMANB NPs") to co-deliver an IDO inhibitor (NLG919) and a chemotherapeutic prodrug to amplify the therapeutic benefits are designed. Attributed to the delicate surface engineering, the RPMANB NPs possess excellent pharmacokinetics and tumor accumulation. The loaded NLG919 are released inside cancer tissues/cells due to the collapse of the metal-organic framework platform triggered by the highly concentrated phosphate, reversing the immunosuppressive tumor microenvironment by suppressing IDO activity. The potent chemotherapeutic drug is precisely activated through a highly efficient plasmon-driven catalysis in the presence of near-infrared light, eliciting antitumor immunity by triggering immunogenic cell death and avoiding side effects through in situ activation of chemotherapy. In vivo studies demonstrate that the chemo-immunotherapy greatly suppresses the tumor growth by promoting intratumoral accumulation of cytotoxic T lymphocytes and downregulating regulatory T cells. This work establishes a robust delivery platform to overcome the current obstacles of tumor treatments by combining precisely activatable chemotherapy with immunotherapy.

Plasmon-Driven Chemistry on Mono- and Bimetallic Nanostructures.

ConspectusHot carriers are highly energetic species that can perform a large spectrum of chemical reactions. They are generated on the surfaces of nanostructures via direct interband, phonon-assisted intraband, and geometry-assisted decay of localized surface plasmon resonances (LSPRs), which are coherent oscillations of conductive electrons. LSPRs can be induced on the surface of noble metal (Ag or Au) nanostructures by illuminating the surfaces with electromagnetic irradiation. These noble metals can be coupled with catalytic metals, such as Pt, Pd, and Ru, to develop bimetallic nanostructures with unique catalytic activities. The plasmon-driven catalysis on bimetallic nanostructures is light-driven, which essentially enables green chemistry in organic synthesis. During the past decade, surface-enhanced Raman spectroscopy (SERS) has been actively utilized to study the mechanisms of plasmon-driven reactions on mono- and bimetallic nanostructures. SERS has provided a wealth of knowledge about the mechanisms of numerous plasmon-driven redox, coupling, and scissoring reactions. However, the nanoscale catalytic properties of both mono- and bimetallic nanostructures as well as the underlying physical cause of their catalytic reactivity and selectivity remained unclear for decades.In this Account, we focus on the most recent findings reported by our and other research groups that shed light on the nanoscale properties of mono- and bimetallic nanostructures. This information was revealed by tip-enhanced Raman spectroscopy (TERS), a modern analytical technique that has single-molecule sensitivity and subnanometer spatial resolution. TERS findings have shown that plasmonic reactivity and the selectivity of bimetallic nanostructures are governed by the nature of the catalytic metal and the strength of the rectified electric field on their surfaces. TERS has also revealed that the catalytic properties of bimetallic nanostructures directly depend on the interplay between the catalytic and plasmonic metals. We anticipate that these findings will be used to tailor synthetic approaches that are used to fabricate novel nanostructures with desired catalytic properties. The experimental and theoretical results discussed in this Account will facilitate a better understanding of TERS and explain artifacts that could be encountered upon TERS imaging of a large variety of samples. Consequently, plasmon-driven chemistry should be considered as an essential part of near-field microscopy.

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.

The influence of oxygen content on the borrowing SERS activity of tin oxides/noble metal composites

Surface enhanced Raman spectroscopy (SERS), as a powerful tool that its sensitive to detect organics hazardous pollutants and analyze the plasmon-driven catalysis reaction with its fingerprint characteristics. And the SERS property of substrate can be effectively enhanced with charge-transferring between the substrate and analyte by utilizing the borrowing SERS activity strategy. Considering the transition metal elements represent multiple valence states, the synergistic interaction of noble metal/transition metal oxides heterostructures can be further modulated with oxygen contents variation of transition metal oxides. In this work, we report the fabrication of high specific area Sn3O4 hollow hierarchical nanostructures with a simple hydrothermal method, which have mixed-valence of Sn2+ and Sn4+. And the composites were prepared with Au coating and the SERS properties of the nanostructures were investigated by detection of rhodamine 6G. The effect of the oxygen content of the transition metal oxides on their SERS performance was analyzed with annealing process. It was found that a high oxygen atomic ratio induced by heat treatment increased the SERS effect of the Au-coated nanostructures for R6G molecules. This property may prove to be very useful in the future research on the borrowing SERS activity of composites of noble metals and metal oxides.

Enhancing Catalytic Activity and Selectivity by Plasmon-Induced Hot Carriers.

SummaryPlasmon-assisted chemical transformation holds great potential for solar energy conversion. However, simultaneous enhancement of reactivity and selectivity is still challenging and the mechanism remains mysterious. Herein, we elucidate the localized surface plasmon resonance (LSPR)-induced principles underlying the enhanced activity (∼70%) and selectivity of photoelectrocatalytic redox of nitrobenzene (NB) on Au nanoparticles. Hot carriers selectively accelerate the conversion rate from NB to phenylhydroxylamine (PHA) by ∼14% but suppress the transformation rate from PHA to nitrosobenzene (NSB) by ∼13%. By adding an electron accepter, the as-observed suppression ratio is substantially enlarged up to 43%. Our experiments, supported by in situ surface-enhanced Raman spectroscopy and density functional theory simulations, reveal such particular hot-carrier-induced selectivity is conjointly contributed by the accelerated hot electron transfer and the corresponding residual hot holes. This work will help expand the applications of renewable sunlight in the directional production of value-added chemicals under mild conditions.

Confirming nonthermal plasmonic effects enhance CO2 methanation on Rh/TiO2 catalysts

In some cases, illumination of traditional thermal catalysts and tailored plasmonic photocatalysts may synergistically combine thermal and nonthermal mechanisms to enhance reaction rates and improve product selectivity at reduced temperatures. To understand how these attributes are achieved in plasmon-driven catalysis, these intertwined thermal and nonthermal effects must be untangled. Here, we show how a novel indirect illumination technique, in conjunction with precisely monitored thermal profiles of the catalyst, can confirm and clarify the role of nonthermal effects in plasmon-enhanced carbon dioxide methanation on a Rh/TiO2 photocatalyst. We find that the extracted nonthermal methane production rate has a linear dependence on the top surface temperature, distinctly different from an exponential dependence for thermal catalysis. We also find that the apparent quantum efficiency from the nonthermal contribution has no dependence on light intensity but maintains a linear dependence on top surface temperatures between 200 and 350 °C. The clear exposition of nonthermal effects in the Rh/TiO2 plasmonic photocatalyst illustrates how this methodology may be applied for the quantitative evaluation of thermal and nonthermal light effects in other plasmon-enhanced catalytic reactions. Open image in new window

Plasmon-driven catalysis of adsorbed p-nitroaniline (PNA) by surface-enhanced Raman scattering (SERS): Platinum versus silver

The adsorption of p-nitroaniline (PNA) on Pt nanoparticles, both in the absence (in aqueous solution) and in the presence of oxygen (in air environment), is studied by SERS for the first time. Differences between the plasmon-driven catalysis of adsorbed PNA on Pt and Ag nanoparticles have been found. In the presence of oxygen, the oxidative coupling of the NH2 group in PNA to yield dinitroazobenzene (DNAB) occurs on both Pt and Ag nanoparticles. However, in the absence of oxygen, PNA behaves clearly differently on Ag than on Pt. Thus, whereas diaminoazobenzene (DAAB) is catalytically produced on Ag nanoparticles by plasmon-driven reduction reactions of the NO2 group, on Pt nanoparticles this reaction does not fully take place as indicated by the presence of NO2 groups on the surface of the nanoparticles. A mechanism for this distinctive behavior is tentatively proposed in which water acts as a sacrificial agent, being reduced to hydrogen by hot electrons coming from the Pt surface, while the hot holes on Pt are proposed to attach to an occupied molecular state of adsorbed PNA. The overall photocatalytic reaction of adsorbed PNA on Pt nanoparticles, in an O2 free solution, would actually be consistent with a dehydrogenation process of water.

Effect of Silica Supports on Plasmonic Heating of Molecular Adsorbates as Measured by Ultrafast Surface-Enhanced Raman Thermometry.

Plasmonic materials show great potential for selective photocatalysis under relatively mild reaction conditions. However, the catalytic activity of these plasmonic catalysts can also depend upon the support material that stabilizes the catalysts, where the composition of the catalytic support may change the overall photocatalytic efficiency and yield. It is unknown how changes in the support material may change the plasmon-driven photocatalysis, which may be initiated by plasmon-derived hot carriers, localized heating, or enhanced electromagnetic fields. Herein, we probe the effects of catalytic supports on heating in plasmon-driven catalysis by examining various gold nanoparticle oxide systems. We use ultrafast surface-enhanced Raman thermometry to measure the effective temperature, equivalent to the vibrational kinetic energy, of reporter molecules located between plasmonic gold nanostructures and local environments ranging from ligands to mesoporous silica shells to silica shells. Upon photoexcitation, the transient effective temperature, equivalent to the energy deposited into a vibrational mode, of adsorbed molecules on the silica-coated samples increases, and the energy quickly dissipates within 3 ps. However, the baseline effective temperature that arises from the surface-enhanced Raman spectroscopy probing process depends upon the encapsulant, where the energy deposition differs by 200-300 K between the ligand-coated (citrate or CTAB) and the silica-coated samples. Adsorbates surrounded by a silica shell experience significantly higher effective temperatures than the adsorbates surrounded by ligands or solvent, likely because of the differing effective heat capacities of these media. Taken together, this work shows that a silica support impacts the localized heating of molecular adsorbates on the gold surface and may play a role in enhanced plasmonic photocatalysis because of increased thermal contributions.

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.

Tin Oxide Nanowires Decorated with Ag Nanoparticles for Visible Light-Enhanced Hydrogen Sensing at Room Temperature: Bridging Conductometric Gas Sensing and Plasmon-Driven Catalysis

We demonstrate that conductometric gas sensing at room temperature with SnO2 nanowires (NWs) is enhanced by visible and supraband gap UV irradiation when and only when the metal oxide NWs are decorated with Ag nanoparticles (NPs) (diameter < 20 nm); no enhancement is observed for the bare SnO2 case. We combine the spectroscopic techniques with conductometric gas sensing to study the wavelength dependency of the sensors’ response, showing a strict correlation between the Ag-loaded SnO2 optical absorption and its gas response as a function of irradiation wavelength. Our results lead to the hypothesis that the enhanced gas response under UV–vis light is the effect of plasmonic hot electrons populating the Ag NPs surface. Finally, we discuss the chemiresistive properties of Ag-loaded SnO2 sensor in parallel with the theory of plasmon-driven catalysis, to propose an interpretative framework that is coherent with the established paradigma of these two separated fields of study.

Utilizing light-triggered plasmon-driven catalysis reactions as a template for molecular delivery and release.

Due to the facile manipulation and non-invasive nature of light-triggered release, it is one of the most potent ways to selectively and remotely deliver a molecular target. Among the various carrier platforms, plasmonic nanoparticles possess advantages such as enhanced cellular uptake and easy loading of "cargo" molecules. Two general strategies are currently utilized to achieve light-induced molecule release from plasmonic nanoparticles. The first uses femtosecond laser pulses to directly break the bond between the nanoparticle and the loaded target. The other requires significant photo-thermal effects to weaken the interaction between the cargo molecules and nanoparticle-attached host molecules. Different from above mechanisms, herein, we introduce a new light-controlled molecular-release method by taking advantage of a plasmon-driven catalytic reaction at the particle surface. In this strategy, we link the target to a plasmon responsive molecule, 4-aminobenzenethiol (4-ABT), through the robust and simple EDC coupling reaction and subsequently load the complex onto the particles via the strong Au-thiol interaction. Upon continuous-wave (CW) laser illumination, the excited surface plasmon catalyzes the formation of 4,4'-dimercaptoazobenzenethiol (DMAB) and simultaneously releases the loaded molecules with high efficiency. This method does not require the use of high-power pulsed lasers, nor does it rely on photo-thermal effects. We believe that plasmon-driven release strategies open a new direction for the designing of next-generation light-triggered release processes.

Selective plasmon-driven catalysis for para-nitroaniline in aqueous environments.

The plasmon-driven oxidation of amine (−NH2) groups and the reduction of nitro (−NO2) groups on a nanostructured metal surface in an aqueous environment have been reported experimentally and theoretically. The question of which process occurs first in the aqueous environment is an interesting question in the field of plasmon-related photochemistry. Para-nitroaniline (PNA), with both nitro (−NO2) and amine (−NH2) groups, is the best candidate for studying the priority of the plasmon-driven oxidation and the reduction reactions in an aqueous environment. Using surface-enhanced Raman scattering (SERS) spectroscopy, our experimental results and theoretical simulations reveal that PNA is selectively catalyzed to 4,4′-diaminoazobenzene (DAAB) through the plasmon-assisted dimerization of the nitro (−NO2) group into an azo group in an aqueous environment. This indicates that the plasmon-driven reduction of the nitro (−NO2) group clearly occurs before the oxidation of the amine (−NH2) group in an aqueous environment. The plasmon-driven reduction of PNA to DAAB is a selective surface catalytic reduced reaction in aqueous environment.