Article Cite This: Acc. Chem. Res. XXXX, XXX, XXX−XXX
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Plasmon-Driven Catalysis on Molecules and Nanomaterials Published as part of the Accounts of Chemical Research special issue “Nanochemistry for Plasmonics and Plasmonics for Nanochemistry”. Zhenglong Zhang,†,§ Chengyun Zhang,†,§ Hairong Zheng,† and Hongxing Xu*,‡ †
School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062, China School of Physics and Technology, Wuhan University, Wuhan 430072, China
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CONSPECTUS: As a new class of photocatalysts, plasmonic noble metal nanoparticles with the unique ability to harvest solar energy across the entire visible spectrum and produce effective energy conversion have been explored as a promising pathway for the energy crisis. The resonant excitation of surface plasmon resonance allows the nanoparticles to collect the energy of photons to form a highly enhanced electromagnetic field, and the energy stored in the plasmonic field can induce hot carriers in the metal. The hot electron−hole pairs ultimately dissipate by coupling to phonon modes of the metal nanoparticles, resulting in a higher lattice temperature. The plasmonic electromagnetic field, hot electrons, and heat can catalyze chemical reactions of reactants near the surface of the plasmonic metal nanoparticles. This Account summarizes recent theoretical and experimental advances on the excitation mechanisms and energy transfer pathways in the plasmonic catalysis on molecules. Especially, current advances on plasmon-driven crystal growth and transformation of nanomaterials are introduced. The efficiency of the chemical reaction can be dramatically increased by the plasmonic electromagnetic field because of its higher density of photons. Similar to traditional photocatalysis, energy overlap between the plasmonic field and the HOMO− LUMO gap of the reactant is needed to realize resonant energy transfer. For hot-carrier-driven catalysis, hot electrons generated by plasmon decay can be transferred to the reactant through the indirect electron transfer or direct electron excitation process. For this mechanism, the energy of hot electrons needs to overlap with the unoccupied orbitals of the reactant, and the particular chemical channel can be selectively enhanced by controlling the energy distribution of hot electrons. In addition, the local thermal effect following plasmon decay offers an opportunity to facilitate chemical reactions at room temperature. Importantly, surface plasmons can not only catalyze chemical reactions of molecules but also induce crystal growth and transformation of nanomaterials. As a new development in plasmonic catalysis, plasmon-driven crystal transformation reveals a more powerful aspect of the catalysis effect, which opens the new field of plasmonic catalysis. We believe that this Account will promote clear understanding of plasmonic catalysis on both molecules and materials and contribute to the design of highly tunable catalytic systems to realize crystal transformations that are essential to achieve efficient solar-to-chemical energy conversion.
1. INTRODUCTION With the aggregation of the energy crisis and current pollution, the effective use of clean and renewable energy is becoming a global challenge. As a promising alternative to conventional fossil fuels, solar energy is extremely important for driving industrial chemical transformations.1 Semiconductor photocatalysts that rely on the interband excitation of electrons have received considerable attention in the field of solar energy conversion and utilization.2−4 However, this is confined to ultraviolet light conversion because of their wide band gaps, and the visible and near-infrared photons with less energy than the band gap are wasted.5 Noble metal nanoparticles (NPs) have been explored as a promising new class of photocatalysts that benefit from their efficient solar energy harvesting across the entire visible spectrum through the excitation of surface plasmons (Figure 1a).1,6 Incorporating plasmonic metal NPs, whose localized surface plasmon resonance (LSPR) is © XXXX American Chemical Society
controllable by tuning their size, shape, material, and surrounding medium, to mediate photocatalytic reactions provides an opportunity to greatly improve the efficiency of solar energy conversion (Figure 1b).7−11 The LSPR excitation of metal NPs produces enhanced light−matter interaction, resulting in a strongly enhanced plasmonic (EM) field on the surface of the NP (Figure 1c).7,12 The oscillation of free electrons quickly decays via excitation of energetic electron−hole pairs (Figure 1d,e).13,14 These initially excited electrons rapidly thermalize and equilibrate via electron−electron scattering, creating a “hot” Fermi−Dirac distribution.14 Then the hot distribution cools via the coupling between the “hot electrons” and the phonons of the metal lattice, which elevates the lattice temperature.15 Plasmon Received: April 30, 2019
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HOMO−LUMO gap of the reactant molecule is needed to realize resonant energy transfer.19 This energy transfer forces the atoms of the molecule to reconfigure to accommodate the potential energy surface, which shows that the molecule evolves along the excited potential energy surface. The evolution ends with chemical reaction in the excited state or decays back down to the ground state with additional vibrational energy, which lowers the reaction barrier (Figure 2a).1 With the same excitation pathway as plasmonic-field-driven catalysis, a direct intramolecular excitation mechanism is proposed (Figure 2b),20−22 in which a plasmon with the same energy as the HOMO−LUMO gap of the adsorbed molecules is used to resonantly excite the direct transition of the molecule to its excited state. For the molecule−Cu/Ag system, the strong hybridization between the molecular orbitals and metal reduces the energy gap of the molecule from the ultraviolet region into the visible-light region, thus providing novel excitation pathways with lower-energy photons. Additionally, the formed LUMO-derived molecular orbitals overlap less with the metal substrate, resulting in longer excited-state lifetimes. Moreover, the LSPR-driven demethylation reaction that transforms methylene blue (MB) to thionine is also attributed to plasmon-enhanced HOMO− LUMO electronic excitation.23 Assisted by the plasmonic field, photocatalytic water splitting can be enhanced up to 66-fold under visible-light illumination (Figure 2c).24 The enhanced local plasmonic field increases the rate of generation of electron−hole pairs at the surface of the TiO2, which contributes to the photocatalytic activity. Similarly, with the assistance of the confined plasmonic field, the efficiency of decomposition of MB on the surface of TiO2 is enhanced by a factor of 7 (Figure 2d).25 The LSPR effect of Ag NPs dramatically enhanced the photon density in the nearUV region, which overlaps the band gap of TiO2. Then more electron−hole pairs are excited in TiO2 to improve its photocatalytic activity. Heterometallic antenna reactor complexes such as the Mo-doped Au system have been reported by the Carter group, who found that the catalytic properties of the catalyst could also be facilitated by amplified resonant energy transfer due to the enhanced plasmonic field.9,18
Figure 1. Surface plasmon excitation (a−c) and decay (d, e). (a) Density of states of a plasmonic metal and the photoexcitation of intraband s-to-s and interband d-to-s transitions. (b) Absorption spectrum of plasmonic metals. (c) EM-field-induced coherent oscillation of electrons, resulting in a highly elevated plasmonic (EM) field at the surface of the NP. (d) Sketches of the photoexcitation and subsequent relaxation processes of the LSPR. (e) Time evolution and energy distribution of hot carriers generated from plasmon decay. EF is the Fermi energy, and the gray shading indicates filled electronic states. Adapted with permission from (a) ref 1, (b, c) ref 16, (d) ref 14, and (e) ref 13. Copyright 2018 Nature Publishing Group, 2017 American Chemical Society, and 2015 Nature Publishing Group, respectively.
excitation and decay provide ways to manipulate light absorption with nanometer-scale precision on subfemtosecond time scales, enabling new levels of control of chemical transformations. Although plasmonic catalysis on molecules has been widely reported, the excitation mechanism and energy transfer pathway are still controversial. Meanwhile, catalysis on nanomaterials is less reported. This Account focuses on the mechanism of plasmonic catalysis and comments on future directions in the field. First, we discuss the excitation mechanisms in plasmonic catalysis on molecules, including the confined plasmonic field, hot carrier excitation, and local heat generation. This is followed by a discussion of plasmonic catalysis on inorganic nanomaterials for both nanomaterial growth and crystal transformation. We conclude by providing our perspective on the current state of the field and opportunities for further advancements.
2.2. Hot-Carrier-Driven Catalysis
Plasmon-mediated hot carriers can be transferred to the molecules through a transient electronic exchange between the metal and reactant (Figure 3a−c).16 With electronic exchange, transient negative ions (molecules with the addition of highenergy electrons) are created and survive on the metal surface for tens of femtoseconds, which is sufficient to induce a chemical reaction or add vibrational energy to the molecule.14 For this mechanism, the energy of hot electrons and holes needs to overlap with the unoccupied orbitals of molecules, and the particular chemical channel can be selectively enhanced by controlling the energy distribution of hot carriers. 2.2.1. Catalysis Mediated by Indirect Electron Transfer. As a result of energy exchange between an EM wave and electrons in the metal, the collective mode of electron oscillations is damped, generating hot electron−hole pairs in the metal NPs (Figure 3a(i)),16 which is termed Landau damping.26 These initially generated hot carriers go through the thermalization process, forming a hot Fermi−Dirac distribution, and then are transferred into the orbitals of adsorbed molecules (Figure 3a(ii)).16 The effectiveness of this
2. PLASMON-DRIVEN CATALYSIS ON MOLECULES 2.1. Plasmonic-Field-Driven Catalysis
A direct consequence of LSPR excitation is the confinement of light energy and photon redistribution, thus increasing the photon density on the surface of metal NPs in the form of an enhanced plasmonic field.17 Similar to traditional photocatalysis, which uses photons to transfer energy to excite reactant molecules, the plasmonic field with a higher density of photons can dramatically increase the rate and efficiency of chemical reactions in the field.18 For plasmonic-field-driven catalysis, energy overlap between the plasmonic field and the B
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Figure 2. Plasmonic-field-driven catalysis. (a) Schematic of the plasmonic-field-induced dissociation reaction on the surface of a plasmonic metal, showing (i) the initial state and (ii) reaction and (iii) relaxation in the excited state of the molecule. (b) Real-space observation of plasmonic-fieldinduced dissociation of a single dimethyl disulfide molecule: (i) schematic illustration of the experiment, (ii) scanning tunneling microscope images and current trace for the dissociation event, (iii) excitation mechanism, and (iv) the potential energy surface for electron-transfer-induced reaction. (c) Schematic of (i) plasmonic photocatalytic water splitting and (ii) photocurrent of anodic TiO2 with and without Au NPs. (d) (i) TEM image of the cross-section of the TiO2/Ag/SiO2 substrate, (ii) optical absorption spectra, and (iii) decomposition rates of MB on TiO2 surfaces. Reproduced with permission from (a) ref 1, (b) ref 20, (c) ref 24, and (d) ref 25. Copyright 2018 Nature Publishing Group, 2018 American Association for the Advancement of Science, and 2011 and 2008 American Chemical Society, respectively.
Figure 3. Plasmon-induced hot electron transfer from the metal to the adsorbed molecule. (a) Two-step indirect electron transfer mechanism: (i) nonthermalized distribution of hot carriers; (ii) Fermi−Dirac distribution of thermalized hot carriers. (b) Direct electron transfer mechanism. (c) Recombination of hot electron−hole pairs in metals with the adsorbed molecule. EF is the Fermi energy, and the gray shading indicates filled electronic states. Adapted from ref 16. Copyright 2017 American Chemical Society.
electron transfer depends on the positioning of the unoccupied states of the molecule relative to the Fermi level of the metal. This two-step transfer process, termed indirect electron transfer, is the primary excitation pathway in plasmonic catalysis, which shows a relatively high transfer efficiency due to the continuous distribution of hot electrons near the Fermi level. However, the Fermi level of the metal is hard to manipulate, which means that the energy of hot electrons cannot be effectively controlled by the excitation light or the wavelength of the LSPR, and this is what ultimately limits the ability to selectively enhance specific chemical pathways. Resonant excitation of the LSPR would only enhance the
efficiency of electron excitation without having much impact on the electron distribution. To date, most of the reported plasmonic catalysis is believed to occur through a conventional indirect hot electron transfer mechanism.27,28 For example, the plasmon induces the in situ chemical reaction of p-nitrothiophenol (PNTP) with highvacuum tip-enhanced Raman spectroscopy (HV-TERS), which can supply a “hot spot” to excite strong LSPR at the tip (Figure 4a).29 The higher density of hot electrons yielded from stronger plasmon resonances could be transferred to the unoccupied state of PNTP near the metal surface and induce its dimerization. The results of Stokes and anti-Stokes HVC
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Figure 4. Hot-electron-driven catalysis. (a) Hot-electron-driven chemical reactions of PNTP revealed by HV-TERS. (b) Hot-electron-driven H2 dissociation on the Au NP surface: (i) hot electron excitation; (ii) indirect transfer from the Au NP to the LUMO of the molecule; (iii) proposed mechanism of H2 dissociation. (c) Mechanisms of hot-electron-induced O2 dissociation: (i) density of states of O2 adsorbed on the Ag surface; (ii) potential energy surface of O2 and O2−; (iii) proposed mechanism of hot-electron-induced O2 dissociation. (d) (i) Plasmonic catalysis of water splitting on Au NP. (ii) Atomic distance of H2O to the surface of the Au NP as a function of time. The laser shows maximum strength at the vertical dotted line (t0 = 6.6 fs). (iii) Time-evolved charge density of the H2O−Au system. (iv) Occupation of the antibonding state of H2O. (v) Wavelength-dependent photocatalytic rates. Reproduced with permission from (a) ref 29, (b) ref 30, (c) ref 31, and (d) ref 32. Copyright 2012 Nature Publishing Group, 2013 American Chemical Society, 2011 Nature Publishing Group, and 2016 American Chemical Society, respectively.
generation of hot electrons in the electron-accepting orbitals of the adsorbate, leaving hot holes in the electron-donating states on the metal surface (Figure 3b).16,36 Without electron− electron scattering in the metal before its transfer, this process can significantly reduce the energy loss of the hot electron and accelerate the overall plasmon dephasing process. Compared with the indirect mechanism, this direct electron transfer process shows a lower efficiency because of the relatively small transition dipole moments of molecule−metal composites and the required formation of hybridized surface states. In addition, the energy overlap between the excited LSPR and the energy gap of the hybridized surface states is also important for the direct transfer process, which allows for a direct resonant transition from occupied to unoccupied orbitals of the molecule−NP complex. Meanwhile, the direct transfer channel can be used to selectively catalyze targeted reactions and improve the rates of targeted chemical transformations by controlling the optical properties of the plasmonic nanostructure and the excitation laser to manipulate the distribution of electrons. The existence of the direct transfer process was demonstrated by the atomic-scale mechanism and real-time ultrafast electron−nuclear dynamics study of water splitting on Au NPs upon exposure to femtosecond laser pulses (Figure 4d).32 For the hybridized system, the electron-donating states of Au NPs and the electron-accepting orbitals of H2O show significant energy and spatial overlap. Accumulation in the antibonding state of H2O is observed, which leads to water splitting. The wavelength-dependent reaction rate depends on not only resonant excitation of the LSPR but also its plasmonic excitation mode. Meanwhile, a specific plasmonic excitation mode brings more effective direct electron transfer because of the better energy overlap between the electron-accepting and -donating states. 2.2.3. Control of Hot Carrier Catalysis. As a result of the ultrafast recombination of electron−hole pairs, the lifetimes of
TERS show that no obvious temperature increase occurs during plasmonic catalysis. In addition, the absorption of the adsorbate molecules is in the UV region, away from the excitation laser. Therefore, both the thermal effects and the photon contribution can be avoided in this system. The effective dissociation of H2 and O2 is of significance for various photochemical transformations.28,30,33 This indirect hot electron transfer mechanism is proposed to accelerate H2 dissociation on the surface of Au NPs (Figure 4b).30 After thermalization, hot electrons are transferred from the Au NPs to the antibonding orbitals of H2 molecules, creating negative ions. Then these hot electrons are quickly transferred back to the Au surface,34 and the H2 molecules return to the ground electronic state with additional vibrational energy, which leads to stretching of the H−H bond and finally results in its dissociation. Effective O2 dissociation can promote most oxidation reactions, while high operating temperatures are always required for this reaction with a conventional approach. Hot electrons formed through the excitation of surface plasmons on Ag NPs can facilitate the dissociation of O2 and promote oxygen activation with O2− generation (Figure 4c).31 In addition, plasmonic catalytic oxidation reactions, such as the oxidations of CO and NH3, are realized at significantly lower temperatures than their conventional counterparts using only thermal stimulus. In this process, the molecules are weakly adsorbed on the surface of the plasmonic metal, forming relatively weak orbital hybridization by van der Waals forces that promotes the indirect electron transfer. 2.2.2. Catalysis Mediated by Direct Electron Transfer. When there are strongly interacting reactants such as chemically adsorbed molecules or semiconductors, hybridized surface states can be formed at the interface as a result of the interactions between the metal and the reactants.16,35 The formed interface states provide an additional pathway for plasmon dephasing through the coupling between the hybridized states and the plasmon, which induces the direct D
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Figure 5. Control of hot-electron catalysis. (a) (i) Schematic structure of a CdSe/Au NR and plasmon-mediated direct electron transfer and (ii) the absorption spectra. (b) (i) Schematic of the Au/SiO2 composite structure and (ii) the enhanced formation rate of product HD with Au/SiO2 and Au/TiO2. (c) (i) Influence of hole scavengers on plasmonic catalysis, (ii) reaction rates with different incident laser powers, and (iii) semiquantitative model of the photon flux dependence of the electron-harvesting rate. (d) (i) TEM image and elemental maps of the core−shell Ag/Pt nanocubes, (ii) reaction rate, and (iii) fast-response mass spectrometry analysis of CO oxidation in excess H2 on Ag/Pt nanocubes. (e) (i) Schematic of the physical processes of the strong coupling between LSPs and SPPs in the Au grating/MoS2/Al2O3/Au/Si heterostructure and (ii) band structure diagram of the Au grating and MoS2 monolayer. Reproduced with permission from (a) ref 40, (b) ref 33, (c) ref 41, (d) ref 42, and (e) ref 43. Copyright 2015 American Association for the Advancement of Science, 2014 American Chemical Society, and 2018, 2017, and 2019 Nature Publishing Group, respectively.
NP/SiO2 composite structure (Figure 5b)33 compared with the dissociation rate on pure Au NPs (Figure 4b). Plasmon-mediated multielectron catalysis has been demonstrated on Au NPs through the harvesting of multiple electron−hole pairs with the help of hole scavengers (Figure 5c).41 The photocatalytic efficiency relies on the ability to generate a charge-separated state through interband transitions (d to sp) and the capture of holes by a scavenger. Interband electron−hole pairs with longer lifetimes than those generated by intraband relaxation are attributed to the harvesting of multiple electrons. In addition, the hybrid core−shell nanostructure is developed by depositing a few monolayers of catalytic Pt onto plasmonic Ag nanocubes (Figure 5d).42 In this system, the core metal can harvest visible-light photons, and the energy stored in the LSPR modes can be selectively dissipated by exciting energetic electron−hole pairs in the Pt shell to drive a photochemical reaction. In addition to generation of hot electron−hole pairs, LSPs also undergo radiative decay by re-emitting photons. Suppression of this radiative decay channel of LSPs can also contribute to the yield of hot electrons. On the basis of this idea, a metal−insulator−metal sandwiched heterostructure has been proposed (Figure 5e),43 in which surface plasmon polaritons (SPPs) with a unique nonradiative feature can act as an “energy recycling bin” to reuse the originally unavailable energy and promote hot electron transfer from a Au grating to a MoS2 monolayer. In this structure, strong coupling between the LSPs and SPPs allows emitted photons to be reabsorbed by the SPPs, resulting in an increased external quantum yield of hot electrons.
plasmon-generated hot electrons are very short (Figure 3c), which leads to a low efficiency of hot-electron catalysis. Electron transfer mediators, such as metal oxide semiconductors, and bimetallic heterojunctions are often used to collect the charge carriers.37 With the assistance of the Schottky barrier formed at the metal−semiconductor interface, hot electrons can be trapped in the conduction band of semiconductors, delaying them in traveling back to the metal and extending their lifetime.38,39 Especially, under visible laser excitation with less energy than the semiconductor band gap, excitation of holes in the valence band that can recombine with transferred hot electrons is avoided, and therefore, the lifetime of hot electrons is much longer. During the indirect electron transfer process, ultrafast relaxation of the initially generated hot electrons is hard to avoid, and it decreases the transfer efficiency because of the energy dissipation. Plasmon decay by direct excitation of an electron in a strongly coupled acceptor reduces the electron− electron scattering and improves the transfer efficiency. Efficient interfacial charge separation has been proven experimentally in the Au/CdSe NR heterostructure (Figure 5a).40 The strong orbital coupling between CdSe and Au, which was verified by the broadened absorption peak, leads to a new plasmon decay pathway in which an electron and a hole are directly generated in the CdSe and Au, respectively. The LSPR of Au NPs is strongly damped through direct electron excitation, effectively enhancing the quantum yield of hot electrons (as high as 24%), and the enhanced value is independent of the frequency of excitation light in the range of the LSPR. Similarly, decored SiO2 or TiO2, which can promote the separation of initially formed nonequilibrated carriers, is also used to inhibit the carriers’ recombination. As a result, the H2 dissociation rate is increased almost 2 orders on the Au
2.3. Plasmonic Thermal Catalysis
The localized thermal effect following LSPR decay is also a promising approach to facilitate plasmon-mediated chemical E
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3. PLASMON-DRIVEN CATALYSIS ON NANOMATERIALS In addition to reactions of molecules, the catalytic effect of noble metal NPs can also drive the reactions of nanomaterials. The dual effects of high spatial confinement and an ultrashort time scale provide a new way to precisely manipulate nanomaterial growth and phase transformation. With the photoexcited LSPR, a catalytic reaction can be induced for molecules decorated on the surface of metal NPs present in solution or in the gas stream, and then the formed metal atoms or other products are deposited resulting in nanomaterial growth. In this process, it is still the reactant molecules whose reaction is catalyzed by the plasmon, and the reaction mechanism discussed in section 2 is applicable here. Meanwhile, for the nanomaterial transformation, the direct catalytic target of the plasmon is inorganic nanocrystals, opening the new field of plasmon-driven reactions for the next generation of plasmonic catalysis.
reactions by providing energy to overcome the reaction barrier. However, the inevitable thermal effect during plasmon decay can only increase the reaction rate and makes no contribution to the selectivity of the reaction. Additionally, it is difficult to distinguish the contribution of the thermal effect from other effects of the plasmon in the plasmonic catalytic reaction. Although the widely accepted idea is that the main role in plasmonic catalysis is played by the excitation of hot electrons rather than the thermal effect, there are also some different conclusions on this issue.44−47 By the use of Rh NPs as both a thermal and plasmonic catalyst, the reaction rates of CO2 were investigated as a function of laser intensity (Figure 6a).44 Measurement of the
3.1. Plasmon-Driven Nanomaterial Growth
The plasmon-mediated growth of triangular Ag nanoprisms is shown in Figure 7a.50 The enhanced local field can effectively accelerate the redox reaction by preferential metal deposition near hot spots, thus realizing spatial control of metal growth. The general effect of plasmonic catalysis on the growth of noble metal nanocrystals is also shown in the plasmon-driven growth of gold nanoprisms (Figure 7b).51 Nanocrystal twinning due to intrinsic structural differences can modulate the growth kinetics of Au nanocrystals by regulating the transport of hot electrons under plasmon excitation. It is clear that the surfactant poly(vinylpyrrolidone) (PVP) not only performs a role as a crystal face blocking ligand but also can facilitate hot electron accumulation on the metal under laser excitation. The targeted deposition of Pt onto the tips of Au NRs was realized with the assistance of plasmonic hot electrons (Figure 7c).52 Hot electrons on the Au surface function as the redox agent to catalyze the reduction of chloroplatinic acid to Pt0 and promote the epitaxial growth of Pt0 over the Au NR tips. Additionally, the inhomogeneous spatial distribution of the local plasmonic field initiates the deposition of Pt onto Au NRs at specific targeted locations, shown as the longitudinal growth of Pt. By utilization of the plasmon heating effect, a flexible strategy to rapidly heat and cool a material at room temperature was developed and applied in the controllable growth of Si nanowires (Figure 7d).53 The localized high temperature was obtained on the noble metal NP, facilitating efficient light to heat conversion through excitation of the LSPR. By local heating of nanoscale metallic catalysts accompanied by control of the position of the laser beam, individual nanostructures can be grown at predefined locations. A high degree of spatial and temporal control of the growth of semiconductor nanowires and carbon nanotubes has been realized with the local heating strategy.
Figure 6. Plasmonic thermal effect catalysis. (a) (i) Schematic of the plasmon- and thermally induced reactions of CO2 with the Rh/TiO2 catalyst and (ii) reaction rates (corresponding to the thermal, nonthermal, and total effects) as functions of laser intensity. (b) Mechanisms of the oxidation reaction induced by (i) plasmongenerated hot holes and (ii) the thermal effect. (c) (i) Schematic of the structure of the plasmonic photocatalyst that was used to quantify the contributions of hot carriers and the photothermal effect and (ii) H2 formation rates in photo- and thermally catalyzed reactions. Reproduced with permission from (a) ref 44, (b) ref 48, and (c) ref 49. Copyright 2018 American Chemical Society and 2019 American Association for the Advancement of Science, respectively.
temperature of the catalyst bed demonstrated that the nonthermal effect of the plasmonic catalysis is collaborative with heat and increased with the higher temperature. The relative contributions of hot carriers and the thermal effect were quantified in plasmon-mediated electrochemical processes by using scanning electrochemical microscopy (Figure 6b).48 It was concluded that the catalytic efficiency can be attributed to both plasmon-generated hot carriers and thermal effects and that their relative contributions vary with the excitation intensity. The concept of a light-dependent activation barrier was introduced to account for the effect of light illumination on electronic and thermal excitations and to try to distinguish thermal from nonthermal effects in the process of plasmonic catalysis (Figure 6c).49 The surface temperature of the catalyst metal was measured with a thermal imaging camera to account for the photothermal effect at different illumination wavelengths and intensities. It was demonstrated that photoinduced reductions of the reaction barrier have an electronic origin. The hot electrons can induce multiple vibrational transitions of the reactant molecule, and as the vibrational energy stored in the bond increases, the activation energy is reduced.
3.2. Plasmon-Driven Nanomaterial Transformation
The transformation of individual Pd nanocubes adjacent to Au nanodiscs from the hydrogen-rich β phase to the hydrogenpoor α phase was employed as a model system to reveal the catalytic effect of plasmonic fields in driving nanomaterial transformation (Figure 8a).54 An environmental electron microscopy method that allows for optical excitation was developed to realize in situ real-time observations of the F
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Figure 7. Plasmon-induced nanomaterial growth. (a) Schematic of plasmon-induced Ag triangular nanosheet growth in solution and STEM images of the products. (b) Plasmon-induced Au nanosheet growth with the help of PVP: (i) SEM image of Au nanostructures after growth; (ii, iii) images of the elemental distributions of (ii) 197Au− and (iii) 12C14N−; (iv, v) SEM images of Au nanoprisms (iv) before and (v) after growth. (c) (i) Mechanism of plasmon-induced Pt4+ reduction to Pt0 at the surface of Au NRs and (ii) schematic and elemental map (scale bars are 20 nm) of Ptdecorated Au NRs. (d) Schematic and SEM images of plasmonic-heat-induced vertically and horizontally grown Si nanowires. The insets show the corresponding wires with scale bars of 100 and 200 nm, respectively. Reproduced with permission from (a) ref 50, (b) ref 51, (c) ref 52, and (d) ref 53. Copyright 2017 American Chemical Society, 2016 Nature Publishing Group, and 2018 and 2007 American Chemical Society, respectively.
Figure 8. Plasmon-driven nanomaterial transformation. (a) Schematics of (i) the dehydrogenation reaction and (ii) the experiment involving plasmon-driven dehydrogenation of Pd nanocubes and (iii) TEM image of a Pd nanocube and Au nanodisc and high-resolution TEM image and (inset) the corresponding Fourier transform of the Pd nanocube. (b) (i) Sketch of the crystal transformation from polycrystalline material to a single crystal, (ii) mechanisms of plasmon-driven nanoparticle transformation and STEM images of polycrystalline fluoride and transformed singlecrystal oxide particle, and (iii, iv) crystal transformation rates with (iii) different wavelengths and (iv) different temperatures. Reproduced with permission from (a) ref 54 and (b) ref 55. Copyright 2018 Nature Publishing Group and 2019 Wiley-VCH, respectively.
high enough. Excitation of the plasmon just affects the rate of the transformation and modifies the nucleation sites of the α phase. In addition, the morphology of the Pd nanocubes after phase transformation shows no obvious changes. Recently we demonstrated the plasmon-induced crystal transformation from a polycrystalline to single-crystalline luminescent nanomaterial accompanied by chemical transformation (Figure 8b).55 The transformation target and reaction rate can be precisely controlled by adjusting the
plasmon-induced phase transformation of Pt NPs with sub-2 nm spatial resolution. The results demonstrate that the dehydrogenation rate is enhanced by the strong EM fields. Additionally, the active sites of the Pd nanocube have a relationship with the formation of plasmonic hot spots, which can be used to modulate the active sites in the actual reaction process. It should be pointed out that without plasmons, a similar phase transformation of Pd nanocubes can also spontaneously happen when the hydrogen pressure is not G
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Accounts of Chemical Research irradiation power, wavelength, and density of plasmonic metal NPs. In particular, this plasmonic transformation is also suitable even at very low temperature, while it is impossible with conventional methods. Such an easy and universal strategy of plasmon-driven crystal transformation reveals the more powerful aspects of plasmonic thermal and catalytic effects and provides an easy and rapid in situ approach to obtain single-crystalline luminescent materials. We believe that this work can help to solve the bottleneck problems of singlecrystal formation in conventional approaches and extend the application of surface plasmons to a much broader field.
Chengyun Zhang is a Ph.D. student under the supervision of Prof. H. Zheng at Shaanxi Normal University. Her research interests are focused on plasmonic catalysis on rare-earth-doped nanocrystals.
4. CONCLUSION AND OUTLOOK In this Account, we have discussed the plasmonic catalysis effect, and the excitation mechanism has been discussed by employing reactions of organic molecules. Meanwhile, we have also introduced the next-generation catalysis system, namely, nanomaterials, focusing on plasmonic-catalyzed material growth and chemical transformation. The recent advances and excitation mechanisms have been reviewed in detail in section 2, including the localized plasmonic field, hot carrier transfer, and thermal effect according to the energy transfer pathway. These are universal and thus also applicable in plasmonic catalysis on nanomaterials. In addition, a new approach to obtain single-crystalline materials rapidly in situ has been presented in section 3. Clearly revealing the catalytic mechanism and independently controlling each reaction channel are essential to design more efficient catalytic systems. Meanwhile, it is a major challenge to clearly distinguish the contributions of the three catalytic pathways, which often coexist in a specific reaction. In the field of plasmonic catalysis, researchers are trying to pick out the dominant mechanism for some reactions, but it is difficult to quantify the contribution of each one, especially for the thermal effect. We believe that once the mechanism is fully clear, the field of plasmonic catalysis will obtain great success in designing highly tunable and selective catalytic systems along with carrying out significant improvement in the effective use of solar energy.
Hongxing Xu is a professor of physics and the dean of the School of Physics and Technology at Wuhan University in China. He is a member of the Chinese Academy of Sciences. He received his B.S. from Peking University in China in 1992 and his Ph.D. from Chalmers University of Technology in Sweden in 2002, both in physics. He then joined the Division of Solid State Physics at Lund University in Sweden as an assistant professor until December 2004. From 2005 to 2014 he was a professor at the Institute of Physics, Chinese Academy of Sciences. He is known for the discovery of the nanogap effect for huge electromagnetic enhancement, the invention of plasmonic logic gates, and the development of plasmonic nanowire waveguides and circuits. His research interests include plasmonics, nanophotonics, surface-/tip-enhanced spectroscopy, and singlemolecule spectroscopy.
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Hairong Zheng is a professor of physics and the dean of the Graduate School at Shaanxi Normal University. She received her Ph.D. in physics at the University of Georgia in 2003. After working at the University of Georgia as a postdoctoral researcher and Georgia Southern University as an assistant professor, she joined Shaanxi Normal University in 2005 as a professor. Her current research interests are rare-earth-doped luminescence, enhanced spectroscopy, and plasmonics.
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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 11674256 and 11574190), the National Key Basic Research Program (Grant 2015CB932400), the National Key R&D Program of China (Grant 2017YFA0205800), the Natural Science Foundation of Shaanxi Province (Grant 2019JQ-142), and the Fundamental Research Funds for the Central Universities (GK201701008, no. 2017TS013).
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REFERENCES
(1) Aslam, U.; Rao, V. G.; Chavez, S.; Linic, S. Catalytic conversion of solar to chemical energy on plasmonic metal nanostructures. Nat. Catal. 2018, 1, 656−665. (2) Fujishima, A.; Honda, K. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 238, 37−38. (3) Mills, A.; Le Hunte, S. An overview of semiconductor photocatalysis. J. Photochem. Photobiol., A 1997, 108, 1−35. (4) Zheng, Z.; Xie, W.; Huang, B.; Dai, Y. Plasmon-Enhanced Solar Water Splitting on Metal-Semiconductor Photocatalysts. Chem. - Eur. J. 2018, 24, 18322−18333. (5) Zhang, P.; Wang, T.; Chang, X.; Gong, J. Effective Charge Carrier Utilization in Photocatalytic Conversions. Acc. Chem. Res. 2016, 49, 911−921. (6) Homola, J.; Yee, S. S.; Gauglitz, G. Surface plasmon resonance sensors: review. Sens. Actuators, B 1999, 54, 3−15. (7) Zhang, Y.; He, S.; Guo, W.; Hu, Y.; Huang, J.; Mulcahy, J. R.; Wei, W. D. Surface-Plasmon-Driven Hot Electron Photochemistry. Chem. Rev. 2018, 118, 2927−2954. (8) Watanabe, K.; Menzel, D.; Nilius, N.; Freund, H.-J. Photochemistry on Metal Nanoparticles. Chem. Rev. 2006, 106, 4301−4320. (9) Spata, V. A.; Carter, E. A. Mechanistic insights into photocatalyzed hydrogen desorption from palladium surfaces assisted by localized surface plasmon resonances. ACS Nano 2018, 12, 3512− 3522. (10) Linic, S.; Christopher, P.; Ingram, D. B. Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy. Nat. Mater. 2011, 10, 911−921.
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Zhenglong Zhang: 0000-0003-1426-4042 Hongxing Xu: 0000-0002-1718-8834 Author Contributions §
Z.Z. and C.Z. contributed equally to this work
Notes
The authors declare no competing financial interest. Biographies Zhenglong Zhang is a professor of physics at Shaanxi Normal University in China. He received his Ph.D. in 2013 from Shaanxi Normal University and the Institute of Physics, Chinese Academy of Sciences. Then he joined the Leibniz Institute of Photonic Technology in Jena, Germany, as an Av-H fellow until September 2016. His research interests include plasmonics and tip-enhanced Raman spectroscopy. H
DOI: 10.1021/acs.accounts.9b00224 Acc. Chem. Res. XXXX, XXX, XXX−XXX
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Accounts of Chemical Research (11) Sun, M.; Xu, H. A novel application of plasmonics: plasmondriven surface-catalyzed reactions. Small 2012, 8, 2777−2786. (12) Bharadwaj, P.; Deutsch, B.; Novotny, L. Optical Antennas. Adv. Opt. Photonics 2009, 1, 438−472. (13) Linic, S.; Aslam, U.; Boerigter, C.; Morabito, M. Photochemical transformations on plasmonic metal nanoparticles. Nat. Mater. 2015, 14, 567−576. (14) Brongersma, M. L.; Halas, N. J.; Nordlander, P. Plasmoninduced hot carrier science and technology. Nat. Nanotechnol. 2015, 10, 25−34. (15) Fang, Z.; Zhen, Y. R.; Neumann, O.; Polman, A.; Garcia de Abajo, F. J.; Nordlander, P.; Halas, N. J. Evolution of light-induced vapor generation at a liquid-immersed metallic nanoparticle. Nano Lett. 2013, 13, 1736−1742. (16) Zhang, Y.; He, S.; Guo, W.; Hu, Y.; Huang, J.; Mulcahy, J. R.; Wei, W. D. Surface-Plasmon-Driven Hot Electron Photochemistry. Chem. Rev. 2018, 118, 2927−2954. (17) Amendola, V.; Pilot, R.; Frasconi, M.; Marago, O. M.; Iati, M. A. Surface plasmon resonance in gold nanoparticles: a review. J. Phys.: Condens. Matter 2017, 29, 203002. (18) Martirez, J. M. P.; Carter, E. A. Prediction of a low-temperature N2 dissociation catalyst exploiting near-IR-to-visible light nanoplasmonics. Sci. Adv. 2017, 3, eaao4710. (19) Kim, Y.; Kazuma, E. Mechanistic studies of plasmon chemistry on metal catalysts. Angew. Chem., Int. Ed. 2019, 58, 4800−4808. (20) Kazuma, E.; Jung, J.; Ueba, H.; Trenary, M.; Kim, Y. Real-space and real-time observation of a plasmon-induced chemical reaction of a single molecule. Science 2018, 360, 521−525. (21) Kazuma, E.; Jung, J.; Ueba, H.; Trenary, M.; Kim, Y. Direct Pathway to Molecular Photodissociation on Metal Surfaces Using Visible Light. J. Am. Chem. Soc. 2017, 139, 3115−3121. (22) Kazuma, E.; Jung, J.; Ueba, H.; Trenary, M.; Kim, Y. STM studies of photochemistry and plasmon chemistry on metal surfaces. Prog. Surf. Sci. 2018, 93, 163−176. (23) Tesema, T. E.; Kafle, B.; Tadesse, M. G.; Habteyes, T. G. Plasmon-Enhanced Resonant Excitation and Demethylation of Methylene Blue. J. Phys. Chem. C 2017, 121, 7421−7428. (24) Liu, Z. W.; Hou, W. B.; Pavaskar, P.; Aykol, M.; Cronin, S. B. Plasmon Resonant Enhancement of Photocatalytic Water Splitting Under Visible Illumination. Nano Lett. 2011, 11, 1111−1116. (25) Awazu, K.; Fujimaki, M.; Rockstuhl, C.; Tominaga, J.; Murakami, H.; Ohki, Y.; Yoshida, N.; Watanabe, T. A plasmonic photocatalyst consisting of silver nanoparticles embedded in titanium dioxide. J. Am. Chem. Soc. 2008, 130, 1676−1680. (26) Li, X.; Xiao, D.; Zhang, Z. Landau damping of quantum plasmons in metal nanostructures. New J. Phys. 2013, 15, 023011− 023025. (27) Naldoni, A.; Montini, T.; Malara, F.; Mróz, M. M.; Beltram, A.; Virgili, T.; Boldrini, C. L.; Marelli, M.; Romero-Ocaña, I.; Delgado, J. J.; Dal Santo, V.; Fornasiero, P. Hot Electron Collection on Brookite Nanorods Lateral Facets for Plasmon-Enhanced Water Oxidation. ACS Catal. 2017, 7, 1270−1278. (28) Sakamoto, H.; Ohara, T.; Yasumoto, N.; Shiraishi, Y.; Ichikawa, S.; Tanaka, S.; Hirai, T. Hot-Electron-Induced Highly Efficient O2 Activation by Pt Nanoparticles Supported on Ta2O5 Driven by Visible Light. J. Am. Chem. Soc. 2015, 137, 9324−9332. (29) Sun, M.; Zhang, Z.; Zheng, H.; Xu, H. In-situ plasmon-driven chemical reactions revealed by high vacuum tip-enhanced Raman spectroscopy. Sci. Rep. 2012, 2, 647. (30) Mukherjee, S.; Libisch, F.; Large, N.; Neumann, O.; Brown, L. V.; Cheng, J.; Lassiter, J. B.; Carter, E. A.; Nordlander, P.; Halas, N. J. Hot electrons do the impossible: plasmon-induced dissociation of H2 on Au. Nano Lett. 2013, 13, 240−247. (31) Christopher, P.; Xin, H.; Linic, S. Visible-light-enhanced catalytic oxidation reactions on plasmonic silver nanostructures. Nat. Chem. 2011, 3, 467−472. (32) Yan, L.; Wang, F.; Meng, S. Quantum Mode Selectivity of Plasmon-Induced Water Splitting on Gold Nanoparticles. ACS Nano 2016, 10, 5452−5458.
(33) Mukherjee, S.; Zhou, L.; Goodman, A. M.; Large, N.; AyalaOrozco, C.; Zhang, Y.; Nordlander, P.; Halas, N. J. Hot-electroninduced dissociation of H2 on gold nanoparticles supported on SiO2. J. Am. Chem. Soc. 2014, 136, 64−67. (34) Liu, J. G.; Zhang, H.; Link, S.; Nordlander, P. Relaxation of Plasmon-Induced Hot Carriers. ACS Photonics 2018, 5, 2584−2595. (35) Chen, Y.-C.; Hsu, Y.-K.; Popescu, R.; Gerthsen, D.; Lin, Y.-G.; Feldmann, C. Au@Nb@HxK1−xNbO3 nanopeapods with near-infrared active plasmonic hot-electron injection for water splitting. Nat. Commun. 2018, 9, 232. (36) Foerster, B.; Joplin, A.; Kaefer, K.; Celiksoy, S.; Link, S.; Sonnichsen, C. Chemical Interface Damping Depends on Electrons Reaching the Surface. ACS Nano 2017, 11, 2886−2893. (37) Wang, P.; Krasavin, A. V.; Nasir, M. E.; Dickson, W.; Zayats, A. V. Reactive tunnel junctions in electrically driven plasmonic nanorod metamaterials. Nat. Nanotechnol. 2018, 13, 159−164. (38) Sjakste, J.; Tanimura, K.; Barbarino, G.; Perfetti, L.; Vast, N. Hot electron relaxation dynamics in semiconductors: assessing the strength of the electron-phonon coupling from the theoretical and experimental viewpoints. J. Phys.: Condens. Matter 2018, 30, 353001. (39) Park, J. Y.; Kim, S. M.; Lee, H.; Nedrygailov, II Hot-electronmediated surface chemistry: toward electronic control of catalytic activity. Acc. Chem. Res. 2015, 48, 2475−2483. (40) Wu, K.; Chen, J.; McBride, J. R.; Lian, T. Efficient hot-electron transfer by a plasmon-induced interfacial charge-transfer transition. Science 2015, 349, 632−635. (41) Kim, Y.; Smith, J. G.; Jain, P. K. Harvesting multiple electronhole pairs generated through plasmonic excitation of Au nanoparticles. Nat. Chem. 2018, 10, 763−769. (42) Aslam, U.; Chavez, S.; Linic, S. Controlling energy flow in multimetallic nanostructures for plasmonic catalysis. Nat. Nanotechnol. 2017, 12, 1000−1005. (43) Shan, H.; Yu, Y.; Wang, X.; Luo, Y.; Zu, S.; Du, B.; Han, T.; Li, B.; Li, Y.; Wu, J.; Lin, F.; Shi, K.; Tay, B. K.; Liu, Z.; Zhu, X.; Fang, Z. Direct observation of ultrafast plasmonic hot electron transfer in the strong coupling regime. Light: Sci. Appl. 2019, 8, 9. (44) Zhang, X.; Li, X.; Reish, M. E.; Zhang, D.; Su, N. Q.; Gutierrez, Y.; Moreno, F.; Yang, W.; Everitt, H. O.; Liu, J. Plasmon-Enhanced Catalysis: Distinguishing Thermal and Nonthermal Effects. Nano Lett. 2018, 18, 1714−1723. (45) Keller, E. L.; Frontiera, R. R. Ultrafast Nanoscale Raman Thermometry Proves Heating Is Not a Primary Mechanism for Plasmon-Driven Photocatalysis. ACS Nano 2018, 12, 5848−5855. (46) Kamarudheen, R.; Castellanos, G. W.; Kamp, L. P. J.; Clercx, H. J. H.; Baldi, A. Quantifying Photothermal and Hot Charge Carrier Effects in Plasmon-Driven Nanoparticle Syntheses. ACS Nano 2018, 12, 8447−8455. (47) Golubev, A. A.; Khlebtsov, B. N.; Rodriguez, R. D.; Chen, Y.; Zahn, D. R. T. Plasmonic Heating Plays a Dominant Role in the Plasmon-Induced Photocatalytic Reduction of 4-Nitrobenzenethiol. J. Phys. Chem. C 2018, 122, 5657−5663. (48) Yu, Y.; Sundaresan, V.; Willets, K. A. Hot Carriers versus Thermal Effects: Resolving the Enhancement Mechanisms for Plasmon-Mediated Photoelectrochemical Reactions. J. Phys. Chem. C 2018, 122, 5040−5048. (49) Zhou, L.; Swearer, D. F.; Zhang, C.; Robatjazi, H.; Zhao, H.; Henderson, L.; Dong, L.; Christopher, P.; Carter, E. A.; Nordlander, P.; Halas, N. J. Quantifying hot carrier and thermal contributions in plasmonic photocatalysis. Science 2018, 362, 69−72. (50) Sutter, P.; Li, Y.; Argyropoulos, C.; Sutter, E. In Situ Electron Microscopy of Plasmon-Mediated Nanocrystal Synthesis. J. Am. Chem. Soc. 2017, 139, 6771−6776. (51) Zhai, Y.; DuChene, J. S.; Wang, Y. C.; Qiu, J.; Johnston-Peck, A. C.; You, B.; Guo, W.; DiCiaccio, B.; Qian, K.; Zhao, E. W.; Ooi, F.; Hu, D.; Su, D.; Stach, E. A.; Zhu, Z.; Wei, W. D. Polyvinylpyrrolidone-induced anisotropic growth of gold nanoprisms in plasmondriven synthesis. Nat. Mater. 2016, 15, 889−895. (52) Forcherio, G. T.; Baker, D. R.; Boltersdorf, J.; Leff, A. C.; McClure, J. P.; Grew, K. N.; Lundgren, C. A. Targeted Deposition of I
DOI: 10.1021/acs.accounts.9b00224 Acc. Chem. Res. XXXX, XXX, XXX−XXX
Article
Accounts of Chemical Research Platinum onto Gold Nanorods by Plasmonic Hot Electrons. J. Phys. Chem. C 2018, 122, 28901−28909. (53) Cao, L.; Barsic, D. N.; Guichard, A. R.; Brongersma, M. L. Plasmon-Assisted Local Temperature Control to Pattern Individual Semiconductor Nanowires and Carbon Nanotubes. Nano Lett. 2007, 7, 3523−3527. (54) Vadai, M.; Angell, D. K.; Hayee, F.; Sytwu, K.; Dionne, J. A. Insitu observation of plasmon-controlled photocatalytic dehydrogenation of individual palladium nanoparticles. Nat. Commun. 2018, 9, 4658. (55) Zhang, C.; Lu, J.; Jin, N.; Dong, L.; Fu, Z.; Zhang, Z.; Zheng, H. Plasmon Driven Rapid In-Situ Formation of Luminescence Single Crystal Nanoparticle. Small 2019, 1901286.
J
DOI: 10.1021/acs.accounts.9b00224 Acc. Chem. Res. XXXX, XXX, XXX−XXX
