Surface Plasmon Catalytic Aerobic Oxidation of Aromatic Amines in

Subscriber access provided by La Trobe University Library

Article

Surface Plasmon Catalytic Aerobic Oxidation of Aromatic Amines in Metal/Molecule/Metal Junctions Liu-Bin Zhao, Xiao-Xiang Liu, Meng Zhang, Zi-Feng Liu, De-Yin Wu, and Zhong-Qun Tian J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b07966 • Publication Date (Web): 21 Dec 2015 Downloaded from http://pubs.acs.org on December 28, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Surface

Plasmon

Catalytic

Aerobic

Oxidation

of

Aromatic

Amines

in

Metal/Molecule/Metal Junctions

Liu-Bin Zhao,*,† Xiao-Xiang Liu,† Meng Zhang,‡ Zi-Feng Liu,‡,§ De-Yin Wu,*,‡ and Zhong-Qun Tian‡,§ †

Department of Chemistry, School of Chemistry and Chemical Engineering,

Southwest University, Chongqing 400715, China ‡

State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of

Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China §

Innovation Center of Chemistry for Energetic Materials, Xiamen University, Xiamen

361005, China

Corresponding Authors *Email: [email protected].

*Email: [email protected].

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract: The surface plasmon catalytic selective aerobic oxidation of aromatic amines to aromatic azo compounds in metal/molecule/metal junctions was explored by density functional theory. The overall reaction could be divided into the initial plasmon-induced oxygen activation and the subsequent photothermal driven dehydrogenation process. The activation of oxygen on silver and gold surfaces is proposed through a surface plasmon-mediated hot electron injection mechanism at solid/gas interface. Resonance absorption of incident light by metal nanostructures generates energetic electron-hole pairs. TD-DFT calculation illustrates that the excited hot electrons created on metal surfaces can transfer to the antibonding 2π* orbital of adsorbed oxygen, which facilitates the dissociation of O2 on metal surfaces. Silver shows better catalytic performance for the oxygen activation due to its stronger SPR absorption intensity and higher hot electron energy level. Aromatic amines adsorbed on the metal surfaces can be selectively oxidized to the corresponding azo compounds by the activated surface oxygen species. The aerobic oxidations of p-aminothiophenol in the nanogaps between metal substrate and three different nanoparticles (Ag, Au, and Au@SiO2) are compared. The activated oxygen species on silver surfaces exhibits the strongest oxidation ability for its lowest reaction barriers of dehydrogenations. This work demonstrates that silver catalyst should be an excellent candidate for the heterogeneous photocatalysis, which can concurrently enhance oxygen dissociation and oxidative dehydrogenation reactions.


Page 2 of 31

Page 3 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction Plasmonic photocatalysis has become a very interesting and active research direction due to the capability of plasmonic nanostructure for high-efficiently harvesting and converting solar energy into either chemical processes (photocatalysis) and/or electricity (photoelectrochemical cell).1-10 The coherent oscillation of conductive electrons of noble metal nanoparticles in resonance with incident optical electric field creates a specific phenomenon known as surface plasmon resonance (SPR).11-12 Following optical excitation, surface plasmons decay by either a radiative scattering of photons, or a non-radiative relaxation.13-14 As for the radiative decay, the SPR effect gives rise to a significant focus of light and the giant enhancement of local electromagnetic field, enabling observation of surface-enhanced Raman spectroscopy (SERS) with ultrahigh detection sensitivity.15-16 For the non-radiative process, the SPR effect can generate energetic electron-hole pairs. These hot carriers are capable of inducing chemical reactions for molecule in the vicinity of the surface of plasmonic nanostructure.17-19 It

has

been

recognized

recently

that

plasmonic

nanostructures

and

metal-semiconductor composite structures can be used for hot carrier generation, photocatalysis, and injection. Noble metal nanoparticles have large absorption cross sections and can efficiently enhance and concentrate light. Plasmonic enhancement of photovoltaics and photocatalysis can be induced via direct photoexcitation of surface metal-molecule

complex

or

indirectly

via

SPR-mediated

charge

injection

mechanism.19 In the indirect charge-transfer mechanism, plasmon relaxation results in an electron distribution above the metal Fermi level. The excited energetic charge carriers can transfer to the adsorbate acceptor state, thereby forming an excited adsorbate and potentially inducing chemical transformation. In the direct charge-transfer mechanism, decay of a resonant plasmon causes direct excitation of an electron to an unoccupied adsorbate state. The process of photon absorption is initiated by the interaction of surface plasmons with the accessible adsorbate electronic states.10, 20-21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The photo-excited hot electrons look very attractive for applications in photochemistry, solar cells, and photodetectors because metal nanocrystals can absorb light much more efficiently compared to inorganic semiconductors and organic dye molecules. An essential issue for the utilization of photo-excited surface plasmons is the energy distributions of the excited hot electron-hole pairs. The time-evolving energetic charge carrier energy distribution was studied by optical pump and probe experiments.22-24 Initially, the electrons in the metal follow a Fermi-Dirac distribution at the thermal temperature. Secondly, the photoexcitation of electrons from filled states to unfilled states generates a non-thermal electron distribution, resulting hot electrons above the Fermi level and remaining hot holes below the Fermi level. Thirdly, the electron distribution thermalizes to a Fermi-Dirac distribution at an elevated electron temperature through electron-electron scattering. Finally, the hot electron distribution cools over time as it couples to substrate phonons. Different theoretical models were developed to describe the dynamics of surface plasmon excitations.17-18,

25-26

Govorov et al. investigated the photo generation of excited

carriers in plasmonic nanocrystal by using quantum linear response theory.17-18 In the theoretical study by Manjavacas et al., the conducting electrons of metal were described as free particles in a finite spherical potential well, and the plasmon-induced hot carrier production was calculated by the Fermi’s golden rule.25 In our recent study, the energy distribution of photo-excited hot electrons and holes in metal clusters was obtained from the orbital energy levels involved in the SPR excitation by TD-DFT calculations.26 Taking the unique advantage of SPR to enhance local electric field, generate high energy electron-hole pairs, and convert the light energy into heat, surface plasmon-enhanced photocatalysis has recently come into focus as a promising technique for high performance solar energy conversion, such as photocatalytic water splitting,27-29 photocatalytic CO2 reduction,30-33 photo-induced dissociation of O2 and H2,34-37 photo-assisted organic catalysis,38-42 and photo-controlled nanocrystal growth.43-45 Additionally, gold and silver nanostructures show excellent catalytic performance in a series of selective aerobic oxidation reactions, such as CO


Page 4 of 31

Page 5 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oxidation,46-47 alcohol oxidation,48 and alkene epoxidation.49-50 It has been demonstrated that aromatic amines adsorbed on gold and silver surfaces can be selectively convert to the corresponding aromatic azo compounds under visible light irradiation.20, 51-57 The surface activated oxygen species play a very important role in the aerobic oxidation reactions.26, 34, 58 Activation of oxygen is the most critical step in the catalytic oxidation reaction. Early studies showed molecular oxygen can be activated by anionic silver and gold clusters and be dissociated into two oxygen atoms.59-60 It was found that oxygen binds more strongly on negative clusters than on neutral ones. The O−O bond length is longer and the Au−O distance is shorter on negative gold cluster.61 Recently, Linic et al. proposed that the dissociation of oxygen can be facilitated by surface plasmon-mediated injection of an excited electron to the adsorbates from the optical excited silver nanoparticle.34-35 Two possible charge transfer (CT) mechanism may be involved for oxygen adsorbed on the surfaces of plasmonic nanostructures, direct CT and indirect CT. However, there is still no consensus as to which of these mechanisms plays the most important role.10 The oxygen activation mechanism is a fundamental problem to be resolved because it is directly related to the catalytic oxidation reaction on plasmonic metal nanoparticles. In this article, density functional theory (DFT) calculation is performed to explore the surface plasmon enhanced oxygen dissociation reaction and subsequent catalyzed aerobic oxidation reaction on plasmonic silver and gold nanostructures. Direct photo-induced metal-to-molecule CT transition and indirect CT through excitation of surface plasmon are discussed by TD-DFT. It is found that oxygen molecules are easier dissociated on silver surfaces for its stronger SPR absorption intensity and higher hot electron energy level. We then test the importance of the activated surface oxygen species to the aerobic oxidation reaction. The potential energy surfaces of p-aminothiophenol oxidation reaction occurred in the nanogaps between metal substrate and three different nanoparticles (Ag, Au, and Au@SiO2) are compared. The activated oxygen species on silver surfaces exhibits strongest oxidation ability and strongly reduces the activation energy of the hydrogen abstraction reaction.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Computational Details Density functional theory (DFT) calculations were carried out with the hybrid exchange-correlation (XC) functional B3LYP, which has an empirically determined contribution (~20%) of the nonlocal Hartree-Fock exchange term.62-63 The basis sets for C, H, N, O, and S atoms of investigated molecules were 6-311+G(d, p), including a polarization function to all the atoms and a diffuse function to C, N, O, and S atoms.64-65 For all metal atoms, the valence electrons and the inner shells were described by the basis set, LanL2DZ, and the corresponding relativistic effective core potentials, respectively.66-67 All calculations including structure optimization and thermodynamic energy computation were carried out by using Gaussian 09 package.68 Electronic excitation was studied within the time-dependent DFT (TD-DFT) approaches, which is an efficient method and offers an orbital picture for a physical understanding of the electronic excitation process.69 Because CT transitions usually occur between high-occupied and low-unoccupied orbitals, the improvement of the XC potential in the density tail region may result in the improvement of the low-lying charge transfer excitations.70 Previous investigations have reported that the B3LYP functional could provide good description of geometry properties and accurate intramolecular CT excitation energies.71-73 This method was also successfully used to treat the CT issues of pyridine adsorbed on metal surfaces and explain the wavelength-dependent SERS phenomenon.74 Oxygen adsorbed on the surfaces of metal nanoparticle was modelled as M20−O2 complexes. The optical properties of M20−O2 complexes were studied by TDDFT calculations. By analyzing the orbital components involved in the optical transitions, the intra-band transitions from the sp orbitals of metal atoms were assigned to the surface plasmon excitation, and the transitions from metal atoms to oxygen were assigned to charge transfer. The simulated absorption spectra are presented in terms of the Lorentzian function with the peak half-width at half height of 0.2 eV.


Page 6 of 31

Page 7 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The frequency calculations were performed on all the intermediates and transition states. For stable intermediate geometries, we verified that there is no imaginary frequency. In the case of the transition states we verified that there is only one imaginary frequency corresponding to the reaction coordinate. These frequency calculations also provided us with the thermodynamic data at a pressure of 1 atm and temperature of 298.15 K.

Results and Discussion Activation of oxygen adsorbed on Ag and Au nanoparticles. Figure 1 shows the schematic illustration of surface plasmon-enhanced oxygen dissociation on silver and gold surfaces. Energy of photons incident on the metal surface drives the resonant collective electron oscillation (Figure 1a), which is well known as surface plasmon resonance. Followed by the optical excitation of surface plasmon, two possible relaxation pathways are involved. Surface plasmon damping occurs via either radiative decay into photons (scattering) or nonradiative decay into electron-hole pairs (absorption). The ratio of scattering to absorption was found to increase with the nanoparticle volume based discrete dipole approximation (DDA) simulation75 and Mie theory calculation.76 For small nanoparticles, the dominant decay channel is electron-hole pair generation (Figure 1b). Various theoretical models were developed to describe the energy levels and dynamics of excited electrons and holes. In our recent work, the photo-induced excitation of small metal clusters were investigated by the first principle TD-DFT calculations.26 TD-DFT calculation results agree with the distributions of plasmonic carriers in gold nanoparticles obtained by solving the quantum equation of motion for the density matrix.19 Because of their higher energy, hot electrons will extend further away from the nanoparticle surface than an equilibrium electron distribution at the Fermi level. If a nearby electron acceptor is present, such as oxygen adsorbed on the surface of nanoparticle, hot electron can transfer into its unoccupied orbitals (Figure 1c). This process can be very efficient and quite similar to that in metal-semiconductor composite structures.17-18



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Schematic illustration of surface plasmon-enhanced oxygen dissociation on silver and gold surfaces. (a) coherent optical excitation of SPR on metal surfaces; (b) hot electron-hole pairs created by nonradiative decay of SPR; (c) surface plasmon-induced hot electron injection to adsorbed oxygen molecules; (d) physisorbed O2 on silver; (e) chemisorbed O2− on silver; (f) dissociated O2 on silver.

TD-DFT calculations were performed to explore the plasmon-excited charge transfer of oxygen-metal systems. The metallic clusters were used to mimic the active sites on the surfaces of metal nanostructures. Oxygen adsorbed on metal surfaces were modelled as Mn−O2 complexes (M = Au or Ag, n = 20). Oxygen can bind to metal clusters on either bridge sites or top sites. Figure 2 shows the simulated absorption spectra of metal-oxygen surface complexes at B3LYP/6-311+G(d, p)/LanL2DZ. The absorption spectrum of bare Ag20 cluster shows a single triply degenerate excitation at 3.59 eV, which matches well with the excitation energy of 3.44 eV calculated by BP86 functional and TZP basis set.77 The absorption spectrum of bare Au20 cluster shows two strong triply degenerate excitations at 3.13 and 3.34 eV, which are slightly larger than the calculated excitation energy of 2.89 eV by considering the scalar relativistic effect.78 The adsorption of oxygen has little influence on the absorption spectra of M20 clusters. The strongest excitation lines of


Page 8 of 31

Page 9 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ag20−O2 complexes are located around 3.59 eV, while Au20−O2 complexes show very strong excitation lines around 3.13 eV and 3.34 eV. The molecular orbitals (MOs) involved in the strongest excitation lines have a wide energy distribution, and all of them are attributed to the sp orbitals of metal clusters. It was demonstrated that these discrete electronic transitions in small metal clusters could be employed as an analogue of surface plasmon frequency and thus serve as a model system to understand the excitation of surface plasmons.77-79 Accordingly, the strongest excitation band of surface metal-molecule complexes is attributed to the SPR excitation. Although the calculated plasmon frequencies are higher than normal experimental observations, the SPR excitation energies should red-shift to longer wavelength with increasing size of metallic cluster as a result of decrease of HOMO−LUMO gap. Note that the SPR frequencies of silver-oxygen complexes are higher than that of gold-oxygen complexes, and the SPR intensities of silver complexes are stronger than those of gold complexes.

Figure 2. Simulated absorption spectra of metal-oxygen complexes by TD-DFT calculation at B3LYP/6-311+G(d, p)/LanL2DZ level.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3 shows the energy diagrams of oxygen adsorbed on the bridge site (a, b), the top site (c, d) of Ag20 (a, c) and Au20 (b, d) clusters. The ground state of oxygen is triplet, with two single electrons occupying in two degenerate antibonding 2π* orbitals. So the metal-molecule complexes were set as triplet, and the electrons in the alpha space and the beta space were shown on the left and right sides of Figures 3a−3d, respectively. The green lines are the antibonding orbitals of oxygen on metal surfaces. It is also found that the energy levels of antibonding O−O 2π*orbitals are similar for oxygen adsorbed on gold and silver. However, the energy levels of the top-site adsorbed O2 (around −3.8 eV) are lower than those of the bridge-site adsorbed ones (around −3.5 eV). The calculated energy level of O2 antibonding orbital in Ag20-O2 complex is located near to the Fermi level of silver, which is consistent with previous DFT calculation by using a slab mode.34

Figure 3. Energy diagrams of oxygen adsorbed on the bridge site (a, b) and top site (c, d) of Ag20 (a, c) and Au20 (b, d) clusters. The blue and red lines present the energy distributions of excited hot electrons and hot holes under the condition of SPR. The green lines are the antibonding orbitals of oxygen on metal surfaces. The black lines are the electronic states not involved in SPR excitation.


Page 10 of 31

Page 11 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The energy distribution of hot electrons and hot holes under the condition of SPR excitation can be obtained from TD-DFT calculations. The energy distributions of the hot holes and hot electrons can be predicted from the MOs involved in the initial and final states of SPR excitation,19 which are marked with red and blue lines in Figures 3a−3d. However, it should be noted that the HOMOs/LUMOs that are involved in excitation do not all become hot electrons/hot holes. It is observed that the energy range of excited hot electrons in silver (−2.7 to −1.3 eV) is higher than that in gold (−3.5 to −3.0 eV). For one reason, the work function of silver (4.52~4.74 eV) is higher than that of gold (5.31~5.47 eV).80 By assuming the Fermi level of metal clusters to be the average value of HOMO and LUMO, the Fermi level of Ag20 cluster (−3.91 eV) is about 1 eV higher than that of Au20 cluster (−4.93 eV). For another reason, the strongest absorption wavelength of Ag20−O2 (350 nm) is 0.3 eV higher in energy than that of Au20−O2 (380 nm). This agrees with higher SPR frequency of Ag nanoparticles observed in the extinction experiment.81 The energies of excited hot electrons are higher than 2π* antibonding orbitals of oxygen as presented with green lines. Due to the energetically favorable band alignment of excited hot electrons, we predict that hot electrons in the metal can be injected to an adsorbed oxygen molecule by tunneling the potential well of molecule-metal interface (solid green arrow shown in Figure 1c).34-35 However, it should be noted that the process for charge transfer from the excited metal cluster to the oxygen molecule is not actually treated. Because of higher energies of excited hot electrons and stronger intensity of absorbance, the plasmon-induced hot electron injection efficiency should be higher for silver. The electron in metal clusters can be also directly excited to the adsorbed oxygen molecule by chemical interface damping (dashed green arrow illustrated in Figure 1c).13 Table 1 lists the calculated excitation wavelength and oscillator strength of SPR (metal to metal) and CT (metal to molecule) transitions for metal-oxygen complexes. As seen, the direct metal-to-molecule charge transfers are less possible than SPR excitations. The oscillator strengths of SPR excitations are much larger than that those of the direct CT transitions. Thus the plasmon-induced hot electron injection



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

mechanism should be the major charge transfer channel for oxygen activation on the surfaces of gold and silver.


Page 12 of 31

Page 13 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Left: simulated absorption spectra of Ag20−4O2, Au20−4O2, Ag20−6O2, and Au20−6O2 complexes by TD-DFT calculation. Right: Energy levels of photo-excited charge carriers and LUMO levels of adsorbates. Table 1. Calculated Excitation Wavelength (in nm) and Oscillator Strength of SPR (Metal to Metal) and CT (Metal to Molecule) Transitions for Metal-Molecule Complexes. Complexes

ω (SPR)

f (SPR)

ω (CT)

f (CT)

Ag20

346

2.4570

Ag20-O2 bridge

346

2.4507

872

0.0025

Ag20-6O2 bridge

347

1.3768

506

0.0139

Ag20-O2 top

346

2.3224

1160

0.0277

Ag20-4O2 top

331

1.8569

784

0.4642

Au20

371

0.2713

Au20-O2 bridge

371

0.2657

519

0.0021

Au20-6O2 bridge

394

0.2729

583

0.0090

Au20-O2 top

374

0.1874

615

0.0301

Au20-4O2 top

368

0.5795

693

0.1886

In Figure 3, the energy levels for single O2 molecule adsorbed on bridge/top site of silver and gold clusters are calculated. However, due to the huge amount of oxygen in air, it is possible that all the surface of metal particle is covered by oxygen. To consider the coverage effect, we calculated the absorption spectrum and the corresponding energy levels of photo-excited charge carriers for oxygen adsorbed on all the bridge/top sites of M20 cluster. As seen in Figure 4, oxygen molecules are adsorbed on all the 4 vertices (M20-4O2 top) and 6 edges (M20-6O2 bridge) of tetrahedral M20 clusters. Similar to the absorption spectra in Figure 2, the absorption cross sections of oxygen-silver complexes are larger than those of oxygen-gold complexes. Meanwhile, the maximum absorption frequencies of oxygen-silver complexes are higher than those of oxygen-gold complexes, which results to higher



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

energy levels of excited hot electrons in oxygen-silver complexes. It is also found that an additional absorption peak attributed to the direct metal-to-oxygen CT transition appears in simulated absorption spectra of M20-4O2 top complexes. It is therefore that the direct metal-to-oxygen electron transfer are more possible for oxygen adsorbed on the top sites than the bridges. The details of transition properties of M20-4O2 top and M20-6O2 bridge complexes are summarized in Table 1.

Figure 5. Optimized adsorption structures of O2 and O2− adsorbed on silver and gold clusters.

Dissociation of activated oxygen molecules. In this study, the M20 clusters was used to model the active site on metal surfaces. M20+-O2− is the species after hot-electron transfer from M20 cluster to adsorbed O2. Since the real nanoparticles are much larger, the metal surface should remain approximate electric neutrality after hot-electron transfer. To avoid the complication in study M20-O2 complex in charge separation state, we use M20-O2− instead of M20+-O2−. The optimized structures of M20-O2 and M20-O2− are shown in Figure 5. By comparing the O−O and O−M bond distances, it is found that the O−O bond distance is stretched, and the O−M bond distance is shortened after an excited hot electron is injected into the antibonding orbital of adsorbed O2. For O2 on the bridge site of silver cluster, the O−O bond length increases from 1.206 to 1.346 Å, and the O−M distance reduces from 4.551 to


Page 14 of 31

Page 15 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.390 Å. For O2 on the top site of silver cluster, the O−O bond length increases from 1.212 to 1.318 Å, and the O−M distance reduces from 2.854 to 2.245 Å. The predicted variation trend of O−O and O−M distances agree with pervious theoretical study of oxygen adsorption on neutral and anionic silver and gold clusters.82 Additionally, the O−O vibrational frequency decreases from 1600 to 1200 cm-1, which agrees with experimental measured 1330 ± 80 cm-1.60 These findings suggest that oxygen can be activated on a metal surface by hot electron attachment. It is also found that the binding interactions between O2− and metal clusters are stronger than those between O2 and metal clusters. The binding energies are very small for O2 adsorbed on metal clusters. However, the binding energies dramatically increase to 46.1 (41.6) and 52.9 (58.3) kcal/mol for O2− adsorbed on the bridge (top) site of gold and silver clusters. Thus, once the excited hot electron is injected into the physisorbed oxygen molecule, the formed O2− can strongly chemisorbed on metal surface. Figure 6 shows the potential energy surfaces of dissociation of O2 and O2−. The electron configuration of O2 is (σ2s)2(σ2s*)2(σ2p)2(π2p)4(π2p*)2, and the antibonding orbital is occupied only partially in the electronic ground state. The O−O distance increases from 1.206 Å for O2 to 1.346 Å for O2−, and the bond order decreases from 2 for O2 to 1.5 for O2− as an extra electron occupies in the antibonding O−O 2π* orbital. The calculated bond length of O2 agrees with experimental value of 1.21 Å, however the calculated bond length of O2− is larger than experimental value of 1.26 Å.83 It is seen from Figure 6 the dissociation barrier of O2− is much smaller than that of O2, and the calculated O−O bond energies of O2 and O2− are 118 and 95 kcal/mol, which are consistent with experimental bond dissociation energies of 118 and 94 kcal/mol.83 Therefore, the formation of O2− anion via plasmon-induced hot electron injection mechanism facilitates the dissociation of O2 on metal surfaces.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. Dissociation energy curves of free O2 and O2−.

The dissociation curves of O2 and O2− adsorbed on gold and silver surfaces are illustrated in Figures 7. As the equilibrium O−O bond distances increases, the dissociation energy decreases from 100 kcal/mol to 78 kcal/mol for O2 and O2− adsorbed on the top site, and from 75 kcal/mol to 50 kcal/mol for O2 and O2− adsorbed on the bridge site (see Figure S1, Supporting Information), which is comparable to the dissociative adsorption energy estimated by the dipped adcluster model (44.0 to 61.4 kcal/mol),84 in which the adcluster (admolecule + cluster) is dipped onto the electron bath of the solid metal and an equilibrium is established for electron exchange between the adcluster and the bulk metal.85 The simulated dissociation curves of O2 and O2− by the cluster model match well with those calculated by the periodic boundary condition slab model.34-35 The equilibrium bond length of O2− is larger than that of O2 and the dissociation barrier of O2− is lower than that of O2. Dissociation of oxygen can be facilitated by plasmon-induced hot electron injection mechanism. Also note that dissociation energies of adsorbed O2 and O2− are lower than those of free O2 and O2− as shown in Figures 6 and 7.


Page 16 of 31

Page 17 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. Dissociation energy curves of O2 (a, b) and O2− (c, d) adsorbed on the top site of silver (a, c) and gold (b, d) surfaces.

The overall plasmon-induced oxygen activation reaction can be divided into three major steps: (1) absorption of light by metal nanostructures to generate hot electrons with energy levels higher than the Fermi level; (2) transfer of excited hot electrons to the unoccupied adsorbate states and the formation of O2− anions; (3) dissociation of O2− on metal surfaces. By comparing the efficiencies of the above three crucial steps taking place on gold and silver catalysts, it is apparent that silver catalysts show better catalytic performance for the oxygen activation reaction for its stronger SPR absorption intensity, higher hot electron energy level, and similar oxygen dissociation barrier. Thermal oxidation coupling reactions of PATP. It has been demonstrated that the activated atomic oxygen species (metal oxides or hydroxides) on the surfaces of metal nanostructures can drive the catalytic oxidation reactions.34 Especially, aromatic amines on gold and silver nanostructures can be selectively converted to the corresponding

aromatic

azo

compounds

as

evidenced


from

the

in-situ


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

surface-enhanced Raman spectroscopic studies.86-87 It is found that the conversion of aromatic amines to azo compounds strongly depends on the nature of metal catalyst. Figure 8 presents a schematic illustration of the aerobic oxidation of p-aminothiophenol (PATP) inserted into the gaps between metal substrates and metal nanoparticles. PATP can be chemisorbed on gold and silver surfaces via the thiol end to form well-organized self-assembled monolayers, and its para position amino end can link to another nanoparticle or PATP can be inserted into the gap of the rough metal surfaces to form metal/molecule/metal junction structure. Under visible light irradiation, PATP molecules adsorbed on gold and silver surfaces undergo catalytic oxidative coupling reaction to produce p,p'-dimercaptoazobenzene (DMAB), which gives very characteristic SERS signature.51-52 On gold and silver surfaces, the dissociation of oxygen was verified by X-ray photoelectron spectroscopy.58 As for the Au(Ag)/PATP/Au@SiO2 structure, the oxygen is isolated from gold nanoparticle by the inert SiO2 shell. Dissociation of oxygen molecules cannot occur on SiO2 surface at a similar condition, so no surface atomic oxygen species is formed.16 Park et al. studied the SERS spectra of Au film/PATP/Au NP and Au film/PATP/Ag NP.88 They observed abnormal intense SERS signals at 1142, 1391, and 1438 cm-1, which were absent in the normally Raman spectrum of PATP. These SERS signatures were originally explained as the charge transfer enhancement of adsorbed PATP,89 but it is proved by recent theoretical and experimental studies that the abnormal SERS signals actually arise from the photogenerated new surface species DMAB.51-53 The SERS from PATP adsorbed on silver and gold surfaces can be viewed as mixed spectra from PATP and DMAB. The 1142 cm-1 was assigned to a characteristic mode of DMAB and the 1595 cm-1 peak was assigned to a characteristic mode of PATP.51-52 It is noticed that the relative intensity between DMAB and PATP (I1142/I1595 ratio) in Au film/PATP/Ag NP junction is larger than that in Au film/PATP/Au NP junction.88 Thus PATP molecules can be converted to DMAB more easily in Au film/PATP/Ag NP junction. Huang et al. studied the SERS spectra of Au film/PATP/Au NP and Au film/PATP/Au@SiO2 NP.58 In N2 atmosphere, no SERS signals of DMAB were observed in both Au film/PATP/Au NP and Au


Page 18 of 31

Page 19 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


film/PATP/Au@SiO2 NP junctions due to the absence of oxygen. When the SERS spectra were measured in air, the SERS signals of DMAB can be only detected in Au film/PATP/Au NP junction because oxygen cannot be activated in Au film/PATP/Au@SiO2 NP. According to the reports in previous literatures, the conversion of PATP to DMAB in three junctions decreases as Au film/PATP/Ag NP > Au film/PATP/Au NP > Au film/PATP/Au@SiO2 NP.

Figure 8. Schematic illustration of the aerobic oxidation of PATP inserted into the gaps between metal substrates and metal nanoparticles. (a) Au(Ag)/PATP/Ag, (b) Au(Ag)/PATP/Au, (c) Au(Ag)/PATP/Au@SiO2.

The aerobic oxidation of PATP to DMAB requires the removal of four hydrogen atoms from the nearby two PATP molecules. Figure 9 presents the potential energy surfaces of the aerobic oxidation of PATP to DMAB in three different metal/molecule/metal junctions as shown in Figure 8. In previous study, we found that PATP adsorbed on the bridge site of Ag5 cluster via the thiol end is the most stable adsorption configuration.51 Ag5 and Au5 clusters are therefore chosen to model the active sites on metal surface. As seen in Figure 1, after dioxygen molecule is dissociated on the metal surface, the oxygen atoms are inserted into the bridge site of two silver atoms. M2O clusters are intercepted from Figure 1f and are employed to



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

model the activated oxygen species that react with amino group of PATP.26 Figure 9a compares the potential energy surfaces of aerobic oxidation of PATP in the nanogaps between gold substrate and three different nanoparticles (Ag, Au, and Au@SiO2). In Au/PATP/Au and Au/PATP/Ag junctions, PATP is oxidized by the surface oxide M2O. However, in Au/PATP/Au@SiO2 junction, the dissociation of oxygen molecules cannot take place. As seen in Figure 9, the oxidative coupling of two PATP molecules to DMAB involves four dehydrogenation steps. The optimized structures of reactant PATP and product DMAB interacting with M5 clusters are shown in the insert of Figure 9. The transition states for the consecutive four hydrogen abstraction reactions are labeled as TS1 to TS4 (see details in Table S1 and S2, Supporting Information). The M2O cluster and the N−H bond of PATP construct a four-membered ring structure N−H−O−M−N (TS1), in which the oxygen atom of M2O approaches the hydrogen atom of PATP and the nitrogen atom of PATP binds to the metal atom of M2O through the nitrogen lone pair. The formation of new O−H and N−M bonds along with the breakage of N−H and O−M bonds generates PATP(NH)−M and MOH. MOH can react with another nearby PATP molecule through TS2 to yield PATP(NH)−M and water. Two PATP(NH) radicals occur the N−N coupling to produce a hydrazo species DMHAB. DMHAB undergoes two consecutive dehydrogenation processes to yield DMAB(H) and DMAB. During the reaction of DMHAB with M2O, a N−H−O linear transition state (TS3) is formed. The hydrogen atom is transferred from DMHAB to M2O, producing DMAB(H)−M and MOH. Finally, DMAB(H) is oxidized to DMAB by MOH via TS4. It is noted that the energies of TS3 and TS4 are lower than the reactants because of the interaction of the metal atom with the benzene ring.26 As seen in Figure 8, PATP molecules are trapped into the gap between metal nanoparticle aggregates via both the thiol end and amino end. Govorov et al. performed a theoretical study on the surface plasmon induced heat effect of nanoparticle ensembles.90-91 It was demonstrated that the heat effect can be enhanced due to the inter-nanoparticle Coulomb interaction, especially in the hot “spot” where


Page 20 of 31

Page 21 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the electric field and heating intensity was greatly amplified. Thus, the surface plasmon induced photothermal effect can provide the energy to overcome the reaction barriers of transition states in the case that PATP is tapped into the junction of nanoparticle ensembles. As for the oxidation of PATP by O2, the oxidation agents for the four dehydrogenation steps probably are O2, •O2H, H2O2, and •OH.26, 58 The activation energies for PATP oxidized by free oxygen are much higher than those by surface activated oxygen species. In this case, PATP can be hardly converted to DMAB on Au@SiO2 nanoparticles as demonstrated by experiment.58 Our calculations indicate that the activation energies of dehydrogenation reactions for different oxidation agents decreases in an order of O2 ≈ H2O2 > Au2O ≈ AuOH > •OH ≈ •O2H > Ag2O ≈ AgOH. The rate determining step for the aerobic oxidation of PATP on gold and silver surfaces is the oxygen activation process, while the rate determining step for PATP oxidation on inert SiO2 surface is the first dehydrogenation step. The formation of Ag and Au oxides (M2O) or hydroxides (MOH) may arise from the oxidation of surface atoms of Ag and Au nanoparticles in the presence of oxygen. A comparative SERS study in basic and acidic solutions was performed to confirm whether the Au and Ag oxides or hydroxides are involved in the activation of O2 on the Au and Ag surfaces under laser light illumination, and then further oxidize the adsorbed PATP on the surface.58 The oxides or hydroxides are stable in basic solutions, and will not be easily removed. In acidic solution, the Au and Ag oxide/hydroxide will be dissolved. It was found that the SERS signals from product DMAB are strong in the basic environment. In acidic solution, the SERS signals from DMAB completely disappear. The experimental result are consistent with our calculations: in basic solution, PATP is easily oxidized to DMAB by the surface oxides (M2O) or hydroxides (MOH); in acidic solution, the oxidation of PATP by O2 is very difficult in the absence of surface oxides or hydroxides.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 9. Potential energy surfaces of aerobic oxidation of PATP on gold (a) and silver (b) substrates. The oxidation agents in Au(Ag)/PATP/Ag, Au(Ag)/PATP/Au, Au(Ag)/PATP/Au@SiO2 junctions are modelled as Ag2O, Au2O, and O2.

We also note that changing the metal substrate from gold (Figure 9a) to silver (Figure 9b) has very slight influence on the shapes of potential energy surfaces of aerobic oxidation of PATP. It is the metal nanoparticle binding to the amino group that greatly affects the conversion of PATP to DMAB. Silver catalyst performs better oxidation activity than gold catalyst due to lower activation energy for hydrogenation


Page 22 of 31

Page 23 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reactions. This finding agrees with previous SERS reports on PATP in metal/molecule/metal junctions.58, 88

Conclusions In conclusion, a DFT study is applied to reveal the reaction mechanisms of the oxygen activation and aerobic oxidation reactions for the plasmonic photocatalysis on different nanoparticles. It is found that the surface activated oxygen species play critical role in the aerobic oxidation of PATP. The overall reaction can be divided into the initial surface plasmon-mediated oxygen dissociation and the subsequent photothermal driven oxidative coupling reaction. The present theoretical investigation demonstrates that silver catalyst should be an excellent candidate for the heterogeneous photocatalysis, which can concurrently enhance oxygen dissociation and oxidative dehydrogenation reactions. For oxygen dissociation reaction, the dissociation of oxygen and the formation of surface active oxygen species are accelerated by attachment of an excited electron to the adsorbate from the optical excited metal cluster. The indirect charge transfer via excitation of surface plasmon other than direct excitation of metal-molecule complex plays a major role to the oxygen activation process. Silver nanoparticle shows better catalytic performance for the oxygen activation reaction for its stronger SPR absorption intensity and higher hot electron energy level. For oxidative dehydrogenation reaction, the amino hydrogen atoms of two nearby PATP molecules are consecutively removed by the surface active oxygen species. The energy required for the cleavage of N−H bonds can be provided by the photothermal effect of SPR. The potential energy surfaces of PATP oxidation in three nanogaps, Au(Ag)/PATP/Ag, Au(Ag)/PATP/Au, and Au(Ag)/PATP/Au@SiO2, are compared. It is the metal nanoparticle binding to the amino group that greatly affects the conversion of PATP to DMAB. Silver nanoparticle exhibits higher catalytic oxidation ability due to lower activation energies for hydrogenation reactions.

ASSOCIATED CONTENT



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Supporting Information. Optimized structures of the adsorbed and dissociated states of O2 and O2− on the bridge site of silver and gold clusters. Optimized structures of transition states of the aerobic oxidation of PATP in three nanostructures. AUTHOR INFORMATION Corresponding Author *Email: [email protected].

*Email: [email protected]. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT This work is supported by National Natural Science Foundation of China (21373712, 21321062 and 21533006), National Key Basic Research Program of China (No. 2015CB932303), Fundamental Research Funds for the Central Universities (SWU 114076 and XDJK2015C100), and Open Funds of State Key Laboratory of Physical Chemistry of Solid Surfaces (Xiamen University No. 201416). L. B. Zhao thanks Miss Li-Wei Chen for improving English writing.

REFERENCES (1) Linic, S.; Christopher, P.; Ingram, D. B. Plasmonic-Metal Nanostructures for Efficient Conversion of Solar to Chemical Energy. Nat. Mater. 2011, 10, 911-921. (2) Zhang, X.; Chen, Y. L.; Liu, R. S.; Tsai, D. P. Plasmonic Photocatalysis. Rep. Prog. Phys. 2013, 76, 046401. (3) Hou, W.; Cronin, S. B. A Review of Surface Plasmon Resonance-Enhanced Photocatalysis. Adv. Funct. Mater. 2013, 23, 1612-1619. (4) Sarina, S.; Waclawik, E. R.; Zhu, H. Photocatalysis on Supported Gold and Silver Nanoparticles under Ultraviolet and Visible Light Irradiation. Green Chem. 2013, 15, 1814-1833. (5) Xiao, M.; Jiang, R.; Wang, F.; Fang, C.; Wang, J.; Yu, J. C. Plasmon-Enhanced Chemical Reactions. J. Mater. Chem. A 2013, 1, 5790-5805. (6) Scaiano, J. C.; Stamplecoskie, K. Can Surface Plasmon Fields Provide a New Way to Photosensitize Organic Photoreactions? From Designer Nanoparticles to


Page 24 of 31

Page 25 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Custom Applications. J. Phys. Chem. Lett. 2013, 4, 1177-1187. (7) Ueno, K.; Misawa, H. Surface Plasmon-Enhanced Photochemical Reactions. J. Photochem. Photobiol. C: Photochem. Rev. 2013, 15, 31-52. (8) Chen, X. J.; Cabello, G.; Wu, D. Y.; Tian, Z. Q. Surface-Enhanced Raman Spectroscopy toward Application in Plasmonic Photocatalysis on Metal Nanostructures. J. Photochem. Photobiol. C: Photochem. Rev. 2014, 21, 54-80. (9) Baffou, G.; Quidant, R. Nanoplasmonics for Chemistry. Chem. Soc. Rev. 2014, 43, 3898-3907. (10) Linic, S.; Aslam, U.; Boerigter, C.; Morabito, M. Photochemical Transformations on Plasmonic Metal Nanoparticles. Nat Mater 2015, 14, 567-576. (11) Moskovits, M. Surface Enhanced Raman Scattering Spectroscopy. Rev. Mod. Phys. 1985, 57, 783-826. (12) Willets, K. A.; Van Duyne, R. P. Localized Surface Plasmon Resonance Spectroscopy and Sensing. Annu. Rev. Phys. Chem. 2007, 58, 267-297. (13) Watanabe, K.; Menzel, D.; Nilius, N.; Freund, H. J. Photochemistry on Metal Nanoparticles. Chem. Rev. 2006, 106, 4301-4320. (14) Boriskina, S. V.; Ghasemi, H.; Chen, G. Plasmonic Materials for Energy: From Physics to Applications. Mater. Today 2013, 16, 375-386. (15) Wu, D. Y.; Li, J. F.; Ren, B.; Tian, Z. Q. Electrochemical Surface-Enhanced Raman Spectroscopy of Nanostructures. Chem. Soc. Rev. 2008, 37, 1025-1041. (16) Li, J. F.; Huang, Y. F.; Ding, Y.; Yang, Z. L.; Li, S. B.; Zhou, X. S.; Fan, F. R.; Zhang, W.; Zhou, Z. Y.; Wu, D. Y., et al. Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy. Nature 2010, 464, 392-395. (17) Govorov, A. O.; Zhang, H.; Gun’ko, Y. K. Theory of Photoinjection of Hot Plasmonic Carriers from Metal Nanostructures into Semiconductors and Surface Molecules. J. Phys. Chem. C 2013, 117, 16616-16631. (18) Zhang, H.; Govorov, A. O. Optical Generation of Hot Plasmonic Carriers in Metal Nanocrystals: The Effects of Shape and Field Enhancement. J. Phys. Chem. C 2014, 118, 7606-7614. (19) Govorov, A. O.; Zhang, H.; Demir, H. V.; Gun’ko, Y. K. Photogeneration of Hot Plasmonic Electrons with Metal Nanocrystals: Quantum Description and Potential Applications. Nano Today 2014, 9, 85-101. (20) Zhao, L. B.; Huang, Y. F.; Liu, X. M.; Anema, J. R.; Wu, D. Y.; Ren, B.; Tian, Z. Q. A DFT Study on Photoinduced Surface Catalytic Coupling Reactions on Nanostructured Silver: Selective Formation of Azobenzene Derivatives from Para-Substituted Nitrobenzene and Aniline. Phys. Chem. Chem. Phys. 2012, 14, 12919-12929. (21) Thrall, E. S.; Preska Steinberg, A.; Wu, X.; Brus, L. E. The Role of Photon Energy and Semiconductor Substrate in the Plasmon-Mediated Photooxidation of Citrate by Silver Nanoparticles. J. Phys. Chem. C 2013, 117, 26238-26247. (22) Bigot, J. Y.; Merle, J. Y.; Cregut, O.; Daunois, A. Electron Dynamics in Copper Metallic Nanoparticles Probed with Femtosecond Optical Pulses. Phys. Rev. Lett. 1995, 75, 4702-4705. (23)Hertel, T.; Knoesel, E.; Wolf, M.; Ertl, G. Ultrafast Electron Dynamics at Cu(111):



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Response of an Electron Gas to Optical Excitation. Phys. Rev. Lett. 1996, 76, 535-538. (24) Voisin, C.; Del Fatti, N.; Christofilos, D.; Vallée, F. Ultrafast Electron Dynamics and Optical Nonlinearities in Metal Nanoparticles. J. Phys. Chem. B 2001, 105, 2264-2280. (25) Manjavacas, A.; Liu, J. G.; Kulkarni, V.; Nordlander, P. Plasmon-Induced Hot Carriers in Metallic Nanoparticles. ACS Nano 2014, 8, 7630-7638. (26)Zhao, L. B.; Zhang, M.; Huang, Y. F.; Williams, C. T.; Wu, D. Y.; Ren, B.; Tian, Z. Q. Theoretical Study of Plasmon-Enhanced Surface Catalytic Coupling Reactions of Aromatic Amines and Nitro Compounds. J. Phys. Chem. Lett. 2014, 5, 1259-1266. (27) Ingram, D. B.; Linic, S. Water Splitting on Composite Plasmonic-Metal/Semiconductor Photoelectrodes: Evidence for Selective Plasmon-Induced Formation of Charge Carriers near the Semiconductor Surface. J. Am. Chem. Soc. 2011, 133, 5202-5205. (28) Lee, J.; Mubeen, S.; Ji, X.; Stucky, G. D.; Moskovits, M. Plasmonic Photoanodes for Solar Water Splitting with Visible Light. Nano Lett. 2012, 12, 5014-5019. (29) Mubeen, S.; Lee, J.; Singh, N.; Kramer, S.; Stucky, G. D.; Moskovits, M. An Autonomous Photosynthetic Device in Which All Charge Carriers Derive from Surface Plasmons. Nat. Nanotechnol. 2013, 8, 247-251. (30) Varghese, O. K.; Paulose, M.; LaTempa, T. J.; Grimes, C. A. High-Rate Solar Photocatalytic Conversion of Co2 and Water Vapor to Hydrocarbon Fuels. Nano Lett. 2009, 9, 731-737. (31) Roy, S. C.; Varghese, O. K.; Paulose, M.; Grimes, C. A. Toward Solar Fuels: Photocatalytic Conversion of Carbon Dioxide to Hydrocarbons. ACS Nano 2010, 4, 1259-1278. (32) Hou, W.; Hung, W. H.; Pavaskar, P.; Goeppert, A.; Aykol, M.; Cronin, S. B. Photocatalytic Conversion of CO2 to Hydrocarbon Fuels Via Plasmon-Enhanced Absorption and Metallic Interband Transitions. ACS Catalysis 2011, 1, 929-936. (33) Wang, C.; Ranasingha, O.; Natesakhawat, S.; Ohodnicki, P. R.; Andio, M.; Lewis, J. P.; Matranga, C. Visible Light Plasmonic Heating of Au-ZnO for the Catalytic Reduction of CO2. Nanoscale 2013, 5, 6968-6974. (34) Christopher, P.; Xin, H.; Linic, S. Visible-Light-Enhanced Catalytic Oxidation Reactions on Plasmonic Silver Nanostructures. Nat. Chem. 2011, 3, 467-472. (35) Christopher, P.; Xin, H.; Marimuthu, A.; Linic, S. Singular Characteristics and Unique Chemical Bond Activation Mechanisms of Photocatalytic Reactions on Plasmonic Nanostructures. Nat. Mater. 2012, 11, 1044-1050. (36) 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. (37) Mukherjee, S.; Zhou, L.; Goodman, A. M.; Large, N.; Ayala Orozco, C.; Zhang, Y.; Nordlander, P.; Halas, N. J. Hot Electron Induced Dissociation of H2 on Au Nanoparticles Supported on SiO2. J. Am. Chem. Soc. 2013, 136, 64-67. (38) Zhu, H.; Ke, X.; Yang, X.; Sarina, S.; Liu, H. Reduction of Nitroaromatic


Page 26 of 31

Page 27 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Compounds on Supported Gold Nanoparticles by Visible and Ultraviolet Light. Angew. Chem., Int. Ed. 2010, 49, 9657-9661. (39) Tsukamoto, D.; Shiraishi, Y.; Sugano, Y.; Ichikawa, S.; Tanaka, S.; Hirai, T. Gold Nanoparticles Located at the Interface of Anatase/Rutile TiO2 Particles as Active Plasmonic Photocatalysts for Aerobic Oxidation. J. Am. Chem. Soc. 2012, 134, 6309-6315. (40) Wang, F.; Li, C.; Chen, H.; Jiang, R.; Sun, L. D.; Li, Q.; Wang, J.; Yu, J. C.; Yan, C. H. Plasmonic Harvesting of Light Energy for Suzuki Coupling Reactions. J. Am. Chem. Soc. 2013, 135, 5588-5601. (41) Hallett-Tapley, G. L.; Silvero, M. J.; González-Béjar, M.; Grenier, M.; Netto-Ferreira, J. C.; Scaiano, J. C. Plasmon-Mediated Catalytic Oxidation of Sec-Phenethyl and Benzyl Alcohols. J. Phys. Chem. C 2011, 115, 10784-10790. (42) Hallett-Tapley, G. L.; Silvero, M. J.; Bueno-Alejo, C. J.; González-Béjar, M.; McTiernan, C. D.; Grenier, M.; Netto-Ferreira, J. C.; Scaiano, J. C. Supported Gold Nanoparticles as Efficient Catalysts in the Solventless Plasmon Mediated Oxidation of Sec-Phenethyl and Benzyl Alcohol. J. Phys. Chem. C 2013, 117, 12279-12288. (43) Jin, R.; Cao, Y.; Mirkin, C. A.; Kelly, K. L.; Schatz, G. C.; Zheng, J. G. Photoinduced Conversion of Silver Nanospheres to Nanoprisms. Science 2001, 294, 1901-1903. (44) Jin, R. C.; Cao, Y. C.; Hao, E. C.; Metraux, G. S.; Schatz, G. C.; Mirkin, C. A. Controlling Anisotropic Nanoparticle Growth through Plasmon Excitation. Nature 2003, 425, 487-490. (45) Maillard, M.; Huang, P.; Brus, L. Silver Nanodisk Growth by Surface Plasmon Enhanced Photoreduction of Adsorbed [Ag+]. Nano Lett. 2003, 3, 1611-1615. (46) Liu, Z. P.; Hu, P.; Alavi, A. Catalytic Role of Gold in Gold-Based Catalysts: A Density Functional Theory Study on the CO Oxidation on Gold. J. Am. Chem. Soc. 2002, 124, 14770-14779. (47) Lopez, N.; Nørskov, J. K. Catalytic CO Oxidation by a Gold Nanoparticle: A Density Functional Study. J. Am. Chem. Soc. 2002, 124, 11262-11263. (48) Wittstock, A.; Zielasek, V.; Biener, J.; Friend, C. M.; Bäumer, M. Nanoporous Gold Catalysts for Selective Gas-Phase Oxidative Coupling of Methanol at Low Temperature. Science 2010, 327, 319-322. (49) Hughes, M. D.; Xu, Y.-J.; Jenkins, P.; McMorn, P.; Landon, P.; Enache, D. I.; Carley, A. F.; Attard, G. A.; Hutchings, G. J.; King, F., et al. Tunable Gold Catalysts for Selective Hydrocarbon Oxidation under Mild Conditions. Nature 2005, 437, 1132-1135. (50) Lei, Y.; Mehmood, F.; Lee, S.; Greeley, J.; Lee, B.; Seifert, S.; Winans, R. E.; Elam, J. W.; Meyer, R. J.; Redfern, P. C., et al. Increased Silver Activity for Direct Propylene Epoxidation Via Subnanometer Size Effects. Science 2010, 328, 224-228. (51) Wu, D. Y.; Liu, X. M.; Huang, Y. F.; Ren, B.; Xu, X.; Tian, Z. Q. Surface Catalytic Coupling Reaction of p-Mercaptoaniline Linking to Silver Nanostructures Responsible for Abnormal SERS Enhancement: A DFT Study. J. Phys. Chem. C 2009, 113, 18212-18222. (52) Huang, Y. F.; Zhu, H. P.; Liu, G. K.; Wu, D. Y.; Ren, B.; Tian, Z. Q. When the



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Signal Is Not from the Original Molecule to Be Detected: Chemical Transformation of Para-Aminothiophenol on Ag During the SERS Measurement. J. Am. Chem. Soc. 2010, 132, 9244-9246. (53) Wu, D. Y.; Zhao, L. B.; Liu, X. M.; Huang, R.; Huang, Y. F.; Ren, B.; Tian, Z. Q. Photon-Driven Charge Transfer and Photocatalysis of p-Aminothiophenol in Metal Nanogaps: A DFT Study of SERS. Chem. Commun. 2011, 47, 2520-2522. (54) Fang, Y.; Li, Y.; Xu, H.; Sun, M. Ascertaining p,p'-Dimercaptoazobenzene Produced from p-Aminothiophenol by Selective Catalytic Coupling Reaction on Silver Nanoparticles. Langmuir 2010, 26, 7737-7746. (55) Huang, Y.; Fang, Y.; Yang, Z.; Sun, M. Can p,p'-Dimercaptoazobenzene Be Produced from P-Aminothiophenol by Surface Photochemistry Reaction in the Junctions of a Ag Nanoparticle−Molecule−Ag (or Au) Film? J. Phys. Chem. C 2010, 114, 18263-18269. (56) Xu, P.; Kang, L.; Mack, N. H.; Schanze, K. S.; Han, X.; Wang, H. L. Mechanistic Understanding of Surface Plasmon Assisted Catalysis on a Single Particle: Cyclic Redox of 4-Aminothiophenol. Sci. Rep. 2013, 3, 2997. (57) Duan, S.; Ai, Y. J.; Hu, W.; Luo, Y. Roles of Plasmonic Excitation and Protonation on Photoreactions of p-Aminobenzenethiol on Ag Nanoparticles. J. Phys. Chem. C 2014, 118, 6893-6902. (58) Huang, Y. F.; Zhang, M.; Zhao, L. B.; Feng, J. M.; Wu, D. Y.; Ren, B.; Tian, Z. Q. Activation of Oxygen on Gold and Silver Nanoparticles Assisted by Surface Plasmon Resonances. Angew. Chem., Int. Ed. 2014, 53, 2353-2357. (59) Hagen, J.; Socaciu, L. D.; Le Roux, J.; Popolan, D.; Bernhardt, T. M.; Wöste, L.; Mitrić, R.; Noack, H.; Bonačić-Koutecký, V. Cooperative Effects in the Activation of Molecular Oxygen by Anionic Silver Clusters. J. Am. Chem. Soc. 2004, 126, 3442-3443. (60) Huang, W.; Zhai, H. J.; Wang, L. S. Probing the Interactions of O2 with Small Gold Cluster Anions (Aun−, n = 1−7): Chemisorption vs Physisorption. J. Am. Chem. Soc. 2010, 132, 4344-4351. (61) Mills, G.; Gordon, M. S.; Metiu, H. The Adsorption of Molecular Oxygen on Neutral and Negative Aun Clusters (n = 2–5). Chem. Phys. Lett. 2002, 359, 493-499. (62) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785-789. (63) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648-5652. (64) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. Self-Consistent Molecular Orbital Methods. XX. A Basis Set for Correlated Wave Functions. J. Chem. Phys. 1980, 72, 650-654. (65) McLean, A. D.; Chandler, G. S. Contracted Gaussian Basis Sets for Molecular Calculations. I. Second Row Atoms, Z = 11-18. J. Chem. Phys. 1980, 72, 5639-5648. (66) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for the Transition Metal Atoms Scandium to Mercury. J.


Page 28 of 31

Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Chem. Phys. 1985, 82, 270-283. (67) Wadt, W. R.; Hay, P. J. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for Main Group Elements Sodium to Bismuth. J. Chem. Phys. 1985, 82, 284-298. (68) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. A.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Revision A.02, Gaussian, Inc.: Wallingford, CT 2009. (69) Bauernschmitt, R.; Ahlrichs, R. Treatment of Electronic Excitations within the Adiabatic Approximation of Time Dependent Density Functional Theory. Chem. Phys. Lett. 1996, 256, 454-464. (70) Tao, J.; Tretiak, S.; Zhu, J.-X. Absorption Spectra of Blue-Light-Emitting Oligoquinolines from Time-Dependent Density Functional Theory. J. Phys. Chem. B 2008, 112, 13701-13710. (71) Jamorski Jödicke, C.; Lüthi, H. P. Time-Dependent Density Functional Theory (TDDFT) Study of the Excited Charge-Transfer State Formation of a Series of Aromatic Donor−Acceptor Systems. J. Am. Chem. Soc. 2003, 125, 252-264. (72)Hrobárik, P.; Sigmundová, I.; Zahradník, P.; Kasák, P.; Arion, V.; Franz, E.; Clays, K. Molecular Engineering of Benzothiazolium Salts with Large Quadratic Hyperpolarizabilities: Can Auxiliary Electron-Withdrawing Groups Enhance Nonlinear Optical Responses? J. Phys. Chem. C 2010, 114, 22289-22302. (73) Crawford, A. G.; Dwyer, A. D.; Liu, Z.; Steffen, A.; Beeby, A.; Pålsson, L. O.; Tozer, D. J.; Marder, T. B. Experimental and Theoretical Studies of the Photophysical Properties of 2- and 2,7-Functionalized Pyrene Derivatives. J. Am. Chem. Soc. 2011, 133, 13349-13362. (74) Wu, D. Y.; Liu, X. M.; Duan, S.; Xu, X.; Ren, B.; Lin, S. H.; Tian, Z. Q. Chemical Enhancement Effects in SERS Spectra: A Quantum Chemical Study of Pyridine Interacting with Copper, Silver, Gold and Platinum Metals. J. Phys. Chem. C 2008, 112, 4195-4204. (75) Jain, P. K.; Lee, K. S.; El-Sayed, I. H.; El-Sayed, M. A. Calculated Absorption and Scattering Properties of Gold Nanoparticles of Different Size, Shape, and Composition: Applications in Biological Imaging and Biomedicine. J. Phys. Chem. B 2006, 110, 7238-7248. (76) Tcherniak, A.; Ha, J. W.; Dominguez-Medina, S.; Slaughter, L. S.; Link, S. Probing a Century Old Prediction One Plasmonic Particle at a Time. Nano Lett. 2010, 10, 1398-1404. (77) Zhao, L. L.; Jensen, L.; Schatz, G. C. Pyridine−Ag20 Cluster: A Model System for Studying Surface-Enhanced Raman Scattering. J. Am. Chem. Soc. 2006, 128, 2911-2919. (78) Aikens, C. M.; Schatz, G. C. TDDFT Studies of Absorption and SERS Spectra of Pyridine Interacting with Au20. J. Phys. Chem. A 2006, 110, 13317-13324. (79) Zhao, L. L.; Jensen, L.; Schatz, G. C. Surface-Enhanced Raman Scattering of Pyrazine at the Junction between Two Ag20 Nanoclusters. Nano Lett. 2006, 6, 1229-1234. (80) Hynes, W. M., Crc Handbook of Chemistry and Physics, 90th Edition. Apple



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Academic Press Inc.: New Jersey, 2010. (81) Mallin, M. P.; Murphy, C. J. Solution-Phase Synthesis of Sub-10 nm Au−Ag Alloy Nanoparticles. Nano Lett. 2002, 2, 1235-1237. (82) Liao, M. S.; Watts, J. D.; Huang, M. J. Theoretical Comparative Study of Oxygen Adsorption on Neutral and Anionic Agn and Aun Clusters (n = 2–25). J. Phys. Chem. C 2014, 118, 21911-21927. (83) Zhou, G. D., Fundamentals of Structural Chemistry. World Scientific Publishing Co Pte Ltd: 1993. (84) Nakatsuji, H.; Nakai, H. Dipped Adcluster Model Study for Molecular and Dissociative Chemisorptions of O2 on Ag Surface. J. Chem. Phys. 1993, 98, 2423-2436. (85) Nakatsuji, H. Dipped Adcluster Model for Chemisorptions and Catalytic Reactions on a Metal Surface. J. Chem. Phys. 1987, 87, 4995-5001. (86) Zhao, L. B.; Huang, Y. F.; Wu, D. Y.; Ren, B. Surface-Enhanced Raman Spectroscopy and Plasmon-Assisted Photocatalysis of p-Aminothiophenol. Acta Chim. Sinica 2014, 72, 1125-1138. (87) Wu, D. Y.; Zhang, M.; Zhao, L. B.; Huang, Y. F.; Ren, B.; Tian, Z. Q. Surface Plasmon-Enhanced Photochemical Reactions on Noble Metal Nanostructures. Sci. China Chem. 2015, 58, 574-585. (88) Park, W. H.; Kim, Z. H. Charge Transfer Enhancement in the SERS of a Single Molecule. Nano Lett. 2010, 10, 4040-4048. (89) Osawa, M.; Matsuda, N.; Yoshii, K.; Uchida, I. Charge Transfer Resonance Raman Process in Surface-Enhanced Raman Scattering from p-Aminothiophenol Adsorbed on Silver: Herzberg-Teller Contribution. J. Phys. Chem. 1994, 98, 12702-12707. (90) Govorov, A. O.; Zhang, W.; Skeini, T.; Richardson, H.; Lee, J.; Kotov, N. A. Gold Nanoparticle Ensembles as Heaters and Actuators: Melting and Collective Plasmon Resonances. Nanoscale Res. Lett. 2006, 1, 84-90. (91) Govorov, A. O.; Richardson, H. H. Generating Heat with Metal Nanoparticles. Nano Today 2007, 2, 30-38.


Page 30 of 31

Page 31 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC GRAPHICS


Surface Plasmon Catalytic Aerobic Oxidation of Aromatic Amines in

Recommend Documents