S1

Supporting Information

Surface Plasmon Enabling Nitrogen Fixation in Pure Water

through a Dissociative Mechanism under Mild Conditions

Canyu Hu,†,‡ Xing Chen,¶,‡ Jianbo Jin,†,‡ Yong Han,§ Shuangming Chen,†

Huanxin Ju,† Jun Cai,§,¦ Yunrui Qiu,† Chao Gao,† Chengming Wang,†

Zeming Qi,† Ran Long,†,* Li Song,† Zhi Liu,§,¦ and Yujie Xiong†,*

†Hefei National Laboratory for Physical Sciences at the Microscale, Collaborative

Innovation Center of Chemistry for Energy Materials (iChEM), School of Chemistry

and Materials Science, and National Synchrotron Radiation Laboratory, University of

Science and Technology of China, Hefei, Anhui 230026, P. R. China.

¶Department of Chemistry, Pennsylvania State University, University Park,

Pennsylvania 16802, United States.

§School of Physical Science and Technology, Shanghai Tech University, Shanghai

201203, China.

¦State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of

Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai

200050, P. R. China.

*Corresponding author. E-mail: yjxiong@ustc.edu.cn; longran@ustc.edu.cn

‡These authors contributed equally.

S2

1. Experimental materials:

Ruthenium(III) chloride hydrate (RuCl3·xH2O, 35.0-42.0% Ru basis) was obtained

from Aladdin. Gold(III) chloride tetrahydrate (HAuCl4·4H2O, 99.95%), diethylene

glycol (C4H10O3, DEG, 99.0%) and acetone (C3H6O, 99.5%) were purchased from

Sinopharm Chemical Reagent Co., Ltd. Polyvinyl pyrrolidone (PVP, average M.W. =

40000) was obtained from Sigma-Aldrich. The water used in all experiments was

deionized (DI). All the chemical reagents were used without further purification.

2. Experimental procedures:

Synthesis of AuRux. AuRux nanostructures were synthesized by following similar

procedures to AuRu0.31 except for the difference in the concentration of RuCl3·xH2O as

well as the usage volume and injection speed of the precursor solution. The

experimental parameters were set as follows: 1) 4 mL precursor solution containing

5.23 mg RuCl3·xH2O and 10.39 mg HAuCl4·4H2O was injected at a rate of 1.2 mL·min-

1 for AuRu0.39; 2) 3.7 mL precursor solution containing 2.62 mg RuCl3·xH2O and 10.39

mg HAuCl4·4H2O was injected at a rate of 1.5 mL·min-1 for AuRu0.23; 3) 3.5 mL

precursor solution containing 1.31 mg RuCl3·xH2O and 10.39 mg HAuCl4·4H2O was

injected at a rate of 1.8 mL·min-1 for AuRu0.14; 4) 3.5 mL precursor solution without

RuCl3·xH2O was injected at a rate of 1.8 mL·min-1 for Au nanoparticles.

3. Instrumentation:

Transmission electron microscopy (TEM) images were taken on a Hitachi Model H-

7700 microscopy at an accelerating voltage of 100 kV. High-resolution transmission

electron microscopy (HRTEM) images and energy dispersive spectroscopy (EDS)

mapping profiles were recorded on a JEOL JEM-2100F field-emission high resolution

transmission electron microscope at an accelerating voltage of 200 kV.

Powder X-ray diffraction (XRD) patterns were collected using a Japan Rigaku DMax-

γA rotation anode X-ray diffractometer equipped with graphite monochromatized Cu

S3

Kα radiation (λ = 1.54178 Å).

The concentrations of elements were measured with a Thermo Scientific PlasmaQuad

3 inductively-coupled plasma mass spectrometry (ICP-MS) after ultrasonic dissolution

with hot Aqua regia.

Ultraviolet-visible (UV-vis) extinction spectra were collected in the spectral region of

200-800 nm with an Agilent Technologies Cary 60 spectrometer. The samples were

dispersed and diluted with DI water to the same concentration before measurement.

4. ESR measurements:

50 µL of aqueous suspension of nanostructures (1 mg/mL for AuRu0.31) was mixed with

500 µL of spin-trapping agent solution (50 mM). The solution was then characterized

with a JES-FA200 electron spin resonance (ESR) spectroscopy at 20C. The

measurements were performed in different chemical environments and incident light

conditions. The Xe lamp irradiation experiment was carried out by USHIO Optical

Modulex SX-U1501XQ (500 W).

5. First-Principles Simulations:

The geometry optimization was performed using the Becke-Perdew (BP86) functional

and Slater-type orbitals represented by double-𝛇 polarized (DZP) functions with large

frozen cores. The relativistic effects were taken into account by means of the scalar

Zero Order Regular Approximation (ZORA).S1-S3 The electron densities were

calculated at the level of BP86/TZP. The unrestricted spin-polarized density

functional theory (DFT) was employed to treat the open-shell system. All calculations

were carried out by the Amsterdam Density Functional (ADF) program package.S4

6. XAFS characterization:

Au L3-edge and Ru K-edge X-ray absorption fine structure (XAFS) measurements were

S4

performed at the beamline 14W1 in Shanghai Synchrotron Radiation Facility (SSRF),

China. The X-ray was monochromatized by a double-crystal Si (311) monochromator.

The storage ring of SSRF was operated at 3.5 GeV with the current of 300 mA. The

acquired extended XAFS (EXAFS) data were processed according to the standard

procedures using the WinXAS3.1 program.S5 Theoretical amplitudes and phase-shift

functions were calculated with the FEFF8.2 code using the crystal structural parameters

of the Au foil and Ru foil.S6

S5

Figure S1. TEM images of (a) Au, (b) AuRu0.14, (c) AuRu0.23 and (d) AuRu0.39.

In the absence of RuCl3·xH2O, our protocol typically produces fivefold twinned Au

nanoparticles with an average size of 61 nm. As RuCl3·xH2O is added into this

synthetic system, the morphologies of the resulting nanostructures are altered. With

the addition of RuCl3·xH2O, the particle sizes are reduced from 61 nm to 37 nm (see

Figure S2) by affecting nucleation stage, while the structure gradually becomes a core-

antenna nanostructure. In our synthesis, we carefully optimize the synthetic condition

(e.g., amount of precursor and injection speed) for each sample so that the sizes of

AuRux samples can be all controlled to about 37 nm. The consistent sizes provide a

platform for reliably comparing the catalytic performance of various AuRux samples.

Since bare Au nanocrystals typically possess very low catalytic activity for N2 fixation,

their relatively larger particle size (61 nm) would not much affect the evaluation results.

S6

Figure S2. Size distribution histograms for (a) bare Au, (b) AuRu0.14, (c) AuRu0.23,

(d) AuRu0.31 and (e) AuRu0.39.

S7

Figure S3. XRD patterns of the as-obtained AuRux nanostructures in reference to

standard patterns for face-centered cubic (fcc) Ru (JCPDS No. 88-2333), fcc Au

(JCPDS No. 89-3697) and hexagonal close-packed (hcp) Ru (JCPDS No. 89-4903).

As shown in Figure S3, the XRD peaks for all the samples can be almost indexed to fcc

Au (JCPDS No. 89-3697). The absence of Ru fcc and hcp peaks indicates the

formation of AuRu alloy in the antenna.

S8

Figure S4. Normalized (a) Au L3-edge and (b) Ru K-edge XANES spectra of AuRu0.31

in reference to Au foil and Ru foil. k3-weighted Fourier-transform (c) Au L3-edge and

(d) Ru K-edge EXAFS spectra.

S9

Figure S5. UV-vis extinction spectra of bare Au and AuRux nanostructures with varied

Ru contents at the same mass concentration.

As displayed in Figure S5, the light extinction of Au nanostructures is gradually

quenched as Ru is incorporated into Au lattice. When the content of Ru atoms reaches

39%, the light harvesting of AuRux is significantly reduced.

S10

Figure S6. TEM image of the AuRu0.31 catalyst after catalytic reaction.

S11

Figure S7. ESR spectrum of DMPO in the presence of AuRu0.31 under light irradiation

in reference to other conditions.

S12

Figure S8. TEM images of (a) hybrid nanostructures by modifying Au nanorods with

Ru atoms, (b) hybrid nanostructures by modifying Au nanospheres with Ru atoms, and

(c) AuRu0.31 without the addition of PVP.

S13

Figure S9. In-situ DRIFTS spectra recorded for Ar + H2O over AuRu0.31 nanostructures

under the same irradiation condition. The background for the water-saturated system

has been subtracted from the spectra.

S14

Figure S10. DRIFTS spectra recorded for H2O adsorbed on sample surface. The

background for the fully dried sample has been subtracted from the spectra.

Figure S10 shows that the absorption bands of H2O are located at 1625-1800 and 3420-

3850 cm-1, which are obviously different from the absorption band of ammonia at 3000-

3600 cm-1 and NH4+ at 1404 cm-1.

S15

Figure S11. The optimized structure of N2 adsorbed on Au22Ru6 cluster without

additional charge or electric field.

S16

Figure S12. The optimized structures of N2 adsorbed on Au22Ru6 cluster: (a) charged

by 1e, and (b) experienced with an electric field of 1.0108 v·m-1.

S17

Table S1. The molar ratios of Ru:Au in the AuRux samples calculated from precursor

usage and experimentally determined by ICP-MS.

Calculated molar ratio of Ru:Au Experimental molar ratio of Ru:Au

Bare Au 0.00 0.00

AuRu0.14 0.25 0.14

AuRu0.23 0.50 0.23

AuRu0.31 0.75 0.31

AuRu0.39 1.00 0.39

S18

Table S2. Photocatalytic N2 fixation over samples under various reaction conditions.

Entry Catalyst Light Atmosphere Solvent

Ammonia

production rate

(μmol∙g-1∙h-1)

1 AuRu0.31 400 mW Nitrogen Acetonitrile Trace

2 Au nanorods

@Ru 400 mW Nitrogen Water 18.2

3 Au nanospheres

@Ru 400 mW Nitrogen Water 83.6

4 400 mW Nitrogen Water Trace

5 400 mW Argon Water Trace

6 AuRu0.31

(no PVP) 400 mW Nitrogen Water 66.1

S19

References:

S1. van Lenthe, E.; Baerends, E. J.; Snijders, J. G. Relativistic Regular Two-component

Hamiltonians. J. Chem. Phys. 1993, 99, 4597.

S2. van Lenthe, E.; Baerends, E. J.; Snijders, J. G. Relativistic Total Energy Using

Regular Approximations. J. Chem. Phys. 1994, 101, 9783.

S3. van Lenthe, E.; Ehlers, A.; Baerends, E.-J. Geometry Optimizations in the Zero

Order Regular Approximation for Relativistic Effects. J. Chem. Phys. 1999, 110,

8943.

S4. te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra, C.; van

Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. Chemistry with ADF. J. Comput.

Chem. 2001, 22, 931.

S5. Ressler, T. WinXAS: a Program for X-ray Absorption Spectroscopy Data Analysis

under MS-Windows. J. Synchrotron Radiat. 1998, 5, 118.

S6. Ankudinov, A. L.; Ravel, B.; Rehr, J. J.; Conradson, S. D. Real-space Multiple-

Scattering Calculation and Interpretation of X-ray-absorption Near-edge Structure.

Phys. Rev. B 1998, 58, 7565.