SUPPORTING INFORMATION

Dual photocatalytic roles of light: Charge separation at theband gap and heat via localized surface plasmon resonanceto convert CO2 into CO above silver–zirconium oxide
Hongwei Zhang,† Takaomi Itoi,‡ Takehisa Konishi,† and Yasuo Izumi†,*†Department of Chemistry, Graduate School of Science, Chiba University, Yayoi 1-33, Inage-ku, Chiba 263-8522, Japan. ‡Department of Mechanical Engineering, Graduate School of Engineering, Chiba University, Yayoi 1-33, Inage-ku, Chiba 2638522, Japan.
The intensity distribution of Xe arc lamp is shown in Figure
S1.
A detailed time course of photocatalytic tests using 13CO2,H2, and Ag–ZrO2 photocatalysts is shown in Figure S2. The
dependence of the rate of CO formation on Ag content in thephotocatalyst is also depicted in Figure S3. To understand theisotope ratio of 13CO versus 12CO, the exchange reaction of13
CO2 with photocatalysts was performed in the dark (FigureS4) as a control for that conducted under the influence of UV–visible light (Figure 2). Table S1 summarizes the formation ratesof 13CO and 12CO obtained from various control tests incomparison to data from the light reaction (Table 1).

Figure S1. The intensity distribution of Xe arc lamp used in thisstudy as a function of wavelength.

Figure S2. Time course of 13CO and 12CO formation during
photocatalytic test exposed to 12CO2 (2.3 kPa) and H2 (21.7 kPa)
using (A) ZrO2, (B) Ag (0.50 wt. %)–ZrO2, (C) Ag (3.0 wt. %)–ZrO2, (D) Ag (5.0 wt. %)–ZrO2, (E) Ag (10 wt. %)–ZrO2, and UV–
visible light. Amount of catalyst used was 0.100 g.

S1

Figure S3. Dependence of 13CO and 12CO formation rates on theAg content in the Ag–ZrO2 photocatalysts (0.100 g) using 13CO2(2.3 kPa), H2 (21.7 kPa), and UV–visible light.
Figure S4. Time course of 13CO2 (0.67 kPa) exchange reaction
exposed to dark conditions using (A) ZrO2 and (B) Ag (5.0 wt.
%)–ZrO2. The quartz reactor was completely wrapped by Al foil.
Amount of catalyst used was 0.100 g.

TABLE S1. Summary of kinetic data on CO2 conversion using the ZrO2-based photocatalyst (control tests).
(A) 13CO2 (2.3 kPa) and H2 (21.7 kPa) under dark conditions
Entry

Catalystab

ZrO2
Ag 5.0%–ZrO2Formation rate (μmol h−1 gcat−1)
13120.0038
0.00890.00250.0036

COCO(B) 13CO2 (2.3 kPa) under UV–visible light
Entry

CatalystaAg 5.0%–ZrO2Formation rate (μmol h−1 gcat−1)
13CO<0.000912CO

H2<0.001<0.002(C) 13CO2 (2.3 kPa) and H2O (2.7 kPa) under dark conditions
Entry

Catalyst

Formation rate (μmol h−1 gcat−1)
13aa ' *1*1

Ag 5.0%–ZrO2CO12CO

H2<0.0009<0.001<0.0020.00600.00280.052

Monitored in dark conditions followed by tests during exposure to UV–visible light.

S2

Table S2. Ag temperature changes in the Ag–ZrO2 photocatalysts monitored by EXAFS under various photocatalytic reaction
conditions.
Maximum σ
EntryabAg content(wt. %)3.0

Ambient gas

CO2 + H2ArcdeLight
irradiatedCO2 + H2(K)

(min)

T(K)

Time afterlight was offNote(min)39290290

12Figure 5367

5030210Figure S636390297<3536590298<35

UV–visible

329/50/(λ > 580 nm)

317

90296

15

UV–visible(full)
UV–visible

5.0

Irradiatio
n timeTMinimum σ(λ > 320 nm)

Figure S5. (A) Fluorescence spectra of ZrO2 with excitation at 200nm (a) and 240 nm (b) and (B) excitation spectra of thefluorescence detection at 370 nm (a) and 396 nm (b). 2 mg ofZrO2 sample powder was suspended in 3 mL of water.

Figure S6. The change of N (A) and σvalues (B) and FT obtainedfrom k3-weighted Ag K-edge EXAFS χ-function (C) for Ag (3.0 wt.
%)–ZrO2 sample irradiated under argon (90 kPa) and UV–visible
light for 60 min is followed under dark.

Surface Debye temperature was reported for verticaldisplacement at the Ag(1 1 1) (155 K), Ag(1 1 0) (152 K), andAg(1 0 0) (104 K) surfaces. We took this effect into account for
one of the three degrees of freedom (one vertical, two lateral)
for surface Ag atoms, e.g., the mean N value for Ag (3.0 wt. %)ZrO2 (9.5 based on Figure 5A) corresponds to a dispersion of0.45. If the surface Ag atoms on the Ag nanoparticle
hemisphere are free for the enhanced degree of freedom, aS3

portion, i.e.,, is enhanced at the surface versus
1 10.45´ ´ = 0.075
2 3
the rest,, which behaves as a bulk
1
1 20.55+ 0.45´ + 0.45´ ´ = 0.925
22 3site.

If we assume that there is a homogeneous intensity
distribution wavelength for the Xe arc lamp (200–1100 nm, 90mW cm−2)1 and that the portion between 360 and 480 nm(Figure 4) effectively induced Ag LSPR in Ag (3.0 wt. %)–ZrO2(125 mg of disk with diameter of 1.0 cm), then this results in an
effective energy of 9.42 mJ s−1. The standard heat capacity for Agand ZrO2 is 25.350 and 56.123 J K−1 mol−1,2,3 respectively, which
results in 56.1 mJ K−1 for 125 mg of a Ag–ZrO2 disk. Therefore,
the rate of increase in the sample’s temperature was calculated
as 10.1 K min−1, which is consistent with observed initialramping rates (3.9–5.3 K min−1; Figures 5B and S6B) if Ag lightabsorption efficiency ranged from 39% to 52% for absorption,scattering, and light reflection.
The time course for Ag–Ag peak intensity and the N and σvalues under CO2 and H2 (Figure 5A–C) were compared withthose in the Ag K-edge EXAFS monitored under argon (90 kPa;
Figure S6). The Ag–Ag peak intensity in the FT significantly
decreased under UV–visible light but recovered after the light
was turned off (panel C), whereas the N value remained
between 8.8 and 10.2 during monitoring (panel A). Based onthe σvalues, the Ag temperature increased from 286 K to 355 K
during a 13 min period of light irradiation and progressively
reached 367 K in 50 min (panel B and Table S2b). These trends
agree with trends under CO2 and H2 (Figure 5B), which
demonstrate that changes in the σ value were due to heat
converted from LSPR.

Figure S7. Time course of 13CO and 12CO formation during
photocatalytic tests when exposed to 12CO2 (2.3 kPa) and H2O(2.7 kPa) using Ag (5.0 wt. %)–ZrO2 and UV–visible light.
Amount of catalyst used was 0.100 g.

The time course of photocatalytic test using 13CO2, moisture,and Ag 5.0 wt. %–ZrO2 is illustrated in Figure S7 showing 3days under UV–visible light followed by 3 days under dark
conditions. The proposed mechanism beginning from CO2 andmoisture is illustrated in Scheme S1.

Scheme S1. Proposed intermediate species starting from CO2 andmoisture to H2.

References(1) https://www.ushio.co.jp/jp/products/1017.html.
(2) Haynes, W. M., Editor, CRC Handbook of Chemistry and Physics
96th Eds., CRC Press, Boca Raton, 2015, p.4-124.
(3) Chase, M.W., Jr., NIST-JANAF Themochemical Tables, 4th Edition, J.
Phys. Chem. Ref. Data, Monograph 9, 1998, 1–1951.

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