Journal of the American Chemical Society
Article
EPR Measurements. EPR measurements were implemented at
5.7 K by a Bruker A300 spectrometer, which operated in the X-band
(9.64 GHz) and 100 kHz magnetic field modulation with 10 G
modulation amplitude. The temperature was controlled using liquid
N2. Each spectrum was added every five scans. Cu SAs/UiO-66-NH2
powder was dispersed in methanol solution (5 mg mL−1) for EPR
measurements. For the “before photoactivation sample”, the samples
were examined in sealed quartz tubes after Ar bubbling. For the “after
photoactivation sample”, visible light from the Xe lamp was irradiated
on the sealed quartz tube for 30 min. O2 was purged into the above
“after photoactivation sample” for 30 min. Before EPR measurements,
all the quartz tubes were frozen and stored in liquid nitrogen at a
maintenance temperature of 77 K.
XAFS Measurements and Analysis. The XAFS spectra data
were collected at the BL1W1B station in the Beijing Synchrotron
Radiation Facility (BSRF, operated at 2.5 GeV with a maximum
current of 250 mA). The solid samples were pelletized as disks with
13 mm diameter and 1 mm thickness. All the samples were collected
at room temperature in fluorescence excitation mode using a Lytle
detector. The obtained EXAFS results were processed on the basis of
the standard procedures using the ATHENA module implemented in
the IFEFFIT software packages.
Photoelectrochemical Performance. The photoelectrochem-
ical tests were performed in a 0.5 M Na2SO4 electrolyte solution using
a three-electrode system and the pH is about 6.8. The as-obtained
films, Ag/AgCl (saturated KCl), and platinum foil (1 × 1 cm2) were
used as the working electrode, reference electrode, and counter
electrode, respectively, and collected on an electrochemical station
(CHI660E, China) under visible light illumination. A 300 W Xe lamp
with a cut off filter of 400 nm was used as the visible light source. Five
milligrams of the as-prepared photocatalysts and 20 μL of 5 wt %
Nafion solution were dispersed in 1 mL of water and then sonicated
for 1 h. Then 100 μL of the catalyst ink was spread on the pretreated
FTO (1.0 × 1.0 cm−2) and dried at room temperature to form
photocatalysts-modified FTO in air. Mott−Schottky plots of photo-
catalysts in N2-purged 0.5 M Na2SO4 electrolyte (pH 6.8) solution
with the same three-electrode system were obtained.
The optimized lattice constants of the Cu surface are a = 10.224 Å,
b = 10.224 Å, c = 19.174 Å, α = β = 90°, γ = 120°, with a 15 Å vacuum
layer.
The optimized lattice constants of the Cu−CuO surface are a =
11.538 Å, b = 12.283 Å, c = 25.390 Å, α = β = 90°, γ = 102.56°, with a
15 Å vacuum layer.
The Gibbs free energy for all reactions was obtained by the
following formula:
ΔG = ΔE + ΔZPE − TΔS
where ΔE represents the reaction energy. ΔZPE and ΔS represent the
changes in zero-point energies and entropy, respectively.
In this work, detailed reaction mechanisms for CO2 photochemical
reduction on Cu NPs/UiO-66-NH2, Cu, and Cu−O catalysts to form
CH3OH were systematically discussed. The free energy change of
each step that involves a proton−electron transfer was analyzed with
the computational hydrogen electrode (CHE) model as developed by
Nørskov et al.65
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
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Detailed supporting figures (TEM, XRD, XPS, and
AUTHOR INFORMATION
Corresponding Authors
■
Junjie Mao − Key Laboratory of Functional Molecular Solids,
Ministry of Education, College of Chemistry and Materials
Science, Anhui Normal University, Wuhu 241002, China;
Dingsheng Wang − Department of Chemistry, Tsinghua
Photocatalytic CO2RR Performance. The photocatalytic
CO2RR was conducted in a continuous-flow (0.1 L min−1) reaction
system using a 300 W Xe lamp with a cut-off filter of 400 nm as a
visible light source at room temperature. In a typical experimental
process, 0.1 g of photocatalyst was dispersed in 50 mL of deionized
water with 100 μL of TEOA mixed under magnetic stirring. CO2
(99.999%) gas was bubbled through the suspension for at least 30 min
before irradiation. The reaction temperature was about 10 °C. The
liquid products were monitored by a TRACE 1300 gas chromato-
graph (Thermo Scientific) and FID detector every hour. No products
could be found when high-purity N2 gas instead of CO2 was injected
into the reaction system under the same reaction conditions,
confirming that CO2 should be the source of CH3OH and
CH3CH2OH.
Authors
Gang Wang − Key Laboratory of Functional Molecular Solids,
Ministry of Education, College of Chemistry and Materials
Science, Anhui Normal University, Wuhu 241002, China
Chun-Ting He − Key Laboratory of Functional Small Organic
Molecule, Ministry of Education, College of Chemistry and
Chemical Engineering, Jiangxi Normal University, Nanchang
330022, China
Rong Huang − Key Laboratory of Functional Molecular Solids,
Ministry of Education, College of Chemistry and Materials
Science, Anhui Normal University, Wuhu 241002, China
Yadong Li − Department of Chemistry, Tsinghua University,
Computational Details. All the computations were conducted
with spin-polarized plane-wave DFT method by using the Cambridge
Sequential Total Energy Package embedded in Materials Studio 2019.
The electron exchange and correlation energy were solved within the
generalized gradient approximation with the Perdew−Burke−
Ernzerhof exchange-correlation functional with the OTFG ultrasoft
pseudopotentials.64 To balance the energy accuracy and calculation
time, we used an energy cutoff of 550 eV and electron smearing with
0.14 eV. The degree of convergence in energy, force, and stress were
set to 1 × 10−5 eV/atom, 3 × 10−2 eV/Å, and 5 × 10−2 GPa,
respectively. A 2 × 2 × 2 k-point mesh was used to sample the
Brillouin zone.
The optimized reduction lattice constants of UiO-66-NH2 from
CCDC are a = b = c = 14.707 Å, α = β = γ = 60°. The Cu atom was
anchored on the constructed UiO-66-NH2 framework. There are four
types of models of the Cu single atom link with amino groups in the
UiO-66-NH2 matrix.
Complete contact information is available at:
Author Contributions
All authors discussed the results and commented on the
manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by the National Key R&D Program
of China (2018YFA0702003), the National Natural Science
Foundation of China (21971002, 21890383, 21671117,
21871159), and the Natural Science Foundation of Anhui
Province (1908085QB45). The authors thank R. Lin who
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J. Am. Chem. Soc. XXXX, XXX, XXX−XXX