A Covalent Organic Framework Bearing Single Ni Sites as a Synergistic Photocatalyst for Selective Photoreduction of CO2 to CO

Article abstract of DOI:10.1021/jacs.9b02997

Photocatalytic reduction of CO₂ into energy-rich carbon compounds has attracted increasing attention. However, it is still a challenge to selectively and effectively convert CO₂ to a desirable reaction product. Herein, we report a design of a synergistic photocatalyst for selective reduction of CO₂ to CO by using a covalent organic framework bearing single Ni sites (Ni-TpBpy), in which electrons transfer from photosensitizer to Ni sites for CO production by the activated CO₂ reduction under visible-light irradiation. Ni-TpBpy exhibits an excellent activity, giving a 4057 μmol g^-1 of CO in a 5 h reaction with a 96% selectivity over H₂ evolution. More importantly, when the CO₂ partial pressure was reduced to 0.1 atm, 76% selectivity for CO production is still obtained. Theoretical calculations and experimental results suggest that the promising catalytic activity and selectivity are ascribed to synergistic effects of single Ni catalytic sites and TpBpy, in which the TpBpy not only serves as a host for CO₂ molecules and Ni catalytic sites but also facilitates the activation of CO₂ and inhibits the competitive H₂ evolution.

Full text of DOI:10.1021/jacs.9b02997

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Article
A Covalent Organic Framework Bearing Single Ni Sites as a
Synergistic Photocatalyst for Selective Photoreduction of CO2 to CO
Wanfu Zhong, Rongjian Sa, Liuyi Li, Yajun He, Lingyun Li,
Jinhong Bi, Zanyong Zhuang, Yan Yu, and Zhigang Zou
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b02997 • Publication Date (Web): 18 Apr 2019
Downloaded from http://pubs.acs.org on April 18, 2019
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A Covalent Organic Framework Bearing Single Ni Sites as a
Synergistic Photocatalyst for Selective Photoreduction of CO2
to CO
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Wanfu Zhong†,#, Rongjian Sa‡, #, Liuyi Li†,*, Yajun He†, Lingyun Li† , Jinhong Bi†, Zanyong
Zhuang†, Yan Yu†,*, Zhigang Zou†,§,*
† Key Laboratory of Eco-materials Advanced Technology, College of Materials Science and Engineering, Fuzhou
University, Fuzhou 350108, China.
‡ Institute of Oceanography, Ocean College, Minjiang University, Fuzhou, Fujian 350108, China.
§ Eco-materials and Renewable Energy Research Center, College of Engineering and Applied Sciences, Nanjing
University, Nanjing 210093, China.
Supporting Information Placeholder
ABSTRACT ： Photocatalytic reduction of CO2 into energy-rich carbon compounds has attracted increasing attention.
However, it is still challenge to selectively and effectively convert CO2 to a desirable reaction product. Herein, we report a
design of a synergistic photocatalyst for selective reduction of CO2 to CO by using a covalent organic framework bearing
single Ni sites (Ni-TpBpy), in which electrons transfer from photosensitizer to Ni sites for CO production by the activated
CO2 reduction under visible-light irradiation. Ni-TpBpy exhibits an excellent activity, giving a 4057 μmol g-1 of CO in a 5 h
reaction with a 96% selectivity over H2 evolution. More importantly, when the CO2 partial pressure was reduced to 0.1
atm, 76% selectivity for CO production is still obtained. Theoretical calculations and experimental results suggest that the
promising catalytic activity and selectivity are ascribed to synergistic effects of single Ni catalytic sites and TpBpy, in
which the TpBpy not only serves as a host for CO2 molecules and Ni catalytic sites but also facilitates the activation of CO2
and inhibits the competitive H2 evolution.
atomically distribution of catalytic metal centers on
■ INTRODUCTION
supporters provide a bridge between the homo and
17
heterogeneous catalysis.16,
In this context, it is
Visible-light-driven CO2 reduction to useful chemical
feedstocks is a promising strategy to utilize CO2 and
imperative to design suitable supporters that not only can
accommodate and shield single metal sites but also
provide a strong interaction with the metal.18
2
simultaneously store solar energy.1,
However, the
product from the photoreduction of CO2 in aqueous
solution is usually a mixture that containing CO, H2, CH4
and HCOOH,3 because of the multielectron reduction
The development of covalent organic frameworks
(COFs)19, 20 opens up new opportunities for catalysis.21, 22
Compared to metal-organic-framework (MOF)-based
photocatalysts,23 COF-based photocatalytic materials have
unique advantages. The 2D structure of COFs originates
from periodic organic building blocks, leading to
delocalization of charges in the conjugated framework.
The layered nanosheets of 2D COFs not only provide
continuous pores for mass transfer, but also offer a fast
response to photoexcitation over MOFs with other
dimensions continuous. Importantly, the catalytic active
sites can be stabilized within the frameworks via the
confinement effects and coordination interactions
between the confined metal ions/nanoparticles and
binding groups in the skeleton of COFs.24-26 The well-
defined structure and synthetic diversity of COFs enable
process and the competing H2 evolution reaction in CO2
5
reduction.4,
Despite continuous efforts have been
devoted to exploring efficient photocatalytic CO2
reduction system, from practical solar-to-fuels
a
conversion viewpoint, it is desirable to finding catalytic
systems that can efficiently transfer CO2 to a specific
product.6-9
Recently, some coordination metal complexes exhibited
excellent catalytic performance in photocatalytic selective
reduction of CO2,10, 11 owing to their maximum efficiency
of catalytic sites and the coordination versatility of the
12-15
metal centers
.
However, the separation of
homogeneous catalysts from the reaction system limited
their industrial application. Single site catalysts featuring
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control over catalytic active sites in COFs with a precision
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(Figure S3). The binding energy of Ni 3p peak at 856 eV is
assigned to Ni2+ (Figure 2b), indicating the successful
loading of Ni ions into the framework. No impurities of
other Ni species such as NiO and metallic Ni were
evident. In comparison with N 1s XPS spectra of TpBpy, a
slight upshift of N 1s peaks in Ni-TpBpy was observed
(Figure 2c), which is ascribed to the coordination of
nitrogen atoms to Ni ions. The UV-vis diffuse reflectance
spectra show that Ni-TpBpy, compared to pristine TpBpy,
has a slight red-shift of the absorption edge and a narrow
optical band gap probably because of the increased
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approaching that of homogeneous metal complex
catalysts by modulating the coordination environment of
isolated metal centers by changing the coordination
group.27, 28 In addition, the heteroatom-rich pore walls of
COFs not only facilitate CO2 adsorption,29 but also
provide special microenvironments around the
coordinated single metal center.30-32 Accordingly, using a
COF with special coordination microenvironment as a
functional supporter for anchoring single metal sites can
be expected to bring new opportunities for designing high
efficient photocatalyst for selective reduction of CO2.
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delocalization
(Figure
S4).30
Scanning
electron
microscopy (SEM) image shows the original three-
dimensional (3D) network morphology of TpBpy is intact
after the loading of Ni (Figure S5). Transmission electron
microscopy (TEM) images does not exhibit observable
nanoparticles of Ni (Figure 2d). The energy-dispersive X-
ray (EDX) mapping images of Ni-TpBpy clearly show C, N
and Ni are homogeneous distributed in the COF matrix
(Figure 2d and S6). The single Ni sites in TpBpy are
evidenced by aberration corrected high-angle annular
dark-field scanning transmission electron microscopy
(HAADF-STEM). As shown in Figure 2e, the bright spots
in Ni-TpBpy correspond to the single Ni ions with
ultrasmall size (≈0.17 nm), suggesting the atomically
dispersed Ni centers in TpBpy.
In this work, we report a 2,2’-bipyridine-based COF
bearing single Ni sites (Ni-TpBpy) as a synergistic
catalyst for selective photoreduction of CO2 to CO (Figure
1). Ni-TpBpy efficiently promoted the selectivity of CO
generation in aqueous media, reaching a 4057 μmol g-1 in
a 5 h reaction with a 96 % selectivity over H2 evolution.
The good catalytic activity and selectivity of Ni-TpBpy
mainly arise from the unique microenvironments around
single Ni sites in TpBpy, in which the bipyridine
coordination units stabilize the catalytic active Ni center,
while the hydrogen-bond interactions between the keto
nodes and the Ni-CO2 reaction intermediate enable the
reduction of CO2 prior to H2 evolution.
■ RESULTS AND DISCUSSION
The porosities of TpBpy and Ni-TpBpy were studied by
N2 adsorption/desorption measurements at 77 K (Figure
s7). The Brunauer-Emmett-Teller (BET) surface area and
pore volumes were decreased from 973 m2 g-1 and 0.6 cm3
g-1 for TpBpy to 580 m2 g-1 and 0.4 cm3 g-1 for Ni-TpBpy,
respectively. Although the interior cavities of TpBpy are
partially filled by Ni ions, the open structure of the TpBpy
remained, ensuing reactants accessibility to Ni ions in
catalysis. Appreciable amounts of CO2 adsorption of
TpBpy and Ni-TpBpy were also observed (Figure 2f),
owing to the combination of microporous character and
the heteroatom-rich channels in the framework.29
Interestingly, Ni-TpBpy shows slightly higher CO2 capture
amounts and isosteric heats of adsorption (Qst) than those
of TpBpy (Inset in Figure 2f), which can be attributed to a
Lewis acid-base interaction between the loaded Ni ions
and absorbed CO2 molecules.34
Figure 1. Schematic diagram photocatalytic selective
reduction of CO2 over Ni-TpBpy.
A 2,2’-bipyridine-based COF (TpBpy) was synthesized
by the condensation of 1,3,5-triformylphloroglucinol and
5,5’-diamino-2,2’-bipyridine
under solvothermal conditions.33 Ni ions were implanted
into TpBpy through a simple treatment of TpBpy with
Ni(ClO4)2 to yield Ni-TpBpy (Figure 1). FTIR spectroscopy
and solid-state 13C NMR of Ni-TpBpy are both similar to
those observed in TpBpy, revealing the retention of
chemical structures during Ni ion loading (Figure S1 and
S2). The powder X-ray diffraction (PXRD) shows that the
crystalline structure of TpBpy is retained in the Ni-TpBpy
(Figure 2a). Further structural details on the coordination
of Ni ions into TpBpy are obtained with X-ray
photoelectron spectroscopy (XPS) measurements. XPS
spectra show the presence of C, N, O and Ni in Ni-TpBpy
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source. A peak at m/z = 29 indicates that the produced
13CO indeed originated from 13CO2 specie (Figure S9),
which evidently confirms that the generated CO comes
from CO2 gas rather than the decomposition of any other
organic species in the photocatalytic reaction.
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We further conducted the photocatalytic CO2 reduction
reaction under a low CO2 concentration. A synthetic gas
containing 10% CO2 and 90% Ar was employed to replace
pure CO2. It was found that 915 µmol g-1 of CO with 76%
selectivity over H2 generation can be produced in a 4 h
reaction although under a low CO2 concentration (Inset
in Figure 3a).
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A series of control experiments were performed to
identify the key factors for CO2-to-CO conversion (Figure
3b). When the CO2 reduction reaction was conducted in
dark, the reaction system is completely inactive to
produce any product. The wavelength dependence of CO
generation showed that the trend of CO evolution
matches well with the absorption spectrum of the
ruthenium complex (Figure S10), further revealing that
the CO2 conversion proceeds by light irradiation. Without
Ni-TpBpy or just with TpBpy, negligible CO and H2
generation were observed, while in the absence of TpBpy,
only 4 μmol h-1 CO with 83% selectivity was obtained. In
addition, the selectivity of CO over H2 is influenced by the
concentration of H2O and 2,2’-bipyridine in the reaction
solvent (Figure S11 and S12). In comparison, when a
physical mixture of Ni ion and TpBpy was used, obviously
lower activity and selectivity than those from Ni-TpBpy
were observed. TpBpy loaded with other metal ions such
as Co2+, Fe3+, Ru3+, Zn2+ and Mn2+ were also tested in the
photocatalytic reduction of CO2. As shown in Figure 3c,
Co ions loaded TpBpy showed a higher photocatalytic
activity than that of Ni-TpBpy, however its selectivity only
reaches 41% (Inset in Figure 3c), manifesting the feature
of integration of single Ni within TpBpy for photocatalytic
selective reduction of CO2 to CO. The production of CO
just decreased slightly as the amount of Ni-TpBpy was
decreased (Figure S13), suggesting the catalytic efficiency
of Ni-TpBpy. Apparently, these results unambiguously
demonstrate that single Ni in TpBpy serves as the
catalytic sites for conversion CO2 to CO, and TpBpy
boosts the activity and selectivity of photoreduction of
CO2 to CO.
Figure 2. PXRD patterns of TpBpy and Ni-TpBpy (a); Ni 2p
XPS spectra of Ni-TpBpy before and after catalytic reaction
(b); N 1s XPS spectra of TpBpy and Ni-TpBpy (c); TEM, EDX
mapping (d) and aberration-corrected HAADF-STEM(e)
images of Ni-TpBpy CO2 sorption isotherms of the TpBpy
and Ni-TpBpy (f). Inset: Isosteric heat of adsorption for CO2
in TpBpy and Ni-TpBpy.
Considering the catalytic properties of Ni-ligand
complexes for CO2 reduction35 and the high affinity of Ni-
TpBpy to CO2 as well as the excellent chemical stability of
TpBpy,31 we investigated the photocatalytic CO2
conversion activity of Ni-TpBpy using [Ru(bpy)3]Cl2 (bpy
= 2,2’-bipyridine) as a visible-light photosensitizer and
triethanolamine (TEOA) as an electron donor in aqueous
solution. Figure 3a shows the evolutions of CO and H2
from Ni-TpBpy catalytic system in a 5-hour photocatalytic
reaction. The total amount of CO and H2 products are
4057 and 170 μmol g-1, respectively, giving a CO selectivity
of 96% over completing H2 generation. The
photocatalytic activity is competitive with other
previously reported COFs and MOFs, and the catalytic
selectivity is among the best based on a review of the
recent visible-light-driven heterocatalysts (Table S2).6, 30,
36-39 The turnover number of Ni-TpBpy for CO evolution is
13.62 after 5 h irradiation. The apparent quantum
efficiency (AQE) for CO evolution at 420 nm is calculated
to be 0.3 %. No other CO2 reduction products (e.g., CH4,
CH3OH, HCOOH) are detected from the reaction (Figure
S8). The participation of CO2 in the reaction was studied
by replacing CO2 with N2 under the same reaction
conditions. After 4h reaction, no CO was detected (Figure
3b). To confirm the origin of the as-produced CO, isotope
experiment was carried out by using 13CO2 as a carbon
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self-assemble formation of Ni(bpy)32+ (Figure 4a).41 The
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CVs of Ni complex in MeCN/H2O solution show two
irreversible reduction waves of Ni complex under both Ar
and CO2 atmosphere (Figure 4b), which can be assigned
to the reduction of Ni ions from NiII to NiI and NiI to Ni0.
The catalytic current was emerged under CO2 atmosphere
after the NiI to Ni0 reduction wave, verifying the reaction
of Ni0 with CO2 in the electrochemical process.42
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Figure 3. Photocatalytic evolutions of CO and H2 by Ni-
TpBpy under 1 atm and 0.1 atm (diluted with Ar, inset) (a);
The research of reaction conditions in a 2 h reaction (b);
Different metal ions loaded in TpBpy for CO2 reduction in a 2
h reaction (c); Stability tests of Ni-TpBpy for selective
photoreduction of CO2 (d).
Figure 4. (a) Self-assembly of [Ni(bpy)3]2+ by consecutive
addition of bpy to Ni(ClO4)2 under a CO2 atmosphere
followed by linear sweep voltammetry (1.0 mM Ni(ClO4)2, 0.1
M TBAPF6 in MeCN/H2O (3:1) solution, 100 mV s−1); (b) Self-
assembled [Ni(bpy)3]2+ under CO2 or Ar (1.0 mM complex, 0.1
M TBAPF6 in MeCN/H2O (3:1) solution, 100 mV s−1, rt); (c)
Ni-TpBpy, Ni-TpPa and Ni-TbBpy for Photocatalytic
reduction of CO2 in a 2 h reaction; (d) DFT-calculated relative
Gibbs free energy (ΔG, kcal mol-1) with Zero-point correction
of CO2 and H+ with and without the optimized building block
of TpBpy, L is 2,2’-bipyridine.
Cycle experiments revealed that the photocatalytic CO
evolution rate could approach up to 966 μmol g-1 h-1 over 3
times in a total of 6 h irradiation time (Figure 3d), which
is consistent with the data in the kinetic curves. A slight
loss of activity for CO production in the 3rd reaction run
may be explained by the coverage of ruthenium species
from the degradation of the ruthenium dye on the
framework. EDX elemental mappings of the recovered Ni-
TpBpy show the appearance of Ru element on the surface
of TpBpy (Figure S14). SEM and TEM images show the
retention of original 3D network of Ni-TpBpy after cycling
reactions. PXRD pattern of the recovered Ni-TpBpy
showed a weak long-range order (Figure S15), which can
be assigned to the exfoliation of the COF during
photocatalysis.40 The crystalline structure of the
recovered sample can be regenerated by subjecting it to
the initial synthesis conditions (Figure S16). No noticeable
changes in FTIR (Figure S17), N 1s (Figure S18) and Ni 2p
XPS (Figure 2c) spectra between the fresh and recovered
Ni-TpBpy demonstrate the chemical stability of Ni-
TpBpy. It is noteworthy that after reloading Ni ions onto
the recovered TpBpy, the photocatalytic reduction of CO2
performance can be restored (Figure S19). To test the
heterogeneity of Ni-TpBpy, a filtration test was conducted
after 2 h of catalysis, after which a significant decrease of
activity was observed (Figure S20). The concentration of
Ni in the filtered solution was 4.6 ppm as determined by
inductively coupled plasma mass spectrometry (ICP),
suggesting that only trace of Ni ions existed in reaction
system.
To identify the function of the building blocks in TpBpy
in improving the selective photoreduction of CO2 to CO,
TpPa without 2,2’-bypridine units (Figure S21),43 an
analogues of TpBpy, was employed into the catalytic
reaction. As shown in Figure 4c, Ni loaded TpPa (Ni-
TpPa) shows much lower activity and selectivity than Ni-
TpBpy, suggesting the importance of bpy units in loading
single Ni sites for catalysis. A new COF without keto
moieties in the framework, TbBpy, was synthesized by a
condensation of 1,3,5-triformylbenzene and 5,5’-diamino-
2,2’-bipyridine (Figure S22). Under the identical reaction
conditions, only 0.7 μmol CO with a selectivity of 58%
was detected by Ni loaded TbBpy (Ni-TbBpy). As the Ni
binding sites of TbBpy and TpBpy are similar, the higher
catalytic efficiency of TpBpy may be attributed to the keto
moieties in TpBpy, which may provide additional effects
on the formation of the key intermediate in the catalytic
reaction.
To gain mechanistic insight into the photocatalytic
reduction of CO2 by Ni-TpBpy, cyclic voltammetry (CV)
was carried out. The growth of the characteristic
reduction waves of Ni(bpy)32+ upon the successive
addition of bpy ligand to Ni(ClO4)2 solution indicates the
Density functional theory (DFT) calculations are
further performed to study the catalytic mechanism by
Ni-TpBpy. It is known that the adsorption of CO2 onto the
catalyst is the rate-determining step in the
photoreduction CO2 reaction.40 The Gibbs free energies of
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CO2 and H2O on the optimized building block of Ni-
Figure 5. (a) DFT-calculated relative Gibbs free energy (ΔG,
kcal mol-1) profiles with Zero-point correction (ZPE) included
for the conversion of CO2 into CO with and without the
optimized building block of TpBpy; (b) Proposed reaction
mechanism for the photoconversion of CO2 into CO on Ni-
TpBpy.
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TpBpy are calculated. As shown in Figure 4d, the addition
of H+ to [L2Ni]0 to give L2Ni-H+ adduct cannot easily occur
because this reaction is extremely endergonic by 141.4 kcal
mol-1 relative to parent [L2Ni]0. The formation of L2Ni-CO2
adduct was found at ΔG= 3.2 kcal mol-1, implying the
stronger affinity of [L2Ni]0 towards CO2. Notably, the
addition of model compound of the keto unit in TpBpy
could significantly decrease the ΔG of the key
intermediate, facilitating the formation of Ni-CO2 adduct,
thus leading to an enhanced selectivity of CO product.
Noteworthy that the ΔG of CO2 on Ni-TpBpy is stronger
than that of Co-TpBpy, while the ΔG of H2O on Ni-TpBpy
is weaker than that of Ni-TpBpy (Figure S23), suggesting
Ni-TpBpy could exhibit superior catalytic activity and
selectivity over Co-TpBpy, and Co-TpBpy just could boost
the activity of reduction because of the competitive H2
evolution, which is consistent with the experimental
results. The photoreduction process of CO2 to CO via a
carboxyl intermediate on the optimized building block
were further calculated. As shown in Figure 5a, a further
protonation of Ni-CO2 adduct to give Ni-COOH adduct is
Based on the experimental and DFT calculations, a
possible reaction mechanism for the photocatalytic
reduction of CO2 over Ni-TpBpy is proposed (Figure 5b).
Upon visible light irradiation, Ru(bpy)32+ is excited and
transfer electrons to reduce the coordinated CO2
molecules on Ni-TpBpy. The affinity of CO2 on Ni sites
over H+ is crucial for the inhibition of H2 formation. The
coordinated CO2 in COF-Ni-CO2 exhibits a bending
configuration, confirming that CO2 was activated by
single Ni sites. In intermediate Ni-COOH, one of the C-O
bonds elongates to 1.314 Å (Table S1), falling within the
typical range of C-O single bond, while the other C-O
bond length is 1.221 Å, remaining a double bond. The
significantly decreased ΔG of the COF-Ni-CO2H
intermediate is mainly ascribed to the formation of
hydrogen bond between COOH and the keto group, thus
promoting the stabilization of the key intermediate, and
thus enhancing the CO2 reduction. The results of this
calculation explicitly elucidate that single Ni sites in
TpBpy truly take the role of the catalytic active sites,
where CO2 molecules are coordinated, activated and
reduced, and the TpBpy not only serves as a host for CO2
molecules and single Ni sites but also contribute to the
catalytic activity and selectivity of the reduction of CO2 to
CO, which are in agreement with experimental
observations.
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thermodynamically feasible.4
The
following
transformation of Ni-COOH to Ni-CO with H+ can
proceed facilely, and the release of CO from Ni-CO just
need to overcome a rather low barriers. The ΔG for COF-
Ni-adducts is much lower than that L2Ni-adducts,
indicating that Ni-TpBpy is kinetically more favorable for
the selectivity of CO product.
■ CONCLUSION
We demonstrated a design of Ni-TpBpy as a synergistic
catalyst for photocatalytic selective conversion of CO2.
Single Ni sites were successfully anchored in TpBpy
through the chelation of bypridine binding units. Ni-
TpBpy exhibits excellent photocatalytic selective
reduction of CO2 to CO either in pure or diluted CO2,
which are mainly ascribed to the synergistic effects of
single Ni catalytic site and TpBpy supporter. Control
experiments and theoretical calculations indicated that
both bipyridine coordination units and the keto nodes in
TpBpy play key roles in stabilization of single Ni sites,
activation and conversion of CO2 in the catalytic reaction.
This work strongly highlights the considerable potential
of COFs for fabrication of single-site catalysts, and should
be simulate the development of novel photocatalysts
through delicate design of their coordination
microenvironments around the catalytic active sites.
■ EXPERIMENTAL SECTION
Synthesis of TpBpy. TpBpy was prepared according to
literature methods with a little modification.33 A Pyrex
tube was charged with triformylphloroglucinol (21 mg,
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0.10 mmol) and 5,5’-diamino-2,2’-bipyridine (27.9 mg,
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of CO2 to CO by adding equal amounts of
[Ru(bpy)3]Cl2·6H2O at each run (0.01 mmol of
[Ru(bpy)3]Cl2·6H2O were carried out in 30 µL CH3CN and
10 µL H2O) to the photocatalytic system after 2 h of
reaction and re-introducing CO2, and then the mixture
was irradiated under a xenon lamp (300 W) with a UV-
cutoff filter (λ ≥ 420 nm) at 298 K .
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0.15 mmol) in 1.1 mL of a 5:5:1 v:v solution of 1,4-dioxane:
mesitylene: 6 M aqueous acetic acid. This mixture was
sonicated for 10 minutes in order to get a homogenous
dispersion. The tube was flash frozen at 77 K (liquid N2
bath), evacuated and flame-sealed. The reaction mixture
was heated at 120 °C for 5 days to afford an orange-red
precipitate. The precipitate was isolated by filtration and
dried under vacuum at 60 °C overnight to afford TpBpy
(40 mg, 82%).
Electrochemical measurements. Cyclic voltammetry
on Ni(ClO4)2·6H2O and 2,2’-bipyridine was carried out in
a mixed solution of MeCN/H2O (3:1 v/v) containing 0.10
M tetrabutylammonium hexafluorophosphate (TBAPF6)
as an electrolyte at 298 K under Ar or CO2 with use of a
glassy carbon as a working electrode, a platinum wire as a
counter electrode, and a Ag/AgCl electrode.
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Synthesis of Ni-TpBpy. TpBpy (50 mg) was treated
with Ni(ClO4)2·6H2O (30 mg) in 20 ml acetonitrile. The
solution was stirred for 8h at room temperature. The solid
was filtered washed with copious amount of acetonitrile
and dried in vacuum at 60 oC overnight to give Ni-TpBpy.
Ni content in Ni-TpBpy was 0.3 mmol g-1 as determined
by ICP.
ASSOCIATED CONTENT
Synthesis of TpPa. TpPa was prepared according to
literature methods with a little modification.39 A Pyrex
tube was charged with triformylphloroglucinol (63 mg,
0.3 mmol), paraphenylenediamine (48 mg, 0.45 mmol) in
3.5 mL of a 3:3:1 v:v solution of 1,4-dioxane: mesitylene: 3
M aqueous acetic acid. This mixture was sonicated for 10
minutes in order to get a homogenous dispersion. The
tube was then flash frozen at 77 K (liquid N2 bath) and
degassed by three freeze-pump-thaw cycles. The tube was
Supporting Information. Materials, methods, detailed
characterization of TpBpy, Ni-TpBpy, TpPa and TbBpy, DFT
calculations. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
* lyli@fzu.edu.cn
* yuyan@fzu.edu.cn
* zgzou@nju.edu.cn
o
sealed off and then heated at 120 C for 3 days. The red
precipitate was collected by filtration and washed with
anhydrous acetone. The powder collected and then dried
at 120 oC under vacuum to afford TpPa (89 mg,80%)
Author Contributions
# W. Zhong and R. Sa contributed equally.
Notes
The authors declare no competing financial interest.
Synthesis of TbBpy. A Pyrex tube was charged with
1,3,5-triformylbenzene (16 mg, 0.10 mmol) and 5,5 ′ -
diamino-2,2’-bipyridine (27.9 mg, 0.15 mmol) in 1.1 mL of
a 9:1:1 v:v solution of 1,4-dioxane: mesitylene: 6 M aqueous
acetic acid. The tube was flash frozen at 77 K (liquid N2
bath), evacuated and flame-sealed. The reaction mixture
was heated at 120 °C for 3 days to afford a yellow
precipitate. The precipitate was isolated by filtration and
dried under vacuum at 80 °C overnight to afford TbBpy
(30 mg, 70%).
ACKNOWLEDGMENT
We thank the National Natural Science Foundation of China
(No. 51672046, 51672047 and 21403238), Natural Science
Foundation of Fujian Province of China (No. 2019J01226,
2019J01648), Open Project Program of the State Key
Laboratory of Photocatalysis on Energy and Environment
(No. SKLPEE-KF201815, SKLPEE-KF201813).
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