Metalloporphyrin-based covalent organic frameworks composed of the electron donor-acceptor dyads for visible-light-driven selective CO2 reduction

Article abstract of DOI:10.1007/s11426-020-9801-3

The visible-light-driven photocatalytic CO₂ reduction with high efficiency is highly desirable but challenging. Herein, we present porphyrin-tetraphenylethene-based covalent organic frameworks (MP-TPE-COF, where M=H₂, Co and Ni; TPE=

Full text of DOI:10.1007/s11426-020-9801-3

SCIENCE CHINA
Chemistry
•
ARTICLES•
https://doi.org/10.1007/s11426-020-9801-3
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Metalloporphyrin-based covalent organic frameworks composed of
the electron donor-acceptor dyads for visible-light-driven selective
CO reduction
2
1
2
1
1
3
1*
Haowei Lv , Rongjian Sa , Pengyue Li , Daqiang Yuan , Xinchen Wang & Ruihu Wang
1
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou 350002, China;
2
Institute of Oceanography, Ocean College, Minjiang University, Fuzhou 350108, China;
3
State Key Laboratory of Photocatalysis on Energy and Environment, Fuzhou University, Fuzhou 350108, China
Received May 8, 2020; accepted June 23, 2020; published online July 30, 2020
The visible-light-driven photocatalytic CO reduction with high efficiency is highly desirable but challenging. Herein, we
2
present porphyrin-tetraphenylethene-based covalent organic frameworks (MP-TPE-COF, where M=H , Co and Ni;
2
TPE=4,4′,4″,4‴-(ethane-1,1,2,2-tetrayl) tetrabenzaldehyde; COF=covalent organic framework) as ideal platforms for under-
standing photocatalytic CO reduction at molecular level. Experimental and theoretical investigations have demonstrated crucial
2
roles of metalloporphyrin units in selective adsorption, activation and conversion of CO as well as in the separation of charge
2
carriers and electron transfer, thus allowing for flexible modulation of photocatalytic activity and selectivity. CoP-TPE-COF
−
1
−1
exhibits high CO evolution rate of 2,414 μmol g
irradiation, while NiP-TPE-COF provides CO evolution rate of 525 μmol g
Moreover, the photocatalytic system is feasible for the simulated flue gas, which provides CO evolution rate of 386 μmol g
h
with the selectivity of 61% over H generation under visible-light
2
−
1
−1
h
and 93% selectivity with superior durability.
−
1
−1
h
and selectivity of 77%. This work provides in-depth insight into the structure-activity relationships toward the activation and
photoreduction of CO2.
covalent organic frameworks, photocatalysis, porous materials, CO reduction, metalloporphyrin
2
Citation:
Lv H, Sa R, Li P, Yuan D, Wang X, Wang R. Metalloporphyrin-based covalent organic frameworks composed of the electron donor-acceptor dyads for
visible-light-driven selective CO reduction. Sci China Chem, 2020, 63, https://doi.org/10.1007/s11426-020-9801-3
2
1
Introduction
[3–6]. The primary challenges so far are still the adsorption
and the activation of stable CO molecules as well as the
2
With ever-increasing energy demands and environment-
separation and migration of photogenerated charge carriers
[7–10]. Therefore, it is pivotal to develop new types of
photocatalytic systems with well-defined structures and
compositions so as to get more insights into the structure-
performance relationships for efficient fixation and selective
reduction of CO2.
related concerns, photocatalytic CO reduction into valuable
2
carbon-based fuels and chemical feedstocks offers one ap-
pealing approach to alleviate the energy crisis and global
climatic change [1–3]. Considerable progress has been made
in the exploration of efficient CO photoreduction systems,
2
but their practical applications are limited by low fuel-con-
version efficiency and low selectivity of reductive products
Covalent organic frameworks (COFs) are one class of
emerging crystalline porous materials composed of strong
covalent bonds and periodic organic building blocks [11–
1
5]. The structural superiorities of COFs have brought tre-
*Corresponding author (email: ruihu@fjirsm.ac.cn)
©
Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
chem.scichina.com link.springer.com

2
Lv et al. Sci China Chem
mendous potentials for photocatalytic applications [16–20].
Recently, a few COFs with chelating coordination groups
have been employed to anchor single metal sites for im-
mixture was heated at 120 °C for 7 d. The resultant dark-red
precipitate was isolated by filtration over a medium glass frit
and washed with tetrahydrofuran and acetone. Subsequent
Soxhlet extractions with tetrahydrofuran and acetone for
24 h, dried at 80 °C under vacuum overnight gave rise to
proving performance of photocatalytic CO reduction [21–
2
2
5]. For examples, 2,2′-bipyridyl-based COFs containing
single metal sites have been prepared through post-synthetic
modification, and they serve as synergistic catalysts for CO2-
to-CO conversion [22–25]. However, the binding ability of
bipyridyl units is not strong enough to stabilize active metal
centers, and unavoidable metal leaching is observed during
H P-TPE-COF.
2
2
.2 Synthesis of NiP-TPE-COF and CoP-TPE-COF
The syntheses of NiP-TPE-COF and CoP-TPE-COF were
photocatalytic CO reduction even in the presence of excess
carried out using the same procedures as that of H P-TPE-
2
2
bipyridyl units [24,25]. The porphyrin units are promising
alternatives owing to their strong chelating coordination
ability toward metal ions [26,27], and they have been in-
troduced into the host frameworks to form metalloporphyrin-
based COFs [28,29]. Both ultrathin Co-porphyrin-based
COF nanosheets and corresponding bulk materials have been
reported to possess high durability and cyclability in visible-
light-driven CO -to-CO conversion [28], but competitive H
COF except H TAP was replaced by NiTAP (14.7 mg,
0.02 mmol) and CoTAP (14.7 mg, 0.02 mmol), respectively.
2
3 Results and discussion
3
.1 Synthesis and structural characterization
H P-TPE-COF and NiP-TPE-COF were synthesized by acid-
2
2
2
generation reaction results in relatively low CO selectivity. It
is highly desirable to find facile and general protocols to get
catalyzed Schiff-base reaction of H TAP and metallized
2
NiTAP with TPE, respectively (Figure 1(a)). Their crystal
structures were defined by powder X-ray diffraction (PXRD)
measurements in conjunction with structural simulations. In
insight into photocatalytic mechanism for improving CO -to-
2
CO selectivity. Taking into account that unambiguous
structures, high density of catalytic sites and strong con-
jugation ability of metalloporphyrin-based COFs [28–31],
the appealing platforms based on their isostructures could be
established to explore chemical interactions of metal active
sites with the reagents and reactive intermediates during CO2
photoreduction.
the PXRD pattern of H P-TPE-COF (Figure S1, Supporting
2
Information online), two diffraction peaks at 5.3° and 10.9°
are indexed to (110) and (220) crystal facets, respectively.
The peaks in NiP-TPE-COF are shifted to 5.4° and 11.2°,
respectively (Figure 1(b)). The structural models were con-
structed using the Materials Studio software package. The
experimental PXRD patterns (black) in both NiP-TPE-COF
As a proof-of-concept study, herein, we report a series of
porphyrin-tetraphenylethene-based COFs (MP-TPE-COF,
and H P-TPE-COF match well with the simulated AA
2
where M=H , Co and Ni; TPE=4,4′,4″,4‴-(ethane-1,1,2,2-
stacking model (blue) in terms of peak positions and relative
intensities, while significant difference is observed when
compared with that of the AB stacking model (orange). The
top and side views show that they feature two-dimensional
rhombus framework (Figure 1(c), and Figure S2) and crys-
tallize in the orthorhombic space group of P222 (Tables S1–
S6, Supporting Information online). The Pawley refinements
provide the following unit cell parameters with good residual
factors (a=22.7001 Å, b=24.1977 Å and c=5.8121 Å, Rwp
=5.49% and R =4.24% for H P-TPE-COF; a=21.8943 Å, b=
2
tetrayl) tetrabenzaldehyde) for visible-light-driven CO -to-
2
CO conversion. MP-TPE-COF consists of the alternate
electron donor-acceptor dyads, which serves as ideal sup-
ports for CO adsorption, activation and photogenerated
2
electron migration. The photocatalytic system exhibits high
catalytic efficiency and superior cyclable stability in the
photoreduction of the atmospheric CO and even for low
2
concentration of CO . The process of photocatalytic CO
2
2
reduction has been disclosed by metalloporphyrin-dependent
selectivity and activity.
p
2
23.6302 Å and c=5.5822 Å, R =10.36% and R =7.37% for
wp
p
NiP-TPE-COF), indicative of the validity of the computa-
tional models [32].
2
Experimental
Fourier transform infrared spectroscopy (FTIR), solid-
1
3
13
state C nuclear magnetic resonance ( C NMR) spectra and
X-ray photoelectron spectroscopy (XPS) measurements
were used to confirm chemical structures of NiP-TPE-COF
2
.1 Synthesis of H P-TPE-COF
2
Pyrex tube was charged with 5,10,15,20-tetrakis(4-amino-
phenyl)-porphyrin (H TAP, 13.5 mg, 0.02 mmol) and TPE
and H P-TPE-COF. In their FTIR spectra (Figure 2(a)), both
2
2
−
1
(8.89 mg, 0.02 mmol) in a mixed solution of o-di-
the carbonyl peak of TPE (1695 cm ) and the N–H
−
1
chlorobenzene (0.9 mL), n-butanol (0.1 mL) and 6 M aqu-
eous acetic acid (0.1 mL). After three freeze-pump-thaw
cycles, the tube was vacuumed and sealed, the reaction
stretching bands of H TAP/NiTAP (3,100–3,400 cm ) are
2
greatly attenuated, concomitant appearance of C=N stretch-
−
1
ing vibration peak at 1,626 cm indicates the formation of

Lv et al. Sci China Chem
3
ergy peaks at 855.34 and 872.39 eV (Figure S6), suggesting
divalent state of metal ion in NiP-TPE-COF. Scanning
electron microscopy (SEM) and transmission electron mi-
croscopy (TEM) images show that H P-TPE-COF and NiP-
2
TPE-COF possess similar morphology, which are assembled
by bulky aggregates consisting of granular particles (Figure
S7). Energy dispersive X-ray spectroscopy (EDS) elemental
mappings corroborate homogeneous distribution of C, N and
Ni elements over NiP-TPE-COF (Figure S8). In the solid-
state ultraviolet-visible spectroscopy (UV-Vis) diffuse re-
flectance spectra, both H P-TPE-COF and NiP-TPE-COF
2
show typical four Q-bands, but an obvious blue shift is ob-
served for NiP-TPE-COF owing to the metalation of por-
phyrin units (Figure S9). The Ni content in NiP-TPE-COF
was determined to be 5.1 wt% by inductively coupled plas-
ma atom emission spectrometry (ICP-AES) analyses. The
Figure 1 (a) Schematic depiction for the synthesis of MP-TPE-COF; (b)
PXRD patterns of NiP-TPE-COF; (c) top and side views for AA-stacking
mode of NiP-TPE-COF (color online).
thermal stabilities of H P-TPE-COF and NiP-TPE-COF
2
were measured by thermogravimetric analysis, which are
stable before 350 °C under N atmosphere (Figure S10).
2
The permanent porosities of H P-TPE-COF and NiP-TPE-
2
COF were evaluated by N physisorption at 77 K (Figure 2
2
(b)). The rapid nitrogen uptake at very low relative pressure
shows typical characteristic of micropore. The Brunauer-
Emmett-Teller (BET) specific surface areas for H P-TPE-
2
2
−1
COF and NiP-TPE-COF are 683 and 1,154 m g , respec-
3
−1
tively. The total pore volumes are 0.48 and 0.70 cm g ,
respectively. The pore size distributions exhibit that their
main pores are centered at 1.15 nm (Figure S11), which are
close to the theoretical pores for the simulated AA stacking
structure, but is much larger than those in AB model (Tables
S1 and S4), which further validates their crystalline struc-
ture.
The CO sorption properties of H P-TPE-COF and NiP-
2
2
TPE-COF were investigated to identify the role of in-
corporated metal ions. The CO adsorption capacities in H P-
Figure 2 (a) FTIR spectra of H TAP, TPE, H P-TPE-COF and NiP-TPE-
2
2
COF; (b) N2 sorption isotherm of H P-TPE-COF and NiP-TPE-COF at
2
2
2
−
1
7
7 K; (c) in situ FTIR spectra of CO , NiP-TPE-COF in the atmosphere of
TPE-COF at 295 and 273 K are 1.4 and 2.3 mmol g , re-
2
−
1
CO and after the release of CO ; (d) CO and N sorption isotherms for
2
2
2
2
spectively. which are increased to 1.6 and 2.7 mmol g in
NiP-TPE-COF, respectively (Figure 2(d), and Figure S12),
NiP-TPE-COF at 273 and 295 K (color online).
which shows that the existence of Ni increase the CO ad-
2
NiP-TPE-COF and H P-TPE-COF, which is further evi-
sorption ability owing to Lewis acid-base interactions be-
2
13
denced by their solid-state C NMR spectra. The char-
acteristic signal of C=N bond occurs at 158.8 ppm, other
peaks in the range of 108–154 ppm are assigned to the aro-
matic carbon atoms (Figure S3) [33]. XPS survey spectrum
of NiP-TPE-COF shows the existence of C, O, N and Ni
elements (Figure S4). In the high-resolution N 1s XPS
tween the adsorbed CO molecules and Ni ions [34]. The
2
adsorption selectivities of CO toward N at 273 K for H P-
2
2
2
TPE-COF and NiP-TPE-COF are 21.0 and 22.5, respec-
tively. The isosteric heat of adsorption (Q ) at zero coverage
st
of H P-TPE-COF and NiP-TPE-COF are 20.1 and
2
−
1
20.9 kJ mol , respectively (Figure S13), which indicates
spectrum of H P-TPE-COF (Figure S5), the binding energy
that CO sorption is mainly physisorption. In situ FTIR
2
2
peaks at 398.02, 399.93 and 399.04 eV correspond to iminic,
pyrrolic and imine nitrogen atoms, respectively. In contrast,
only two prominent nitrogen signals at 398.64 and 399.04 eV
are identified in NiP-TPE-COF owing to the same chemical
environment of porphyrinic nitrogen atoms [31]. The de-
convoluted Ni 2p XPS spectrum provides two binding en-
spectrum of molecular CO exhibits a typical asymmetric
2
−
1
stretching band at 2,335 cm (Figure 2(c)). The introduction
of NiP-TPE-COF induces the occurrence of a new adsorp-
−
1
tion peak at 2,364 cm owing to the electron donation from
II
the oxygen lone pairs of CO to the unoccupied Ni orbitals
2
[35]. Notably, the vibration peaks are still observed after the

4
Lv et al. Sci China Chem
release of CO , indicating strong interactions of the adsorbed
2
CO molecules with NiP-TPE-COF. As total results, the in-
2
corporation of Ni ions in NiP-TPE-COF enhances CO ad-
2
sorption capacity, CO selectivity over N and CO affinity,
2
2
2
which are favorable for CO catalytic conversion [36].
2
3
.2 Photocatalytic CO reduction
2
The application of NiP-TPE-COF in photocatalytic CO re-
2
duction was initially evaluated under 1 atm CO in H O/
2
2
acetonitrile solution upon visible-light irradiation (λ≥
20 nm). [Ru(bpy) ]Cl (bpy=2,2′-bipyridine) and trietha-
4
3
2
nolamine (TEOA) are used as the photosensitizer and the
electron donor, respectively, which are typical reaction
conditions because the excited photoelectrons are not strong
enough to reduce metal ions into active low-valent states
Figure 3 (a) Time-dependent evolutions of CO and H over NiP-TPE-
2
2
+
[
1,37]. Time-dependent evolutions of CO and H are shown
COF and filtration test; (b) CO
H P-TPE-COF+Ni , NiP-TPE-COF and CoP-TPE-COF; (c) photocatalytic
2
2
photoreduction over H
P-TPE-COF, Ni ,
2
2
2
+
in Figure 3(a). The total evolution amounts of CO and H in
2
−
1
CO reduction under various reaction conditions; (d) recyclability test of
2
3
h are 1,575 and 124 μmol g , respectively, corresponding
NiP-TPE-COF in photocatalytic CO reduction. Reaction conditions: cat-
2
to the selectivity of CO evolution over H generation as high
as 93%. No other reaction byproducts, such as HCOOH, and
alysts (15 mg), [Ru(bpy) ]Cl (30 mg), acetonitrile (3 mL), H O (2 mL),
2
3
2
2
TEOA (1 mL), CO (1 atm) and visible light irradiation (λ≥420 nm) for 2 h
2
(color online).
CH OH, are detected (Figure S14). Notably, the photo-
3
catalytic system is also effective for low concentration of
CO at 0.1 atm, a typical CO concentration of the exhaust
2+
when the physical mixture of H P-TPE-COF and free Ni
2
2
2
gas from coal-fired power stations. When the simulated flue
gas consisting of 10% CO and 90% N was used to replace
ions was used. Notably, ICP-AES analysis shows that the Ni
content in the isolated solid is negligible after photocatalytic
2
2
pure CO , CO evolution rate and selectivity over H gen-
CO reduction. These observations reveal that Ni serves as
2
2
2
−
1
−1
eration are 386 μmol g
h
and 77%, respectively (Figure
the active sites, and the presence of H P-TPE-COF could
2
S15). The photocatalytic activity and selectivity are com-
parable with those in the reported visible-light-driven cata-
lytic systems Tables S7 and S8). As comparison, COF-366-
Ni and COF-367-Ni with similar morphology were also
prepared through Schiff-based reaction of NiTAP with 1,4-
benzenedicarboxaldehyde and 4,4′-biphenyldialdehyde, re-
spectively (Figure S16) [38]. The CO evolution rates in 2 h
for COF-366-Ni and COF-367-Ni decrease to 78 and
facilitate CO photoreduction, but NiP-TPE-COF could not
be formed in situ during photocatalytic reaction. The pho-
2
tocatalytic system is inactive in the absence of [Ru(bpy) ]-
3
Cl , TEOA or light irradiation. When N was used to replace
2
2
CO , only a small amount of H is produced, and no CO
2
2
evolution is detected, which suggests that CO originates
from CO molecules, rather than other organic species in the
2
photocatalytic system. The observation has been further
evidenced by the isotropic experiments under the same
conditions. The gas chromatography-mass spectrometry
(GC-MS) analysis of the evolved gases only exhibits the
−
1
−1
110 μmol g h , respecitvely, their selectivities over H
2
generation are 26% and 53%, respectively (Figure S17).
Higher catalytic activity of NiP-TPE-COF is mainly attrib-
uted to stronger conjugation ability than that of COF-366/
1
3
13
peak of CO (m/z=29) when CO is used as the gas source
2
3
67-Ni. The cyclic voltammogram (CV) and optical tests of
(Figure S20).
TPE and NiTAP have validated the integration of the elec-
tron-donating TPE and electron-accepting NiTAP in NiP-
TPE-COF (Figures S18 and S19), the electron donor-
acceptor dyad is favorable for transfer of the photogenerated
electrons from TPE to Ni-TAP [39–41].
NiP-TPE-COF possesses superior structural robustness
and durability, no apparent variations in both catalytic ac-
tivity and selectivity were observed after NiP-TPE-COF was
used at least four times (Figure 3(d)). The recovered NiP-
TPE-COF (NiP-TPE-COF-4run) was also investigated. SEM
image, PXRD pattern, FTIR and XPS spectra of NiP-TPE-
COF-4run are almost identical with those of as-synthesized
NiP-TPE-COF (Figures S21–S23). The hot filtration ex-
periment has validated heterogeneous behavior of NiP-TPE-
To identify the role of NiP-TPE-COF in photocatalytic
CO reduction, a series of control experiments were carried
2
out (Figure 3(b, c)). When NiP-TPE-COF was replaced by
H P-TPE-COF or in the absence of NiP-TPE-COF under the
2
identical conditions, negligible CO was generated. Direct use
COF in photocatalytic CO reduction (Figure 3(a)).
To establish the ideal platforms for better understanding
2
2+
of free Ni ions afforded the CO evolution amount of
−
1
−1
2
66 μmol g in 2 h, which was increased to 347 μmol g
CO photoreduction, Co ion with one d-orbital electron less
2

Lv et al. Sci China Chem
5
than Ni ion was also introduced into H P-TPE-COF to form
2
isostructural CoP-TPE-COF counterpart with the same
morphology (Figures S24, S25, and Tables S9–S11). When
photocatalytic CO reduction was conducted using CoP-
2
TPE-COF as the catalyst under the same conditions, CoP-
TPE-COF shows much higher catalytic activity than NiP-
TPE-COF. The evolution amounts of CO and H in 2 h are
2
2
−
1
4
,828 and 3,080 μmol g , respectively, but the selectivity
is as low as 61% (Figure 3(b)). The results show that the
photocatalytic CO reduction is dependent on metallopor-
2
phyrin units in MP-TPE-COF. The metallization of Co
significantly improves catalytic activity, while the me-
tallization of Ni is responsible for high CO -to-CO se-
2
lectivity.
Figure 4 (a) Steady-state PL spectra of the reaction systems upon irra-
3
.3 Mechanism for photocatalytic CO reduction
2
diation at 500 nm; DFT-calculated ΔG profiles with ZPE for (b) the CO -to-
2
CO conversion and (c) H generation; (d) proposed mechanism for CO
photoreduction over NiP-TPE-COF (color online).
2
2
To get insight into the roles of MP-TPE-COF in photo-
catalytic CO reduction, the photoelectronical measurements
2
were carried out. The electrochemical impedance spectro-
scopy (EIS) measurements show that the semicycle arc ra-
dius of Nyquist plot in CoP-TPE-COF is smaller than that of
NiP-TPE-COF (Figure S26), which suggests that more rapid
interfacial charge transfer in CoP-TPE-COF [23,40]. The
steady-state photoluminescence (PL) spectrum of the reac-
tion system without catalysts shows a strong and broad band
at 620 nm upon irradiation at 500 nm (Figure 4(a)). The in-
troduction of MP-TPE-COF has significantly declined PL
intensities. Moreover, PL signal gradually attenuates with the
rise of the NiP-TPE-COF contents (Figure S27), which in-
dicates the electron transfer from the excited [Ru(bpy) ]Cl
(Figure S29). The Co–C bond distance of 2.035 Å on CoP-
TPE-COF is shorter than that of the Ni–C bond (2.122 Å),
which further confirms stronger binding interactions be-
tween CO and Co species [39,42]. Thus, CoP-TPE-COF
2
exhibits superior catalytic activity over NiP-TPE-COF,
which is further confirmed by the process of *CO desor-
ption to form free CO molecules. For H generation (Figure
2
4(c)), the ΔG barrier corresponding to the reduction of the
+
adsorbed water to H transition state for NiP-TPE-COF
−
1
(18.1 kcal mol ) is higher than that of CoP-TPE-COF
−
1
(1.92 kcal mol ), revealing that CoP-TPE-COF is more
3
2
to NiP-TPE-COF [31]. It should be mentioned that CoP-
TPE-COF shows lower charge transfer resistance and
weaker PL intensity than NiP-TPE-COF, which well ex-
plains their photocatalytic activity. The time-resolved PL
decay spectroscopy shows that the PL lifetime is decreased
from 274 to 245 and 236 ns after the addition of NiP-TPE-
COF and CoP-TPE-COF, respectively (Figure S28). Thus,
MP-TPE-COF could effectively suppress the recombination
of photogenerated charge carriers and facilitate the electron
migration by the extended π-conjugated framework, thereby
markedly promoting the reduction of the adsorbed CO2
molecules to CO.
active than NiP-TPE-COF. In addition, ΔG of the proton-
+
−
electron transfer reduction process (CO *+H +e →
2
+
−
COOH*, COOH*+H +e → CO*+H O) for CoP-TPE-COF
2
is lower than that for NiP-TPE-COF, suggesting that NiP-
TPE-COF is more inclined to get protons for the evolution
of CO and inhibition of H generation. Thus, CoP-TPE-
2
COF exhibits higher catalytic activity than NiP-TPE-COF,
but the selectivity for CO production is lower than NiP-
TPE-COF, which are agreement with the experimental re-
sults.
Based on the aforementioned observations, a plausible
mechanism for photocatalytic CO reduction over NiP-TPE-
2
To better understand metalloporphyrin-dependent se-
COF has been proposed (Figure 4(d)). Upon visible-light
irradiation, the photogenerated electrons are transferred from
lectivity and activity for CO photoreduction, density func-
2
II
tional theory (DFT) calculations for whole catalytic process
have been performed based on the carboxyl intermediate
step. As shown in Figure 4(b), the calculated Gibbs free
the photosensitizer to Ni P-TPE-COF, resulting in the for-
0
mation of Ni P-TPE-COF. The CO molecules are adsorbed
2
0
and activated by the Ni active sites, subsequent protonation
II
2−
energies (ΔG) for the formation of the CO -CoP-TPE-COF
generates the [COOH-Ni P-TPE-COF] intermediate. After
the intermediate undergoes further protonation and the re-
2
and CO -NiP-TPE-COF adducts are −38.97 and
2
−
1
−
23.58 kcal mol , respectively, showing that CoP-TPE-
moval of water molecule, the conversion process of CO to
2
COF has stronger affinity for CO . Moreover, CO exhibits a
bent configuration after interacting with MP-TPE-COF
CO is completed with the release of CO and the regenaration
of Ni P-TPE-COF.
2
2
II

6
Lv et al. Sci China Chem
G, Gottschling K, Nuss J, Ochsenfeld C, Lotsch BV. J Am Chem Soc,
019, 141: 11082–11092
Zheng C, Zhu J, Yang C, Lu C, Chen Z, Zhuang X. Sci China Chem,
019, 62: 1145–1193
4
Conclusions
2
1
3
The metalloporphyrin-based COFs consisting of electron
donor-acceptor dyads have been constructed for under-
standing CO photoreduction at molecular level. The rela-
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