Triphenylamine based conjugated microporous polymers for selective photoreduction of CO2 to CO under visible light

Article abstract of DOI:10.1039/c9gc03131f

Organic π-conjugated polymers (CPs) have been intensively explored for a variety of critical photocatalytic applications in the past few years. Nevertheless, CPs for efficient CO₂ photoreduction have been rarely reported, which is mainly due to

Full text of DOI:10.1039/c9gc03131f

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Triphenylamine based conjugated microporous
polymers for selective photoreduction of CO2
to CO under visible light†
Cite this: Green Chem., 2019, 21,
6606
Received 6th September 2019,
Accepted 18th November 2019
Chunhui Dai, ‡a Lixiang Zhong, ‡b Xuezhong Gong,b Lei Zeng, b Can Xue,
b
a
Shuzhou Li *b and Bin Liu
*
DOI: 10.1039/c9gc03131f
rsc.li/greenchem
Organic π-conjugated polymers (CPs) have been intensively makes it difficult to develop efficient photocatalysts. Since the
explored for a variety of critical photocatalytic applications in the pioneering report of heterogeneous CO2 photoreduction using
past few years. Nevertheless, CPs for efficient CO2 photoreduction TiO2 as the catalyst,7 numerous inorganic semiconductors
have been rarely reported, which is mainly due to the lack of suit- have been under active exploration. However, most inorganic
able polymers with sufficient solar light harvesting ability, appro- photocatalysts suffer from limited tunability, potential heavy
priate energy level alignment and good activity and selectivity in metal toxicity and wide band gap,7–10 which hinder their prac-
multi-electron-transfer photoreduction of CO2 reaction. We report tical applications and thus require the exploration of
here the rational design and synthesis of two novel triphenylamine alternatives.
(TPA) based conjugated microporous polymers (CMPs), which can
Conjugated microporous polymers (CMPs), a subclass of
efficiently catalyze the reduction of CO2 to CO using water vapor structurally diverse polymeric materials, have many advantages
as an electron donor under ambient conditions without adding such as permanent porosity, large surface area, strong visible
any co-catalyst. Nearly 100% selectivity and a high CO production light activity, facile synthesis, tunable optoelectronic pro-
rate of 37.15 μmol h−1 g−1 are obtained for OXD-TPA, which is sig- perties, and high chemical and thermal stability, making them
nificantly better than that for BP-TPA (0.9 μmol h−1 g−1) as a result attractive candidates for a range of applications, such as gas
of co-monomer change from biphenyl to 2,5-diphenyl-1,3,4-oxa- sequestration and separation,11–15 heterogeneous catalytic
diazole. This difference could be mainly ascribed to the synergistic reaction,16–20 sensing,21,22 and energy storage and
effect of a decreased optical band gap, improved interface charge conversion.23–27 Recent studies have revealed that porous con-
transfer and increased CO2 uptake for OXD-TPA. This contribution jugated polymers (CPs) are promising photocatalysts for CO2
is expected to spur further interest in the rational design of porous reduction and their photocatalytic activities could be effec-
conjugated polymers for CO2 photoreduction.
tively enhanced by rational molecular design. For instance, Liu
et al. reported photocatalytic CO2 reduction using a series of
pyrene-based porous CPs in a CO2-saturated ionic liquid,
which yielded CO with a rate of 47.37 μmol h−1 g−1 and reac-
tion selectivity reached 98.3% (>420 nm).28 By copolymeriza-
tion between 2,4,6-triphenyl-1,3,5-triazine and different co-
monomers, the charge separation of the resulting polymers
could be improved to give a maximum CO production rate of
18.2 µmol h−1 g−1 with 81.6% selectivity in the presence of
CoCl2 and dipyridyl as the co-catalysts.29 Crystalline covalent
organic framework (COF) based CO2-reduction photocatalysts
were reported by Huang et al., in which Re(bpy)(CO)3Cl was
incorporated into the 2D COF to reduce CO2 using triethanol-
For the past few decades, artificial photocatalysis has been
well established as a sustainable technology for CO2 conver-
sion into carbonaceous chemical fuels such as CO, CH3OH,
CH4, etc.1–6 The technology is particularly appealing as it not
only holds great promise to handle environmental issue
caused by excess CO2 release, but also provides fuels for energy
supply. However, high energy input is required for CO2 trans-
formation owing to its remarkable stability with the dis-
sociation energy of CvO bond up to 750 kJ mol−1 6
, which
aDepartment of Chemical and Biomolecular Engineering, National University of
Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore.
E-mail: cheliub@nus.edu.sg
bSchool of Materials Science and Engineering, Nanyang Technological University, 50
Nanyang Avenue, Singapore 639798, Singapore. E-mail: lisz@ntu.edu.sg
†Electronic supplementary information (ESI) available: Experimental methods
and supporting figures. See DOI: 10.1039/c9gc03131f
amine as
a sacrificial agent and 98% selectivity was
obtained.30 Despite this exciting progress, these CO2 reduction
reactions were carried out in CO2-saturated liquid media,
which required the use of organic electron donors, co-catalysts
or ionic liquids, adding cost and complexity. Moreover, the
limited solubility of CO2 in liquid media is unfavorable for
‡These authors contributed equally to this work.
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achieving high reaction efficiency. By contrast, the reduction mophenyl)-1,3,4-oxadiazole was obtained in three high yield-
reaction performed on a gas–solid interface relies on CO2 che- ing steps as depicted in Scheme S1.† A condensation reaction
misorption and activation by the photocatalysts, which elimin- between 4-bromobenzoyl chloride and hydrazine hydrate
ates the need for liquid media. This simple and environmen- afforded 1,2-bis(4-bromobenzoyl)hydrazide, followed by cyclo-
tally-friendly approach uses only a trace amount of water vapor dehydration to give 2,5-bis(4-bromophenyl)-1,3,4-oxadiazole in
as the electron donor, which significantly inhibits the compet- 71% yield.35 BP-TPA and OXD-TPA were synthesized from
ing process of water reduction and favors the selectivity of CO2 tris(4-ethynylphenyl)amine with 4,4′-dibromodiphenyl and 2,5-
reduction.1,3 However, to the best of our knowledge, the diphenyl-1,3,4-oxadiazole, respectively, by the Sonogashira
exploration of efficient polymers for CO2 reduction on a gas– coupling reaction in an Et3N/DMF (1 : 1, v/v) mixture with
solid system remains a great challenge.31 Very recently, Eosin Pd(PPh3)4 and CuI as catalysts. The resulting product was suc-
Y-based conjugated porous polymers were developed for CO2 cessively washed with water, acetone and methanol followed
photoreduction, which resulted in a CO production rate of by Soxhlet extraction (THF and then CH2Cl2). BP-TPA and
33 μmol h−1 g−1 with 92% selectivity.31 To achieve better OXD-TPA are insoluble in all common solvents such as DMF,
photocatalytic performance, new polymers and useful mole- THF and CH2Cl2. The structural characterization of the two
cular design strategies to reveal the critical parameters that polymers was studied by solid-state 13C NMR spectroscopy,
control their photoactivities are highly desirable.
FT-IR spectroscopy, and elemental analysis. Both polymers
In this study, we present two specially designed CMPs as show aromatic peaks at 120–150 ppm and peaks at ∼91 ppm
visible-light-active photocatalysts for the reduction of CO2 to for quaternary alkynes (Fig. S1 and S2†), consistent with the
CO only in the presence of water vapor under ambient con- CMPs synthesized by the Sonogashira polymerization.34 In
ditions. The polymer structures are shown in Scheme 1. addition, the peak at 163 ppm in the NMR spectrum of
Triphenylamine (TPA) based CMPs were developed owing to OXD-TPA is ascribed to the carbon atom of oxadiazole.
their inherent advantages of high surface area for effective CO2 Fourier-transform infrared (FT-IR) spectra analysis confirmed
absorption, facile preparation, and fine optimization of energy the alkynyl linker of the two polymers by the evidence of
levels.32,33 The optical band gaps of the as-prepared CMPs stretching vibrations of triple bonds appearing around
could be tuned from 2.38 to 2.22 eV by replacing biphenyl (BP) 2200 cm−1 (Fig. S3†). BP-TPA and OXD-TPA show similarly
with 2,5-diphenyl-1,3,4-oxadiazole (OXD). More importantly, spherical morphologies revealed by scanning electron
the CO production rate could be enhanced to 37.15 µmol h−1 microscopy (SEM) measurement (Fig. S4†). Negligible Pd
g−1 with ∼100% selectivity under visible light irradiation residual was detected in both polymer networks and the
(>420 nm). In addition, we provide a comprehensive under- content is 0.34% for BP-TPA and 0.54% for OXD-TPA, respect-
standing of the photocatalytic activity of polymers by comp- ively. The powder X-ray diffraction (PXRD) patterns demon-
lementary experimental and computational studies, which is strated that both polymers exhibited broad diffraction peaks
critical for future development of conjugated polymers for CO2 with low intensities in the wide region, indicative of their
photoreduction.
amorphous nature (Fig. S6†). Thermal gravimetric analysis
The synthetic details and characterization of the monomers (TGA) demonstrated their excellent thermostability with 5%
and conjugated microporous polymers are given in the ESI.† weight loss for BP-TPA and OXD-TPA observed at 463 °C and
Tris(4-ethynylphenyl)amine was prepared by the Pd(II)-cata- 412 °C, respectively (Fig. S7†).
lyzed coupling of tris(4-bromophenyl)amine and ethynyltri-
The porosity of BP-TPA and OXD-TPA was evaluated by N2
methylsilane and subsequent deprotection promoted by sorption isotherm measurements at 77 K. As shown in Fig. 1a,
K2CO3.34 Starting from 4-bromobenzoyl chloride, 2,5-bis(4-bro- both polymer networks give rise to type I isotherms and
exhibit a steep increase in the low relative pressure regions
(<0.01) due to their microporosity. The apparent BET surface
area of BP-TPA is 512 m2 g−1, which is lower than that of
OXD-TPA (686 m2 g−1).
Scheme 1 Chemical structures of the conjugated microporous poly-
Fig. 1 (a) N2 sorption isotherm curves of the polymers obtained at 77 K.
mers for CO2 photoreduction in this study.
(b) CO2 adsorption isotherm curves of the polymers at 298 K.
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Table 1 Optical and electrochemical properties, BET surface area and
CO2 uptake data of the polymers
Both polymers have similar pore size distributions with
pore widths at about 1.1, 1.5 and 2.7 nm, respectively
(Fig. S5†). The CO2 uptake capacities of the two polymers at
298 K were evaluated by CO2 adsorption isotherms. OXD-TPA
LUMO/
a
Eg
HOMOc
SBET
CO2 uptaked
Polymers (eV) Ered, onset b (V) (V, vs. NHE) (m2 g−1
)
(cm3 g−1
)
exhibited
a higher volumetric CO2 uptake than BP-TPA
(Fig. 1b). In particular, the difference of CO2 uptake became
more distinct with increasing pressure. At P = 100 kPa, the CO2
uptake capacities of BP-TPA and OXD-TPA were 24.1 and
30.3 cm3 g−1, respectively. The enhanced CO2 absorbing ability
of OXD-TPA compared to BP-TPA is attributed to its higher
BET surface area and the dipole-induced electrostatic inter-
actions between the N or O atoms of the oxadiazole unit and
the C atoms of CO2.36–38
BP-TPA
OXD-TPA 2.22 −1.07
2.38 −1.04
−0.41/1.97
−0.44/1.78
2.38
2.22
24.1
30.3
a Estimated from the UV/vis diffuse reflectance spectra onset (Eg
1240/λonset). b Versus Fc/Fc+ in acetonitrile solution, 50 mV s−1 scan
rate. c ENHE = EFc/Fc+ + 0.63 V, EHOMO = ELUMO − Eg, opt d At P = 100 kPa.
=
.
OXD-TPA (Table 1). Accordingly, the HOMO levels of BP-TPA
and OXD-TPA were calculated to be 1.97 V and 1.78 V, respect-
ively. The energy band structures of both polymers are well
positioned for the reduction of CO2 to CO, indicating that they
are thermodynamically capable of generating CO from CO2
photoreduction under light irradiation (Fig. 2b).41
Photoelectrochemical measurements were conducted to
compare the photogenerated charge carrier transport of the
two polymers. As shown in Fig. 2c, the Nyquist plot of
OXD-TPA exhibits a smaller diameter of the semicircular than
that of BP-TPA, revealing a decrease of the charge-transfer re-
sistance by replacing biphenyl with 2,5-diphenyl-1,3,4-oxadia-
zole. The improved photoinduced charge transport can be
further supported by an increased transit photocurrent
response of OXD-TPA as shown in Fig. 2d, which reveals a
visible-light photocurrent of ∼2 µA cm−2 for OXD-TPA and
∼0.5 µA cm−2 for BP-TPA.
The CO2 photoreduction reactions over the as-synthesized
polymers were carried out in the presence of CO2 and water
vapor under ambient conditions. Interestingly, CO was
detected as the only reductive product in the photocatalytic
system (Fig. S10b†). As shown in Fig. 3a, after the four-hour
irradiation of visible light (>420 nm), OXD-TPA produced
148.6 μmol g−1 CO, which is much more than that by BP-TPA
(3.6 μmol g−1). At 420 nm, the quantum efficiencies are about
0% and 0.19% for BP-TPA and OXD-TPA (Fig. S19†), respect-
ively. To the best of our knowledge, the photocatalytic activity
of OXD-TPA (37.15 μmol h−1 g−1) is much better than that of
commonly used g-C3N4 and many newly reported CPs under
similar conditions (Table S1†).
The UV/vis diffuse reflectance spectra (DRS) and photo-
luminescence spectra of BP-TPA and OXD-TPA are displayed in
Fig. 2a. OXD-TPA with extended π-conjugation shows broader
absorption than BP-TPA. Accordingly, the optical band gaps
estimated from the absorption onset of the DRS spectra are
2.38 eV for BP-TPA and 2.22 eV for OXD-TPA. Upon excitation
at 380 nm, BP-TPA exhibits emission centered at 562 nm,
which is slightly blue-shifted to 557 nm for OXD-TPA. Notably,
the emission of OXD-TPA is significantly stronger than that of
BP-TPA. This is largely due to the twisted conformation
between phenyl and oxadiazole in 2,5-diphenyl-1,3,4-oxadia-
zole, which interrupts the π-conjugation and molecular stack-
ing, thus blue-shifts the emission and enhances the fluo-
rescence intensity.39,40 In addition, time-resolved photo-
luminescence decay spectra demonstrated a slightly longer
fluorescence lifetime of 0.82 ns for OXD-TPA than that of
BP-TPA (0.61 ns) (Fig. S8†). The LUMO levels of polymers were
evaluated using cyclic voltammetry (Fig. S9†). Both exhibited
well-defined reversible reduction waves with the LUMO levels
of −0.41 V (vs. NHE) for BP-TPA and −0.44 V (vs. NHE) for
Fig. 2 (a) UV/vis diffuse reflectance spectra (solid line) and photo-
luminescence (PL) spectra (dashed lines; λex = 380 nm) of BP-TPA and
OXD-TPA in the solid state. (b) Energy levels of BP-TPA and OXD-TPA
relative to the potentials of CO2 reduction to CO and water oxidation,
respectively, vs. the NHE at pH = 0. (c) EIS Nyquist plots and (d) periodic
transient photocurrent response of polymer electrodes in 0.5 M Na2SO4
aqueous solution.
Fig. 3 (a) CO production from the photocatalytic CO2 reduction over
BP-TPA and OXD-TPA after 4 h irradiation (>420 nm). Reaction con-
ditions: 15 mg polymer, CO2 (1.0 atm), water vapor, room temperature.
(b) Time course of photocatalytic CO2 reduction over OXD-TPA.
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To confirm the photocatalytic process, we have performed a
series of control experiments. No reductive products were
detected under dark conditions. Upon replacing CO2 with N2,
only a trace amount of CO could be detected, indicating that
CO2 is the reductive agent in the system. When no H2O is
added to the reaction system, negligible CO could be
measured, which suggests that H2O plays an important role as
an electron donor. Notably, H2 and other carbonaceous pro-
ducts, such as CH4, HCHO, HCOOH, and CH3OH were not
found in our tests, demonstrating that the separated electrons
on the surface of the polymer network are almost exclusively
used for CO2 reduction to CO and ∼100% selectivity was
obtained for OXD-TPA in the photocatalytic reaction.
Fig. 4 Different adsorption sites on (a) BP-TPA and (b) OXD-TPA, and
(c) the corresponding adsorption energies for COOH*.
To study the source of generated CO during the photo-
catalytic process, an isotopic experiment with 13CO2 (Fig. S11†)
was conducted under the same reaction conditions (>420 nm).
When 12CO2 was replaced by 13CO2 in the reactor, a gas
product with a retention time of 4.026 min was detected,
which was different from that of 12CO at 3.958 min (Fig. S10b
and c†). In addition, after adding concentrated NaOH aqueous
solution into the reactor to remove unreacted 13CO2, the gas
sample was subsequently analyzed by MS spectrometry and a
peak at m/z = 29 was found (Fig. S12†), which was assigned to
13CO. This peak was not due to the fragmentation of 13CO2
during the MS analysis as the unreacted 13CO2 was completely
removed prior to the analysis. Based on all these results, it
could be concluded that CO originated from the reduction of
CO2 on OXD-TPA.
The photocatalytic CO2 reduction stability and recyclability
of OXD-TPA was evaluated by four cyclic testing (4 h-irradiation
in each run). The photocatalytic reactor was treated under
vacuum and then refilled with the mixture of CO2 and water
vapor after each run. Steady CO production is observed over
four runs (Fig. 3b). After the photocatalysis experiments, the
recycled polymer did not show any significant structural
changes (Fig. S13–S15†), indicating that OXD-TPA is highly
stable during the photocatalytic process.
DFT calculations were performed to understand the elec-
tronic properties of both polymers. The optimized structures
are shown in Fig. S16.† The excited electrons for both BP-TPA
and OXD-TPA are distributed all over the backbone, whereas
the excited holes are mainly localized in TPA due to its strong
electron-donating feature (Fig. S17a and S17b†). Moreover,
compared to the BP moiety, the more electronegative OXD
moiety impairs the density of excited electrons within the TPA
part, which decreases the overlap between the excited electrons
and holes in OXD-TPA as compared to that of BP-TPA, indicat-
ing less recombination of photogenerated charges in
OXD-TPA.
tion is ∼0.2 eV more stable on OXD-TPA, which facilitates the
reduction of CO2.
DFT calculations revealed that the band gaps for BP-TPA
and OXD-TPA are 2.47 and 2.38 eV, respectively, which are in
agreement with the optical bandgaps obtained in our experi-
ments (2.38 eV for BP-TPA and 2.22 eV for OXD-TPA as shown
in Table 1). Notably, the theoretically predicted HOMOs and
LUMOs for BP-TPA and OXD-TPA are depicted in Fig. S18a.†
The HOMO potential of BP-TPA (0.79 V) is approximate to the
one required for water oxidation (0.82 V, neutral conditions),
while it is 0.27 V more positive for OXD-TPA. The LUMO poten-
tials of both BP-TPA (−1.68 V) and OXD-TPA (−1.31 V) are
much more negative than the reduction potential of CO2 to CO
(−0.53 V). The results reinforced the sufficient redox ability of
the two polymers to trigger the photocatalytic reactions in our
system. The possible CO2 photoreduction process for the poly-
mers is described as follows: the CO2 gas can be absorbed and
activated by the porous polymers. Upon the illumination of
visible light, the photogenerated electrons (e−) could migrate
from the LUMO levels to the HOMO levels of the polymer.
Subsequently, the absorbed CO2 captures electrons on the
polymer surface, forming CO and H2O (CO2 + 2H+ + 2e−
→
CO + H2O), while the photoinduced holes were utilized for
oxidizing water to generate oxygen and hydrogen ions via the
half-reaction (2H2O + 4h+ → O2 + 4H+) (Fig. S18b†). The low
water concentration in the reaction system could efficiently
inhibit the competitive reaction to give H2, CH3OH, CH4, etc.
This is beneficial for the high selectivity of polymers. The
much better photocatalytic performance of OXD-TPA could be
attributed to its smaller band gap, increased dissociation of
photogenerated excitons, and more stable COOH*.
Conclusions
We further studied the adsorption energy of COOH*, which In conclusion, we present the rational design of two novel tri-
is proposed to be the intermediate for CO2 reduction to CO, on phenylamine based CMPs for CO2 photoreduction to CO
different positions of BP-TPA and OXD-TPA (Fig. 4a and b), under visible light irradiation. The CO production rate could
and the corresponding adsorption energies are shown in be significantly enhanced from 0.9 to 37.15 µmol h−1 g−1
Fig. 4c. The most stable configurations of COOH* are shown (>420 nm) with ∼100% selectivity, which is much better than
in the insert of Fig. 4c and Fig. S17c.† The most stable the newly reported CPs in similar photocatalytic systems
adsorbed COOH* has similar configurations but the adsorp- (Table S1†). The enhancement in the photocatalytic activity of
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polymers resulting from molecular tuning was fully investi- 17 K. Zhang, D. Kopetzki, P. H. Seeberger, M. Antonietti and
gated by experiments and theoretical calculations. Accordingly, F. Vilela, Angew. Chem., Int. Ed., 2013, 52, 1432.
we expect that this study will stimulate research interest in 18 Z. J. Wang, S. Ghasimi, K. Landfester and K. A. I. Zhang,
designing stable and highly efficient conjugated polymers for
Adv. Mater., 2015, 27, 6265.
CO2 photoreduction.
19 Y.-B. Zhou, Y.-Q. Wang, L.-C. Ning, Z.-C. Ding, W.-L. Wang,
C.-K. Ding, R.-H. Li, J.-J. Chen, X. Lu, Y.-J. Ding and
Z.-P. Zhan, J. Am. Chem. Soc., 2017, 139, 3966.
20 R. Li, J. Byun, W. Huang, C. Ayed, L. Wang and
K. A. I. Zhang, ACS Catal., 2018, 8, 4735.
21 X. Liu, Y. Xu and D. Jiang, J. Am. Chem. Soc., 2012, 134,
8738.
Conflicts of interest
There are no conflicts to declare.
22 C. Gu, N. Huang, J. Gao, F. Xu, Y. Xu and D. Jiang, Angew.
Chem., Int. Ed., 2014, 53, 4850.
Acknowledgements
23 Y. Kou, Y. Xu, Z. Guo and D. Jiang, Angew. Chem., Int. Ed.,
2011, 50, 8753.
24 F. Vilela, K. Zhang and M. Antonietti, Energy Environ. Sci.,
2012, 5, 7819.
25 C. Gu, N. Huang, Y. Chen, L. Qin, H. Xu, S. Zhang, F. Li,
Y. Ma and D. Jiang, Angew. Chem., Int. Ed., 2015, 54,
13594.
We are grateful for financial support from the Singapore
National Research Foundation (R279-000-444-281 and R279-
000-483-281), the National University of Singapore (R279-000-
482-133), the Singapore MOE AcRF-Tier1 (2018-T1-001-072, RG
9/18) and MOE AcRF-Tier2 (MOE2016-T2-2-056).
26 C. Zhang, Y. He, P. Mu, X. Wang, Q. He, Y. Chen, J. Zeng,
F. Wang, Y. Xu and J.-X. Jiang, Adv. Funct. Mater., 2018, 28,
1705432.
Notes and references
1 J. L. White, M. F. Baruch, J. E. Pander, Y. Hu,
I. C. Fortmeyer, J. E. Park, T. Zhang, K. Liao, J. Gu, Y. Yan, 27 J. Zhu, C. Yang, C. Lu, F. Zhang and Z. Yuan, Acc. Chem.
T. W. Shaw, E. Abelev and A. B. Bocarsly, Chem. Rev., 2015,
Res., 2018, 51, 3191.
115, 12888.
28 Y. Chen, G. Ji, S. Guo, B. Yu, Y. Zhao, Y. Wu,
H. Zhang, Z. Liu, B. Han and Z. Liu, Green Chem., 2017, 19,
5777.
2 M. Marszewski, S. Cao, J. Yu and M. Jaroniec, Mater. Horiz.,
2015, 2, 261.
3 K. Li, B. Peng and T. Peng, ACS Catal., 2016, 6, 7485.
4 R. Shi, G. I. N. Waterhouse and T. Zhang, Sol. RRL, 2017, 1,
1700126.
5 J. Ran, M. Jaroniec and S.-Z. Qiao, Adv. Mater., 2018, 30,
1704649.
29 C. Yang, W. Huang, L. C. da Silva, K. A. I. Zhang and
X. Wang, Chem. – Eur. J., 2018, 24, 17454.
30 S. Yang, W. Hu, X. Zhang, P. He, B. Pattengale, C. Liu,
M. Cendejas, I. Hermans, X. Zhang, J. Zhang and J. Huang,
J. Am. Chem. Soc., 2018, 140, 14614.
6 Z. Sun, N. Talreja, H. Tao, J. Texter, M. Muhler, J. Strunk 31 X. Yu, Z. Yang, B. Qiu, S. Guo, P. Yang, B. Yu, H. Zhang,
and J. Chen, Angew. Chem., Int. Ed., 2018, 57, 7610.
7 T. Inoue, A. Fujishima, S. Konishi and K. Honda, Nature,
1979, 277, 637.
8 A. Dhakshinamoorthy, S. Navalon, A. Corma and H. Garcia,
Energy Environ. Sci., 2012, 5, 9217.
Y. Zhao, X. Yang, B. Han and Z. Liu, Angew. Chem., Int. Ed.,
2019, 58, 632.
32 T. Geng, Z. Zhu, W. Zhang and Y. Wang, J. Mater. Chem. A,
2017, 5, 7612.
33 Z. Chen, W. Li, Y. Dai, N. Xu, C. Su, J. Liu and C. Zhang,
Electrochim. Acta, 2018, 286, 187.
9 S.
N.
Habisreutinger,
L.
Schmidt-Mende
and
J. K. Stolarczyk, Angew. Chem., Int. Ed., 2013, 52, 7372.
10 K. Li, B. Peng and T. Peng, ACS Catal., 2016, 6, 7485.
34 Z. Xie, Y. Wei, X. Zhao, Y. Li, S. Ding and L. Chen, Mater.
Chem. Front., 2017, 1, 867.
11 A. Li, R. F. Lu, Y. Wang, X. Wang, K. L. Han and 35 W.-Y. Wong and Y.-H. Guo, J. Mol. Struct., 2008, 890, 150.
W. Q. Deng, Angew. Chem., Int. Ed., 2010, 49, 3330.
12 R. Dawson, E. Stockel, J. R. Holst, D. J. Adams and
A. I. Cooper, Energy Environ. Sci., 2011, 4, 4239.
36 M. Saleh, H. M. Lee, K. C. Kemp and K. S. Kim, ACS Appl.
Mater. Interfaces, 2014, 6, 7325.
37 S. Hug, L. Stegbauer, H. Oh, M. Hirscher and B. V. Lotsch,
Chem. Mater., 2015, 27, 8001.
13 Q. Chen, M. Luo, P. Hammershøj, D. Zhou, Y. Han,
B. W. Laursen, C.-G. Yan and B.-H. Han, J. Am. Chem. Soc., 38 K. Yuan, C. Liu, L. Zong, G. Yu, S. Cheng, J. Wang, Z. Weng
2012, 134, 6084. and X. Jian, ACS Appl. Mater. Interfaces, 2017, 9, 13201.
14 Y. H. Xu, S. B. Jin, H. Xu, A. Nagai and D. L. Jiang, Chem. 39 C. Wang, L.-O. Pålsson, A. S. Batsanov and M. R. Bryce,
Soc. Rev., 2013, 42, 8012. J. Am. Chem. Soc., 2006, 128, 3789.
15 Y. Yuan, H. Huang, L. Chen and Y. Chen, Macromolecules, 40 Y. Tao, Q. Wang, C. Yang, C. Zhong, K. Zhang, J. Qin and
2017, 50, 4993. D. Ma, Adv. Funct. Mater., 2010, 20, 304.
16 L. Chen, Y. Yang, Z. Guo and D. Jiang, Adv. Mater., 2011, 41 W. Fan, Q. Zhang and Y. Wang, Phys. Chem. Chem. Phys.,
23, 3149.
2013, 15, 2632.
6610 | Green Chem., 2019, 21, 6606–6610
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