Design of D-A1-A2 Covalent Triazine Frameworks via

Subscriber access provided by Nottingham Trent University

Article

Design of D-A1-A2 Covalent Triazine Frameworks via Copolymerization for Photocatalytic Hydrogen Evolution Liping Guo, Yingli Niu, Shumaila Razzaque, Bien Tan, and Shangbin Jin ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b01951 • Publication Date (Web): 27 Aug 2019 Downloaded from pubs.acs.org on August 27, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Design of D-A1-A2 Covalent Triazine Frameworks via Copolymerization for Photocatalytic Hydrogen Evolution Liping Guo,†,§ Yingli Niu,‡,§ Shumaila Razzaque,† Bien Tan,*,† and Shangbin Jin*,† † Key

Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of

Education, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Luoyu Road No. 1037, 430074, Wuhan, China. ‡

Department of Physics, School of Science, Beijing Jiaotong University, Shangyuancun No. 3,

100044, Beijing, China.

ABSTRACT: Conjugated porous polymers (CPPs) are recently emerged as prospective materials for photocatalytic hydrogen evolution. In the design of CPPs photocatalysts, one of the essences is to find ways to inhibit backward charge recombination and promote forward charge transfer/separation. Conjugated donor-acceptor polymers are capable to favor forward intramolecular charge separation; however, they often suffer from backward charge recombination simultaneously, which causes the decrease of the quantum efficiency for the solar-energy conversion. Herein, a photoinduced electron transfer system via constructing D-A1A2 conjugated polymers for photocatalytic hydrogen evolution is developed. Such kind of D-A1A2 system can not only boost charge separation, but also suppress charge recombination owing ACS Paragon Plus Environment

1

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 30

to the cascade energy levels of the comprised units and large charge delocalization structures. Thereby, an apparent quantum yield (AQY) up to 22.8 % at 420 nm is achieved and the highest hydrogen evolution rate (HER) can be up to 966 μmol h-1 (19.3 mmol g-1 h-1) under visible light irradiation. These values are comparable to the state-of-the-art CPPs as well as part of inorganic photocatalysts. This work provides an alternative strategy and insight for the design of CPPs photocatalytic systems for photocatalytic applications in high efficiency.

KEYWORDS: covalent triazine framework, donor-acceptor, photoinduced electron transfer, charge recombination, photocatalytic hydrogen evolution

1. INTRODUCTION

Conjugated porous polymers (CPPs), including conjugated covalent organic frameworks (COFs),1-14 conjugated microporous polymers (CMPs),15-30 and covalent triazine frameworks (CTFs),31-43 have recently emerged as potential materials for photocatalysis. Specifically, thanks to the advantages of high surface area, structural flexibility of building blocks and tailorable polymer skeletons, CPPs have witnessed a rapid development in the application of photocatalytic hydrogen evolution. More and more CPPs with versatile structural designs are developed as promising photocatalysts for hydrogen evolution.1,3-5,7-9,12,16-19,21,25-27,29,30,32,33,36,37,41,43 To increase the photocatalytic activity of hydrogen production, much endeavors are devoted to the design of heterostrucutre systems1,11 or molecular engineering,4,16,19,29,39 with the aims to modulate energy levels and charge transfer/separation processes. However, even many progresses have been made, the quantum efficiency of these porous polymers are mostly confined within 10%.12,25,42

ACS Paragon Plus Environment

2

Page 3 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Construction of donor-acceptor conjugated polymers with building blocks bearing different electron affinities is a valuable approach to enhance solar-energy conversion,27,43, 44-47 because the conjugated donor-acceptor systems could enable efficient forward charge separation. However, their conjugated systems are also vulnerable to rapid backward charge recombination simultaneously, which would result in low quantum efficiency in the photocatalytic applications.48 Therefore, it is of great value to find an effective way to suppress charge recombination in order to increase the efficiency.49 In natural photosynthesis system II, charge recombination is mitigated through the adoption of multiple electron donors and acceptors,50 which is due to the photinduced electron transfer system comprised of multiple donors and acceptors with energy level gradients that could effectively inhibit the backward charge recombination, and facilitate the separation of photogenerated charges in the photosynthesis.51,52 Inspired by the natural system, constructing systems with multiple electron donors or acceptors with energy levels gradients can be a promising approach for the construction of artificial solarenergy conversion systems. Herein, we report a strategy to inhibit charge recombination and promote charge separation by the construction of a D-A1-A2 system in CPPs which is serving as a photoinduced electron transfer system so as to achieve high photocatalytic activity with high quantum efficiency in photocatalytic

hydrogen

evolution.

The

resulting

CTFs

are

designed

through

the

copolymerization of a mixture of 4,7-bis(4-formylphenyl)-2,1,3-benzothiadiazole (M-BT) and 3,6-dicarbaldehyde-N-ethylcarbazole (M-CBZ) in designated ratios with terephthalimidamide dihydrochloride, in which benzothiadiazole (BT) is as a secondary acceptor unit. Thus, a series of terpolymers with donor (D)-acceptor 1 (A1)-acceptor 2 (A2) system are formed, where the carbazole unit serves as D, and triazine and benzothiadiazole units act as A1 and A2, respectively.


3

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 30

Due to the energy level gradients in the donor and acceptors, the copolymer constitutes an efficient photoinduced electron transfer system through HOMO-LUMO transition (Scheme 1a), which allows the electrons favorably flow along a directional route from the fragments with higher energy levels to the fragments with lower energy levels. Moreover, the backward charge recombination is effectively mitigated owing to the larger delocalization system and the longer distance between D and A2 which make the separated charges harder to recombine.53, 54 Thus, it would be a useful strategy to increase the quantum efficiency. The decrease of the charge recombination was clearly evidenced by the much lower photoluminescence intensity and the enhanced charge separation was supported by electronic paramagnetic resonance (EPR) as well as theoretical calculations. Furthermore, the photocatalytic hydrogen evolution rates (HER) of the polymers can be finely tuned by varying the ratio of A2. As a result, a high HER up to 966 μmol h-1 under visible light irradiation and an excellent apparent quantum yield (AQY) of 22.8 % at 420 nm are achieved in the best copolymer sample, which outperforms the state of the art CPPs,12,25,42 and even comparable to some other materials.46, 55, 56 2. EXPERIMENTAL SECTION 2.1 Synthesis of CTFs. Taking ter-CTF-0.7 as an example, the mixture of 3,6-dicarbaldehydeN-ethylcarbazole (M-CBZ, 0.27 g, 0.7 mmol), 4,7-bis(4-formylphenyl)-2,1,3-benzothiadiazole (M-BT, 0.10 g, 0.3 mmol), terephthalamidine dihydrochloride (0.47 g, 2.0 mmol) and Cs2CO3 (1.31 g, 4.0 mmol) were dissolved into 40.0 mL DMSO, and heated through temperatureprogrammed route with stirring at 60 °C for 12 h, 80 °C for 12 h, 100 °C for 12 h, 120 °C for 36 h and 150 °C for 36 h. Then the suspension is cooled to room temperature, and the polymer was collected by filtration, washed with water, DMF and then freeze-dried. The final product terCTF-0.7 was obtained as a bright yellow powder (yield: 85%). The other polymers were


4

Page 5 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

synthesized following the same procedure as ter-CTF-0.7 with only changing the ratio of aldehyde monomers. The summary data of synthesized CTFs in this work were listed in Table S1. 2.2 Photocatalytic Measurement. The photocatalytic performances were measured under the irradiation of visible light (> 420 nm) at 15 A current with 300 W Xe lamp (Beijing PerfectLight Co. Ltd., PLS-SXE300). The diameter of the photoreactor is 7.8 cm. 50.0 mg photocatalysts with or without Pt were dispersed in 100 mL TEOA aqueous solution (10 vol%, v/v). Pt nanoparticles were loaded on CTFs by chemical reduction method via NaBH4 reductant before photocatalysis.43 The whole photocatalytic process was kept at room temperature (25 °C) with the light intensity of 130 mW cm-2. The amounts of the hydrogen production were determined by gas chromatography (SHIMADZU, GC-2014C). The apparent quantum yields (AQY) were measured using the following conditions: 100 mL TEOA aqueous solution (10 vol%, v/v), 25 °C, bandpass filters (420 nm or 500 nm). The light intensity at 420 nm and 500 nm was 5.2 mW cm-2 and 6.4 mW cm-2, respectively. The final AQY at certain light irradiation wavelength was calculated according to the literature method.57 3. RESULTS AND DISCUSSION 3.1. Synthesis and Structural Characterization The terpolymers were synthesized through polycondensation between an amidine monomer and a mixture of aldehyde monomers (M-BT and M-CBZ) (Scheme 1b and Table S1). The ratios of M-CBZ and M-BT are variable to tune the structures of terpolymers in order to obtain an optimal D-A1-A2 system for photocatalytic performance. As described in Scheme 1b, the D-A1-A2 CTFs samples are named as ter-CTF-X, where X refers to the percentage of the M-CBZ in the total


5

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 30

aldehyde monomers, and the amount of the M-CBZ is gradually reduced by 10%. We proposed three model fragments (M1-M3) which are possibly distributed in the copolymers (Scheme 1c). Scheme 1. (a) The comparison of D-A system with D-A1-A2 system in the photoinduced electron transfer process. (b) The synthesis of ter-CTF-X (X was referred to the percentage of the M-CBZ in the total aldehyde monomers). (c) Three proposed model fragments in ter-CTF-X. (M1: CBZ combined with triazine; M2: CBZ combined with triazine and BT; M3: BT combined with triazine).


6

Page 7 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

As shown in Figure 1a, the triazine structures in these terpolymers are formed as the product of the condensation reaction as confirmed by the C=N stretching band (1520 cm-1) and C-N stretching vibration band (1351 cm-1) in the FT-IR spectra. The solid-state

13C-NMR

spectra

further verified the copolymer structures. Among the copolymers, ter-CTF-0.7 was selected as a representative sample to characterize the structure as shown in Figure S1. Both BT unit and CBZ unit are coexisted in the copolymer according to the characteristic chemical shifts at 154, 108 and 37 ppm originated from the BT, CBZ and ethyl group in ter-CTF-0.7, respectively. Notably, the signal of the triazine carbon in ter-CTF-0.7 shifts to a lower field (170.6 ppm) than that of CTF-CBZ (170.1 ppm), whereas to a higher field as compared with CTF-BT (170.8 ppm) (Figure 1b). The chemical shift difference of the triazine carbon between CTF-CBZ and terCTF-0.7 is caused by the BT unit, which has strong electron withdrawing ability and thus decreases the electron density around triazine carbon. These results clearly indicate the coexistence of the three units (i.e. CBZ, BT and triazine) in the copolymer, although the position of the fragments cannot be precisely defined owing to the random copolymerization. XPS spectra were measured to explore the chemical bonding state of the elements. In the XPS survey (Figure S2) and high-resolution spectra of S 2p (Figure 1c), signal deriving from sulphur (S) is clearly found in ter-CTF-0.7 sample, whereas it is not observed in CTF-CBZ. The detailed comparison of the high-resolution spectra of N 1s (Figure 1d) shows the binding energy of sp2 hybridized aromatic N bond of ter-CTF-0.7 (399.0 eV) lies between that of CTF-CBZ (398.7 eV) and CTF-BT (399.1 eV). The difference is mainly caused by the introducing of C=NS moiety originating from BT unit, which is also an evidence for the copolymer structure. In addition, the content of elements in ter-CTF-X are obtained according to the elemental analysis (Table S2). Notably, the contents of the sulfur in the copolymer samples are mostly a little bit


7

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 30

higher than the theoretical calculated values, which might be attributed to the slightly higher activity of the BT unit as compared to the CBZ unit. It is also found that the sum of the elemental content (C, N, H and S) are less than 100%, which is mainly due to the incomplete combustion of the carbon components. This phenomenon is commonly found in such kind of conjugated porous polymers. 12, 25

Figure 1. (a) FT-IR spectra of CTFs. (b) The chemical shift of carbon atoms from triazine in the solid-state 13C-NMR spectra. High-resolution XPS spectra of S 2p (c) and N 1s (d). From the SEM images (Figure S3), the CTFs particulates display as tightly stacked irregular slices. The lamellar structures were clearly observed by TEM measurements (Figure S4). These copolymers are porous materials with high BET surface areas (Figure S5a and Table S1) and abundant micropore structures, as revealed by nitrogen sorption measurements and pore size distributions (Figure S5b). Both layer structures and high BET surface areas are favorable for


8

Page 9 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

improving the dispersity of catalysts and their contact with reactants, and thereby are profitable to the hydrogen production.

58, 59

The CTFs are also revealed to bear high thermal stability

through thermo-gravimetric analysis measurement (Figure S6), which assures the stable catalytic activity during the photocatalytic process. From powder X-ray diffraction (PXRD) measurement (Figure S7), the CTFs only showed low crystallinity as indicated by the weak and broad diffraction peaks. It is notable that the XRD peaks at around 7.8 are gradually decreased with the content of BT unit increased in the terpolymer, indicating the BT units are inserted into the polymer networks and changed the stacking structures of the resulting CTFs.45 3.2 Photocatalytic Performance of CTFs The photocatalytic hydrogen evolution activities of CTFs were next investigated under visible light (>420 nm). In photocatalytic process, the photocatalytic activity of these CTFs without Pt loading were initially explored (Figure S8). The hydrogen evolution rates (HERs) of D-A1-A2 CTFs are highly correlated with the content of the secondary acceptor unit (BT) in the copolymers. The results show that ter-CTF-0.7 exhibits the highest performance (5.98 mol h-1). After adding Pt as cocatalyst, the HERs of these CTFs dramatically enhanced (Table S3 and Figure S9-S10). As the results exhibited in Figure 2a-b, the average HER of ter-CTF-0.7 after adding Pt cocatalyst reaches the highest value (966 mol h-1), which is 2 times of the pristine CTF-CBZ and 5.3 times of the pristine CTF-BT. Then the HER gradually decreases when further increased the content of BT. To verify the stability, several photocatalytic cycles were measured for ter-CTF-0.7 sample (Figure 2c). The average HER of ter-CTF-0.7 retains to be 917 mol h-1 after five photocatalytic cycles, indicating the good stability of the photocatalytic system. After photocatalytic experiment, ter-CTF-0.7 showed no obvious structural change according to FT-IR


9

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 30

spectra (Figure S11). In addition, the influence of the amount of photocatalyst (ter-CTF-0.7) on photocatalysis were investigated (Figure S12-S13). The hydrogen evolution performance is not proportional to the mass of catalysts used in the reaction because the increased amount of photocatalysts will cause the weak light transmittance and thus make the utilization of the light less efficient. When 5.0 mg, 10.0 mg, or 25.0 mg ter-CTF-0.7 are used, the HER are measured to be 452 mol h-1 (90 mmol h-1g-1), 631 mol h-1 (63 mmol h-1g-1) and 860 mol h-1(34 mmol h-1 g-1), respectively. The AQY of the CTFs were also measured to evaluate the photocatalysis efficiency (Table S3). ter-CTF-0.7 exhibits the highest AQY of 22.8 % at 420 nm and 14.7 % at 500 nm (Figure 3d). As a result, these values apparently outperform the state-of-the-art CPPs, such as COFs (5 mg, 82 mol h-1; ~7.5 % at 420 nm),12 CMPs (50 mg, 426 mol h-1; 6.1 % at 400 nm),25 or other CTFs (50 mg, 275 mol h-1; 6 % at 420 nm).42


10

Page 11 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Figure 2. (a) Time course of H2 production of CTFs. (b) HER of CTFs. (c) Recycle tests for H2 evolution. (d) AQY measurements of H2 under 420 nm and 500 nm of CTFs. 3.3 Mechanism of High Photocatalytic Activity With the aim to probe the mechanism of the excellent photocatalytic performance of CTFs, the light absorption ability of CTFs was firstly explored through the measurement of UV/Vis diffuse reflectance spectroscopy (DRS). As shown in Figure 3a, the absorption regions are gradually red-shifted with increased content of BT unit and then blue-shifted when the content of BT exceeds 30%. These results imply the light absorption ability and bandgaps of CTFs are mildly tunable by varying the ratios of M-CBZ and M-BT.

Figure 3. (a) UV-Visible DRS spectra. (b) The PL intensity excited by 365 nm. (c) The representative EPR in the dark. (d) The transient photocurrent response under the visible light irradiation.


11

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 30

Then we further measured the steady-state photoluminescence (PL) spectra as shown in Figure 3b. In contrast to UV-visible spectra, the PL response was distinctly quenched after introducing the secondary acceptor unit (BT). Notably, ter-CTF-0.7 exhibited the lowest PL intensity, which indicates the recombination of the electrons and holes are effectively suppressed as compared with other samples.47 Electron paramagnetic response (EPR) of the CTF-CBZ, CTF-BT and ter-CTF-0.7 were also studied in the dark condition. As shown in Figure 3c, terCTF-0.7 has the highest response in the dark condition. This indicates ter-CTF-0.7 has a more delocalized structure for charge migration than CTF-CBZ and CTF-BT.

60

Such kind of large

delocalized structure could make the charge recombination harder. The obvious asymmetrical EPR spectra of the CTFs is attributed to the hyperfine structure of peak splitting, which was induced by coupling the radical with 14N nuclei from CBZ unit.61, 62 As shown in Figure 3d, terCTF-0.7 also exhibits higher photocurrent than CTF-CBZ and CTF-BT. It is the highest current response among the copolymers under visible light irradiation, indicating ter-CTF-0.7 bears the highest charge transfer and separation efficiency in the series. 63, 64 To get insight into the photocatalytic processes, the orbital energy levels are calculated. The optical bandgaps of CTFs are estimated according to Tauc-plot (Figure S14) and the LUMO values of the polymers are determined by Mott-Schottky plots (Figure S15). As the energy alignments shown in Figure 4a, the bandgaps are ranged from 2.11 eV to 2.26 eV, in which terCTF-0.7 has the smallest bandgap. According to Mott-Schottky plots, the LUMO energy values shift to less negative ones when the amount of BT unit increased. Therefore, introducing BT unit can slightly tune the energy levels of the terpolymers. In order to investigate the mechanism of the intramolecular excited electron transfer process, density functional theory (DFT) and linear response time-dependent density functional


12

Page 13 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

theory (LR-TDDFT) with B3LYP functional and 6-311G (d, p) basis set in Gaussian 16 package65 were applied to optimize the ground state geometry and to calculate the molecular orbitals and charge density difference between the first excited state and ground state (Figure S16). The theoretical energy levels were calculated based on the structural model of building blocks (i.e. CBZ, triazine and BT) (Fig. 4b). According to the theoretical calculation results, CBZ act as electron donor, triazine and BT act as electron acceptors. Moreover, BT shows stronger electron affinity than that of triazine. As shown in Figure 4c, HOMO mostly localizes on the CBZ unit, and LUMO mostly localizes on triazine and BT unit in M1 fragment and M2 fragment, while HOMO and LUMO are almost overlapped in M3 fragment. Especially in M2 fragment, LUMO mostly localizes on the BT unit and only small portions stays on triazine ring unit with the conjugated interaction, which means the excited electrons would be more inclined to concentrate on these sites. The effective separation of HOMO and LUMO indicates the structure may have a more efficient charge separation ability via HOMO-LUMO transition. Here, the charge separation performance is assessed with electron distribution in terms of the electron density difference between the first excited state and the ground state. According to the simulation results (Figure 4e), M1 fragment and M2 fragment have better separation performance than M3 fragment. The electrons are excited from CBZ unit (the negative differences of electron density, blue regions) and finally migrate to triazine unit (the positive differences of electron density, red regions) in M1 fragment and to BT unit (the positive differences of electron density, red regions) in M2 fragment. With spatial effects, M2 fragment delivers first-rate separation efficiency, which is highly desirable in photocatalytic process. In D-A1-A2 system, the higher ratio of BT unit increases the amount of M2 fragment, which is beneficial for the photocatalytic efficiency. But with further increasing the ratio of BT, the content of M3 fragment increases and


13

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 30

the electron relay system would be reduced consequently. Therefore, when the ratio of CBZ to BT is optimized to be 0.7: 0.3, the resulting terpolymer exhibits the most efficient charge separation among the series, and comprises the highest photocatalytic efficiency. To get insight into the charge excitation and separation performance, femtosecond transient absorption (fs-TA) spectra of CTF-CBZ (D-A system) and ter-CTF-0.7 (D-A1-A2 system) were studied. Under the excitation at 400 nm, negative peaks around 521 nm were observed at the different indicated time delays (Figure S17), in which both ground state bleaching and excited state absorption appear simultaneously. According to the leaping signals from the delay time 100 ps to 350 ps, the exhibited signals are the competing results between ground state bleaching and excited state absorption in the first 350 Ps. With the prolonged delay time more than 350 ps, ground state bleaching is dominant in relaxation process. Thus, the decay of bleaching was analyzed to get the excited charge lifetime. The overall decay kinetics of CTF-CBZ and ter-CTF0.7 at 521 nm were showed in Figure S18. According to the fitting results, the excited charge lifetime of ter-CTF-0.7 (D-A1-A2 system) increases largely (11.6 ns) as compared to that of CTF-CBZ (3.6 ns), which indicates that the electron transfer process supported by D-A1-A2 system can largely benefit for charge separation. EPR under light irradiation experiments were performed to further confirm the charge transfer and separation performance. When the presence of oxygen, the generated electrons and holes from the excited CTFs will undergo the following processes as described in the following equations66:

CTFs  h  e   h  e   O2  O2 h   H 2O  OH  H 


14

Page 15 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Figure 4. (a) Energy diagram of CTFs from experimental results. (b) The molecular orbital energy levels of building blocks from theoretical calculations. (c) The isosurface of molecular orbital distribution of proposed fragments in D-A1-A2 CTFs. (d) The radical intensity according to EPR under visible light irradiation of CTF-CBZ, ter-CTF-0.7 and CTF-BT. (e) The electron


15

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 30

density differences between the first excited state and the ground state in the fragments with the isovalue density of 0.0004 e Å-3. Accordingly, the superoxide radical (•O2-) and hydroxyl radical (•OH) would be formed when electron and hole meet with oxygen and water molecules, respectively. Therefore, the charge separation efficiency could be evaluated by the intensity of •O2- and •OH radicals detected through EPR in the presence of O2 and using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap.67 According to the results in Figure S19-S21, no signal of DMPO-•O2- or the DMPO-•OH in CTF-CBZ, ter-CTF-0.7 and CTF-BT is detected in the dark. In contrast, they show strong signals in CTF-CBZ, ter-CTF-0.7 and CTF-BT samples after light irradiation and the intensities increased with prolonged irradiation time. In Figure 4d, much higher response intensities of DMPO-•O2- and DMPO-•OH in ter-CTF-0.7 were observed than those in CTFCBZ and CTF-BT, indicating more electrons and holes are generated in ter-CTF-0.7 under the same condition. These results prove that D-A1-A2 system in ter-CTF-0.7 can inhibit the backward charge recombination and have a much better charge separation efficiency than CTFCBZ (D-A system), which is responsible for the higher photocatalytic performance. 3.4 Structural Insights To demonstrate the necessity of the present co-polymerization strategy, a series of possible controlled samples were designed and synthesized. In these samples, the CBZ, triazine and BT units are reacted or physically mixed in different modes (Figure S22-24). The first control terpolymer sample is synthesized by 3,6-dibenzimidamide-9-ethylcarbazole dihydrochloride (MCBZ-2) (ter-CTF-Alt), in which the CBZ, triazine and BT could connect alternatively and should have a closer distance between these units as compared with ter-CTF-0.7 (Scheme S1). The


16

Page 17 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

second terpolymer is a mixture of two polymers, which is prepared by physically mixing the CTF-CBZ and CTF-BT in the ratio of 70% to 30% (ter-CTF-0.7-P). And the third sample is synthesized by adding M-BT monomer separately to the polymerization system, forming a terpolymer system like a block copolymer (ter-CTF-0.7-Blo). Then the photocatalytic hydrogen evolution rates of the controlled samples were measured. It is revealed that the HER of ter-CTFAlt, ter-CTF-0.7-P and ter-CTF-0.7-Blo are 162 μmol h-1, 455 μmol h-1, 682 μmol h-1, respectively, which are obviously inferior to ter-CTF-0.7 (966 μmol h-1) (Figure S25). Then, we studied the photoluminescence properties and found that the controlled samples are exhibiting higher PL intensity than that of ter-CTF-0.7. These results indicate the samples are having more charge recombination, which is the reason for the lower photocatalytic activity (Figure S26). The reason for more serious charge recombination in ter-CTF-Alt may be due to the shorter distance between CBZ and BT than that of the ter-CTF-0.7 copolymer, which result in the quick charge recombination. In ter-CTF-0.7-P, the electron transfer occurs between the D and A1-A2 located in the two different polymers, which may result in lower efficiency for charge separation and faster charge recombination (Figure S26). While in ter-CTF-0.7-Blo, even with the coexistence of three components (D, A1 and A2) in the whole polymer, but the CBZ and BT units are located in different regions, making electron relay system have a much longer migration distance than ter-CTF-0.7. According to these results, organization mode and the distance of the D and A units play the critical roles in the design of conjugated materials for photocatalytic hydrogen evolution. 4. Conclusion In summary, we successfully demonstrated an effective strategy to maximize photocatalytic performance by construction of D-A1-A2 conjugated system into donor-acceptor conjugated


17

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 30

porous polymers as inspired by the natural photosynthesis processes. The resulting CTFs (terCTF-X) were constructed with different ratios of donor (carbazole) and acceptors (triazine and benzothiadiazole) through polycondensation method and formed a type of D-A1-A2 CTFs. Owing to the photoinduced electron transfer system that can suppress charge recombination and facilitate charge separation, the best terpolymer sample (ter-CTF-0.7) can exhibit a highest HER up to 966 mol h-1 under visible light irradiation and a highest AQY of 22.8 % at 420 nm, which is superior to most of the conjugated porous polymers. We further showed the terpolymer resulted from the copolymerization system are superior to the alternative copolymer, physical mixed copolymers and block copolymer systems, indicating the advantages of the present structural mode. This work opens up a new way and provides a new insight for the design and synthesis of artificial photocatalysts based on conjugated porous polymers to maximize photocatalytic efficiency. ASSOCIATED CONTENT Supporting Information The supporting information is available free of charge. This file is comprised of the experiment details and characterization results of ter-CTF-X, the photocatalytic performance of ter-CTF-X, molecular geometry based on DFT calculations, synthesis and characterization of ter-CTF-Alt and ter-CTF-0.7-Blo, comparison of photocatalytic performance according to reported literatures. AUTHOR INFORMATION Corresponding Author


18

Page 19 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

* [email protected] * [email protected] Author Contributions §These two authors (L. G. and Y. N.) contributed equally to this work. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by National Natural Science Foundation of China (Grant No. 21875078, 21604028), the International S & T Cooperation Program of China (Grant No. 2016YFE0124400), and the Program for HUST Interdisciplinary Innovation Team (Grant No. 2016JCTD104). We also gave our thanks to the Analysis and Testing Center of Huazhong University of Science and Technology. REFERENCES (1)

Thote, J.; Aiyappa, H. B.; Deshpande, A.; Diaz Diaz, D.; Kurungot, S.; Banerjee, R. A Covalent Organic Framework-Cadmium Sulfide Hybrid as a Prototype Photocatalyst for Visible-Light-Driven Hydrogen Production. Chem. Eur. J. 2014, 20, 15961-15965.

(2)

Calik, M.; Auras, F.; Salonen, L. M.; Bader, K.; Grill, I.; Handloser, M.; Medina, D. D.; Dogru, M.; Löbermann, F.; Trauner D.; Hartschuh, A.; Bein, T. Extraction of Photogenerated Electrons and Holes from a Covalent Organic Framework Integrated Heterojunction. J. Am. Chem. Soc. 2014, 136, 17802–17807.


19

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(3)

Page 20 of 30

Stegbauer, L.; Schwinghammer, K.; Lotsch, B. V. A Hydrazone-Based Covalent Organic Framework for Photocatalytic Hydrogen Production. Chem. Sci. 2014, 5, 2789-2793.

(4)

Vyas, V. S.; Haase, F.; Stegbauer, L.; Savasci, G.; Podjaski, F.; Ochsenfeld, C.; Lotsch, B. V. A Tunable Azine Covalent Organic Framework Platform for Visible Light-Induced Hydrogen Generation. Nat. Commun. 2015, 6, 8508.

(5)

Banerjee, T.; Haase, F.; Savasci, G.; Gottschling, K.; Ochsenfeld, C.; Lotsch, B. V. SingleSite Photocatalytic H2 Evolution from Covalent Organic Frameworks with Molecular Cobaloxime Co-Catalysts J. Am. Chem. Soc. 2017, 139, 16228-16234.

(6)

Yang, S.; Hu, W.; Zhang, X.; He, P.; Pattengale, B.; Liu, C.; Cendejas, M.; Hermans, I.; Zhang, X.; Zhang, J. 2D Covalent Organic Frameworks as Intrinsic Photocatalysts for Visible Light-Driven CO2 Reduction. J. Am. Chem. Soc. 2018, 140, 14614-14618.

(7)

Pachfule, P.; Acharjya, A.; Roeser, J.; Langenhahn, T.; Schwarze, M.; Schomacker, R.; Thomas, A.; Schmidt, J. Diacetylene Functionalized Covalent Organic Framework (COF) for Photocatalytic Hydrogen Generation. J. Am. Chem. Soc. 2018, 140, 1423-1427.

(8)

Stegbauer, L.; Zech, S. Savasci, G.; Banerjee, T.; Podjaski, F.; Schwinghammer, K.; Ochsenfeld, C.; Lotsch, B. V. Tailor‐Made Photoconductive Pyrene‐Based Covalent Organic Frameworks for Visible‐Light Driven Hydrogen Generation. Adv. Energy Mater. 2018, 8, 1703278.

(9)

Banerjee, T.; Gottschiling, K.; Savasci, G.; Ochsenfeld, C.; Lotsch, B. V. H2 Evolution with Covalent Organic Framework Photocatalysts. ACS Energy Lett. 2018, 3, 400-409.

(10) Wei, P. F.; Qi, M. Z.; Wang, Z.; Ding, S.; Yu, W.; Liu, Q.; Wang, L.; Wang, H.; An, W.; Wang,

W.

Benzoxazole-Linked

Ultrastable

Covalent

Organic

Frameworks

for

Photocatalysis. J. Am. Chem. Soc. 2018, 140, 4623-4631.


20

Page 21 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(11) Zhang, F. M.; Sheng, J. L.; Yang, Z. D.; Sun, X. J.; Tang, H. L.; Lu, M.; Dong, H.; Shen, F. C.; Liu, J.; Lan, Y. Q. Rational Design of MOF/COF Hybrid Materials for Photocatalytic H2 Evolution in the Presence of Sacrificial Electron Donors. Angew. Chem. Int. Ed. 2018, 57, 12106. (12) Wang, X.; Chen, L.; Chong, S. Y.; Little, M. A.; Wu, Y.; Zhu, W. H.; Clowes, R.; Yan, Y.; Zwijnenburg, M. A.; Sprick, R. S.; Cooper, A. I. Sulfone-Containing Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution from Water. Nat. Chem. 2018, 10, 1180-1189. (13) Bhadra, M.; Kandambeth, S.; Sahoo, M. K.; Addicoat, M.; Balaraman, E.; Banerjee, R. Triazine Functionalized Porous Covalent Organic Framework for Photo-Organocatalytic E-Z Isomerization of Olefins. J. Am. Chem. Soc. 2019, 141, 6152-6156. (14) Chen, R.; Shi, J.; Ma, Y.; Lin, G.; Lang, X.; Wang, C. Designed Synthesis of a 2D Porphyrin-Based sp2 Carbon-Conjugated Covalent Organic Framework for Heterogeneous Photocatalysis. Angew. Chem. Int. Ed. 2019, 58, 6430-6434. (15) Wang, Z. J.; Ghasimi, S.; Landfester, K.; Zhang, K. Molecular Structural Design of Conjugated Microporous Poly(Benzooxadiazole) Networks for Enhanced Photocatalytic Activity with Visible Light. Adv. Mater. 2015, 27, 6265-70. (16) Sprick, R. S.; Jiang, J. X.; Bonillo, B.; Ren, S.; Ratvijitvech, T.; Guiglion, P.; Zwijnenburg, M. A.; Adams, D. J.; Cooper, A. I. Tunable Organic Photocatalysts for Visible-LightDriven Hydrogen Evolution. J. Am. Chem. Soc. 2015, 137, 3265-3270. (17) Li, L.; Cai, Z.; Wu, Q.; Lo, W. Y.; Zhang, N.; Chen, L. X.; Yu, L. Rational Design of Porous Conjugated Polymers and Roles of Residual Palladium for Photocatalytic Hydrogen Production. J. Am. Chem. Soc. 2016, 138, 7681-7686.


21

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 30

(18) Sprick, R. S.; Bonillo, B.; Sachs, M.; Clowes, R.; Durrant, J. R.; Adams, D. J.; Cooper, A. I. Extended Conjugated Microporous Polymers for Photocatalytic Hydrogen Evolution from Water. Chem. Commun. 2016, 52, 10008-10011. (19) Yang, C.; Ma, B. C.; Zhang, L.; Lin, S.; Ghasimi, S.; Landfester, K.; Zhang, K.; Wang, X. Molecular Engineering of Conjugated Polybenzothiadiazoles for Enhanced Hydrogen Productionby Photosynthesis. Angew. Chem. Int. Ed. 2016, 55, 9202-9206. (20) Ghasimi, S.; Bretschneider, S. A.; Huang, W.; Landfester, K.; Zhang, K. I. A Conjugated Microporous Polymer for Palladium-Free, Visible Light-Promoted Photocatalytic StilleType Coupling Reactions. Adv. Sci. 2017, 4, 1700101. (21) Wang, L.; Wan, Y.; Ding, Y.; Wu, S.; Zhang, Y.; Zhang, X.; Zhang, G.; Xiong, Y.; Wu, X.; Yang, J.; Xu, H. Conjugated Microporous Polymer Nanosheets for Overall Water Splitting Using Visible Light. Adv. Mater. 2017, 29, 1702428. (22) Yang, C.; Huang, W.; Caire da Silva, L.; Zhang, K.; Wang, X. Functional Conjugated Polymers for CO2 Reduction Using Visible Light. Chem. Eur. J. 2018, 24, 17454-17458. (23) Ayed, C.; Caire da Silva, L.; Wang, D.; Zhang, K. I. Designing Conjugated Microporous Polymers for Visible Light-Promoted Photocatalytic Carbon-Carbon Double Bond Cleavage in Aqueous Medium. J. Mater. Chem. A 2018, 6, 22145-22151. (24) Li, R.; Ma, B. C.; Huang, W.; Wang, L.; Wang, D.; Lu, H.; Landfester, K.; Zhang, K. I. Photocatalytic Regioselective and Stereoselective [2+2] Cycloaddition of Styrene Derivatives Using a Heterogeneous Organic Photocatalyst. ACS Catal. 2017, 7, 3097-3101. (25) Zhao, Y.; Ma, W.; Xu, Y.; Zhang, C.; Wang, Q.; Yang, T.; Gao, X.; Wang, F.; Yan, C.; Jiang, J. X. Effect of Linking Pattern of Dibenzothiophene-S, S-Dioxide-Containing


22

Page 23 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Conjugated Microporous Polymers on the Photocatalytic Performance. Macromolecules, 2018, 51, 9502-9508. (26) Wang, Z.; Yang, X.; Yang, T.; Zhao, Y.; Wang, F.; Chen, Y.; Zeng, J. H.; Yan, C.; Huang, F.; Jiang, J. X. Dibenzothiophene Dioxide Based Conjugated Microporous Polymers for Visible-Light-Driven Hydrogen Production. ACS Catal. 2018, 8, 8590-8596. (27) Xu, Y.; Mao, N.; Zhang, C.; Wang, X.; Zeng, J.; Chen, Y.; Wang, F.; Jiang, J. X. Rational Design of Donor-π-Acceptor Conjugated Microporous Polymers for Photocatalytic Hydrogen Production. Appl. Catal., B: Environ. 2018, 228, 1-9. (28) Wang, B.; Xie, Z.; Li, Y.; Yang, Z.; Chen, L. Dual-Functional Conjugated Nanoporous Polymers for Efficient Organic Pollutants Treatment in Water: A Synergistic Strategy of Adsorption and Photocatalysis. Macromolecules, 2018, 51, 3443-3449. (29) Sprick, R. S.; Wilbraham, L.; Bai, Y.; Guiglion, P.; Monti, A.; Clowes, R.; Cooper, A. I.; Zwijnenburg, M. A. Nitrogen Containing Linear Poly (Phenylene) Derivatives for PhotoCatalytic Hydrogen Evolution from Water. Chem. Mater. 2018, 30, 5733-5742. (30) Sprick, R. S.; Bai, Y.; Guilbert, A. Y.; Zbiri, M.; Aitchison, C. M.; Wilbraham, L.; Yan, Y.; Woods, D. J.; Zwijnenburg, M. A.; Cooper, A. I. Photocatalytic Hydrogen Evolution from Water Using Fluorene and Dibenzothiophene Sulfone-Conjugated Microporous and Linear Polymers. Chem. Mater. 2019, 31, 305-313. (31) Jiang, X.; Wang, P.; Zhao, J. 2D Covalent Triazine Framework: A New Class of Organic Photocatalyst for Water Splitting. J. Mater. Chem. A 2015, 3, 7750-7758. (32) Schwinghammer, K.; Hug, S.; Mesch, M. B.; Senker, J.; Lotsch, B. V. Phenyl-Triazine Oligomers for Light-Driven Hydrogen Evolution. Energy. Environ. Sci. 2015, 8, 33453353.


23

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 30

(33) Bi, J.; Fang, W.; Li, L.; Wang, J.; Liang, S.; He, Y.; Liu, M.; Wu, L. Covalent TriazineBased Frameworks as Visible Light Photocatalysts for The Splitting of Water. Macromol. Rapid. Comm. 2015, 36, 1799-1805. (34) Huang, W.; Wang, Z. J.; Ma, B. C.; Ghasimi, S.; Gehrig, D.; Laquai, F.; Landfester, K.; Zhang, K. A. I. Hollow Nanoporous Covalent Triazine Frameworks Via Acid VaporAssisted Solid Phase Synthesis for Enhanced Visible Light Photoactivity. J. Mater. Chem. A 2016, 4, 7555-7559. (35) Huang, W.; Ma, B. C.; Lu, H.; Li, R.; Wang, L.; Landfester, K.; Zhang, K. Visible-LightPromoted Selective Oxidation of Alcohols Using a Covalent Triazine Framework. ACS Catal. 2017, 7, 5438-5442. (36) Li, L.; Fang, W.; Zhang, P.; Bi, J.; He, Y.; Wang, J.; Su, W. Sulfur-Doped Covalent Triazine-Based Frameworks for Enhanced Photocatalytic Hydrogen Evolution from Water Under Visible Light. J. Mater. Chem. A 2016, 4, 12402-12406. (37) Kuecken, S.; Acharjya, A.; Zhi, L.; Schwarze, M.; Schomaecker, R.; Thomas, A. Fast Tuning of Covalent Triazine Frameworks for Photocatalytic Hydrogen Evolution. Chem. Commun. 2017, 53, 5854-5875. (38) Lan, Z. A.; Fang, Y.; Zhang, Y.; Wang, X. Photocatalytic Oxygen Evolution from Functional Triazine‐Based Polymers with Tunable Band Structures. Angew. Chem. Int. Ed. 2018, 57, 470-474. (39) Huang, W.; Byun, J.; Rorich, I.; Ramanan, C.; Blom, P.; Lu, H.; Wang, D.; Caire da Silva, L.; Li, R.; Wang, L.; Landfester, K.; Zhang, K. A. I. Asymmetric Covalent Triazine Framework for Enhanced Visible‐Light Photoredox Catalysis via Energy Transfer Cascade. Angew. Chem. Int. Ed. 2018, 57, 8316-8320.


24

Page 25 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(40) Cheng, Z.; Fang W.; Zhao T.; Fang, S.; Bi, J.; Liang, S.; Li, L.; Yu, Y.; Wu, L. Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution on Phosphorus-Doped Covalent Triazine-Based Frameworks. ACS Appl. Mater. Interfaces 2018, 10, 41415-41421. (41) Liu, M.; Huang, Q.; Wang, S.; Li, Z.; Li, B.; Jin, S.; Tan, B. Crystalline Covalent Triazine Frameworks by in Situ Oxidation of Alcohols to Aldehyde Monomers. Angew. Chem. Int. Ed. 2018, 57, 11968-11972. (42) Xie, J.; Shevlin, S. A.; Ruan, Q.; Moniz, S.; Liu, Y.; Liu, X.; Li, Y.; Lau, C. C.; Guo, Z. X.; Tang, J. Efficient Visible Light-Driven Water Oxidation and Proton Reduction by an Ordered Covalent Triazine-Based Framework. Energy Environ. Sci. 2018, 11, 1617-1624. (43) Guo, L.; Niu, Y.; Xu, H.; Li, Q.; Razzaque, S.; Huang, Q.; Jin, S.; Tan, B. Engineering Heteroatoms with Atomic Precision in Donor–Acceptor Covalent Triazine Frameworks to Boost Photocatalytic Hydrogen Production. J. Mater. Chem. A 2018, 6, 19775-19781. (44) Xu, X.; Bi, Z.; Ma, W.; Wang, Z.; Choy, W.; Wu, W.; Zhang, G.; Li, Y.; Peng, Q. Highly Efficient Ternary-Blend Polymer Solar Cells Enabled by a Nonfullerene Acceptor and Two Polymer Donors with a Broad Composition Tolerance. Adv. Mater. 2017, 29, 1704271. (45) Randell, N. M.; Radford, C. L.; Yang, J.; Quinn, J.; Hou, D.; Li, Y.; Kelly, T. L. Effect of Acceptor

Unit

Length

and

Planarity

on

the

Optoelectronic

Properties

of

Isoindigo−Thiophene Donor−Acceptor Polymers. Chem. Mater. 2018, 30, 4864-4873. (46) Yu, F.; Wang, Z.; Zhang, S.; Ye, H.; Kong, K.; Gong, X.; Hua, J.; Tian, H. Molecular Engineering of Donor–Acceptor Conjugated Polymer/g-C3N4 Heterostructures for Significantly Enhanced Hydrogen Evolution Under Visible-Light Irradiation. Adv. Funct. Mater. 2018, 28, 1804512.


25

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 30

(47) Ou, H.; Chen, X.; Lin, L.; Fang, Y.; Wang, X. Biomimetic Donor–Acceptor Motifs in Conjugated Polymers for Promoting Exciton Splitting and Charge Separation. Angew. Chem. Int. Ed. 2018, 57, 8729-8733. (48) Magnuson, A.; Anderlund, M.; Johansson, O.; Lindblad, P.; Lomoth, R.; Polivka, T.; Ott, S.; Stensjo, K.; Styring, S.; Sundstron V.; Hammarstrom, L. Biomimetic and Microbial Approaches to Solar Fuel Gneration. Acc. Chem. Res. 2009, 42, 1899-1909. (49) Nguyen, C. C.; Vu, N. N.; Chabot, S.; Kaliaguine, S.; Do, T. O. Role of CxNy-Triazine in Photocatalysis for Efficient Hydrogen Generation and Organic Pollutant Degradation Under Solar Light Irradiation. Sol. RRL. 2017, 1, 1700012. (50) Barber, J. Photosynthetic Energy Conversion: Natural and Artificial. Chem. Soc. Rev. 2009, 38, 185-196. (51) Lau, V. W.; Klose, D.; Kasap, H.; Podjaski, F.; Pignié, M-C.; Reisner, E.; Jeschke, G.; Lotsch, B. V. Dark Photocatalysis: Storage of Solar Energy in Carbon Nitride for Time‐Delayed Hydrogen Generation. Angew. Chem. Int. Ed. 2017, 56, 510-514. (52) Li, Y. B.; Li, T.; Dai, X. C.; Huang, M. H.; He, Y.; Xiao, G.; Xiao, F. X. Cascade Charge Transfer Mediated by in-situ Interface Modulation Toward Solar Hydrogen Production. J. Mater. Chem. A 2019, 7,8938-8951. (53) Lee, J.; Lee, S. M.; Chen, S.; Kumari, T.; Kang, S. H.; Cho, Y.; Yang, C. Organic Photovoltaics with Multiple Donor–Acceptor Pairs. Adv. Mater. 2018, 1804762. (54) Wang, T.; Weerasinghe, K. C.; Sun, H.; Hu, X.; Lu, T.; Liu, D.; Hu, W.; Li, W.; Zhou, X.; Wang, L. Effect of Triplet State on the Lifetime of Charge Separation in Ambipolar D-A1A2 Organic Semiconductors. J. Phys. Chem. C, 2016, 120, 11338-11349.


26

Page 27 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(55) Kampouri, S.; Nguyen, T. N.; Ireland, C. P.; Valizadeh, B.; Ebrahim, F. M.; Capano, G.; Ongari, D.; Mace, A.; Guijarro, N.; Sivula, K. Photocatalytic Hydrogen Generation from a Visible-Light Responsive Metal–Organic Framework System: the Impact of Nickel Phosphide Nanoparticles. J. Mater. Chem. A 2018, 6, 2476-2481. (56) Yang, X.; Hu, Z.; Yin, Q.; Shu, C.; Jiang, X. F.; Zhang, J.; Wang, X.; Jiang, J. X.; Huang, F.; Cao, Y. Water-Soluble Conjugated Molecule for Solar-Driven Hydrogen Evolution from Salt Water. Adv. Funct. Mater. 2019, 29, 1808156. (57) Zhang, X.; Peng, B.; Zhang, S.; Peng, T. Robust Wide Visible-Light-Responsive Photoactivity for H2 Production over a Polymer/Polymer Heterojunction Photocatalyst: The Significance of Sacrificial Reagent. ACS Sustain. Chem. Eng. 2015, 3, 1501-1509. (58) Hu, Z.; Wang, Z.; Zhang, X.; Tang, H.; Liu, X.; Huang, F.; Cao, Y. Conjugated Polymers with Oligoethylene Glycol Side Chains for Improved Photocatalytic Hydrogen Evolution. iScience 2019, 13, 33-42. (59) Zhou, C.; Shi. R.; Shang, Lu.; Wu, L. Z.; Tung, C. H.; Zhang, T. Template-Free LargeScale Synthesis of g-C3N4 Microtubes for Enhanced Visible Light-Driven Photocatalytic H2 Production. Nano Res. 2018, 11, 3462–3468. (60) Shi, L.; Chang, K.; Zhang, H.; Hai, X.; Yang, L.; Wang, T.; Ye, J. Drastic Enhancement of Photocatalytic Activities over Phosphoric Acid Protonated Porous g‐C3N4 Nanosheets under Visible Light. Small, 2016, 12, 4431-4439. (61) Cai, S. L.; Zhang, Y. B.; Pun, A. B.; He, B.; Yang, J.; Toma, F. M.; Sharp, I. D.; Yaghi, O. M.; Fan, J.; Zheng, S. R.; Zhang, W. G.; Liu, Y. Tunable Electrical Conductivity in Oriented Thin Films of Tetrathiafulvalene-based Covalent Organic Framework. Chem. Sci. 2014, 5, 4693–4700.


27

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 30

(62) Cao, W.; Wang, W. D.; Xu, H. S.; Sergeyev, I. V.; Struppe, J.; Wang, X.; Mentink-Vigier, F.; Gan, Z.; Xiao, M. X.; Wang, L. Y.; Chen, G. P.; Ding, S. Y.; Bai, S.; Wang, W. Exploring Applications of Covalent Organic Frameworks: Homogeneous Reticulation of Radicals for Dynamic Nuclear Polarization. J. Am. Chem. Soc. 2018, 140, 6969-6977 (63) Yu, H.; Shi, R.; Zhao, Y.; Bian, T.; Zhao, Y.; Zhou, C.; Waterhouse, G. I. N.; Wu, L. Z.; Tung, C. H.; Zhang T. Alkali-Assisted Synthesis of Nitrogen Defcient Graphitic Carbon Nitride with Tunable Band Structures for Efficient Visible-Light-Driven Hydrogen Evolution. Adv. Mater., 2017, 29, 1605148. (64) Zhao, H.; Ding, X.; Zhang, B.; Li, Y.; Wang, C. Enhanced Photocatalytic Hydrogen Evolution Along with Byproducts Suppressing Over Z-scheme CdxZn1-xS/Au/g-C3N4 Photocatalysts under Visible Light. Sci. Bull. 2017, 62, 602–609. (65) Gaussian 16, Revision B.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2016.


28

Page 29 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(66) Hirakawa, T.; Kominami, H.; Ohtani, B.; Nosaka, Y. Mechanism of Photocatalytic Production of Active Oxygens on Highly Crystalline TiO2 Particles by Means of Chemiluminescent Probing and ESR Spectroscopy. J. Phys. Chem. B. 2001, 105, 69936999. (67) She, X.; Wu, J.; Xu, H.; Zhong, J.; Wang, Y.; Song, Y.; Nie, K.; Liu, Y.; Yang, Y.; Rodrigues, M. High Efficiency Photocatalytic Water Splitting Using 2D α‐Fe2O3/g‐C3N4 Z‐Scheme Catalysts. Adv. Energy Mater. 2017, 7, 1700025.


29

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 30

Design of D-A1-A2 conjugated polymers to form a photoinduced electron transfer system fabricated by incorporating a secondary acceptor unit into donor-acceptor covalent triazine frameworks (CTFs) that leads to a more efficient electron migration with the suppression of charge recombination and enhanced charge separation, resulting in dramatically improved photocatalytic efficiency.


30

Design of D-A1-A2 Covalent Triazine Frameworks via

Recommend Documents