thiazole-Linked Conjugated Microporous Polymers with Heteroatom

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Functional Nanostructured Materials (including low-D carbon)

Layered Thiazolo[5,4-d] thiazole-Linked Conjugated Microporous Polymers with Heteroatom Adoption for Efficient Photocatalysis Application Qi Huang, Liping Guo, Ning Wang, Xiang Zhu, Shangbin Jin, and Bien Tan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 27 Mar 2019 Downloaded from http://pubs.acs.org on March 27, 2019

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ACS Applied Materials & Interfaces

Layered Thiazolo[5,4-d] thiazole-Linked Conjugated Microporous Polymers with Heteroatom Adoption for Efficient Photocatalysis Application Qi Huang†, Liping Guo†, Ning Wang†, Xiang Zhu‡*, Shangbin Jin†*, Bien Tan† †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 Chemistry, Texas A&M University, College Station, USA, 77840. KEYWORDS: conjugated microporous polymer; layered architectures; nitrogen and sulphur co-doped; band gap; dye degradation.

ABSTRACT. Conjugated microporous polymers (CMPs) with high surface areas, tunable building blocks and fully conjugated structures have found important applications in optoelectronic. Here we report a new series of CMPs with tunable band gaps by introducing thiazolo[5,4-d] thiazole as the linkage. Because they are synthetic polymers, the geometries and structures could be rationally designed. Their intrinsic wide visible light absorption

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properties and layered architectures endow them with promising photocatalysis performance. The role of the geometries, surface areas and morphologies of the CMPs on the photocatalysis abilities are examined and discussed. The results indicate that geometries have a direct impact on the surface areas and morphologies of the CMPs and thus exert great influence on the photocatalysis.

INTRODUCTION Layered nanomaterials with high surface areas are widely researched materials for optoelectronic applications.1-3 For example, graphene with layered structures are advanced materials with excellent mechanical, thermal electrical and high carrier mobility properties for optoelectronic applications.4,

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However, large band gaps greatly restrict their practical

applications in optoelectronic area. Therefore, modification of graphene to enlarge the band gaps is highly desired. Among various strategies, introducing heteroatoms into graphene by chemical doping is an effective method.6-8 However, these modifications are mostly randomly distributed and difficult to be precisely controlled. Thus, the clear structure-function relationship is hard to be elucidated. In addition, the structural diversities of graphene are limited. Therefore, the search and synthesis of other synthetic layered materials with tunable structures and band gaps are of great interest and importance.9 Conjugated microporous polymers (CMPs), emerged as one of unique type of advanced porous materials,10-12 have drawn significant attentions in recent decades for a wide variety of


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applications, for example, optoelectronics, mainly due to their high porosities, robust and tunable linking scaffolds.13-15 Recently, CMPs with layered graphene-like structures are developed.16 Comparing to conventional photocatalyst, the advantages of layered CMPs include high surface area and easy of synthesis. The high surface area combining with layer structures can accelerate charge diffusion to the surface and facilitate photo-redox reactions. In addition, layer structures also have great impact on their band gaps and performance,12 because it can influence the light absorption and photogenerated charge carriers. However, such layered structure is usually hard to be controlled in the process of synthesis. The intrinsic salient advantages, including high surface area and layered morphologies, have inspired the discovery of new uses for CMPs, such as photo-chemical applications.17-19 The fast charge diffusion and efficient photo-redox reactions on pores or surfaces give rises to forming high performance CMPs.20, 21 In this context, it is critically important to control their band gaps,2224

which influence the light absorption and photogenerated charge carriers.25-27 Heteroatom

doping has been demonstrated as an effective strategy to modulate electronic properties and enlarge the absorption range of visible light.28, 29 Since CMPs are synthetic polymers,30 various building blocks and linkages with versatile heteroatoms doping could be expected.31, 32 With these points in mind, we hypothesize that the generation of layered CMPs together with rich heteroatom doping may enable promising optoelectronic applications of CMPs. Here we report a new series of CMPs with nanosheet morphologies and tunable band gaps by introducing thiazolo[5,4-d] thiazole (TzTz) as the desired linkage,33 which endows the


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polymers with nitrogen and sulphur co-doped.34 The TZCPs were synthesized via incorporating TzTz unit and polyphenyl molecules with C2, C3, D2h symmetric group. The phenyl units with different symmetry were incorporated as reactive functional groups into the TzTz-linked polymeric backbone to vary the conjugated structure, thus tuning the band position and band gap energy of the polymers. The high surface areas, wide visible light absorption and thin layer structures of these CMPs were confirmed by the nitrogen sorption measurements, UV-visible spectroscopy and electronic microscopy studies. Such twodimensional open-channel structure of CMPs avoid the aggregation. Enhanced visible light absorption capability and photocatalytic activity in the dye’s oxidation degradation was achieved. Superior photocatalytic activities of three porous polymers were indicated by degrading Rhodamine B (RhB) and methylene orange (MO) dyes under visible light, where only 5 mg·mL-1 of optimized CMP can completely degrade 10 mg·L-1 RhB in 30 mins, which is comparable to the traditional g-C3N4 and the other polymeric photocatalysts.35 EXPERIMENTAL SECTION Materials and method Tris (4-formylphenyl)-benzene and tetra (4-formylphenyl)-benzene were synthesized according to literature procedures.36, 37 Dithiooxamide, 4,4'-Biphenyldicarboxaldehyde, a, a'dichloro-pxylene, triphenylphosphine, t-BuOK, Pd(PPh3)4, 1,2,4,5-Tetrabromoben1,3,5Tribromobenzene, 4-formyl -phenylboronic acid, potassium carbonate, hydrochloric acid and


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other common solvents were purchased from commercial suppliers (Sigma-Aldrich, Aladdin, TCI) without further purification. N, N-Dimethylformamide (DMF) was dried by CaH2 before using. Fourier-transformed infrared (FT-IR) spectra were obtained by using a Bruker Vertex 70 FTIR spectrometer and collected on dried KBr disks, over the range 500-4000 cm-1. Ultraviolet–visible spectra were measured on a UV-VIS-NIR spectrophotometer (UV-3600, Shimadzu Japan) under room temperature, using BaSO4 as base, over the wavenumber range 200-800 cm-1. Solid-state NMR experiments were carried out to check chemical structure of TZCPs by using a 400MHz Bruker Avance II with a standard 4 mm magic angle spinning double resonance probe head. Surface area and pore size distributions (77 K) were measured by using Micromeritics ASAP 2020 M surface area and porosity analyzer. Before analysis, the samples were degassed in a vacuum (10–5 bar) at 110 °C for 8 h. The surface areas were calculated based on nitrogen adsorption isotherms by Brunauer Emmett-Teller (BET) or Langmuir analysis. Pore size distributions were calculated by DFT methods via the adsorption branch. Elemental analysis (C, H, N, S) were analysed on a VarioMicrocube Elemental Analyser (Elementary, Germany). The thermal stabilities of TZCPs were evaluated by using Thermogravimetric analysis (TGA) with Perkin-Elmer Pyrisl TGA under N2 atmosphere with a heating rate of 10 °C min-1 and over the temperature range 25-800 °C. X-ray diffraction (XRD) were performed on Philips X’ Pert Pro. Transmission electron microscopy (TEM) images of the TZCPs were obtained by Tecnai G2 F30 (FEI Holland) transmission electron microscope. High resolution images of polymer morphologies were obtained using FEI Sirion 200 field emission scanning electron microscope (FE-SEM). Atomic force microscopy (AFM) images


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were obtained on a scanning probe microscopy. Electrochemical measurements were tested in three electrode system (CHl760E workstation) by depositing samples in ITO as the working electrode, Ag/AgCl electrode as the reference electrode, Pt flake as counter electrode. MottSchotty measurements were carried out in 0.1 M Na2SO4 solution. LUMO levels were calculated from results of Mott-Schotty measurements. Synthesis of TZCP-1, TZCP-2 and TZCP-3 Dithiooxamide (0.110 g, 0.90 mmol), and 4,4'-Biphenyldicarboxaldehyde (0.189 g, 0.90 mmol)/ tris(4-formylphenyl)-benzene (0.234 g, 0.60 mmol)/ tetra(4-formylphenyl)-benzene (0.222 g, 0.45 mmol) were refluxed in anhydrous DMF (10 mL) with stirring under N2 for 3 days. The reaction mixture was cooled to the room temperature and filtered, washed with H2O and MeOH several times, then, polymers were further washed with MeOH in a Soxhlet extraction over 48 h before being dried under vacuum, finally, the products were obtained. Synthesis of PTFB PTFB was polymerized by general procedure for Wittig reaction. Firstly, bisphosphonium salt was prepared from a, a'-dichloro-p-xylene (1.0 g, 5.70 mmol) and triphenylphosphine (3.31 g, 12.6 mmol) in boiling dimethylformamide (DMF, 20 mL). The white product was obtained by filtration and used directly without further purification. 1H NMR (300 MHz, CDCl3): δ=5.38 (d, 4H, 2 CH2-P), 6.94 (s, 4H), 7.66–7.75 (m, 30H) ppm; Then, tetra(4-formylphenyl)-benzene (96.3 mg, 0.20 mmol ), Bisphosphonium salt (0.3 g, 0.43 mmol) and t-BuOK (109.2 mg) were


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added in anhydrous DMF (10 mL) , the red solution was stirring and bubbled with N2 for 30 min and then refluxed for 2 days , when reaction temperature was increased, the red color of solution faded and turned to yellow and green. The reaction mixture was cooled to the room temperature and filtered, washed with H2O and MeOH several times, then, the green solid was further washed with MeOH in a Soxhlet extraction over 48 h and dried under vacuum over night to get the final polymer. Synthesis of PTZCP-3 Dithiooxamide (0.110 g, 0.90 mmol), and tetra(4-formylphenyl)-benzene (0.222 g, 0.45 mmol) were refluxed in anhydrous DMF (10 mL) without stirring under N2 for one day. The reaction mixture was cooled to the room temperature and filtered, washed with H2O and MeOH several times, then, polymers were further washed with MeOH in a Soxhlet extraction over 48 h before being dried under vacuum, finally, the products were obtained. Photocatalytic measurement The photocatalytic activity of polymers was characterized by degradation of RhB and MO (methyl orange) under irradiation of 300W Xenon lamp (equipped with 420 nm optical filter to filtrate off the ultraviolet light). For the degradation of RhB, 5 mg synthesized polymers were dispersed in 10 mg·L-1 100 mL RhB solution and stirring for one hour in darkness to get adsorption–desorption equilibrium, after that, the stirring solution was irradiated by visible


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light. The decomposed RhB solution was periodically withdrawn every 5 min. The absorption spectrum

Scheme 1. Synthesis routes of the TZCPs based conjugated porous polymers.

of RhB was obtained by UV–visible spectrophotometer (specific absorbing peak of RhB is 554 nm). The mechanism of degradation of RhB was measured by adding different scavengers with other condition unchanged. RESULTS AND DISCUSSION Herein, a series of conjugated TzTz-linked polymers were rationally designed for photocatalytic application, which were named as TZCP-1, TZCP-2, TZCP-3, respectively (Scheme 1). Owning to the introduction of heteroatom-S/N and conjugated structure,


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polymers were endowed with different colors, among which, TZCP-1 was a red powder, TZCP-2 was a green powder, and TZCP-3 was a deep green bulk. All of polymers are insoluble in common organic solvents and stable in water and the dramatically decomposition are occurring at approximately 600 °C in thermal gravimetric analysis (TGA) spectrum (Fig. S1b).

Figure 1. (a) Solid state 13C CPMAS NMR spectra of TZCP-1 (black line) ,TZCP-2 (red line) and TZCP-3 (blue line); (b) FT-IR spectrum of TZCP-1 (black line) ,TZCP-2 (red line) and TZCP-3 (blue line).

The successful synthesis of TZCPs was validated by solid state 13C CPMAS NMR combined with Fourier-transformed infrared (FT-IR). Because of the similar structures, there is no big difference among the signals of TZCPs in the 13C CPMAS NMR spectra (Fig.1a). The peaks at 169 ppm may be assigned to the N=C carbon from TzTz moiety that is bonded to the aromatic ring and the weak peaks at 150 ppm may be attributed to the aromatic carbon that is bonded to TzTz. moiety. The broad peaks respectively at 140 ppm and 126 ppm correspond to the aromatic carbon species. The presence of sp2 carbons (150 and 168 ppm) proved the existence of an in situ generated thiazolo thiazole ring within the networks. In FT-IR spectrum (Fig.1b),


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the signal at 1695 cm-1 indicates the presence of unreacted aldehyde groups, which are overlapped with the peaks at 1650 cm-1 which belong to the C=N double bond of thiazole rings. And the intense peaks at 830 cm-1 are associated with C-S-C bond of thiazole rings. The result of element analysis (Table.S3) indicates that real carbon, hydrogen, nitrogen and sulphur content of TZCPs are closed to theoretical results, which further proves the successful synthesis of TZCPs.

Figure 2. SEM images of (a) TZCP-1, (b) TZCP-2 and (c) TZCP-3 dispersed in alcohol; AFM images of (d) TZCP-1 , (e) TZCP-2 and (f) TZCP-3 dispersed in alcohol.

The morphologies of polymers were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From SEM images (Fig. 2a, b, c), both TZCP-2 and TZCP-3 show the stacking layered structure, which also can be observed by the edges of


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sheets in TEM images (Fig.S3). A sheet like morphology of TZCP-1 is found in SEM image. After dispersing in alcohol and a long time sonification, it looks more like graphene without broken in a large scar (Fig.S3). Such layered structures of TZCPs can be further verified by AFM images (Fig. 2d, e, f). We can clearly see the stacking layers of TZCPs like ladders, and the thickness of monolayer of TZCP-1, TZCP-2 and TZCP-3 are around 4.1 nm, 4.4 nm and 4.8 nm respectively (Fig.S4). The different size of sheets also can be found in SEM images where TZCP-3 shows the uniform smallest sheets which can help improve contacting area between the catalysts and organic dyes. In contrast, TZCP-1 bears the largest sheet morphology. This indicate the geometry of the aldehyde monomers have direct impact on the morphology of the polymers. The higher branched monomers tend to form smaller nanostructures. Due to the sheets-like morphology and stacking layered structure, TZCP-1 shows two broad peaks at 6.5° and 20° in XRD pattern (Fig.S1a), however, no obvious peak of TZCP-2 and TZCP-3 is found in XRD pattern, which indicates their amorphous nature. The

porosities

of

the

obtained

polymers

were

then

evaluated

by

nitrogen

adsorption/desorption measurements at 77 K. As shown in Figure S5 (a). TZCP-3 shows a far faster uptake of N2 compare to TZCP-1 and TZCP-2 Under the low pressure (P/P0 < 0.001), indicating larger content of microporous structure of TZCP-3. The additional steep rise of TZCP-1 under high pressure (P/P0 ≈ 1) may be attributed to condensed macropore formed by aggregation of nanosheets. Adsorption and desorption isotherms of TZCP-1 and TZCP-3 show a hysteresis loop, which indicates the existence of mesopore. The surface areas were evaluated


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based on Brunauer–Emmett–Teller (BET) and calculated to be 110 m2·g-1 for TZCP-1, 385 m2·g1

for TZCP-2 and 673 m2·g-1 for TZCP-3. Much higher BET value of TZCP-3 can be attributed

to its rigid structure with more benzene ring, which resulted in strong steric hindrance and formation of pores. Interestingly, the porous structure of liner polymer (TZCP-1) with a BET surface of 110 m2·g-1 may be caused by a molecular chain twist combined with a stacking effect, thus leading to a certain pore formation in the solid. The pore size distribution (PSD) of the polymers were calculated by using the nonlocal density functional theory (NLDFT) method. As showed in Figure S5 (b). All TZCPs exhibit different kinds of pore structures with different pore sizes, especially for the TZCP-3 which contains the large amount of macropore. These results also show the geometry can determine the porous structure of the resulting polymers. Such porous structure and monolayer or multilayer adsorption of nanosheets can efficiently increase contact area with dyes in solution.


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Figure 3. (a) RhB adsorption process of TZCPs before light irradation. (b) MO adsorption process of TZCPs before light irradation. (c) Photocatalytic degradation of RhB of TZCPs and g-C3N4. C is the concentration of RhB after light irradiation for a certain period and C0 is the concentration of RhB after reaching adsorption/desorption equilibrium in the darkness; (d) Photocatalytic degradation of MO of TZCPs. C is the concentration of MO after light irradiation for a certain period and C0 is the concentration of MO after reaching adsorption/desorption equilibrium in the dark.(e) Colour change of RhB during the process of degradation.

We also studied the optical properties of these TZCPs samples and found that all samples’ absorption of light can be extended to 800 nm, which include the whole region of visible light (Fig. S2). The band gaps of TZCP-1, TZCP-2, TZCP-3 are 1.88 eV, 1.89 eV and 2.31 eV,


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respectively, based on their UV-visible absorption spectra. The different color of TZCPs associated with different optical properties and band gaps of three samples indicate that band gap can be tunable by changing different building blocks. Among the colored wastes, MO and RhB are water soluble organic dyes and fairly stable under irradiation of visible light without photocatalyst.38 In our work, we evaluated the photocatalytic activity of TZCPs for degrading RhB and MO and compared them to the traditional g-C3N4. Before the degradation of RhB and MO, all TZCPs had been milled to powders to ensure that the catalysts can be well dispersed in water solution. Firstly, RhB and MO aqueous solutions were exposed to visible light irradiation without catalysts, however, no obvious decomposition of RhB or MO was found, which excluded the influence of their selfphotodegradation. Then, only 0.05 mg·mL-1 TZCPs were employed to degrade 10 mg·L-1 RhB, which was fairly low concentration for catalysis. After darkness treatment and adsorption– desorption equilibrium, TZCP-3 has adsorbed highest amount of RhB, up to ca. 57%, because of its highest BET surface area. In addition, TZCP-1 and TZCP-2 can adsorb RhB as high as 9% and 13%, respectively, whereas nearly no RhB can be adsorbed in g-C3N4 (Fig. S6). Such high adsorption capacity can largely increase the reaction interface between TZCPs and RhB. In the process of visible light irradiation of TZCPs, degradation results were summarized in Fig. 3(a). Degradation processes of TZCPs and g-C3N4 all belong to the first-order reaction (Fig. S7). The TZCP-3 shows the highest first order kinetic constant , up to 0.116 min-1 that it can completely degrade the RhB in 30 min, while TZCP-2 costs 60 min and, TZCP-1 and g-C3N4


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cost 140 min. Then we chose same concentration of TZCP-2 and TZCP-3 as photocatalyst to degrade 3×10-5 mol·L-1 MO aqueous solution under the irradiation of visible light which was tougher to be decomposed than RhB under the same condition. The results were shown in Fig. 3 (b) and Fig. S9. After getting adsorption–desorption equilibrium, TZCP-3 adsorbs the highest amount of MO (ca. 57%) and exhibits the better performance than that TZCP-2 as well. It takes 60 mins for TZCP-3 to degrade 80% MO, while TZCP-2 only degrades 70% MO. Although TZCP-1 shows similar activity with g-C3N4 toward RhB degradation, TZCP-1 can degrade 12% MO while g-C3N4 almost shows no photo-degradation activity of MO in the same time. These results not only further prove the superior photocatalytic performance of TZCP3 but also prove that all the TZCPs show higher photocatalytic activity than g-C3N4. The photocatalytic efficiency of TZCP-2 and TZCP-3 are also comparable to some reported CMP materials and inorganic semiconductors under the same condition (Table.S2) even with much lower concentration of catalysts (0.05 mg·mL-1). Such a superior photocatalytic performance may be attributed to the obtained high porosity that help catalysts adsorb higher content of dyes in darkness and increase the reaction interface between the samples and dyes. To get a further understanding of the obtained superiority photocatalytic activity of TZCP3, electrochemical impedance spectroscopy and photocurrent measurement (Fig. S14) were performed. The photocurrent of TZCP-3 is higher than TZCP-2 and both of them show higher photocurrent than the g-C3N4, which is in good agreement with the photocatalytic activities. The EIS suggests the resistance of TZCP-3 is smaller than TZCP-2 and TZCP-1, indicating that


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the better charge transport in TZCP-3, which is beneficial to enhance photo-catalytic performance. Therefore, the superior photocatalytic performance is not only ascribed to high porosity, but also to the better charge transport ability. Photocatalytic reaction is initiated when a photoelectron is promoted from the filled valence band of semiconductors to empty conducting band due to the fact that the absorbed photon has an equal or greater energy than the band gap of semiconductors.39 Thus, the excitation process generates a hole in the valence band and an electron in conducting band. Then the photo-generated

Figure 4. (a) The effect of different scavengers, isopropanol (IP), ammonium oxalate (AO), potassium dichromate (K2Cr2O7), benzoquinone (BQ), and the absence of oxygen (under nitrogen) on the degradation of RhB over TZCP-3 under 30 min of visible light irradiation; (b) band structure diagram for the TZCPs and g-C3N4.

holes can react with water to produce hydroxyl radical and electron can be taken up by oxygen to generate the anionic superoxide radical.40, 41 Both of them can play an important role in the


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further oxidation process. In order to investigate the function of holes (h+), electrons (e−), singlet oxygen, superoxide (O2•−) and hydroxyl radicals (·OH) during the process of degradation of RhB, a series of controlled experiments were attempted by adding different scavengers and TZCP-3 as photo-catalyst. Isopropanol (IP, an ·OH radical scavenger), ammonium oxalate (AO, the h+ scavenger), the potassium dichromate (K2Cr2O7) scavenger for electrons and benzoquinone (BQ, the O2•− scavenger) were separately added to the photocatalysis system and nitrogen was also bubbled to remove the oxygen. The results were summarized in Fig. 4a. The addition of AO only caused slightly decrease of degradation efficiency of TZCP-3 and Isopropanol didn’t seem to influence degradation efficiency of TZCP-3. On the contrary, an obvious decrease of catalytic efficiency was observed with the existence of K2Cr2O7 and only a small quantity of RhB was degraded after the addition of BQ. In addition, only a small amount of RhB was degraded when the photocatalysis was carried out under the nitrogen atmosphere. This phenomenon suggests that O2•− and oxygen are primary responsible for the photocatalysis and electrons on the conduction band also play an important role in the process of photocatalysis, because the oxygen acts as an efficient electron trap, leading to the generation of O2•− and preventing the recombination of electrons and holes. To estimate the relative positions of the conduction band (CB) and valence band (VB), electrochemical Mott-Schottky plots (Fig. S13) were recorded for TZCPs photoelectrode in a three-electrode cell. The negative slope shows that all TZCPs belong to typical n-type semiconductor. The relative band gap positions are shown in Fig 4b. It should be noted that


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all LUMO energies of TZCPs are lower than the oxygen reduction potential, which make them suitable for reducing the oxygen to superoxide in solution theoretically and then degrading the organic dyes. It has been demonstrated that O2•− and oxygen are primary responsible for the photocatalysis. Compared to TZCP-1 and TZCP-2, TZCP-3 shows the highest VB position, which endows it strongest reduction ability for oxygen trapping, thereby displaying the best degradation performance. Although TZCP-2 nearly has the same band gap position with TZCP-1, the higher photocatalytic activity of TZCP-2 is attributed to the higher surface area and faster charge transport ability (Fig. S14). As for g-C3N4, the largest band gap leads to the weakest absorption of visible light and photocatalytic performance. In order to investigate the stability of TZCP-3 for the photo-degradation of RhB, five recycle experiments have been carried out with each cycle TZCP-3 recycled by filtration. (Fig S11). After five recycling experiments, the degradation efficiency didn’t decrease and each cycle almost costed the same time around 40 min to completely degrade the RhB, suggesting good stability and recyclability of TZCP-3 under the long time visible light irradiation. The procession of degradation was shown by the UV/vis absorption of RhB (Fig. S12). In order to prove the stability of organic


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Figure 5. (a) Photocatalytic degradation of RhB TZCP-3 and PTPB; C is the concentration of RhB after light irradiation for a certain period and C0 is the concentration of RhB after reaching adsorption/desorption equilibrium in the dark;( b) UV-Vis absorption spectrum of PTPB and TZCP-3.

linker (thiazolo thiazole) during the process of degradation. The FT-IR spectrum (Fig. S15) of recycled TZCP-3 after 5 times reuse has been tested. Comparing to the origin TZCP-3, the peak type of recycled TZCP-3 does not change, which means the structure of TZCP-3 keeps stable after 5 times reuse. Apart from that, the layered morphology also keeps unchanged according to AFM images (Fig. S16) of recycled TZCP-3. Therefore, the degradation process did not affect the morphology of TZCP-3, which further proved the stability of TZCP-3. In order to explore the influence of TzTz linkage with heteroatom (N/S) co-doped on the sample for photo-degradation of RhB, we further synthesized a controlled sample, PTPB, without any heteroatom adoption by copolymerizing tetra(4-formylphenyl)- benzene and bisphosphonium salt based on the Wittig reaction. It should be noted that this is also a new strategy to prepare a CMP with a BET value of 52 m2·g-1 by using Wittig reaction. The structure of PTPB was characterized by FT-IR spectrum (Fig. S17a) that the disappearing of aldehyde


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group and the forming of carbon double bond proved the successful synthesis of PTPB which also can be further proved by Solid state

13C

CPMAS NMR spectra of PTPB (Fig. S17b).

Thermal gravimetric analysis (TGA) spectrum also shows the good thermal stability of PTPB up to 400 °C. Then we studied the photo-catalytic degradation performance on PTPB under the same condition and the result was shown in Fig. 5(a). After the irradiation of visible light for 40 min, nearly no RhB was degraded by using PTPB, however, a complete degradation on TZCP-3 was achieved within 30 mins. Clearly, without heteroatom adoption, PTPB almost shows no photo-degradation activity of RhB. Compared to PTPB, great improvement of catalytic activity of TZCP-3 may arise from the enhancement of visible light absorption from UV-visible light absorption spectrum of PTPB and TZCP-3 (Fig. 5b). With heteroatom (N/S) co-doped, the absorption edge red shifts obviously and visible light absorption enhances deeply. Theoretical calculations are made to estimate the electronic structure (Fig. S20). we carried out the calculation for the orbital energies of building blocks and the charge distribution in different electronic state based on oligomer structures of TZCP-3 and PTPB. According to the theoretical calculation, after hetero-adoption of PTPB, the electrons of excited TZCP-3 are easier to be trapped by oxygen and the holes of TZCP-3 have stronger ability to oxide the OH- to OH·, which is consistent with the experimental results. Finally, we can get the conclusion that the TzTz linkage with heteroatom (N/S) co-doped can effectively improve the visible light absorption and catalytic performance.


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Apart from designing the controlled sample without any heteroatom adoption, the control sample with suppressed layered structure was also investigated. By cancelling the stirring and shorten the reaction time during the synthesis process, the PTZCP-3 showed particle morphology rather than layered structure, which can be seen from AFM image and SEM image (Fig. S21). Meanwhile, FT-IR spectrum (Fig. S21a) shows that the structure still maintained the same. Then, we investigated the Photocatalytic performance of PTZCP-3 by degrading RhB. Comparing to the layered TZCP-3, the PTZCP-3 suggests the far lower photocatalytic performance (Fig. S23), which may be attributed to the lower surface area of PTZCP-3, 127 m2·g-1 and narrowed visible light absorption (Fig. S21b). Therefore, such layered structure of TZCP-3 is beneficial to the photocatalytic performance. Considering the better degradation performance of PTZCP-3 than PTPB, we may conclude that heteroatom adoption should be more important in degradation performance of TZCP-3 than layered structure. CONCLUSION In summary, we successfully synthesized a series of porous organic conjugated polymeric nanosheets with nitrogen and sulfur co-doping by three different building blocks with C2, C3,

D2h symmetry groups. The different symmetric structure caused the different surface area of TZCPs. Among them, TZCP-3 shows the highest BET value of 673 m2·g-1, which help TZCP-3 adsorb the highest content of RhB/MO and show the best photo-degradation performance, because the adsorbed dyes can efficiently improve the interaction area between catalysts and dyes. In addition, All the TZCPs shows obviously layered structure and TZCP-3 indicates the


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smallest size of layers in AFM images which also can accelerate the mixture of dyes and catalysts and then increase the contact area. Such layered structure was proved to be beneficial to the photocatalytic activity of TZCP-3. Then we further demonstrated a new strategy to construct a controlled catalyst PTPB without any heteroatom doping based on Wittig reaction, which could provide a new avenue to construct other large π system porous polymers. We got the conclusion that heteroatom doping can effectively enhance the absorption of visible light and further improve the photo-catalytic performance of CMPs. ASSOCIATED CONTENT Supporting Information XRD, TGA curves, UV-visible light absorption, TEM images, Nitrogen adsorption and desorption isotherms, pore size distribution of TZCPs; Adsorption content of RhB/MO of TZCPs after adsorption–desorption equilibrium and Recycling experiments of TZCPs; MottSchottky plots, Photocurrent response and EIS Nyquist plots of TZCPs; FT-IR spectrum, Solid state 13C CPMAS NMR spectra, SEM image, TGA curve, Nitrogen adsorption and desorption isotherms and pore size distribution of PTPB. AUTHOR INFORMATION Corresponding Author Email: [email protected]


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Email: [email protected]. ACKNOWLEDGMENT We appreciate the assistance of Analysis and Testing Center, Huazhong University of Science and Technology for the characterization of materials. This work was financially supported by funding from National Natural Science Foundation of China (Grant No 21875078, 21604028), the International S&T Cooperation Program of China (Grant No. 2016YFE0124400), the China Postdoctoral Science Foundation funded project (No. 2017M622423) and the Program for HUST Interdisciplinary Innovation Team (Grant No. 2016JCTD104). REFERENCES (1) Wen, J.; Luo, D.; Cheng, L.; Zhao, K.; Ma, H. Electronic Structure Properties of TwoDimensional π-conjugated Polymers. Macromolecules. 2016, 49, 1305-1312. (2) Kobayashi, N.; Kijima, M. Microporous Materials Derived from Two- and ThreeDimensional Hyperbranched Conjugated Polymers by Thermal Elimination of Substituents. J.

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thiazole-Linked Conjugated Microporous Polymers with Heteroatom

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