View PDF VersionPrevious ArticleNext Article
 
DOI: 10.1039/D0QM01076F (Research Article) Mater. Chem. Front., 2021, 5, 2255-2260

A 2D porphyrin-based covalent organic framework with TEMPO for cooperative photocatalysis in selective aerobic oxidation of sulfides†

Keyu Feng‡ , Huimin Hao‡ , Fengwei Huang , Xianjun Lang * and Cheng Wang *
Sauvage Center for Molecular Sciences and Key Laboratory of Biomedical Polymers (Ministry of Education), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China. E-mail: xianjunlang@whu.edu.cn; chengwang@whu.edu.cn

Received 21st December 2020 , Accepted 16th January 2021

First published on 18th January 2021

Abstract

Two-dimensional covalent organic frameworks (2D COFs) have received increasing attention in photocatalysis recently. Merging their photocatalytic process with an additional redox mediator could improve the corresponding chemical conversion efficiency, leading to an interesting cooperative behaviour. Herein, we report the photocatalytic performance of a 2D imine-linked porphyrin-based COF (Por-COF) with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) in a selective organic transformation. After being irradiated with white light-emitting diodes, Por-COF showed moderate activity in selective aerobic oxidation of sulfides. Interestingly, by using TEMPO as an electron transfer mediator, the photocatalytic efficiency could be significantly improved, due to a paradigm of cooperative photocatalysis between Por-COF and TEMPO. This work foreshadows that 2D COFs can provide a unique platform to construct cooperative photocatalysts with a redox mediator.

Introduction

Covalent organic frameworks (COFs) represent an emerging class of crystalline materials with extended periodic structures and inherent porosity.1–5 Since the seminal work reported by Yaghi and co-workers in 2005,6 COFs have aroused extensive interest and found promising applications in gas adsorption and separation,7,8 sensing,9–11 catalysis,12–15 optoelectronics,16,17 energy storage18,19 and so on.20–26 Two-dimensional (2D) COFs, in which the molecular building blocks are covalently connected to form a layered structure with aligned π-columns, can particularly possess pre-organized pathways for facilitating the charge carrier transport.27,28 Accordingly, the photoexcited electron–hole recombination of 2D COFs can be inhibited to some extent, which will allow them to be used as heterogeneous photocatalysts.28 In 2014, Lotsch and co-workers reported the first example of utilizing 2D COFs for photocatalytic hydrogen evolution under visible-light irradiation.29 Since then, their application in photocatalysis has received increasing attention, and 2D COFs have been realized as efficient catalysts in photocatalytic hydrogen evolution,30–33 CO2 reduction,34–36 selective organic transformations37,38 and dye degradation.39,40

Among these tested reactions, photocatalytic selective organic transformations are very attractive as they can offer a simple but environment friendly and sustainable way to synthesize important chemicals.41–43 The integration of a redox mediator (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) within the photocatalytic process, which can create a novel strategy for cooperative photocatalysis,44 has shown the ability to improve the efficiency of selective organic transformations.45–47 In principle, considering the unique properties of 2D COFs, their photocatalysis merged with TEMPO may also lead to interesting cooperative behaviour. Recently, for the first time, we presented enhanced performance in photocatalytic selective aerobic oxidation of amines to imines by combining an sp2 carbon-conjugated 2D COF with TEMPO, indicating cooperative photocatalysis.48 To further verify the universality of this concept, we report herein the integration of semiconductor photocatalysis of a 2D imine-linked porphyrin-based COF (Por-COF) with TEMPO. After irradiation with white light-emitting diodes (WLEDs), Por-COF showed moderate activity in selective aerobic oxidation of sulfides. Interestingly, the photocatalytic efficiency was improved by 50% or more when 2 mol% TEMPO was introduced, due to a paradigm of cooperative photocatalysis between Por-COF and TEMPO.

Results and discussion

Considering the unique photophysical and photochemical properties of porphyrin units, we chose to construct Por-COF (Fig. 1a) according to our reported literature49 by condensation of 5,10,15,20-tetrakis(4-benzaldehyde)porphyrin (p-Por-CHO) and p-phenylenediamine. We then recorded the powder X-ray diffraction (PXRD) pattern of Por-COF, which exhibited two main peaks at 3.6 and 7.2 (Fig. 1b). Obviously, this is consistent with the reported data, indicating the AA stacking model of Por-COF. Besides, the porosity of Por-COF was investigated using the nitrogen adsorption isotherm at 77 K (Fig. 1c) and the Brunauer–Emmett–Teller (BET) surface area was calculated to be 1228 m2 g−1, a little bit higher than the reported value.49 Moreover, from the solid-state UV/vis spectrum, Por-COF shows broad absorption in the visible region that overlaps with the spectrum of WLEDs (Fig. S5, ESI†), and the calculated optical band gap is 1.76 eV.
image file: d0qm01076f-f1.tif
Fig. 1 (a) Synthesis of Por-COF. (b) PXRD pattern of Por-COF. (c) N2 adsorption and desorption isotherms of Por-COF.

In light of the porous structure and semiconducting behaviour of Por-COF, we then tested its photocatalytic activity in aerobic oxidation of sulfides to sulfoxides, which holds great practical value to synthesize important pharmaceutical intermediates sulfoxides with the concept of atomic economy.50 As shown in Fig. 2 and Table S1 (ESI†), after irradiation with WLEDs, Por-COF can catalyse the oxidation of sulfides with different substituents, but its photocatalytic activity was only moderate. Therefore, based on the concept of cooperative photocatalysis,44 we decided to utilize TEMPO as an electron transfer mediator to improve the photocatalytic efficiency. Remarkably, with the addition of TEMPO, the photocatalytic transformation yields of sulfoxides were 1.5 times or more than before. In addition, from the PXRD experiments, the crystallinity of Por-COF was maintained after photocatalysis for three runs (Fig. S6, ESI†). Moreover, the photocatalytic behaviour is closely related to the light intensity (Table S3, ESI†), indicating that this is a photocatalytic reaction.


image file: d0qm01076f-f2.tif
Fig. 2 The influence of TEMPO on the selective aerobic oxidation of sulfides by Por-COF photocatalysis. Reaction conditions: sulfide (0.3 mmol), Por-COF (0.005 mmol), O2 (0.1 MPa), WLEDs (3 W × 4), CF3CH2OH (1 mL), 0.5 h. The yield of sulfoxides was determined by GC-FID using bromobenzene as the internal standard.

To study the photocatalytic mechanism, quenching experiments were executed to determine the reactive oxygen species (ROS) of the TEMPO-mediated selective aerobic oxidation of sulfides. When using N2 instead of O2, the oxidation process cannot occur, suggesting that O2 is the only oxidant in the photocatalytic reaction (Table 1, entries 1 and 2). In addition, the conversion decreases sharply when superoxide anion O2˙− or electrons are trapped (Table 1, entries 3 and 4), and there is no obvious change when singlet oxygen (1O2) is quenched by DABCO (Table 1, entry 5). Therefore, the ROS in this photocatalytic process are mainly O2˙− rather than 1O2.

Table 1 Quenching experiments of TEMPO-mediated selective oxidation of thioanisole to methyl phenyl sulfoxide by Por-COF photocatalysisa

image file: d0qm01076f-u1.tif
Entry Quencher (equiv.) Role Conv.b [%] Sel.b [%]
a Reaction conditions: thioanisole (0.3 mmol), Por-COF (0.005 mmol), TEMPO (0.006 mmol), O2 (0.1 MPa), WLEDs (3 W × 4), CF3CH2OH (1 mL), 0.5 h. b Determined by GC-FID using bromobenzene as the internal standard, conversion of methyl phenyl sulfide, selectivity of methyl phenyl sulfoxide. c p-BQ, p-benzoquinone. d DABCO, 1,4-diazabicyclo[2.2.2]octane.
1 — Standard conditions 83 99
2 N2 (—) O2 replacement 0 —
3c p-BQ (0.2) O2˙− scavenger 6 99
4 AgNO3 (1) Electron scavenger 0 —
5d DABCO (0.1) 1O2 scavenger 77 99

Moreover, electron paramagnetic resonance (EPR) has illustrated the formation of O2˙− by using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the trapper (Fig. 3a). According to these data, we speculated that, under visible light irradiation, electrons were excited and enriched to the lowest occupied molecular orbital (LUMO) energy level of Por-COF, which can be further captured by O2 to form O2˙−. The EPR signals of TEMPO weakened with the extension of the irradiation time (Fig. 3b), revealing that TEMPO participated in the photocatalytic cycle and transformed into an EPR inactive substance.


image file: d0qm01076f-f3.tif
Fig. 3 (a) EPR detection of O2˙− trapped by DMPO; and (b) EPR detection of the TEMPO transformation process in the selective aerobic oxidation of sulfides by Por-COF photocatalysis.

Logically, the mechanism for the photocatalytic selective oxidation of sulfides has been proposed (Fig. 4). Driven by irradiation with WLEDs, electrons of Por-COF migrate from the highest occupied molecular orbital (HOMO) to the LUMO, generating separated electron–hole (e−–h+) pairs. Next, O2 catches the electrons to form O2˙− for the following oxidative evolution, and TEMPO is oxidized into 2,2,6,6-tetramethylpiperidine-1-oxoammonium (TEMPO+) by holes. After that, TEMPO+ seizes an electron of sulfide back to TEMPO, leaving a charged sulfur radical cation which combines with O2˙− to afford persulfoxide intermediates. Finally, with the assistance of protons from the solvent, the product of sulfoxide is obtained.


image file: d0qm01076f-f4.tif
Fig. 4 The proposed mechanism of the TEMPO-mediated selective aerobic oxidation of sulfides by Por-COF photocatalysis.

In order to explore the applicability of this protocol, we chose sulfides with different substituents as substrates for photocatalytic selective aerobic oxidation (Table 2). When the benzene ring is functionalized by an electron-donating group or electron-withdrawing group, the photocatalytic selective oxidation can proceed smoothly with no major difference (Table 2, entries 1–12), indicating that electronic effects do not play an important role in the oxidative reaction. Besides, further studies demonstrate that the position of the substituents affects the conversion of organic sulfides. For methoxythioanisole and chlorothioanisole, the reaction rates stand in the order of para-position > meta-position > ortho-position, which is attributed to steric hindrance of the substituents (Table 2, entries 2–4 and entries 8–10). Sulfides with more hindered substituents, such as naphthalene ring and ethyl substituted sulfides, can achieve excellent conversion within one hour under irradiation with WLEDs (Table 2, entries 13 and 14). Furthermore, highly selective aerobic oxidation of aliphatic sulfides into the corresponding sulfoxides is also realized in a shorter time span (Table 2, entries 15 and 16).

Table 2 TEMPO-mediated selective oxidation of sulfides to sulfoxides by Por-COF photocatalysisa

image file: d0qm01076f-u2.tif
Entry Substrate Product T (h) Conv.b [%] Sel.b [%]
a Reaction conditions: sulfide (0.3 mmol), Por-COF (0.005 mmol), TEMPO (0.006 mmol), O2 (0.1 MPa), WLEDs (3 W × 4), CF3CH2OH (1 mL). b Determined by GC-FID using bromobenzene as the internal standard, conversion of sulfides, selectivity of sulfoxides.
1 image file: d0qm01076f-u3.tif image file: d0qm01076f-u4.tif 0.6 90 99
2 image file: d0qm01076f-u5.tif image file: d0qm01076f-u6.tif 0.6 94 99
3 image file: d0qm01076f-u7.tif image file: d0qm01076f-u8.tif 0.8 93 99
4 image file: d0qm01076f-u9.tif image file: d0qm01076f-u10.tif 0.8 90 99
5 image file: d0qm01076f-u11.tif image file: d0qm01076f-u12.tif 0.5 91 99
6 image file: d0qm01076f-u13.tif image file: d0qm01076f-u14.tif 0.5 95 99
7 image file: d0qm01076f-u15.tif image file: d0qm01076f-u16.tif 0.7 94 99
8 image file: d0qm01076f-u17.tif image file: d0qm01076f-u18.tif 0.6 92 99
9 image file: d0qm01076f-u19.tif image file: d0qm01076f-u20.tif 0.8 91 99
10 image file: d0qm01076f-u21.tif image file: d0qm01076f-u22.tif 1.0 93 99
11 image file: d0qm01076f-u23.tif image file: d0qm01076f-u24.tif 0.6 92 98
12 image file: d0qm01076f-u25.tif image file: d0qm01076f-u26.tif 0.5 90 98
13 image file: d0qm01076f-u27.tif image file: d0qm01076f-u28.tif 0.9 98 98
14 image file: d0qm01076f-u29.tif image file: d0qm01076f-u30.tif 0.8 90 99
15 image file: d0qm01076f-u31.tif image file: d0qm01076f-u32.tif 0.7 94 99
16 image file: d0qm01076f-u33.tif image file: d0qm01076f-u34.tif 0.7 93 99

Conclusions

In summary, we reported the photocatalytic performance of Por-COF with TEMPO in selective aerobic oxidation of organic sulfides. Compared to Por-COF, this joint system shows enhanced photocatalytic activity, indicating cooperative behaviour. In addition, this study represents an example of the underexplored cooperation between a semiconductor photocatalyst and a redox mediator. Together with our reported results, we strongly believe that the photocatalysis of 2D COFs merged with TEMPO offers an interesting demonstration of cooperative photocatalysis. This work also foreshadows the importance of 2D COFs in semiconductor photocatalysis to address the environmental and energy challenges in cooperation with other redox mediators.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

C. W. gratefully acknowledges financial support from the National Natural Science Foundation of China (21975188 and 21772149), and the Fundamental Research Funds for the Central Universities (2042020kf0213). X. J. L. acknowledges the financial support from the National Natural Science Foundation of China (22072108 and 21773173) and the start-up fund of Wuhan University.

References

  1. C. S. Diercks and O. M. Yaghi, The atom, the molecule, and the covalent organic framework, Science, 2017, 355, eaal1585 CrossRef .
  2. S. Y. Ding and W. Wang, Covalent organic frameworks (COFs): from design to applications, Chem. Soc. Rev., 2013, 42, 548–568 RSC .
  3. Y. Jin, Y. Hu and W. Zhang, Tessellated multiporous two-dimensional covalent organic frameworks, Nat. Rev. Chem., 2017, 1, 0056 CrossRef .
  4. B. Gui, G. Q. Lin, H. M. Ding, C. Gao, A. MaI and C. Wang, Three-Dimensional Covalent Organic Frameworks: From Topology Design to Applications, Acc. Chem. Res., 2020, 53, 2225–2234 CrossRef CAS .
  5. H. M. Ding, A. Mal and C. Wang, Tailored covalent organic frameworks by post-synthetic modification, Mater. Chem. Front., 2020, 4, 113–127 RSC .
  6. A. P. Cote, A. I. Benin, N. W. Ockwig, M. O'Keeffe, A. J. Matzger and O. M. Yaghi, Porous, Crystalline, Covalent Organic Frameworks, Science, 2005, 310, 1166–1170 CrossRef CAS .
  7. L. Jiang, Y. Tian, T. Sun, Y. Zhu, H. Ren, X. Zou, Y. Ma, K. R. Meihaus, J. R. Long and G. Zhu, A Crystalline Polyimide Porous Organic Framework for Selective Adsorption of Acetylene over Ethylene, J. Am. Chem. Soc., 2018, 140, 15724–15730 CrossRef CAS .
  8. Z. Kang, Y. Peng, Y. Qian, D. Yuan, M. A. Addicoat, T. Heine, Z. Hu, L. Tee, Z. Guo and D. Zhao, Mixed Matrix Membranes (MMMs) Comprising Exfoliated 2D Covalent Organic Frameworks (COFs) for Efficient CO2 Separation, Chem. Mater., 2016, 28, 1277–1285 CrossRef CAS .
  9. G. Das, B. P. Biswal, S. Kandambeth, V. Venkatesh, G. Kaur, M. Addicoat, T. Heine, S. Verma and R. Banerjee, Chemical sensing in two dimensional porous covalent organic nanosheets, Chem. Sci., 2015, 6, 3931–3939 RSC .
  10. F. Z. Cui, J. J. Xie, S. Y. Jiang, S. X. Gan, D. L. Ma, R. R. Liang, G. F. Jiang and X. Zhao, A gaseous hydrogen chloride chemosensor based on a 2D covalent organic framework, Chem. Commun., 2019, 55, 4550–4553 RSC .
  11. Q. Gao, X. Li, G. H. Ning, K. Leng, B. Tian, C. Liu, W. Tang, H. S. Xu and K. P. Loh, Highly photoluminescent two-dimensional imine-based covalent organic frameworks for chemical sensing, Chem. Commun., 2018, 54, 2349–2352 RSC .
  12. X. Han, Q. Xia, J. Huang, Y. Liu, C. Tan and Y. Cui, Multivariate Chiral Covalent Organic Frameworks with Controlled Crystallinity and Stability for Asymmetric Catalysis, J. Am. Chem. Soc., 2017, 139, 8693–8697 CrossRef CAS .
  13. Y. Wang, H. Liu, Q. Pan, C. Wu, W. Hao, J. Xu, R. Chen, J. Liu, Z. Li and Y. Zhao, Construction of Fully Conjugated Covalent Organic Frameworks via Facile Linkage Conversion for Efficient Photoenzymatic Catalysis, J. Am. Chem. Soc., 2020, 142, 5958–5963 CrossRef CAS .
  14. H. Xu, J. Gao and D. Jiang, Stable, crystalline, porous, covalent organic frameworks as a platform for chiral organocatalysts, Nat. Chem., 2015, 7, 905–912 CrossRef CAS .
  15. C. He, Q. Wu, M. Mao, Y. Zou, B. Liu, Y. Huang and R. Cao, Multifunctional Gold Nanoparticles@Imidazolium-Based Cationic Covalent Triazine Frameworks for Efficient Tandem Reactions, CCS Chem., 2020, 2, 2368–2380 CrossRef .
  16. H. Ding, J. Li, G. Xie, G. Lin, R. Chen, Z. Peng, C. Yang, B. Wang, J. Sun and C. Wang, An AIEgen-based 3D covalent organic framework for white light-emitting diodes, Nat. Commun., 2018, 9, 5234 CrossRef CAS .
  17. A. C. Jakowetz, T. F. Hinrichsen, L. Ascherl, T. Sick, M. Calik, F. Auras, D. D. Medina, R. H. Friend, A. Rao and T. Bein, Excited-State Dynamics in Fully Conjugated 2D Covalent Organic Frameworks, J. Am. Chem. Soc., 2019, 141, 11565–11571 CrossRef CAS .
  18. M. Yu, N. Chandrasekhar, R. K. M. Raghupathy, K. H. Ly, H. Zhang, E. Dmitrieva, C. Liang, X. Lu, T. D. Kuhne, H. Mirhosseini, I. M. Weidinger and X. Feng, A High-Rate Two-Dimensional Polyarylimide Covalent Organic Framework Anode for Aqueous Zn-Ion Energy Storage Devices, J. Am. Chem. Soc., 2020, 142, 19570–19578 CrossRef CAS .
  19. M. Li, J. J. Liu, Y. S. Li, G. L. Xing, X. Yu, C. X. Peng and L. Chen, Skeleton Engineering of Isostructural 2D Covalent Organic Frameworks: Orthoquinone Redox-Active Sites Enhanced Energy Storage, CCS Chem., 2020, 2, 696–706 CrossRef .
  20. C. Qian, W. Zhou, J. Qiao, D. Wang, X. Li, W. L. Teo, X. Shi, H. Wu, J. Di, H. Wang, G. Liu, L. Gu, J. Liu, L. Feng, Y. Liu, S. Y. Quek, K. P. Loh and Y. Zhao, Linkage Engineering by Harnessing Supramolecular Interactions to Fabricate 2D Hydrazone-Linked Covalent Organic Framework Platforms toward Advanced Catalysis, J. Am. Chem. Soc., 2020, 142, 18138–18149 CrossRef CAS .
  21. X. Li, H. Wang, H. Chen, Q. Zheng, Q. Zhang, H. Mao, Y. Liu, S. Cai, B. Sun, C. Dun, M. P. Gordon, H. Zheng, J. A. Reimer, J. J. Urban, J. Ciston, T. Tan, E. M. Chan, J. Zhang and Y. Liu, Dynamic Covalent Synthesis of Crystalline Porous Graphitic Frameworks, Chem., 2020, 6, 933–944 CAS .
  22. S. Yan, X. Guan, H. Li, D. Li, M. Xue, Y. Yan, V. Valtchev, S. Qiu and Q. Fang, Three-dimensional Salphen-based Covalent-Organic Frameworks as Catalytic Antioxidants, J. Am. Chem. Soc., 2019, 141, 2920–2924 CrossRef CAS .
  23. Y. Chen, Z. L. Shi, L. Wei, B. Zhou, J. Tan, H. L. Zhou and Y. B. Zhang, Guest-Dependent Dynamics in a 3D Covalent Organic Framework, J. Am. Chem. Soc., 2019, 141, 3298–3303 CrossRef CAS .
  24. Q. Sun, C. W. Fu, B. Aguila, J. Perman, S. Wang, H. Y. Huang, F. S. Xiao and S. Ma, Pore Environment Control and Enhanced Performance of Enzymes Infiltrated in Covalent Organic Frameworks, J. Am. Chem. Soc., 2018, 140, 984–992 CrossRef CAS .
  25. P. Wang, F. Zhou, C. Zhang, S. Y. Yin, L. Teng, L. Chen, X. X. Hu, H. W. Liu, X. Yin and X. B. Zhang, Ultrathin two-dimensional covalent organic framework nanoprobe for interference-resistant two-photon fluorescence bioimaging, Chem. Sci., 2018, 9, 8402–8408 RSC .
  26. B. Y. Lu, Z. Q. Wang, F. Z. Cui, J. Y. Li, X. H. Han, Q. Y. Qi, D. L. Ma, G. F. Jiang, X. X. Zeng and X. Zhao, A Covalent Organic Framework with Extended π-Conjugated Building Units as a Highly Efficient Recipient for Lithium-Sulfur Batteries, ACS Appl. Mater. Interfaces, 2020, 12, 34990–34998 CrossRef CAS .
  27. J. Guo and D. Jiang, Covalent Organic Frameworks for Heterogeneous Catalysis: Principle, Current Status, and Challenges, ACS Cent. Sci., 2020, 6, 869–879 CrossRef CAS .
  28. G. B. Wang, S. Li, C. X. Yan, F. C. Zhu, Q. Q. Lin, K. H. Xie, Y. Geng and Y. B. Dong, Covalent organic frameworks: emerging highperformance platforms for efficient photocatalytic applications, J. Mater. Chem. A, 2020, 8, 6957–6983 RSC .
  29. L. Stegbauer, K. Schwinghammer and B. V. Lotsch, A hydrazone-based covalent organic framework for photocatalytic hydrogen production, Chem. Sci., 2014, 5, 2789–2793 RSC .
  30. P. Pachfule, A. Acharjya, J. Roeser, T. Langenhahn, M. Schwarze, R. Schomacker, A. Thomas and J. Schmidt, Diacetylene Functionalized Covalent Organic Framework (COF) for Photocatalytic Hydrogen Generation, J. Am. Chem. Soc., 2018, 140, 1423–1427 CrossRef CAS .
  31. W. Chen, L. Wang, D. Mo, F. He, Z. Wen, X. Wu, H. Xu and L. Chen, Modulating Benzothiadiazole-Based Covalent Organic Frameworks via Halogenation for Enhanced Photocatalytic Water Splitting, Angew. Chem., Int. Ed., 2020, 59, 16902–16909 CrossRef CAS .
  32. X. Wang, L. Chen, S. Y. Chong, M. A. Little, Y. Wu, W. H. Zhu, R. Clowes, Y. Yan, M. A. Zwijnenburg, R. S. Sprick and A. I. Cooper, Sulfone-containing covalent organic frameworks for photocatalytic hydrogen evolution from water, Nat. Chem., 2018, 10, 1180–1189 CrossRef CAS .
  33. J. Xu, C. Yang, S. Bi, W. Wang, Y. He, D. Wu, Q. Liang, X. Wang and F. Zhang, Vinylene-Linked Covalent Organic Frameworks (COFs) with Symmetry-Tuned Polarity and Photocatalytic Activity, Angew. Chem., Int. Ed., 2020, 59, 23845–23853 CrossRef CAS .
  34. Y. N. Gong, W. Zhong, Y. Li, Y. Qiu, L. Zheng, J. Jiang and H. L. Jiang, Regulating Photocatalysis by Spin-State Manipulation of Cobalt in Covalent Organic Frameworks, J. Am. Chem. Soc., 2020, 142, 16723–16731 CrossRef CAS .
  35. M. Lu, J. Liu, Q. Li, M. Zhang, M. Liu, J. L. Wang, D. Q. Yuan and Y. Q. Lan, Rational Design of Crystalline Covalent Organic Frameworks for Efficient CO2 Photoreduction with H2O, Angew. Chem., Int. Ed., 2019, 58, 12392–12397 CrossRef CAS .
  36. C. S. Diercks, S. Lin, N. Kornienko, E. A. Kapustin, E. M. Nichols, C. Zhu, Y. Zhao, C. J. Chang and O. M. Yaghi, Reticular Electronic Tuning of Porphyrin Active Sites in Covalent Organic Frameworks for Electrocatalytic Carbon Dioxide Reduction, J. Am. Chem. Soc., 2018, 140, 1116–1122 CrossRef CAS .
  37. P. F. Wei, M. Z. Qi, Z. P. Wang, S. Y. Ding, W. Yu, Q. Liu, L. K. Wang, H. Z. Wang, W. K. An and W. Wang, Benzoxazole-Linked Ultrastable Covalent Organic Frameworks for Photocatalysis, J. Am. Chem. Soc., 2018, 140, 4623–4631 CrossRef CAS .
  38. S. Li, L. Li, Y. Li, L. Dai, C. Liu, Y. Liu, J. Li, J. Lv, P. Li and B. Wang, Fully Conjugated Donor-Acceptor Covalent Organic Frameworks for Photocatalytic Oxidative Amine Coupling and Thioamide Cyclization, ACS Catal., 2020, 10, 8717–8726 CrossRef CAS .
  39. Y. Li, C. X. Yang, H. L. Qian, X. Zhao and X. P. Yan, Carboxyl-Functionalized Covalent Organic Frameworks for the Adsorption and Removal of Triphenylmethane Dyes, ACS Appl. Nano Mater., 2019, 2, 7290–7298 CrossRef CAS .
  40. H. Fan, J. Gu, H. Meng, A. Knebel and J. Caro, High-Flux Membranes Based on the Covalent Organic Framework COF-LZU1 for Selective Dye Separation by Nanofiltration, Angew. Chem., Int. Ed., 2018, 57, 4083–4087 CrossRef CAS .
  41. T. P. Yoon, M. A. Ischay and J. Du, Visible light photocatalysis as a greener approach to photochemical synthesis, Nat. Chem., 2010, 2, 527–532 CrossRef CAS .
  42. C. M. Li, Y. Xu, W. G. Tu, G. Chen and R. Xu, Metal-free photocatalysts for various applications in energy conversion and environmental purification, Green Chem., 2017, 19, 882–899 RSC .
  43. N. Corrigan, S. Shanmugam, J. T. Xu and C. Boyer, Photocatalysis in organic and polymer synthesis, Chem. Soc. Rev., 2016, 45, 6165–6212 RSC .
  44. X. J. Lang and J. C. Zhao, Integrating TEMPO and Its Analogues with Visible-Light Photocatalysis, Chem. – Asian J., 2018, 13, 599–613 CrossRef CAS .
  45. H. Xu, Y. F. Zhang and X. Lang, TEMPO visible light photocatalysis: The selective aerobic oxidation of thiols to disulfides, Chin. Chem. Lett., 2020, 31, 1520–1524 CrossRef CAS .
  46. X. M. Ma and X. J. Lang, Titanate nanotube confined merger of organic photocatalysis and TEMPO catalysis for highly selective aerobic oxidation of sulfides, Sustainable Energy Fuels, 2020, 4, 1754–1763 RSC .
  47. H. M. Hao, X. Li and X. J. Lang, Anthraquinones as photoredox active ligands of TiO2 for selective aerobic oxidation of organic sulfides, Appl. Catal., B, 2019, 259, 118038 CrossRef CAS .
  48. J. L. Shi, R. Chen, H. Hao, C. Wang and X. Lang, 2D sp2 Carbon-Conjugated Porphyrin Covalent Organic Framework for Cooperative Photocatalysis with TEMPO, Angew. Chem., Int. Ed., 2020, 59, 9088–9093 CrossRef CAS .
  49. H. Liao, H. Wang, H. Ding, X. Meng, H. Xu, B. Wang, X. Ai and C. Wang, A 2D porous porphyrin-based covalent organic framework for sulfur storage in lithium–sulfur batteries, J. Mater. Chem. A, 2016, 4, 7416–7421 RSC .
  50. M. Niakan, Z. Asadi and M. Masteri-Farahani, Fe(III)-salen complex supported on dendrimer functionalized magnetite nanoparticles as a highly active and selective catalyst for the green oxidation of sulfides, J. Phys. Chem. Solids, 2020, 147, 109642 CrossRef CAS .

Footnotes

† Electronic supplementary information (ESI) available: Supplemental information related to the synthesis of Por-COF; FTIR spectra, SEM images, TEM images, TGA profile, UV-vis absorption spectra; the influence of TEMPO and the light intensity on the oxidation of sulfides; PXRD pattern after photocatalysis. See DOI: 10.1039/d0qm01076f
‡ These authors contributed equally to this work.
This journal is © the Partner Organisations 2021
Click here to see how this site uses Cookies. View our privacy policy here.