Construct three-dimensional COFs with scu topology to achieve efficient photocatalysis

At 23:00 beijing time on August 19, 2022, the research group of researcher Zhang Zhenjie of Nankai University published a latest research result entitled “Rationally Fabricating 3D Porphrinic Covalent Organic Frameworks with scu Topology as Highly Efficient Photocatalysts” in the journal Chem.

The author first passed[8+4]The monomer connection method constructed two cases of porphyrin-based three-dimensional COFs materials, and with the help of continuous rotational electron diffraction technology and structural simulation, it was determined that it had the first casescuTopology. Thanks to the material’s good light absorption properties and matching band structure, it can efficiently catalyze the cyclization reaction of diphenylmethanine and maleimide and the oxidative coupling reaction of benzylamine under room temperature and visible light conditions. This work not only enriches the topology types of three-dimensional COFs, but also provides a reference for the development of heterogeneous photocatalysts. The corresponding author of the paper is Zhang Zhenjie; The co-first authors are Jin Fazheng and Lynn.

Due to the characteristics of orderly structure, high porosity, low skeleton density, high stability and easy functionality, covalent organic frameworks (COFs) have important application prospects in adsorption and separation, energy storage and catalytic conversion, and have received wide attention at home and abroad. Compared with the rapid development of two-dimensional COFs, the types and quantities of three-dimensional COFs constructed are limited, and the structural analysis is very difficult, making their development still in its early stages. At present, the construction of three-dimensional COFs is mainly through[4+2]、[4+3]、[4+4]、[6+2]、[6+3]、[6+4]and[6+6]Ishizovar connection method, the resulting topology is only ~20 kinds (dia,ctn,bor,ffc,rra,srs,pts,lon-b,stp,acs,sql-c,tbo,bcu,fjh,ljh,pcu,soc,ceq,nboandhea), the new topology needs further development.

Based on this, Zhang Zhenjie’s team at Nankai University worked in the early stage (J. Am. Chem. Soc. On the basis of 2022, 144, 5643-5652), octalaldehyde monomer and tetraaminophenylporphyrin monomer were used as construction units, and it was passed for the first time[8+4]The monomer connection method is designed to synthesize two novel three-dimensional COFs (NKCOF-25-H and NKCOF-25-Ni). The authors conducted a comprehensive study of the composition and structure of the material through a variety of test characterizations, and determined that NKCOFs have the characteristics of continuous rotational electron diffraction (cRED) technology combined with structural simulationscuTopology. X-ray powder diffraction (PXRD) data and nitrogen total desorption curve indicate that NKCOFs have good crystallinity and porosity, and their pore size distribution data and high-resolution transmission electron microscopy (HRTEM) images indicate that the pore size of the material is consistent with the simulated structure.

Figure 1: (A) Schematic diagram of the chemical structure, synthetic route, and topology of NKCOF-25-X; (B-D) Infrared spectra (B), solid 13C NMR spectra (C) and SEM images (D) of NKCOF-25-H

Figure 2: (A, B) PXRD spectrogram and structure diagram of NKCOF-25-X; (C) Three-dimensional electron diffraction data for NKCOF-25-H; (D, E) HRTEM images of NKCOFs

The authors studied the photophysical properties of the material and found that NKCOFs have a wide visible light absorption range, which is conducive to the effective use of light energy by the material. The Mott-Schottky (M-S) curve shows that NKCOFs have typical n-type semiconductor characteristics and have significant photocurrent response performance. After calculations, NKCOFs have a suitable band structure with the ability to catalyze the production of reactive oxygen species molecules under visible light. Based on this, the authors demonstrated the ability of both COFs to catalyze the production of single-line oxygen (1O2) and superoxide anions (O2•−) through electron paramagnetic resonance (EPR) tests and ultraviolet variation experiments of feature indicators (DPBF and NBT).

Figure 3: (A) Ultraviolet-visible diffuse reflection spectra of NKCOF-25-X and TAPP-X; (B) Mott-Schottky (M-S) curve of NKCOF-25-Ni; (C) Illustration of the band structure of NKCOF-25-X; (D) Photocurrent response curve of NKCOF-25-X

Figure 4: (A, B) EPR detection diagram of TEMP capture 1O2 and DMPO capture O2•−; (C, D) In the presence of NKCOFs, the UV-Vis absorption spectrum of DPBF and NBT changes over time

Subsequently, the authors used NKCOFs as heterogeneous photocatalysts to catalyze the cyclization of paraxylaniline with maleimide. After screening and optimization of the catalytic conditions, the authors finally chose to use 2 mol% of the catalyst to perform the catalytic reaction at room temperature and visible light. Both cases of COFs had excellent catalytic effects on the reaction, and their catalytic yield exceeded all currently reported COFs materials. Substrate expansion experiments and cycle experiments show that NKCOF-25-Ni has good substrate universality for this reaction and can be recycled more than 10 times. Similarly, NKCOFs can also be used to catalyze the oxidative coupling reactions of various benzylamine compounds, showing good catalytic properties and cycle stability. Finally, the authors studied the mechanism of the catalytic reaction. By designing multiple control experiments and adding molecular trappers, the authors found that superoxide anions (O2•−) played a leading role in the progression of the reaction. In addition, photogenerated electrons and holes are also involved in two types of catalytic reactions.

Figure 5: Substrate expansion results of NKCOF-25-Ni catalyzed reaction of dimethylaniline with maleimide compounds.

Figure 6: Substrate expansion results of NKCOF-25-Ni catalyzed oxidative coupling of benzylamines.

(Source: Science Network)

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