Linkage-Affected Donor–Acceptor Covalent Organic Frameworks for Photocatalytic Hydrogen Production

Abstract

The depletion of traditional fossil energy and the resulting environmental pollution forces people to explore new energy sources. Direct use of solar energy is now a viable solution for solving these problems. Covalent organic frameworks (COFs) are a porous crystalline material; their well-defined two-dimensional or three-dimensional frameworks can ensure the orderly arrangement of photoelectric active units, giving them potential photoelectric conversion applications. The tunable structural features endow COFs many advantages in photocatalytic hydrogen production under visible light. This review comprehensively summarizes the research progress on photoelectronic donor–acceptor (D-A) COFs with tunable structure for photocatalytic hydrogen evolution and will provide a feasible guiding strategy for applying this type of COFs in photocatalytic hydrogen production.

Recent progress on covalent organic frameworks for photocatalytic hydrogen generation via water splitting

“…78,86,87 (3) The modification of the D-A skeleton implies the adjustment of the energy levels, which can be tuned by using different building blocks with the electron donor and electron acceptor nature. 88 In the past few years, great efforts have focused on constructing D-A COFs.…”

“…10) for photocatalytic hydrogen generation through the base-catalysed solvothermal reaction. 96 Integrating the strongly electronegative F atom rendered COF-F with excellent photocatalytic activity, showing the highest photocatalytic hydrogen conversion of 10.58 mmol g À1 h À1 compared to COF-H and COF-Cl. This is attributed to the key role of F in charge separation and transfer.…”

Lattice Shrinkage of 2D-COFs under Electron Beam Irradiation

“…The Fourier transform infrared spectroscopy (FT-IR) spectra were collected using an FT-IR spectrometer (VERTEX 70v) in vacuum. For solid state NMR, 13 C cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C CP/MAS NMR) spectra were recorded on a Bruker Avance III 400MHz spectrometer. Samples were packed in 4 mm ZrO 2 rotors, which were spun at 8 kHz in a double resonance MAS probe.…”

“…Therefore, after the crystal structure is confirmed, it is necessary to confirm the correctness of its chemical structures. Fourier transform infrared spectroscopy (FTIR) and 13 C nuclear magnetic resonance (NMR) were used to characterize the TAPT-TFPT COF (Figure 2a,b). Disappearance of the aldehyde carbonyl peak (1700 cm −1 ) and appearance of a new stretching signal at 1624 cm −1 corresponding to the imine bond indicated that TAPT and TFPT were fully reacted to form the imine networks.…”

“…The network-like chemistry of covalent organic frameworks enables top-down design at the molecular level, leading to alignments guided by geometric structures [2][3][4]. The advantages of such structural diversity and control over functions 2 of 12 are perfectly reflected in COFs, which are widely used in fields such as gas storage [5,6], separation [7][8][9], catalysis [10][11][12][13], optoelectronics [14][15][16][17], sensing [18][19][20] and biological fields [6,21]. It is worth noting that the unique physical and chemical properties of COF materials are closely related to their crystal structures [22,23].…”