Modulating Charge Transfer Pathways to Enhance Photocatalytic Performance of the Metal–Organic Layer Nanosheet

Abstract

Two-dimensional metal–organic layer (MOL) nanosheets, as nonhomogeneous catalysts, show better optical activity in the field of photocatalysis due to their unique structural advantages. Current research focuses on how to modify the structure of 2D nanosheets by means of crystal engineering to modulate the intralayer electron transfer pathway and systematically investigate the impacts of size effect and electron transfer pathway on the energy utilization efficiency of crystalline materials. In the present work, a triple lophine-derived ligand was designed and prepared, which exhibits a large π-conjugation system and multiple D–A (D: donor, A: acceptor) electron transfer pathways. 2D MOL constructed with Cd ions can be exfoliated by physical sonication to obtain double-walled 2D MOL nanosheets. Compared with the bulk crystalline material, the 2D nanosheets exhibit better photovoltaic properties. Benefiting from the excellent structural advantages, 2D MOL nanosheets could be used as photocatalysts for a variety of aerobic oxidation reactions under mild conditions (10 W white LED, room temperature), such as the trifluoromethylation of coumarins, the synthesis of benzimidazole derivatives from aromatic diamines and aromatic aldehydes, and the preparation of 2,4,6-triarylpyridine derivatives, all with high conversion rates and selectivity (yield typically greater than 88%). The related results illustrate that the introduction of the photoactive triple-lophine unit into 2D MOL nanosheets can effectively modulate the electron transport mode and enhance energy utilization, which provides a new research idea for the development of nonhomogeneous photocatalysts aimed at the applications of visible light-driven organic conversion.

Precise Modulation of Conjugative Structure and Porosity in Covalent Organic Frameworks for Transition Metal Free Visible-Light Catalysis of Trifluoromethylation

“…The trifluoromethylation with precisely defined number and position of trifluoromethyl groups in organic compounds is essentially important in medicinal chemistry as it can regulate the p K a value and lipid solubility of drug molecules, enhance the permeability and metabolic stability, and thereby effectively improve their absorption, delivery, and diffusion in the body. − Over the past decades, numerous trifluoromethylation methods have been developed with fluorinated reagents such as CF 3 SiMe 3 , CF 3 H, CF 3 I, CF 3 SO 2 Na, CF 3 SO 2 Cl, and so on. − However, most of the reported syntheses are catalyzed with the participation of transition metals. The subsequent purification procedure is tedious because the thorough removal of transition metal is difficult, whereas its residue in the final product is severely restricted in some fields, particularly in biomedical applications.…”

Rapid Exciton Dissociation and Charge Transfer Endowed by Reinforced Interfacial Interaction in a Mixed-Dimensional 2D/3D Heterojunction Nanocatalyst for High-Efficiency Photocatalysis

“…Semiconductor-based photocatalysis technology is regarded as a new entryway to overcoming the huge consumption of energy. − The key difficulty is to look for stable photocatalysts because of their high efficiency and low cost. Though a series of photocatalysts like metal oxides (sulfides, nitrides), − metal–organic framework material, , and Bi-based photocatalysts have been designed, , nevertheless, the unsatisfactory light absorption, rapid charge recombination, and limited active sites greatly restrict the efficient photocatalytic H 2 evolution, CO 2 reduction, and pollutant removal . Recently, graphitic carbon nitride (CN) has been confirmed as an earth-abundant visible-light photocatalyst due to its outstanding layered structure, better chemical and thermal stability, and applicable band gap. , Nevertheless, the bulk CN obtained by traditional thermal polymerization exhibits inherently limited photocatalytic performance due to its certain intrinsic drawbacks, such as the incomplete absorption of visible light, insufficient surface-active site, and rapid recombination of photogenerated hole–electron pairs. − In particular, the strong exciton effect from the Frenkel excitons interaction may hinder the dissociation of singlet exciton and is often ignored. − Free charge carriers will compete against neutral excitons during a photocatalytic reaction. , How to obtain a sufficient quantity of charge carriers via the dissociation of excitons into electrons and holes is still a vital challenge.…”