Precision Reticular Synthesis of Anisotropic 2D Metal–Covalent Organic Frameworks as High-Performance Photocatalysts for CO2 Reduction

Abstract

The topologies and pore architectures of 2D covalent organic frameworks (COFs) are theoretically abundant, but symmetry-enforced 2D multicomponent frameworks still remain rarely reported due to the limited organic building blocks available. Herein, an in situ trinodal strategy has been conceived and demonstrated by two kinds of 2D metallosalphen COFs, HATP-TFEB-M and HATN-TFEB-M (M = Co and Zn) with hcb-b3 topology and anisotropic honeycomb tiling. Multicomponent reaction of metal salt, tritopic 1,3,5-tri(3-hydroxy-4-formylethynylphenyl)benzene, and either hexatopic 2,3,6,7,10,11-hexaaminotriphenylene or 2,3,6,7,10,11-hexa(diphenylmethanimine) hexaazatrinaphthalene affords HATP-TFEB-M and HATN-TFEB-M, respectively. Four crystalline COFs display permanent porosity with the Brunauer-Emmett-Teller surface area of 370–634 m2 g−1. Fusing cobalt-salphen units with the bigger conjugation unit enables the higher visible light photocatalytic CO2 reduction activity of HATN-TFEB-Co than HATP-TFEB-Co with the help of [Ru(bpy)3]Cl2·6H2O photosensitizer. The remarkable CO evolution rate of HATN-TFEB-Co amounts to 22 986 µmol g−1 h−1, ranking one of the most excellent framework catalysts. This work not only illustrates the fabrication of functional COFs with unknown hcb-b3 topology and symmetry-enforced adjustable hexagon pores, but also provides a proof-of-concept for achieving anisotropic reticular chemistry of COFs with structure anisotropy.