Superheterojunction covalent organic frameworks: Supramolecular synergetic charge transfer for highly efficient photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into value–added chemicals under visible light irradiation is very appealing but challenging due to the easy recombination of hole–electron pairs in traditional photocatalysts. π–π stacking interactions can be favorable for efficient separation and transfer of photo–irradiated charges to promote photocatalysis, but are rarely studied in crystalline porous frameworks like covalent organic frameworks (COFs). Herein, we report a series of thienothiophenes–porphyrin based 2D COFs, denoted as TT–Por(M)–COF (M = 2 H/Co/Cu/Ni), which show enhanced intralayer and interlayer charge separation and migration due to the donor-acceptor heterojunctions and π–stacked columns. The TT–Por(Co)–COF achieves enhanced CO evolution rate than COF–366–Co without the heterojunctions and π–columns (10.05 mmol g–1 h–1 versus 7.10 mmol g–1 h–1) under visible light irradiation. This work not only shows the important role of π–π stacking interactions of COFs for CO2 conversion, but also provides insight into the mechanistic aspect for photocatalysis.