Morpholine-linked metal-phthalocyanine covalent organic frameworks for enhanced photocatalytic CO2 reduction

Abstract

Developing technology of artificial photosynthetic CO₂ reduction is essential to improve the issues of global carbon emissions and climate change. However, it is still limited by the low charge separation efficiency and poor transport capacity of photocatalysts. Herein, two novel morpholine-linked metal-phthalocyanine COFs, Co-DA-COF and Co-DB-COF, were synthesized through the nucleophilic aromatic substitution reaction of cobalt perfluorophthalocyanine (CoPcF₁₆) with 2,5-phenylenediamine-1,4-diphenol (DHA) and 3,3′-dihydroxybenzidine (DHB). The introduction of morpholine bonds and the specific photosensitivity of metal phthalocyanines resulted in remarkable photocatalytic CO₂ reduction reaction (CDRR) activity. Notably, Co-DB-COF exhibited enhanced electron delocalization owing to its expanded π-conjugated system, which facilitated the process of separating and transporting photogenerated charge carriers. This resulted in a notable rate of CO production of 25.7 mmol g⁻¹ h⁻¹, exhibiting a selectivity of 92.3% and an AQE of 0.65% at 450 nm, which surpasses the majority of previously documented visible-light-driven COF-based photocatalysts. This work demonstrated the capability of morpholine-linked metal-phthalocyanine COFs in CO₂ photocatalytic conversion, providing fresh insights for designing novel artificial photosynthesis catalysts.