A hydrazone-based covalent organic framework/iridium (III) complex for photochemical CO2 reduction with enhanced efficiency and durability

Abstract Metal complexes have been one of the most promising photocatalysts for highly selective conversion of CO2 to carbon-based products. However, the aggregation-induced deactivation and narrow absorption range of sunlight impede their catalytic performance. Here, a heterogeneous photocatalytic system with a hydrazone-based covalent organic framework (COF) as photosensitizer and a metal complex [Ir-ppy] as photocatalyst is designed for efficient and durable photochemical CO2 reduction. Under visible-light irradiation, this heterogeneous system achieves CO yield of 88.6 μmol in 1 h’s reaction with the selectivity of 98%. This reactivity is 2.3 times higher than that of bare [Ir-ppy]. Significantly, comparing with the poor catalytic durability (30 min) of [Ir-ppy], the COF/[Ir-ppy] catalyst still be active after irradiation of 7 h. The extended catalytic reactivity may result from the promoting dispersion of [Ir-ppy] on NAHN-Tp COF which restrains the aggregation-induced deactivation of [Ir-ppy]. The enhanced reactivity may originate from the efficient electron transfer from COF to [Ir-ppy] and facilitated photo-induced charge separation as evidenced by matched band alignment of COF and [Ir-ppy], steady-state photoluminescence, time-resolved fluorescence.