Engineering covalently integrated COF@CeO2 Z-scheme heterostructure for visible light driven photocatalytic CO2 conversion

Abstract

The porphyrin-based covalent organic frameworks (COFs) are promising candidates for photocatalytic CO2 conversion account for their long-range ordered mesopores and excellent semiconducting properties, but the insufficient oxidative capacity of valence band is less efficient for photooxidation of H2O, which hinders the photocatalytic performance. Herein, the stable organic–inorganic Z-scheme heterostructure was constructed through covalently connecting COF-366-Fe consisting of Fe-porphyrin and terephthaldehyde units with CeO2 by Schiff base reaction with an in-situ reaction strategy. The COF-366-Fe@CeO2 core–shell Z-scheme heterojunction not only effectively integrated the light-harvesting capability, active metal centers of COF-366-Fe and strong oxidation ability of CeO2, but also promoted the separation and transfer of photoexcited carriers. The as-prepared COF-366-Fe@CeO2 exhibited a photocatalytic CO yield of 66.2 μmol g−1 in 8 h with a 99 % selectivity under the visible light irradiation without additional photosensitizers and sacrificial agents, which was far superior to COF-366-Fe and CeO2. The remarkable promoted performance is ascribed to the covalently contact Z-scheme heterojunction interface, which benefited to facilitate the separation of photoexcited electron-hole pairs, as confirmed by the results of electronic paramagnetic resonance, time-resolved photoluminescence and in-situ XPS. This study provides an idea for designing highly-effective COF-based photocatalysts for artificial photosynthesis.