A Cobalt-Modified Covalent Triazine-Based Framework as an Efficient Cocatalyst for Visible-Light-Driven Photocatalytic CO2 Reduction

Photocatalytic CO2 reduction into carbonaceous feedstock chemicals is a promising renewable energy technology to convert solar energy and greenhouse gases into chemical fuels. Here, a covalent triazine-based framework (CTF) is demonstrated as an efficient cocatalyst to reduce CO2 under visible-light irradiation. The nitrogen-rich triazine moieties in CTF contribute to CO2 adsorption, while the periodical pore structure of CTF favors the accommodation of CO2 and electron mediator. Immobilization of cobalt species onto CTF promotes the photocatalytic activity with a 44-fold enhancement over pristine CTF and the optimal CO production rate of the obtained Co/CTFs was up to 50 mu mol g(-1) h(-1). The results of solid-state UV-vis diffuse reflectance spectra (UV-vis DRS), CO2 adsorption and electrochemical impedance spectroscopy (EIS) illustrated that the increased activity was ascribed to the enhanced CO2 capture capacity, improved absorption of visible-light and facilitated the transfer of charge from CTF to CO2 molecules. The CTF not only serves as a substrate for active Co species, but also bridges the photosensitizer with cobalt catalytic sites for the efficient transfer of photoexcited electrons. This work highlights the capability and ease of fabricating covalent organic framework-based photocatalytic systems that are potentially useful for energy-conversion applications.