Ingenious Artificial Leaf Based on Covalent Organic Framework Membranes for Boosting CO₂ Photoreduction

Abstract

Covalent organic frameworks (COFs) hold the potential in converting CO 2 with water into value-added fuels and O 2 to save the deteriorating ecological environment. However, reaching high yield and selectivity is a grand challenge under metal-, photosensitizer-, or sacrificial reagent-free conditions. Here, inspired by microstructures of natural leaves, we designed triazine-based COF membranes with the integration of steady light-harvesting sites, efficient catalytic center, and fast charge/mass transfer configuration to fabricate a novel artificial leaf for the first time. Significantly, a record high CO yield of 1240 μmol g −1 in a 4 h reaction, approximately 100% selectivity, and a long lifespan (at least 16 cycles) were achieved under gas−solid conditions without using any metal, photosensitizer, or sacrificial reagent. Unlike the existing knowledge, the chemical structural unit of triazine-imide-triazine and the unique physical form of the COF membrane are predominant for such a remarkable photocatalysis. This work opens a new pathway to simulating photosynthesis in leaves and may motivate relevant research in the future.

Organic polymer facilitated CO2 photoreduction: a minireview

“…Lately, a novel triazine-based COF membrane with steady light-harvesting sites was developed by Gao et al 105 A superior CO yield of 1240 μmol g −1 with 100% selectivity was obtained under visible light irradiation over this triazine-based COF membrane. The reaction can even be performed under natural sunlight.…”

Supramolecular cages and metal organic frameworks of porphyrins for a sustainable tomorrow: challenges and applications

“…A record high CO yield of 1240 μmol g −1 was achieved in 4 h reaction with 100% selectivity and a long lifespan (at least 16 cycles) under gas solid conditions without using any metal, photosensitizer or sacrificial reagent. 245…”

Selective Metal-Free CO2 Photoreduction in Water Using Porous Nanostructures with Internal Molecular Free Volume

“…However, their moderate photocatalytic performance and selectivity may be due to their amorphous or semicrystalline properties, which can cause the possible recombination of photogenerated electrons and holes. Furthermore, some metal-free systems require the formation of membranes and gas–solid conditions, which further limits their applications . Therefore, to develop a metal-free photocatalyst with good photocatalytic activity and selectivity, critical factors such as band gaps, surface area, CO 2 adsorption, energy level alignments, and photogenerated charge separation must be considered.…”

“…Furthermore, some metal-free systems require the formation of membranes and gas−solid conditions, which further limits their applications. 15 Therefore, to develop a metal-free photocatalyst with good photocatalytic activity and selectivity, critical factors such as band gaps, surface area, CO 2 adsorption, energy level alignments, and photogenerated charge separation must be considered. The low solubility of CO 2 in aqueous media with only 1 molecule of CO 2 per 1300 H 2 O molecules at 1 atm pressure limits its reduction in water.…”