Boosting CO₂ Photoreduction via Regulating Charge Transfer Ability in a One‐Dimensional Covalent Organic Framework

Abstract

Two‐dimensional (2D) imine‐based covalent organic frameworks (COFs) hold potential for photocatalytic CO2 reduction. However, high energy barrier of imine linkage impede the in‐plane photoelectron transfer process, resulting in inadequate efficiency of CO2 photoreduction. Herein, we present a dimensionality induced local electronic modulation strategy through the construction of one‐dimensional (1D) pyrene‐based covalent organic frameworks (PyTTA‐COF). The dual‐chain‐like edge architectures of 1D PyTTA‐COF enable the stabilization of aromatic backbones, thus reducing energy loss during exciton dissociation and thermal relaxation, which provides energetic photoelectron to traverse the energy barrier of imine linkages. As a result, the 1D PyTTA‐COF exhibits significantly enhanced CO2 photoreduction activity under visible‐light irradiation when coordinated with metal cobalt ion, yielding a remarkable CO evolution of 1003 μmol g−1 over an 8‐hour period, which surpasses that of the corresponding 2D counterpart by a factor of 59. These findings present a valuable approach to address in‐plane charge transfer limitations in imine‐based COFs.

Regulating Benzene Ring Number as Connector in Covalent Organic Framework for Boosting Photosynthesis of H2O2 from Seawater

“…A comparison in both the H 2 O 2 production rate and raw material cost among reported COF photocatalysts and our cases is shown in Figure b. It is clear that our COF photocatalysts show a comparable H 2 O 2 production rate with most reported COF photocatalysts − but the lowest raw material cost among all reported COF photocatalysts, thereby implying the outstanding advantage of our photocatalysts in industrial application. Catalytic stability represents another factor for industrial application.…”

“…Furthermore, we also measured the temperature-dependent photoluminescence (TD-PL) spectra to deduce the exciton binding energy (E b ) (Figure 4d,e), which can be experimentally obtained from the plot of temperature versus PL intensity through fitting the Arrhenius equation. Notably, the E b values are 18.64 and 20.32 meV (Figure 4d), which are far lower than all reported photocatalysts for such use, such as PyTTA-COF (113 meV) 40 and TT-CTP (74.5 meV), 42 thereby implying a small energy loss for exciton dissociation into free charges and more effective charge separation. All of the above characteristics indicate the superiority of ECUT-COF-31 as a photocatalyst over ECUT-COF-30; this is in good agreement with the experimental results.…”

“…Mott–Schottky (MS) analysis (Figure S5 and S6) was used to estimate the lowest unoccupied molecular orbital (LUMO) level, which gave −0.52 V for ECUT-COF-30 and −0.86 V for ECUT-COF-31. Note that the LUMO levels are more negative than the reduction potential of the oxygen reduction reaction (ORR) in the direct 2e – (+0.68 V) or stepwise 1e – (−0.33 V) fashion (Figure S7), which suggests that our photocatalysts are thermodynamically favorable for photosynthesis of H 2 O 2 through an ORR route. − Moreover, on the basis of the equation E HOMO = E LUMO + E g , we can obtain the highest occupied molecular orbital (HOMO) level of 1.35 V for ECUT-COF-30 and 1.09 V for ECUT-COF-31 (Figure S7), which excludes the possibility of of H 2 O 2 production through water oxidation reaction (WOR, +1.76 V). − …”

Fabrication of p–n Heterostructured Photocatalysts with Triazine-Based Covalent Organic Framework and CuInS2 for High-Efficiency CO2 Reduction

“…Differing from the above materials, covalent organic frameworks (COFs), as emerging crystalline organic materials constructed from organic monomers by covalent bonds, would be an excellent platform for water splitting, organic transformations, and CO 2 reduction due to the advantages of high surface area, easy structural regulation, and abundant π-conjugated electronic system. − Among them, triazine-based COFs possess abundant N-containing groups and π-conjugated electric systems, and the triazine groups can be excited under visible light irradiation to serve as electron reservoirs, facilitating the adsorption and activation of CO 2 and the photogenerated charge transfer, which has attracted extensive attention recently . However, the current research on CO 2 reduction using COFs as photocatalysts is still unsatisfactory, and their photocatalytic activities are extremely low.…”

Anthraquinone-based covalent organic framework as a recyclable direct hydrogen atom transfer photocatalyst for C–H functionalization

“…27,28 For example, catalytic COFs have been designed using catalytically active units as the building units. 29–51 The high porosity of COFs allows facile access of catalytically active sites to substrates and diffusion of products through COF channels. The use of appropriate linkages for COF construction has allowed the synthesis of stable COF catalysts.…”