Design and synthesis of metal-free ethene-based covalent organic framework photocatalysts for efficient, selective, and long-term stable CO2 conversion into methane

Ahmed F M El-Mahdy; Hossam A E Omr; Zeid A ALOthman; Hyeonseok Lee

doi:10.1016/j.jcis.2022.11.098

Design and synthesis of metal-free ethene-based covalent organic framework photocatalysts for efficient, selective, and long-term stable CO₂ conversion into methane

J Colloid Interface Sci. 2023 Mar:633:775-785. doi: 10.1016/j.jcis.2022.11.098. Epub 2022 Nov 24.

Authors

Ahmed F M El-Mahdy¹, Hossam A E Omr², Zeid A ALOthman³, Hyeonseok Lee⁴

Affiliations

¹ Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan. Electronic address: ahmedelmahdy@mail.nsysu.edu.tw.
² Department of Photonics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan.
³ Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia; International Research Center for Materials Nanoarchitechtonics (WPI-MANA) and International Center for Young Scientists (ICYS), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
⁴ Department of Photonics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan. Electronic address: hslee611@mail.nsysu.edu.tw.

PMID: 36493742
DOI: 10.1016/j.jcis.2022.11.098

Abstract

The efficient and selective photocatalytic CO₂ conversion into higher-valued hydrocarbon products (e.g., methane and ethane) over covalent organic frameworks (COFs) remains a challenge, with all previously reported attempts producing carbon monoxide as the dominant product. Herein, we report a new ethene-based COF, through polycondensation of electron-rich (E)-1,2‑diphenylethene and 1,3,6,8‑tetraphenylpyrene units. The synthesized ethene-based COF functioned as an efficient metal-free photocatalyst for the conversion of CO₂ into methane under visible light irradiation, with a selectivity of 100 %, a production rate of 14.7 µmol g^-1h^-1, and an apparent quantum yield of c.a. 0.99 % at 489.5 nm, which are the most promising values reported for CO₂ conversion by a metal-free COF photocatalyst, without any support from a co-catalyst. The carbon origin of CH₄ product is confirmed by isotope tracer ¹³CO₂ experiment. Moreover, the photocatalytic system consistently produces methane for > 14 h with recyclability.

Keywords: CO(2) conversion; Covalent organic framework; Metal-free; Methane; Photocatalysis.