Stable and selective C( sp 3)–H halogenation over COF-modified β -Fe2O3 photoanodes

Abstract

Photoelectrocatalytic synthesis provides a sustainable route to high-value organic chemicals, yet achieving high selectivity while maintaining long-term stability remains challenging because of limited interfacial reactant availability and competing radical-mediated reaction pathways. Here, we develop a COF-modified photoanode by integrating a functionalized covalent organic framework (COF) onto β-Fe2O3 to regulate aqueous C(sp3)–H halogenation. Using cyclohexane chlorination as a model reaction, the COF-modified β-Fe2O3 photoanode achieves a monochlorination selectivity of up to 96.8% under AM 1.5 G illumination (100 mW cm−2), far exceeding the 53.9% obtained over bare β-Fe2O3. Under one-sun illumination, the photoanode delivers a photocurrent density of 2.8 mA cm−2 and remains stable for 300 h, retaining approximately 95% chlorocyclohexane selectivity at the end of the test. Even under 13-sun illumination, the photocurrent density reaches approximately 35 mA cm−2, with a chlorocyclohexane selectivity of 91.9% after 100 h. The COF-modified photoanode also shows enhanced monobromination and monoiodination selectivities, demonstrating the generality of this approach.