Abstract
Photoelectrochemical cells are emerging as powerful tools for organic synthesis. However, they have rarely been explored for C–H halogenation to produce organic halides of industrial and medicinal importance. Here we report a photoelectrocatalytic strategy for C–H halogenation using an oxygen-vacancy-rich TiO2 photoanode with NaX (X=Cl−, Br−, I−). Under illumination, the photogenerated holes in TiO2 oxidize the halide ions to corresponding radicals or X2, which then react with the substrates to yield organic halides. The PEC C–H halogenation strategy exhibits broad substrate scope, including arenes, heteroarenes, nonpolar cycloalkanes, and aliphatic hydrocarbons. Experimental and theoretical data reveal that the oxygen vacancy on TiO2 facilitates the photo-induced carriers separation efficiency and more importantly, promotes halide ions adsorption with intermediary strength and hence increases the activity. Moreover, we designed a self-powered PEC system and directly utilised seawater as both the electrolyte and chloride ions source, attaining chlorocyclohexane productivity of 412 µmol h−1 coupled with H2 productivity of 9.2 mL h−1, thus achieving a promising way to use solar for upcycling halogen in ocean resource into valuable organic halides.
Highlights
Photoelectrochemical cells are emerging as powerful tools for organic synthesis
In a typical PEC cell for water splitting, the photoexcited electrons from the photoanode are transferred to the photocathode to drive H2O reduction to produce H2, and the photogenerated holes left on the photoanode are employed for the oxidation of H2O to O2 (Fig. 1a)[1,2]
We speculate that halogenation reaction can proceed in the PEC cell with halogen ions if the photogenerated holes in the valence band (VB) of photoanodes is more positive than the oxidation potential of the halogen ions to halogen radicals (Fig. 2c)
Summary
Photoelectrochemical cells are emerging as powerful tools for organic synthesis. they have rarely been explored for C–H halogenation to produce organic halides of industrial and medicinal importance. Significant developments have been made on C–H functionalization in PEC cell system, achieving the construction of carbon–heteroatom bonds to produce high value-added chemicals over the photoanode at mild conditions (Fig. 1b)[12,13,14]. We report a photoelectrocatalytic strategy for C–H halogenation with NaX (X=Cl−, Br−, I−) over an oxygenvacancy-rich TiO2 photoanode, producing high value-added organic halides coupled with cathodic H2 production (Fig. 2c). The strategy exhibits broad substrate scope for arenes, heteroarenes, nonpolar cycloalkanes, and aliphatic hydrocarbons Both experimental and theoretical results indicate that the oxygen vacancies on TiO2 help enhance the adsorption of halogen ion and their enrichment in local environment, together with the enhanced photo-induced carriers separation efficiency. We achieve a promising way to use solar for upcycling halogen in ocean resource into valuable organic halides
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call