Solar-Driven Lignin Oxidation via Hydrogen Atom Transfer with a Dye-Sensitized TiO₂ Photoanode

Abstract

Molecular-based dye-sensitized photoelectrochemical cells (DSPECs) have traditionally targeted solar-driven water splitting for the conversion of solar energy into fuels in aqueous media. This work reports the use of a DSPEC-type photoanode specifically designed to carry out chemoselective oxidation of benzylic alcohol moieties in lignin model compounds and real lignin in organic media. The TiO2-based photoanode incorporates a surface-bound Ru(II)-based photocatalyst and solution-dissolved hydrogen atom transfer (HAT) co-catalyst to perform solar-driven photocatalytic oxidation of the lignin substrates. Under aerobic conditions with simulated solar illumination, conversion efficiencies in excess of 90% are observed for the formation of the oxidized ketone product from model compounds. The DSPEC half-cell exhibited impressive long-term durability, sustaining photocatalytic oxidation of the lignin model compound over a net illumination period of 80 h. This photoelectrochemical heterogeneous catalytic process provides a unique foundation to perform selective C–O bond cleavage for real lignin conversion technologies.