Hematite-based photoelectrochemical lignin depolymerization and redox biotransformation

Abstract

Lignin is the world's largest origin of renewable aromatic building block. Developing a route to lignin valorization against its recalcitrant nature has been an outstanding challenge. As a sustainable option, herein we report the solely solar powered lignin reformation coupled with redox biotransformation in a photoelectrochemical (PEC) platform consisting of a hematite photoanode and mesoporous indium tin oxide (mesoITO) wired with silicon photovoltaic(PV). Hematite as an attractive, cost-effective semiconductor that performs excellent photoelectrocatalytic properties with high chemical stability, its function for lignin depolymerization is newly discovered. Hematite-catalyzed photoelectrochemical lignin depolymerization ended up yielding of small molecular weight aromatic compounds while mesoITO-catalyzed reduction of synthetic nicotinamide cofactor analogues (mNAD$^+$s) is applied to trans-hydrogenation of conjugated C=C bonds driven by Old Yellow Enzyme (OYE). Our findings open up a greener and sustainable possibility of unbiased lignin valorization to value-added chemicals using solar energy.