Selective photocatalytic aerobic oxidative cleavage of lignin C–O bonds over sodium lignosulfonate modified Fe3O4/TiO2

Abstract

Lignocellulose shows significantly potential in sustainable conversion to high-quality fuel and value-added chemicals with the demands for realizing the rapid cycle of carbon resources and helping to reach carbon neutrality in nature. Selective tailoring of α-O-4, β-O-4, etc. linkages in lignin has always been viewed as “death blow” for its depolymerization. Herein, novel sodium lignosulfonate (SL) modified Fe3O4/TiO2 (SL-Fe3O4/TiO2) spherical particles have been developed and used as catalysts for selectively photocatalytic oxidative cleavage of organosolv lignin. As expected, 80% selective conversion of lignin in C2–C4 esters has been achieved, while C–O bonds in lignin model compounds can be effectively cleaved. Other than normal hydroxyl radical-mediated photocatalytic depolymerization of lignin over TiO2-based materials, in this contribution, mechanism studies indicate that photogenerated holes and superoxide anion radicals are main active species, which trigger the cleavage of α/β-O-4 bond, and the isotope-labeling study confirms the crucial factor of Cβ–H dehydrogenation in cleavage of β-O-4 bonds.