Graphene/hemin hybrid material as a catalyst for degradation of alkaline lignin with hydrogen peroxide

Abstract

A graphene/hemin (H-GN) catalyst for lignin degradation was prepared by a wet-chemistry method with graphene oxide and hemin. Hemin was absorbed onto the graphene surface through p-p interaction. Graphene served as a supporting material for hemin, providing a large contact area between the active molecules of catalyst and substrate, as well as protecting hemin from self-oxidation and maintaining its active molecules. The H-GN catalyst showed high catalytic efficiency in the degradation of alkaline lignin under gentle conditions. At pH 13.0, the degradation rate was 49.7% with H-GN and H2O2 (mass ratio of H2O2 to lignin of 10:1) under 60 °C, which was higher than 34.9% for non-catalyst degradation. At pH 13.2, it was as high as 92.9 wt.% at 100 °C. The lignin was decomposed into small molecules with styrene as the main final product below pH 13 and with the major products of 4-hydroxy-4-methyl-2-pentanone and bis(2-ethylhexyl) phthalate at pH 13.2.