Abstract
Photocatalytic depolymerization of lignin to prepare value-added chemicals by breaking lignin Cα-Cβ bonds (LCCD) is sustainable because of its green and mild reaction conditions. However, photocatalytic cleavage of LCCD still faces great challenges because of the complexity and stubbornness of lignin structure. Here, Fe-doped graphene carbon nitride (g-C3N4) photocatalysts were successfully prepared. The doping of Fe ions reduces the band gap of g-C3N4 and accelerates the migration ability of photogenerated carriers. 8FeCN can efficiently break LCCD in β-1 lignin model compounds and ethanol organosolv lignin, producing aromatic aldehydes, alcohol and acids as the main products. Hydroxyl radicals are generated through Fe-induced Fenton reactions, which increase the reaction pathway for breaking LCCD. The mechanism studies showed that photocatalytic cleavage of LCCD mainly followed the improved Cβ radical and single electron transfer mechanism. In addition, micellar aqueous media further accelerates the cleavage of LCCD, as water participates in the photocatalytic reaction and provided the O and H atoms needed for the formation of photocatalytic products. This work offers a fresh concept for the high-value utilization of lignin by oxidizing cleavage of LCCD.
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