Biosolar Oxygenation of Hydrocarbons by Photocatalytic Artificial Wood

Lignin is the most abundant renewable and sustainable source of aromatic compounds to replace fossil resources, causing environmental issues. However, most lignin generated from pulping and biorefinery processes is combusted or discarded as waste. In this work, we first propose a photocatalytic artificial wood platform consisting of lignin and cellulose, inspired by woody cell walls, where lignin is arranged around cellulose fibers. The wood-mimetic particles were fabricated through reconstitution after the complete dissolution of lignin and cellulose. Intensive characterization revealed that the introduction of cellulose suppressed lignin’s self-aggregation, which limits its practical photocatalytic applications. As a result, the artificial wood photocatalyst exhibited a 3.2 times higher production rate of H₂O₂ from oxygen and water than lignin under solar light. The wood-mimetic photocatalyst was further coupled with an unspecific peroxygenase (UPO) biocatalyst to catalyze the selective oxygenation of inert C-H bonds using H₂O₂ as an oxidant. The wood-UPO hybrid catalyst demonstrated a universal photobiocatalytic oxyfunctionalization of various hydrocarbons with a higher total turnover number and turnover frequency than the lignin-UPO catalyst. This work suggests a practical strategy to utilize waste lignin as a photocatalyst and further demonstrates sustainable biosolar oxygenation reactions using sunlight and water as green energy and electron sources, respectively.