Hydrothermal Reinforcement of Lignin toward Artificial Bio-Leaves and Application in H ₂ O ₂ Photosynthesis

Fabricating artificial bioleaves from biomass offers a sustainable strategy for harnessing inexhaustible solar energy to drive chemical production. As Earth’s most abundant natural reservoir of aromatic building blocks, lignin inherently contains donor–acceptor motifs that confer photocatalytic potential. Nevertheless, its practical utilization is constrained by loosely packed π-conjugated domains and limited structural tunability. These limitations can be effectively alleviated by subjecting a cetyltrimethylammonium bromide/lignosulfonate (CTAB/LS) colloidal system to hydrothermal carbonization. During this process, aromatization and condensation reactions afford spherical hydrothermal carbons (HTC-LS) featuring reinforced π-conjugated polyaromatic frameworks. The resulting HTC-LS exhibits broadened light absorption (>1400 nm) and abundant paramagnetic defects, enabling superior photon harvesting and charge-carrier generation. Benefiting from a favorable band structure with valence band maximum (VBM) and conduction band minimum (CBM) at 1.46 V and −0.67 V vs SHE, HTC-LS demonstrates significantly improved photocatalytic efficiency in H2O2 synthesis via a successive single-electron O2 reduction pathway in pure water without sacrificial agents. Remarkably, beyond artificial illumination, 0.13 mmol·L–1 H2O2 is obtained under natural sunlight in a simple water–air system without forced aeration. The present work presents a feasible strategy to convert lignin feedstocks into artificial bioleaves for sustainable solar-to-chemical conversion.