Structural Regulation of Lignin Using an Al3+/Zn2+ Bimetallic Lewis Acid System to Enhance Enzymatic Saccharification.

This study employed AlCl3/ZnCl2 bimetallic salt catalysis with ethanol organic solvent for sugar cane bagasse pretreatment. The process retained 80.12% cellulose while removing ∼70% xylan and 80.56% lignin, achieving 90.18% glucose conversion during enzymatic hydrolysis. Comprehensive characterization and DFT calculations revealed a synergistic dual-action mechanism: strong Lewis acid Al3+ extensively cleaved β-O-4 bonds (reducing them to 40.68%), whereas weak Lewis acid Zn2+ interacted broadly with side chains and aromatic rings. This synergy facilitated substantial lignin removal and minimized total phenolic OH content in residual lignin (1.32 mmol/g), thereby suppressing unproductive cellulase adsorption. Additionally, the bimetallic system exhibited stronger overall interactions with the model compound GG compared to single-component systems. This integrated approach establishes a robust foundation for efficient lignocellulose fractionation and downstream bioconversion.