A ZnCl2-lactic acid deep eutectic solvent enables efficient cleavage of bamboo derived condensed lignin after ultra low phytic acid hydrolysis for xylooligosaccharide production.

Conventional organic acid hydrolysis for xylooligosaccharide (XOS) production often demands high acid concentrations, causing catalyst loss and environmental burdens. This work establishes a mechanistically tunable dual-acid cascade that couples ultra-dilute bio-derived phytic acid (PA) hydrolysis with a Lewis-Brønsted synergistic deep eutectic solvent (DES, ZnCl₂:lactic acid:ethylene glycol = 1:2:2), introducing an unexplored cooperative depolymerization pathway for selective bamboo valorization. The ultra-dilute PA catalyst enabled selective hemicellulose depolymerization, yielding up to 55.2% XOS at 0.05% (w/v) PA, which is 20- to 50-fold lower acid loading than common systems demonstrating that natural organophosphorus acids can act as effective proton donors at ultra-low dosages. The subsequent DES pretreatment achieved 90.3% delignification and retained 90.3% cellulose, with 89% enzymatic glucose conversion. Combined 31P and 2D two-dimensional heteronuclear single-quantum coherence NMR (2D HSQC NMR) analyses provide spectroscopic evidence supporting a plausible mechanism in which Lewis-acidic Zn2+ and Brønsted-acidic protons jointly promote β-O-4 cleavage, while ethylene glycol stabilizes reactive intermediates through hydrogen bonding. This synergistic Lewis-Brønsted-solvation mechanism represented a previously unexplored pathway for lignin activation and stabilization in DES media. This cascade design demonstrated a low-cost, high-selectivity, and environmentally benign biorefinery route for bamboo, offering a new paradigm of natural acid-enabled catalytic systems for sustainable lignocellulose fractionation.