Polyoxometalate-assisted fractionation of larch biomass: Mechanistic into selective lignin extraction and structural...

Efficient and selective extraction of structurally intact lignin from lignocellulosic biomass remains a central challenge in biorefinery research. Here, we develop a polyoxometalate (POM)-assisted strategy for lignin extraction from larch wood powder using a dioxane-based solvent system. Three representative POMs-phosphomolybdic acid (PMA), silicotungstic acid (STA), and phosphotungstic acid (PTA)-were systematically evaluated to elucidate the role of POM type and loading in controlling lignin structure. All three POMs effectively promoted lignin separation, with PMA exhibiting superior performance. At low PMA loading, the extracted lignin retained a high proportion of β-O-4 linkages (74.6%), indicating minimal structural disruption. In contrast, high POM loadings induced extensive cleavage of β-O-4 bonds and condensation reactions, yielding lignin with a markedly higher molecular weight (12,431 g/mol) and reduced β-O-4 content (35.7%). These results reveal a delicate balance between oxidative activity and structural preservation governed by POM type and dosage. This work provides a mechanistic understanding of POM-mediated lignin extraction and establishes a tunable platform for isolating lignin with tailored molecular architectures.