One-Step Solvent-Free Fe-Complex Catalyzed Bioinspired Oxidation of Lignocellulosic Biomass to Cellulose Nanospheres

Abstract

Lignocellulosic biomass, the most abundant natural biopolymer, is often regarded as agricultural waste, contributing to environmental pollution. Several reports have demonstrated its use for generating nanocellulosic materials using multistep harsh treatments involving strong acids and bases, generating incalcitrant liquid and solid waste that harms the environment. To address these challenges and efficiently utilize bioresources, we present a single-step, solvent-free approach to convert lignocellulosic biomass into water-dispersible carboxylate-functionalized cellulose nanospheres (CNSs). This method employs an ecofriendly catalyst, (Et4N)2[Fe-(Ph,Me)bTAML] (1), and sodium percarbonate as the oxidant. The catalyst mimics the dual functions of Lytic Polysaccharide Monooxygenase (LPMO) and lignin peroxidase, enabling the efficient breakdown of biomass into cellulose nanospheres without producing harmful byproducts. The reaction mechanism, validated using glucose and cellobiose as model compounds, follows a pathway similar to LPMO, unlike TEMPO-mediated oxidation. The study of the morphological and compositional transformation of corncob microfiber into nanospherical structures reveals that lignin initially oxidizes into smaller, water-soluble fragments, enabling the subsequent transformation of cellulose fibers into dispersible nanospheres. Ecotoxicological assessments confirmed that CNSs and related byproducts are nontoxic and environmentally safe. Furthermore, due to their superior surface activity, CNSs were explored as stabilizers for O/W Pickering emulsions and as environment-friendly alternatives to commercial detergents.