Alkali-induced “intrinsic redox” system for room-temperature synthesis of carboxylic acid-functionalized cellulose nanocrystals

Abstract

The synthesis of carboxylic acid-functionalized cellulose nanocrystals (CNCs) is frequently constrained by high energy consumption, excessive oxidant usage, and stringent reaction conditions. In this work, we propose an “intrinsic redox” system utilizing alkali-enhanced electron-donating capacity of cellulose to overcome these challenges. By deprotonating its hydroxy groups (pKa ~13), cellulose's electron-donating ability is enhanced, allowing it to serve as both the raw material and a reducing agent for the synthesis of CNCs. Mechanistic studies indicate that alkali-induced deprotonation significantly enhances the electron density of hydroxy groups on the surface of cellulose, resulting in a 579 % increase in the nucleophilicity index. This system facilitates CNC extraction at room temperature within 30 min, with a low oxidant-to-cellulose mass ratio (0.6 g/g) and a high yield of 73.05 ± 1.06 wt%. The resulting CNCs exhibit uniform dimensions (206.2 ± 38.5 nm in length, 11.0 ± 2.1 nm in diameter), high crystallinity (72.2 %), and colloidal stability (ζ = −38.8 mV). With 89.5 % closed-loop reagent recovery and value-added byproduct utilization, our methodology offers an industrially scalable platform for green production of nanocellulose.