Preparation of Quaternary Ammonium-Functionalized Chitosan Adsorbent: For the Removal of Reducing Sugar Alkaline Degradation Products

Decolorization is critical in sugar refining, where reducing sugar alkaline degradation products (RSADPs) constitute major colorants. Conventional decolorants face limitations including non-renewability, high cost, and narrow applicability. This study developed quaternary ammonium-functionalized chitosan adsorbents (QA) as high-performance and cost-effective alternatives. QA was synthesized via (3-chloro-2-hydroxypropyl) trimethylammonium chloride modification, followed by chemical cross-linking with glutaraldehyde and freeze-drying. QA displayed a more intricate surface morphology with rougher pore walls, while increasing quaternary ammonium-functionalized chitosan (QACS) content contributed to the preservation of the porous framework. Additionally, QA exhibited a stable positive charge (pH 3–11) and industrial-grade thermal stability. Compared to the unmodified chitosan adsorbent, QA exhibited superior adsorption performance and maintained pH-independent functionality, with adsorption capacity increasing with rising QACS content. QA 5 (with 5 wt.% quaternary ammonium-functionalized chitosan) performed optimally, achieving 95.9% RSADPs removal with 172.6 mg/g equilibrium capacity (theoretical max of 287.7 mg/g) and > 15% higher efficiency than unmodified adsorbent. The adsorption kinetics followed the pseudo-second-order model (chemisorption-dominated), and the isotherms fitted the Freundlich model, indicating multilayer heterogeneous adsorption. The QA thus provides an efficient, eco-friendly solution with broad pH tolerance for industrial sugar decolorization.