Balancing Amine Density and Mesoporosity in Chitosan Cryogels for Multifunctional Water Purification

Achieving efficient removal of chemically diverse water contaminants remains a major challenge for sustainable adsorption technologies. Here, amine-functionalized chitosan cryogel beads with tunable surface chemistry and mesoporosity are developed as biobased adsorbents for pharmaceuticals, nutrient anions, and dyes. Chitosan cryogels were modified with ethanolamine (ETA), triethanolamine (TEA), triethylenetetramine (TETA), and polyethylenimine (PEI), enabling systematic tuning of amine density, surface charge, and pore accessibility. Structural characterization confirmed preserved mesoporosity (3–6 nm) with surface areas of 81–189 m 2 /g, while X-ray photoelectron spectroscopy (XPS) and ζ-potential analyses indicated progressive nitrogen enrichment and increased positive surface charge after functionalization. Adsorption experiments conducted under unified conditions (30 mg/L pollutant, 1 g/L adsorbent, neutral pH) showed enhanced removal of anionic contaminants. PEI- and ETA-modified cryogels achieved >97% removal of Methyl Orange and Reactive Black 5, up to 76% phosphate removal, and 89% ibuprofen uptake. In contrast, TEA-functionalized cryogels exhibited lower performance due to reduced effective charge density and steric hindrance. Adsorption performance was governed by the balance between amine density and accessible mesoporosity, highlighting the importance of preserving pore architecture while enriching surface functionality. This work provides a scalable strategy for designing chitosan-based cryogel adsorbents for water purification.