Sustainable Chitosan-Based Biopolymeric Aerogels Reinforced with Activated Carbon, Biochar, Magnesium Oxide and Nanolignin as Bioderived Additives for High-Performance Green Water Sorbents

Abstract

Sustainable biopolymer aerogels based on chitosan (CS) combined with carboxymethyl cellulose (CMC) or dextran (Dex) were successfully reinforced with bioderived additives as activated carbon (AC), biochar (BC), magnesium oxide (MgO), and nanolignin (nLG) to develop high-performance green sorbents. FTIR analysis confirmed effective cross-linking, with glutaraldehyde (GLA) forming Schiff base (C═N) linkages via amino groups, while epichlorohydrin (ECH) reacted with hydroxyl groups to generate ether bridges, resulting in a more compact network. All aerogels exhibited predominantly amorphous structures, as confirmed by XRD analysis. Additionally, SEM images demonstrated hierarchical porous architectures, and the highest porosity was observed for CS/CMC/AC0.5-GLA (96.35%), while increased cross-linking reduced pore size to 57–70 μm in CS/Dex/BC2-GLA. Aerogel densities ranged from 0.052 to 0.23 g cm–3, with low-filler compositions showing the lowest values. Exceptional water sorption was achieved for CS/CMC/AC0.5-GLA (3440% at 10 min), attributed to multiscale porosity and heteroatom-rich AC surfaces, whereas ECH-cross-linked samples exhibited lower water sorption capacity but superior structural stability (e.g., CS/Dex/BC0.5-ECH: 971% at 1440 min). The measured thermal conductivity values are close to those of silicate aerogels, i.e., approaching the thermal conductivity of air (approximately 0.026 W m–1 K–1), measured under identical conditions, particularly for CS/Dex/BC composites, confirming excellent insulation performance. AC incorporation slightly increased λ (0.045–0.06 W m–1 K–1). Diffuse reflectance spectroscopy indicated strong visible absorption due to carbon additives and π–π transitions, suggesting enhanced surface functionality. Overall, low-content bioadditive incorporation combined with optimized cross-linking yielded lightweight, highly porous, thermally insulating stable aerogels with enhanced water sorption capacity for sustainable sorption applications.