Comparative Evaluation of Copper Adsorption Performance in Nanochitosan-Based Foams Reinforced with Crystalline and Fibrillated Nanocellulose

Abstract Copper (Cu 2+ ) contamination in industrial effluents represents a serious environmental risk, requiring efficient and sustainable adsorbents. In this study, six different nanochitosan-based composite foam formulations were developed and evaluated. These foams were reinforced with two forms of nanocellulose, crystalline (CNC) and fibrillated (CNF), and crosslinked with glutaraldehyde to investigate their structural stability and Cu 2+ adsorption equilibrium. A critical discovery was that non-crosslinked foams suffered from dimensional instability, which physically restricted the diffusion of the metal. On the other hand, crosslinking with glutaraldehyde maintained an open three-dimensional architecture, allowing greater permeation of the aqueous solution and full access to internal binding sites. Analysis of the isotherms revealed complex multiphase behavior. At low equilibrium concentrations (< 160 mg/L), adsorption followed a monolayer profile, with an excellent fit to the Langmuir model. At higher concentrations, a change in adsorption behavior is observed, suggesting the activation of secondary mechanisms in multilayers, followed by agglomeration and precipitation of the metal within the porous structure. The cellulose nanofiber-reinforced crosslinked group (NCSR-CNF) showed the best performance, reaching a maximum monolayer adsorption capacity ( q max ) of 90.3 mg/g. At higher concentrations, the mechanism shifted to multilayer adsorption and subsequent macroscopic precipitation on the surface. Overall, the results demonstrate that the combined effect of CNF reinforcement and covalent crosslinking is critical to overcoming the physical limitations of previous-generation biopolymer foams, providing a highly effective and structurally stable adsorbent for heavy metal remediation.