Cross-Linked Chitosan-Grafting Modification Improves the Adsorption and Removal Capacity of Cellulose Acetate Membrane for Urea in Diafiltration

To improve the urea adsorption and removal capacity of cellulose acetate (CA) biobased membranes in diafiltration, this study targeted the weak urea adsorption capacity of CA membranes by modifying the surface of carboxylated CA membranes with dialdehyde cellulose (DAC) cross-linked chitosan (CS). Characterization and testing results showed that the surface and structural changes in the modified CA membranes improved their hydrophilicity and mechanical properties. Increasing the amount of DAC cross-linker promoted the CS grafting and the formation of a cross-linked network, leading to enhanced urea adsorption and removal during diafiltration through hydrogen bonding and ion–dipole interactions. Kinetic studies demonstrated that the increase in spontaneous urea adsorption on CA membranes was temperature dependent, with the adsorption rate being proportional to the CS grafting amount. The adsorption and removal process was controlled by mass transfer, characterized by rapid surface accumulation and slow diffusion within the membrane. This study demonstrates that cross-linked CS grafting plays a significant role in enhancing urea adsorption and removal in diafiltration using CA membranes.