Kinetic study on urea uptake with chitosan based sorbent materials

A one-pot kinetic uptake study of urea in aqueous solution with various chitosan sorbent materials such as pristine chitosan, cross-linked chitosan with glutaraldehyde from low (C-1) to higher (C-2) glutaraldehyde content, and a Cu(II) complex of a glutaraldehyde cross-linked chitosan material (C-3) is reported herein. The kinetic uptake profiles were analyzed by the pseudo-first order (PFO) and pseudo-second-order (PSO) models, respectively. The uptake rate constant of urea and the sorption capacity (qe) of high molecular weight (HMW) chitosan, C-1, C-2, and C-3 were best described by the PFO model. The uptake rate constant of urea with the various sorbents is listed in ascending order: HMW chitosan < C-1 < C-2 ≈ C-3. The qe values (mg urea/g sorbent) for the sorbent/urea systems are listed in ascending order: HMW chitosan (48.1) ≈ C-1 (44.7) < C-2 (51.3) < C-3 (66.4 mg/g), revealing good agreement with uptake values obtained independently at equilibrium conditions. Cross-linked chitosan displays relatively rapid urea uptake and greater adsorption capacity when compared with pristine chitosan. The observed trends are in agreement with the greater surface accessibility and pore structure properties of cross-linked chitosan based on scanning electron microscopy studies. These results further illustrate the rational design of chitosan-based materials for the controlled uptake of urea in aquatic environments.