Fabrication of chitosan/PAA multilayer onto magnetic microspheres by LbL method for removal of dyes

• A novel magnetic adsorbent (Na-(CS/PAA)n/MPC) was prepared by LbL method.
• This adsorbent exhibits high loading capacity for removal of cationic dyes.
• The uptake capacity increases linearly with the number of coated (CS/PAA) bilayer.
• The adsorption behavior is endothermic monolayer chemisorptions.
• This adsorbent shows excellent reusability and good magnetic separability.

A novel magnetic adsorbent (Na-(CS/PAA)n/MPC) was a deprotonated product of (CS/PAA)n/MPC, which was synthesized by fabrication of chitosan/polyacrylic acid (CS/PAA) multilayer onto magnetic Fe3O4 microspheres via LbL method. (CS/PAA)n/MPC and Na-(CS/PAA)n/MPC were characterized by SEM, FTIR, XRD, TGA and VSM, and then applied in adsorption of two kinds of cationic dyes, methylene blue (MB) and crystal violet (CV). The result revealed that the uptake capacity of MB and CV on Na-(CS/PAA)n/MPC increased linearly with the number of coated (CS/PAA) bilayer. In addition, as one of represents of Na-(CS/PAA)n/MPC, the adsorption kinetics for Na-(CS/PAA)4/MPC followed the mechanism of the pseudo-second order kinetic model, and its equilibrium data were fitted with the Langmuir isothermal model well, which suggest that the adsorption mechanism is a homogeneous monolayer chemisorptions process. The maximum adsorption capacity of Na-(CS/PAA)4/MPC was found to be 305.8 and 243.6 mg g−1 for MB and CV at pH 8 (25 °C), respectively. Moreover, the adsorption process of Na-(CS/PAA)4/MPC was endothermic nature, and further recycle experiments showed that there was almost no loss in the adsorption capacity of Na-(CS/PAA)4/MPC for cationic dyes after 5 times reuse. All the results suggest that Na-(CS/PAA)4/MPC could be a potential recyclable magnetic adsorbent in the practical wastewater treatment.