Preparation of fibrous chitosan/sodium alginate composite foams for the adsorption of cationic and anionic dyes

Highlights: • Fibrous chitosan/sodium alginate composite foam was prepared by lyophilization method. • Ternary acetic acid/water/tetrahydrofuran solvents was used. • The amphoteric adsorbent could effectively remove anionic and cationic dyes. • The excellent adsorption capacity is due to the interconnective pores and microscale fibers. Natural polysaccharide is attractive for preparing the environmentally friendly and highly efficient adsorbent. However, to obtain an efficient amphoteric absorbent for dealing with complex wastewater is still challenging. Herein, fibrous chitosan/sodium alginate composite foams were prepared by lyophilization with ternary acetic acid/water/tetrahydrofuran solvents, which had suitable morphology of interconnected pores and microscale fibers for dye adsorption. The amphoteric composite foams showed high adsorption capacities for both anionic Acid Black-172 (817.0 mg/g) and cationic Methylene Blue (1488.1 mg/g), which were far superior to those of the control samples prepared with traditional solvents of acetic acid/water. The adsorption kinetics and isotherm data showed that the adsorption followed the pseudo-second-order and Langmuir model. Further thermodynamics analysis revealed the adsorption was a spontaneous process. Meanwhile, the foams achieved effective adsorption capacity of AB-172 and MB dyes under a wide range of environmental pH, and maintained high adsorption efficiency even after four cycles. The adsorption mechanism is chemisorption, where the adsorption capacities for the anionic and cationic dyes were dependent on the mass ratio of chitosan to sodium alginate. As a novel amphoteric adsorbent, the fibrous chitosan/sodium alginate composite foam shows the potential to remove both cationic and anionic dyes from wastewaters.