Excellent regeneration, easy separation and high capacity of 3D chitosan-melamine sponge composites for anionic dye removal

Numerous micro/nanoscale powdered adsorbents face the problems of poor reusability and difficult separation, which severely restrict their application in effluent treatment. How to effectively solve these problems is still a challenge. In this study, a chitosan-melamine sponge (CTS-MS) composite (CTS/MS = 3 : 2), as a promising adsorbent material with excellent regeneration, easy separation and high adsorption capacity, was tactfully prepared by crosslinking chitosan with a 3D melamine sponge. The obtained CTS-MS composite was employed to evaluate the adsorption properties towards Orange II (OII) anionic dye in wastewater. The characterization results indicated that the CTS-MS composite possessed macropores inside the sponge, which could facilitate the mass transfer of adsorbates from aqueous solutions, and chitosan was well distributed on the surface of the 3D melamine sponge. The adsorption data for OII demonstrated that the adsorption process could be described by the Sips isotherm model and the pseudo-second-order kinetic model, showing a maximum adsorption capacity of 712 mg g(-1). The entire adsorption process was found to be spontaneous and endothermic in nature. More importantly, the new composite could be directly separated and desorbed effectively, and the adsorption efficiencies still remained over 99.10% after 10 cycles. Under optimal conditions, the adsorption equilibrium could be basically achieved within 10 min (50 mg L-1, 100 mL, dosage 64.4 mg), and it could be almost desorbed within only 10 s, which could facilitate the recycling of both the CTS-MS composite and the OII dyes. Besides, combined with the results of pH, FT-IR spectroscopy and XPS, the adsorption mechanisms were ascribed to the electrostatic attraction and hydrogen bonding between the CTS-MS composite and dye anions. It is believed that the new 3D CTS-MS composite is a very promising adsorbent for dyeing effluents.