Synthesis of spherical magnetic calcium modified chitosan micro-particles with excellent adsorption performance for anionic-cationic dyes.

In this present study, spherical magnetic calcium modified chitosan micro-particles (MG-Ca-CMPs) were synthesized by using embedding/cross-linking method and employed as an efficient adsorbent for Orange II (OII) in single system and coexisted with methylene blue (MB) in binary system. The obtained MG-Ca-CMPs were characterized by fourier transform infrared spectrometer, transmission electron microscopy, scanning electron microscope, X-ray diffraction and magnetic property measurement system analyses, which demonstrated that the MG-Ca-CMPs possessed core-shell structure and excellent superparamagnetic property. The adsorption behaviors for OII in single system and coexisted with MB in binary system were systematically studied. Adsorption experiments data showed that MG-Ca-CMPs presented an excellent high affinity to acid dye OII (qmax = 962 mg·g-1) in single system, which followed the Langmuir isotherm model and pseudo-second order kinetics model. Interestingly, MB, hardly adsorbed in acidic solution, had effective adsorption performance (increased from 20 mg·g-1 to 350 mg·g-1) in binary system by MG-Ca-CMPs. This result was attributed to the synergistic effect caused by the positive and negative charge attraction between OII and MB, forming the positive-negative-positive adsorption mechanism. It is believed that MG-Ca-CMPs could be used as a potential adsorbent for the adsorption and separation of coexisting anionic-cationic dyes from dye wastewater.