Simultaneous removal of mercury ions and cationic and anionic dyes from aqueous solution using epichlorohydrin cross-linked chitosan @ magnetic Fe3O4/activated carbon nanocomposite as an adsorbent

An economical epichlorohydrin cross-linked chitosan @ magnetic Fe3O4/activated carbon nanocomposite, CH-EP@Fe3O4/AC, was successfully synthesized and used as a suitable adsorbent material for removal of a triphenylmethane cationic dye, Malachite green (MG), an anionic dye, Reactive red 120 (RR120), and Mercury ions (Hg2+) from aqueous solution. The prepared adsorbent has been characterized with Fourier transform infrared spectroscopy, X-ray diffraction, Scanning electron microscopy, Thermogravimetric analysis, Brunauer-Emmett-Teller analysis as well as Vibrating sample magnetometer. According to the result of Brunauer-Emmett-Teller isotherm, the prepared adsorbent has a specific surface area of 287 m(2)/g, which offers relatively high adsorption capacity for the dyes and heavy metal ions. The Box-Behnken design was employed to assist in the tuning of optimum adsorption conditions, such as dosage of adsorbent, solution pH and contact time. Under optimized conditions, kinetics results exhibited that the adsorption well fitted the pseudo-second-order model. The Langmuir isotherms fitted well with experimental data of Hg2+, MG and RR120 in single component solutions, which demonstrates adsorption is along with monolayer process. Also, the experimental data for adsorption of pollutants in binary and multicomponent solutions exhibited best fit with Freundlich model, which shows multilayer adsorption on the surface of the CH-EP@Fe3O4/AC adsorbent. The efficiency of removal towards Hg2+ ions in multicomponent solution (Hg2+/MG + RR120) exceeds 88% and the maximum adsorption capacity is 166.6 mg/g. In addition, the removal efficiency of towards MG in multicomponent solution (MG/RR120 + Hg2+) is about 81% with the maximum adsorption capacity of 146.3 mg/g and the removal efficiency and the maximum adsorption capacity of RR120 in that solution is 78% and 140.7 mg/g, respectively. Also, thermodynamic studies demonstrate that the adsorption of pollutants was spontaneous, that follow an endothermic way with an enhance in entropy. It was observed that the prepared adsorbent was stable after five runs of adsorption-desorption. Therefore, it was concluded that the prepared nanocomposite is a potential applicant for the adsorption of dyes and heavy metal ions from mixed aqueous solution.