Adsorption mechanism of polyethyleneimine modified magnetic core–shell Fe(3)O(4)@SiO(2) nanoparticles for anionic dye removal

In this paper, polyethyleneimine modified magnetic core–shell Fe(3)O(4)@SiO(2) nanoparticles (Fe(3)O(4)@SiO(2)/PEI) were innovatively synthesized and investigated using various techniques such as TEM, TGA, FT-IR, XRD, VSM and XPS. The adsorption performance based on the removal of the anionic dyes Methyl orange and Congo red from aqueous solution was studied systematically. The results showed that the adsorption rate of anionic dyes MO and CR increased rapidly then decreased gradually as the pH increased, the adsorption capacity of Fe(3)O(4)@SiO(2)/PEI for MO was better than that for CR, and the maximum adsorption capacity for MO and CR was 231.0 mg g(−1) at pH 4 and 134.6 mg g(−1) at pH 6, respectively. The equilibrium adsorption capacities for MO and CR increased rapidly in the initial 40 min, and reached equilibrium in approximately 180 min, while the adsorption capacity for MB was relative low even negligible, demonstrating the strong adsorptive affinity of Fe(3)O(4)@SiO(2)/PEI toward anionic compounds. Both of the adsorption processes followed the pseudo-second-order kinetics model and the Freundlich isotherm model. The mechanism of adsorption was mainly related to electrostatic attraction and the number of active sites occupied by anionic dyes. This study provides valuable guidance and is an effective method for the removal of anionic dyes from aquatic environments.