Facile Preparation of Magnetic Chitosan Coprecipitated by Ethanol/NH₃·H₂O for Highly Efficient Removal toward Cr(VI)

The adsorption ability of chitosan (CS) usually decreases with the introduction of magnetic particles, and thus magnetic CS has to be chemically modified further to improve its adsorption performance. Herein, a novel magnetic chitosan composite (Fe₃O₄-CS3) with porous structure and evenly distributed Fe₃O₄ was successfully prepared via the reduction of the solubility of CS by ethanol (physical reaction), and followed the coprecipitation of the mixture of FeCl₃/FeCl₂/CS by ethanol/NH₃·H₂O. Without any modification, its maximum adsorption capacity toward Cr(VI) ions can achieve 242.1 mg/g (≈468.6 mg/g of CS). This significant progress could be ascribed to the very fast precipitate rate of CS due to the decrease in solubility induced by ethanol. Ethanol causes rigorous solidification of CS, so that there is not enough time to densify, resulting in a looser CS matrix with a larger pore size. After adsorption, this Fe₃O₄-CS3 could not only be easily separated but also be effectively regenerated by NaOH solution in a rather wider concentration range, showing great potential in the field of heavy metal wastewater treatment.