Chitosan functionalized iron nanosheet for enhanced removal of As(III) and Sb(III): Synergistic effect and mechanism

Neutral trivalent arsenic (As(III)) and antimony (Sb(III)) species are more toxic and harder to remove from wastewater environment than their pentavalent counterparts. Herein, a natural polysaccharide chitosan (CS) functionalized iron nanosheet using an in-situ doping method was designed, aiming to attract As(III) and Sb(III) from aqueous solution. The surface area of the optimum sample was 111.8 cm2/g, a good dispersion of the iron nanocomposite was observed by the TEM and element mapping characterization. In the batch adsorption experiment the factors of doping contents of CS and solution properties (pH, co-existing anions and humic acid) were studied systematically. The result showed that 0.5 wt% CS functionalized iron nanosheet had higher removal capacity, affinity, selectivity and reusability for Sb(III) than As(III). The optimum adsorption were achieved at the adsorbent dosage of 0.4 g/L at a wide pH values, and the maximum adsorption capacity were 108.6 and 138.8 mg/g for As(III) and Sb(III) calculated from Langmuir non-linear fitting, respectively. Both As(III) and Sb(III) removal were independent on pH values, indicating electrostatic attraction was not the dominate removal mechanism. The detailed removal mechanism was confirmed by a synergetic interaction of As-Fe/Sb-Fe complexes and hydrogen bonding using the combined characterization of FTIR and XPS spectra. This study demonstrated that the CS functionalized iron nanosheet with the properties of environmental friendly, low-cost and facile preparation could have potential applications in water purification.