The present work demonstrates the synthesis of CS/MWCNTs/Fe beads and their ability to adsorb Cr(VI) from polluted water. The CS/MWCNTs/Fe beads were prepared by combining chitosan (CS) and sodium alginate with iron-laden MWCNTs (MWCNTs/Fe). The physicochemical properties of CS/MWCNTs/Fe beads were characterized before and after the adsorption experiments. The outer to inner structural characterization of composite beads shows that the MWCNTs/Fe coated with CS were dispersed inside the alginate beads and were fully loaded with amine, hydroxyl, and carboxyl functional groups. The chromium speciation chemistry combined with the MWCNTs/Fe and CS surface chemistry during both batch and column adsorption experiments rendered pH at 4 to be the optimized condition in which the uptake of Cr(VI) was quantitatively most effective. During the batch operations, we demonstrated that these CS/MWCNTs/Fe beads can achieve a high Cr(VI) removal performance with an optimal mass distribution ratio of CS: MWCNTs/Fe: alginate = 1: 1: 1. The pseudo second-order model showed the finest fit (r2 &gt; 0.99) with experimental data and the intra-particle diffusion model further elucidated that the multiphasic rate-limiting steps included external mass transfer resistance and intra-particle diffusion. The Langmuir isotherm with a maximum adsorption capacity of 119 mg g-1 was attained. The XPS analysis further elucidated the presence of Cr(III) because of Cr(VI) reduction by the possible charge transfer effect of Fe2+/Fe3+ mediated through conductive carbon nanotubes. During the dynamic adsorption process, the maximum breakthrough time (~ 4 hrs) was achieved at a low flow rate (1 mL/min) and the highest bed height (8 cm). The Yoon–Nelson models were found suitable to describe the breakthrough curves under all experimental conditions, while the Adams–Bohart model was applicable only for an initial part of the dynamic behavior of the column. The bed depth service time (BDST) model was also used to predict the service time of the adsorption bed at different outlet concentrations using other flow rates and inlet concentrations to scale up the system. Moreover, the higher selectivity of Cr(VI) adsorption in simulated wastewater during the presence of other heavy metal ions (Cu2+ and Cd2+) and background anion (PO43-) suggests the applicability of CS/MWCNTs/Fe beads in the removal of Cr(VI) from industrial wastewater.

Chitosan-modified iron-laden multi-Walled carbon nanotubes beads for efficient Cr(VI) uptake and conversion

ACS Spring Meeting 2021

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