Fabrication of zirconium/chitosan functionalized magnetic carbon nanotubes for enhanced adsorption of alizarin red.

In this study, a composite adsorbent (Zr-CMCNTs) based on modification of magnetic carbon nanotubes (MCNTs) with chitosan (CS) and zirconium oxychloride octahydrate (ZrOCl·8HO) was synthesized and showed excellent adsorption ability for alizarin red (AR) in aqueous solution. The maximum adsorption capacity of Zr-CMCNTs for AR could reach 889 mg·g at 313 K (pH = 3.4). The performance was not significantly affected by the presence of common ions, showing good salt tolerance. The adsorption equilibrium process was consistent with Langmuir, Freundlich, Koble-Corrigan, and Temkin models, suggesting that both monolayer and multilayer adsorption were involved. The adsorption kinetic process was well described by the pseudo-second-order, Elovich and Double constant kinetic models. The thermodynamic parameters calculated confirm the adsorption process to be spontaneous, endothermic and entropy-increasing. Analyses of the underlying mechanism shows that the adsorption process was mainly due to complexation, hydrogen bonding, π-π stacking and electrostatic attraction. The magnetic property enables Zr-CMCNTs to be recovered easily following adsorption. After three desorption and regeneration cycles, the removal rate of AR still reached 60 %, indicating good reusability. Overall, Zr-CMCNTs composite adsorbent shows great potential in dye wastewater treatment.