Selective Adsorption of Gd3+ on a Magnetically Retrievable Imprinted Chitosan/Carbon Nanotube Composite with High Capacity

A novel magnetic imprinting nanotechnology for selective capture of Gd3+ from a mixed solution of rare earth ions was developed by simply adding Gd3+-imprinted chitosan/carbon nanotube nanocomposite (IIP-CS/CNT) and silica-coated magnetite nanoparticle (SiO2@Fe3O4). The IIP-CS/CNT was prepared for the first time via a facile "surface deposition–crosslinking" method, exhibiting a well-defined coating structure. Interestingly, the neighboring IIP-CS/CNT monomers were held together as bundles, like a network, containing abundant interstitial spaces. When IIP-CS/CNT and SiO2@Fe3O4 were dispersed in a mixed solution of rare earth ions, the magnetic SiO2@Fe3O4 submicrospheres would be trapped in or adhere to the IIP-CS/CNT network, leading to the magnetization of IIP-CS/CNT; meanwhile, Gd3+ ions could be selectively captured by the magnetized IIP-CS/CNT. Saturation adsorption capacity for Gd3+ was up to 88 mg g–1 at 303.15 K, which is significantly higher than the Gd3+ adsorption capacities for the reported rare earth ion-imprinted adsorbents over recent years. The selectivity coefficients relative to La3+ and Ce3+ were 3.50 and 2.23, respectively, which are very similar to those found for other reported CS-based imprinted materials. Moreover, the imprinted adsorbents could be easily and rapidly retrieved by an external magnetic field without the need of additional centrifugation or filtration, greatly facilitating the separation process. Test of reusability demonstrated that the magnetized IIP-CS/CNT could be repeatedly used without any significant loss in binding capacity. Overall, this work not only provides new insights into the fabrication of magnetic imprinted CS-based composite, but also highlights its application for selective adsorption toward rare earth ions.