Recovery of lanthanum cations by functionalized magnetic multi-walled carbon nanotube bundles

Rare-earth elements (REE), including La, are critical raw materials in many technological advancements. Collection of physically adsorbed REEs on clay minerals can be realized first by ion-exchange leaching, followed by adsorption enrichment. Ever increasing demand and limited resources of REEs have fueled the development of nanostructured adsorbents. In this paper, multi-walled carbon nanotubes (MWCNTs) were purified using concentrated H₂SO₄ and HNO₃, then coupled with magnetic Fe₃O₄ nanoparticles to make low concentration La ion extraction from water possible. The MWCNT@Fe₃O₄ composites were further crosslinked with 0.1 wt% epichlorohydrin and functionalized with 0.5 wt% carbon disulfide to achieve a La³⁺ adsorption capacity of 23.23 mg g^-1. We fully probed the morphology, crystallinity, chemical composition, and magnetic properties of the as-prepared adsorbent by scanning/transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, vibrating-sample magnetometry, and thermal gravimetry. These results indicated that the MWCNT@Fe₃O₄ nanohybrid may be a promising candidate for recovering La ions from aqueous solutions.