Excellent Adsorption of Lead (II) and Chromium (VI) from Water Using Zwitterions (−NH₃⁺ and −COO^–) Functionalized Nano Lanthanum Oxide: Kinetic, Isotherm, Thermodynamic, and Surface Mechanism

Zwitterion amino acid l -cysteine functionalized lanthanum oxide nanoparticles ( l -Cyst-La 2 O 3 NPs) have been synthesized for the first time with lanthanum acetate as the precursor, NH 4 OH as the base, and l -cysteine as the in situ functionalized mediator. The typical size of l -Cyst-La 2 O 3 NPs was obtained in the range of 15–20 nm from the TEM technique. A cytotoxicity test of l -Cyst-La 2 O 3 NPs was performed in Raw 264.7 cell lines, which were shown to be highly biocompatible. The point zero charge pH (pH PZC ) of bare and l -Cyst functionalized La 2 O 3 NPs was obtained at pH 6 and 2. The maximum uptake capacities of l -Cyst-La 2 O 3 NPs at temperatures 25–45 °C were obtained as 137–282 mg/g for Pb 2+ and 186–256 mg/g for Cr 6+ . All of these values are much higher than those reported in the literature with other nanomaterials. The presence of −SH, −NH 2, and −COOH functional groups in zwitterion l -cysteine provides multiple binding sites leading to the high adsorption of Pb 2+ and Cr 6+ . Five-cycle desorption studies were successfully performed to regenerate the spent l -Cyst-La 2 O 3 NPs.