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-La2O3NPs) have been synthesized for the first time with lanthanum acetate as the precursor, NH4OH as the base, and l-cysteine as the in situfunctionalized mediator. The typical size of l-Cyst-La2O3NPs was obtained in the range of 15–20 nm from the TEM technique. A cytotoxicity test of l-Cyst-La2O3NPs was performed in Raw 264.7 cell lines, which were shown to be highly biocompatible. The point zero charge pH (pHPZC) of bare and l-Cyst functionalized La2O3NPs was obtained at pH 6 and 2. The maximum uptake capacities of l-Cyst-La2O3NPs at temperatures 25–45 °C were obtained as 137–282 mg/g for Pb2+and 186–256 mg/g for Cr6+. All of these values are much higher than those reported in the literature with other nanomaterials. The presence of −SH, −NH2, and −COOH functional groups in zwitterion l-cysteine provides multiple binding sites leading to the high adsorption of Pb2+and Cr6+. Five-cycle desorption studies were successfully performed to regenerate the spent l-Cyst-La2O3NPs.