A Biocompatible Nanodendrimer for Efficient Adsorption and Reduction of Hg(II)

Mercury is a neurotoxic metal at very low concentrations and can lead to severe human health problems. In this work, we synthesized a novel heterogeneous dendrimer for the elimination and reduction of Hg­(II) from H2O using SiO2–Al2O3 nanoparticles individually grafted with l-cysteine methyl ester (LCME), triazine, and diethylenetriamine. Applying Freundlich, Langmuir, and Sips isotherm equilibrium along with the pseudo-first-order (PFO), and pseudo-second-order (PSO) kinetic models, we studied how the nanobiodendrimer’s Hg­(II) adsorption was affected by various parameters, like initial amount of Hg­(II), adsorbent dosage, reaction time, solution temperature, interfering ions, and initial pH. Our results concluded that only 10 min of reaction time was needed to attain equilibrium (2639 mg g–1). The uptake kinetics also indicated the mechanism of adsorption is according to a PSO model, proving that the rate-confining stage of the Hg­(II) ion uptake is chemical adsorption. Thermodynamic parameters (ΔG, ΔS, and ΔH) concluded from the van’t Hoff model demonstrated that the uptake of the toxic metal was exothermic, spontaneous, and feasible in nature. The nanodendrimer containing LCME demonstrated high reusability, with high adsorption capacity after eight adsorption–desorption periods. We also showed how the nanobiodendrimer could adsorb mercury ions from a real source of water (Cayuga Lake), even after three cycles of use. Finally, we explored the chemical removal mechanism of Hg­(II) by the LCME using several techniques, including infrared spectroscopy, energy dispersive X-ray spectroscopy (EDX), zeta potential, diffuse reflectance ultraviolet–visible (DRUV–vis), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), demonstrating that Hg­(II) were converted to metallic Hg(0) after adsorption on the nanobiodendrimer.