Modification of aluminum–silicate nanoparticles by melamine-based dendrimer l-cysteine methyl esters for adsorptive characteristic of Hg(II) ions from the synthetic and Persian Gulf water

Abstract

l-Cysteine methyl ester-cyanuric-Si/Al (Si/Al@CN@CME) with high adsorption selectivity for Hg(II) ions was synthesized by covalent immobilization of an amino acid on the modified SiO2/Al2O3 mixed oxide nanoparticle. The synthesized nanomaterials were characterized by nuclear magnetic resonance spectrum (1H NMR and 13C NMR), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance UV–vis spectroscopy (DR UV–vis), inductively coupled plasma atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and elemental analysis. Results showed that l-cysteine methyl ester groups were successfully anchored onto the surface of SiO2/Al2O3. Equilibrium and kinetic models for Hg(II) ions sorption was applied by considering the effect of the contact time, initial Hg(II) ions concentrations, effect of temperature, and initial pH. The contact time to attain equilibrium for maximum adsorption was 45min (3079mgg−1). The adsorption of mercury ions has been studied in terms of pseudo-first- and second-order kinetics, and the Freundlich, Langmuir and Langmuir–Freundlich isotherms models have also been used to the equilibrium adsorption data. The adsorption kinetics followed the mechanism of the pseudo-second order equation, confirming chemical sorption as the rate-limiting step of adsorption mechanisms and not involving mass transfer in solution, which was confirmed by techniques of DS UV–vis. The thermodynamic parameters (ΔG, ΔH and ΔS) indicated that the adsorption of Hg(II) ions was feasible, spontaneous and chemically exothermic in nature between 25 and 80°C. The nanoadsorbent showed high reusability due to its high adsorption capacity after 12th adsorption–desorption cycles. The developed adsorbent could also be used to remove the mercury(II) from the real sample (Persian Gulf water).