Facile Hydrothermal Synthesis of Novel Zeolite Nanostructures for the Efficient Removal of Pb(II) and Hg(II) Ions from Aqueous Media

Lead and mercury ions cause severe damage to the kidneys, central nervous system, and immunity. Consequently, nepheline hydrate/sodium aluminum silicate hydroxide hydrate and paragonite-2M1/sodium aluminum silicate hydroxide hydrate novel zeolite adsorbent nanostructures were fabricated using the hydrothermal approach in the absence and presence of a novel Gemini cationic surfactant, respectively. The zeolite adsorbent nanostructures, which were synthesized in the absence and presence of the Gemini cationic surfactant, were abbreviated as ED1 and ED2, respectively. The Gemini cationic surfactant was synthesized by reacting N,N'-(2,2'-(ethane-1,2-diylbis(azanediyl))bis(ethane-2,1-diyl))dinicotinamide with lauryl-2-chloroaetate. Besides, Gemini cationic surfactant acted as a structure directing agent to convert nepheline hydrate/sodium aluminum silicate hydroxide hydrate nanostructures into paragonite-2M1/sodium aluminum silicate hydroxide hydrate nanostructures. After that, the Gemini cationic surfactant has been removed from the nanostructures by calcination at 650 °C for 6 h. The chemical structure of gemini cationic surfactant was confirmed by proton nuclear magnetic resonance (1HNMR) and Fourier-transform infrared spectroscopy (FT-IR). The zeolite adsorbent nanostructures were characterized by field emission scanning electron microscopy (FE-SEM), N2 adsorption/desorption analyzer, X-ray diffraction (XRD), FT-IR, and energy-dispersive X-ray spectroscopy (EDX). The average crystallite size of the ED1 and ED2 samples was 28.15 and 9.78 nm, respectively. The synthesized zeolite nanostructures were employed for the efficient disposal of Hg(II) and Pb(II) ions from aqueous solutions. The maximum removal capacities of the ED1 and ED2 products towards Pb(II) ions are 160.77 and 295.86 mg/g, respectively. In addition, the maximum removal capacities of the ED1 and ED2 products towards Hg(II) ions are 130.89 and 271.00 mg/g, respectively. The adsorption of Hg(II) and Pb(II) ions by the ED1 and ED2 products is exothermic, chemical, spontaneous, and fits well with the Langmuir isotherm and pseudo-2nd-order model. The complete desorption of Hg(II) and Pb(II) ions from the ED1 and ED2 samples was accomplished by 1 M of ethylenediaminetetraacetic acid disodium salt dihydrate solution. Over four consecutive cycles, the removal capacities of the ED1 and ED2 samples remained unchanged, and hence the ED1 and ED2 samples can be utilized multiple times without compromising their efficacy.