Synthesis of hierarchical micro-mesoporous LDH/MOF nanocomposite with in situ growth of UiO-66-(NH2)2 MOF on the functionalized NiCo-LDH ultrathin sheets and its application for thallium (I) removal

Abstract

Thallium (TI) is an element which is so highly toxic to mammals called “the element being cursed at birth”. Consequently, the development and use of highly efficient methods for its removal from aqueous environments are of great importance for the environmental scientist. In the present study, a nanocomposite of functionalized layered double hydroxide/metal-organic framework (LDH/MOF) with bimodal micro-mesoporous architecture was prepared by chemical in situ growth of UiO-66-(NH2)2 MOF particles on the surface of Ni50Co50-LDH ultrathin sheets treated with (3-chloropropyl) triethoxysilane by using a facile ultrasonic-assisted hydrothermal treatment. Structural characterization of the synthesized LDH/MOF NC by FESEM, FTIR, XRD, and nitrogen adsorption-desorption techniques confirmed the successful uniform growth of nanosize UiO-66-(NH2)2 MOF particles on the surface of Ni50Co50-LDH ultrathin sheets. The adsorption behavior toward Tl (I) ions on the LDH/MOF NC was evaluated and the influence of important parameters, including initial solution pH, adsorbent amount, initial thallium concentration, solution temperature, and, contact time, on the adsorption efficiency of the adsorbent was investigated. Different isotherm and kinetic models were applied to fit the obtained experimental data in order to evaluate the dominant adsorption mechanism involved in the removal process. Among the isotherm models used, the Langmuir model showed the best fit with experimental data representing a calculated maximum adsorption capacity of 650.0, 677.2, and 711.8 mg g−1 at 293, 303, and 313 K, respectively, under constant conditions (pH=7.0, adsorbent amount=2.0 mg, solution volume=30 mL, contact time=30 min, shaking speed=200 rpm). Thermodynamic adsorption studies were conducted and the results demonstrated that the adsorption of thallium by the synthesized LDH/MOF NC is endothermic (ΔH0=52.780 kJ mol−1) and spontaneous (ΔG0=−33.069 to −38.929 kJ mol−1) with a physicochemical adsorption nature which includes an randomness enhancement at the solid/liquid interface with rising temperature (ΔS0=0.293 kJ mol−1 K−1). Also, the results of regeneration studies revealed that the LDH/MOF NC particles possess acceptable reusability in four cycles.