Removal of Pb(II) from Aqueous Solutions by Adsorption Using Nano Mesoporous Silica MCF Adsorbent: Kinetic, Thermodynamic, Isotherm and Equilibrium Studies

Abstract

Introduction: Pb2+ is a very toxic heavy metal and its pollution to environment is very harmful and to remove its pollution is a very important issue. Methods: In this work, nano Mesocellular Foams (MCF) silica material was synthesized by hydrothermal method in this research. Power X-ray diffraction and scanning electron miccroscopy, etc. were used to characterize the sample. In this paper, the adsorption of heavy metal ion Pb2+ by MCF was studied. Results: The sample showed spherical particles and the morphology was regular. Its average particle diameter was 2.2 μm. Transmission electron microscopic result showed that the structure of the MCF synthesized has honeycomb structure pore channels which are benefitial for adsorbing heavy metal ions. The nitrogen adsorption-desorption experimental results at low temperature of 77 K showed that the adsorption pore diameter of the MCF synthesized was 19.62 nm. The research results showed that when pH value was 4.5, temperature was 25 ± 1°C, the adsorbent material MCF was 0.2000 g:Pb2+ = 5 and the contact time was 40 min, the adsorption effect was the best and the adsorption rate reached 97.16 ± 0.03%, while the adsorption capacity reached 194.32 ± 0.13 mg/g. Conclusion: By studying, it has been found that the adsorption belongs to the quasi-second-order kinetic model, simultaneously, it also fits the Freundlich equation and in accordance with heterogeneous adsorption. The results of adsorption thermodynamics showed that when temperature is 25 ~ 45°C, the adsorption is a spontaneous exothermic reaction, ΔG° is less than zero, the adsorption enthalpy ΔH° is -31.856 kJ/mol and the adsorption entropy change ΔS° is -45.092 J/(mol·K).