Silver nanoparticles (Ag-NPs) are among the most widely used nanoparticles in the world. These nanoparticles are used in various scientific and technological fields, including medical and pharmaceutical sciences, chemical industries, cosmetics production, electronics, energy production, environmental practices, food industry, optics and mechanics. The ever growing use of Ag-NPs increases their concentration in soils and water resources. Several previous studies have focused on the behavior of Ag-NPs in soil, but very little research has been performed on the interaction of Ag-NPs with clays. Study of Ag-NPs sorption on clay minerals is important to eva‎luate the potential of these clays in removing Ag-NPs from polluted waters and to better understand the fate of Ag-NPs in soil and sediment environments. Therefore, this research was conducted to study the kinetics and isotherms of Ag-NPs sorption on bentonite as well as the effect of solution ionic strength and temperature on the Ag-NPs sorption reactions. In this research, PVP-coated Ag-NPs were used as the sorbate and the Mehrjan bentonite was applied as the sorbent. At first, the Mohr's sediment titration was used to determine the amount of Ag ions released from silver nanoparticles during the experiment. The sorption kinetics of Ag-NPs was studied at a constant Ag-NPs concentration of 140 mg/L at eight different reaction times of 0.5, 1, 2, 4, 8, 16, 20 and 24 h. The sorption isotherms were studied in eight different Ag-NPs concentrations (10, 20, 50, 75, 100, 125, 150 and 200 mg/L) at a constant temperature of 25 °C and a reaction time of 6 h. The effect of ionic strength on Ag-NPs sorption by bentonite was studied in three ionic strengths of 0.03, 0.15 and 0.1 at two Ag-NPs concentrations of 75 and 150 mg/L. The effect of temperature on the Ag-NPs sorption was also assessed at two Ag-NPs concentrations of 75 and 150 mg/L at three different temperatures of 15, 25 and 35 °C. All experiments were carried out in three replicates. The results of the dissolution test showed that approximately 1% of the Ag-NPs were dissolved as Ag ions during the experiment time applied in this study. The results of kinetic studies showed that the power function, pseudo-second order and pseudo-first order kinetic models well described the Ag-NPs sorption kinetics by bentonite clay with R2 values of 0.986, 0.982 and 0.965, respectively. Based on the kinetic modeling, the equilibrium time of Ag-NPs sorption by bentonite was determined to be about 6 h. The results of isotherm studies showed that the Toth, Langmuir, Freundlich and Langmuir-Freundlich models were well fitted to the Ag-NPs sorption data, with R2 values of 0.957, 0.956, 0.829 and 0.829, respectively. The capacity of bentonite for Ag-NPs sorption obtained from the Toth, Langmuir and Langmuir-Freundlich isothermal models was 22.24, 20.71 and 18.93 mg/kg, respectively. The removal efficiency of Ag-NPs from water by bentonite was almost 100%, up to the initial concentration of 50 mg/L of these nanoparticles. The results of the effect of ionic strength of solution and temperature on adsorption of Ag-NPs by bentonite clay showed that at ionic strength of 0.03 and temperature of 25 °C, the maximum sorption of Ag-NPs by bentonite clay can be achieved in 6 hours. Results of an energy-dispersive X-ray spectroscopy (EDX) confirmed a uniform distribution of Ag-NPs on the clay surfaces. In conclusion, the results of this study suggest that bentonite can be used as an efficient sorbent to remove Ag-NPs from polluted waters. Key words: Nanomaterials, Clay minerals, Sorption kinetics, Sorption isotherm, Ionic strength, Water treatment.

مهران شيرواني جوزداني

حسين شريعتمداري , جهانگير عابدي كوپائي

حسين خادمي موغاري , جهانگير عابدي كوپائي