Title: Kinetics and equilibrium study of the adsorption of silver ions by polymeric composites containing zeolite and methacrylic acid

Abstract

Environmental and water pollution caused by heavy metals, especially silver, is considered a threat to humans, ecosystem, and all living species. Therefore, with the development of industrialization, it is a very important effort to remove heavy metals from the environment and wastewaters. For this reason, in the present study, we synthesized two polymeric composites of ethylene glycol dimethacrylate (EGDM), methacrylic acid (MA), and different amounts of zeolite (25 g and 50 g) (PMAZ25 and PMAZ50) by using BPO-DMA initiator system at room temperature (298 K). Fourier Transform Infrared (FTIR) was used to show the presence of functional groups in the synthesized composites, and Thermal Gravimetric Analysis (TGA) was used to test the thermal stability of the copolymeric composites. Batch adsorption method was applied to examine the effect of polymeric composites on silver ion adsorption at different pH values, contact time, initial Ag(I) concentrations, and adsorbent dosage. The adsorption process was found to be most efficient at pH 6. When we tested the most commonly used, Langmuir and Freundlich isotherm models, in the adsorption process in this study, both isotherm models fitted well. The monolayer adsorption capacity of poly(EGDM-methacrylic acid-25 g zeolite) (PMAZ25) and poly(EGDM-methacrylic acid-50 g zeolite) (PMAZ50) was found as 0.116 mg/g and 0.139 mg/g respectively. The adsorption data were also used for the Dubinin-Radushkevich (D-R) isotherm model, and the adsorption energies obtained from this model (EPMZA25 = 15.384 kJ/mol, EPMZA50 = 14.72 kJ/mol) indicated that the adsorption of Ag(I) on polymeric composites could be of ion exchange type. The time dependency experiments indicated that the adsorption rate of Ag(I) onto the polymeric composites was quite fast in the first 60 min and reached adsorption equilibrium after 100 min. Some kinetic models such as the Elovich, pseudo-first-order, and pseudo-second-order models were examined to deeply understand the adsorption kinetics. The kinetic data can be well fitted to the pseudo-second order kinetics model.