Amidoxime Modified Polymers of Intrinsic Microporosity (PIM-1); A Versatile Adsorbent for Efficient Removal of Charged Dyes; Equilibrium, Kinetic and Thermodynamic Studies

Abstract

Polymers of Intrinsic Microporosity (PIMs) are recognized as promising polymers for active separation of organic pollutants. These highly porous and solution-processable polymers could be tailored to remove specific targets from an aqueous system. In this study, PIM-1 powder was modified to amidoxime PIM-1 powder and adsorption of charged dyes which are Methylene Blue (MB, cationic) and Methyl Orange (MO, anionic) from an aqueous system was explored to evaluate the influence of contact time, initial concentration, solution pH and temperature on the removal of dyes. The adsorption reached the equilibrium within three hours in a batch adsorption process for both dyes. Experimental adsorption capacity (q(e, exp)) of Amidoxime PIM-1 was found as 79.8 mg g(-1) and 69.8 mg g(-1) for MO and MB, respectively at pH 6 and 298 K. The Amidoxime PIM-1 was also able to remove a mixture of anionic and cationic dyes simultaneously from aqueous system. The removal ability is dependent on the solution pH and the selectivity can be tuned by shifting solution pH such as at low pH (pH 3) anionic dye adsorption is more favourable, while at high pH (pH 10) cationic dye adsorption is preferable. Equilibrium data acquired from batch adsorption experiments have been examined by four two-parameter (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich), four three-parameter (Redlich-Peterson, Sips, Khan and Liu) isotherm models, and by kinetic models such as the pseudo-first-order, the pseudo-second-order, Elovich equation and intraparticle diffusion using non-linear regression technique. Combination of several errors analysis techniques was applied to find the best fitting isotherm and kinetic models. Liu isotherm was the best to define the experimental data and the maximum adsorption capacities (q(m)) were calculated as 86.7 mg g(-1) and 81.3 mg g(-1) for MO and MB, respectively at pH 6 and 298 K. Adsorption data have the best consistency with the pseudo-second-order kinetic model. Furthermore, thermodynamic parameters were determined and the experiments suggested that the adsorption of MB and MO onto Amidoxime PIM-1 is a physical, spontaneous and exothermic. Graphic