Adsorption of malachite green onto Styrene-Methacrylate based molecularly imprinted polymer

Abstract

The adsorption of malachite green (MG) from aqueous medium by non-imprinted and molecularly imprinted styrene/methacrylate polymers was studied. The synthesized materials were characterized by powder X-ray diffraction, Fourier transform infra-red spectroscopy, scanning electron microscopy, and energy dispersive Xray spectroscopy. The effects of initial dye concentration, contact time and temperature on the adsorption  capacity for malachite green were investigated and found to be about 200 g kg^-1 for the imprinted polymer and 44 g kg^-1 for the non-imprinted polymer. The X-ray diffraction peaks at 2θ = 18°, 30° and 42° indicate the crystalline nature of the polymers. Uptake of malachite green increased with rise in contact time and concentration, for both polymers, while decrease in uptake was observed with rise in temperature. The kinetics of the adsorption  of the dye on the imprinted polymer followed the pseudo-second order (R² = 0.97), while that of the non-imprinted polymer followed the pseudo-first order (R²= 0.87). Equilibrium study showed that the Freundlich isotherm better describes the adsorption of the dye on both polymers, indicating a multilayer adsorption. The values of ΔG° indicate the spontaneity and non-spontaneity of the dye removal by the imprinted and nonimprinted polymers respectively. The negative ΔH° and ΔS° for the imprinted polymer signify that the process is exothermic and occurred with decrease in the degree of randomness. Thus, the high quantity of MG adsorbed onto the imprinted polymer indicates the high potential of the use of the imprinting technology in the removal of toxic waste from water.

Keywords: Styrene-methacrylate, Imprinted polymer, Malachite green, Adsorption, Equilibrium