Experimental and computational studies of microwave-assisted watermelon rind – styrene based molecular imprinted polymer for the removal of malachite green from aqueous solution

A microwave-assisted watermelon rind imprinted biosorbent polymer (MAWIMOS) was successfully synthesized and applied as an effective removal of malachite green (MG) dye from wastewater. The successful incorporation of imprinted cavities into the MAWIMOS was confirmed by scanning electron microscopy (SEM), X-ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR). A sequence of adsorption studies was carried out to evaluate the influence of operational parameters such as contact time, initial analyte concentration and temperature on MG removal by the prepared polymer. Equilibrium dye removal was attained within 60 min, giving a % removal of 95.2% at initial MG concentration of 200 mg/L. This value was much higher than 59.3% recorded with non-imprinted polymer (NIP). Thermodynamic studies revealed the spontaneous and exothermic nature of the adsorption process. Kinetic and equilibrium data fitted better to the pseudo-second-order and Freundlich models, respectively. Density functional theory (DFT) study suggested the main interaction mechanism to be by chelation through charge flow from the adsorbent to the MG in solution; and that MG and styrene monomer formed ordered complexes via π−π interactions when the molar ratio between MG and styrene was 1:5. The high quantity of malachite green removed by the MAWIMOS strongly positions the material as an efficient adsorbent for wastewater treatment.