Preparation of styrene-based imprinted polymer for the adsorption of hazardous bromocresol green dye: Equilibrium, kinetics and thermodynamics study

In this study, styrene was used as a functional monomer for the production of molecularly imprinted polymer (MIP) via free radical  polymerization method, using bromocresol green dye (BCG) as template. A non-imprinted polymer (NIP), that excluded the template,  was also synthesized. Both polymers were applied for the removal of BCG from aqueous medium. The synthesized polymers were  characterized with Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray powder diffraction spectroscopic  techniques. The effect of operating variables, such as pH, contact time, initial dye concentration and process temperature, on the efficiencies of the polymers in removing the dye were evaluated. Equilibrium time of BCG adsorption onto the  MIP was reached within  40 min, with adsorption capacity of 49.68 mg g-1 . The adsorption process followed the pseudo-second-order kinetic and Freundlich  isotherm models, while chemisorption mechanism was predicted. The adsorption process was spontaneous and exothermic in nature,  with DH values of -140.03 and -25.01 kJ/mol-1 recorded for BCG removal by MIP and NIP, respectively. The styrene-based MIP showed  good mechanical stability, and retained up to about 99% of its adsorption capacity after six sequential cycles of   regeneration.  Comparatively, the MIP (99.81mg g-1 ) performed considerably better than its NIP (59.00 mg g-1 ) analogue in the removal of BCG from  aqueous medium, thus affirming the potentials of the molecular imprinting technique in the production of efficient adsorbents for  adsorption of toxic dyes from industrial effluents.