Adsorption of Bromocresol Green Dye on Onion Skin-based Molecularly Imprinted Polymers: Kinetics, Equilibrium, Thermodynamics Studies and DFT Simulation

Abstract

This research focuses on the sequestration of Bromocresol green dye (BCGD), an anionic dye, from aqueous medium using onion skin-based molecularly imprinted polymer (OSMIP). The OSMIP was prepared using distilled water as porogen, BCGD as template, divinyl benzene as crosslinker, styrene as functional monomer, and benzoyl peroxide as initiator; while with the non-imprinted analogue (OSNIP) was similarly prepared, but with the exclusion of BCGD. The imprinted polymers were characterized by scanning electron microscopy coupled with energy dispersive x-ray (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and Thermogravimetry analysis (TGA). The characterization results indicated a successful cavity imprinting and higher thermal stability of OSMIP when compared with OSNIP. The integrity of the polymer material was also observed to be maintained. Batch experimental method was adopted for the adsorption process. OSMIP demonstrated a significantly higher BCGD removal efficiency, compared to OSNIP, possibly due to the imprinted cavities on the polymer. A dye removal efficiency of 99.8% was attained at an initial dye concentration of 25 mg L^-1 and  for OSMIP. Kinetic data were well described by the pseudo-second-order model, while equilibrium data best fitted the Langmuir isotherm. Maximum adsorption capacity of 86.96 mg g^-1 was obtained.  OSMIP reusability study showed appreciable efficiency up to ten consecutive adsorption/desorption cycles, with a minimal loss in efficiency of just 7.4%. The density functional theory analysis provided support for the experimental findings, indicating the high potential of OSMIP in removing organic dyes from real textile wastewater.