Efficient removal of pharmaceutical contaminant in wastewater using low-cost zeolite 4A derived from kaolin: Experimental and theoretical studies

Abstract

The present report describes the easy preparation of zeolite 4 A from Cameroonian raw kaolin using a hydrothermal method. Highly crystalline, microporous pure-phase zeolite 4 A with cubic morphology was confirmed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (MAS-NMR), Thermogravimetric analysis and N2 adsorption-desorption. The synthesized zeolite 4 A was applied as an adsorbent for the effective removal of ciprofloxacin in aqueous solution. Subsequent adsorption mechanism and interactions between ciprofloxacin and the surface of zeolite 4 A (001) was studied using density functional theory (DFT) and Monte Carlo molecular simulation. The maximum elimination efficiency by zeolite4A under optimal conditions with a contact time of 80 min, pH = 8, the ciprofloxacin concentration of 60 ppm and with an adsorbent mass of 20 mg at 25 °C was 91.75 %. The adsorption of ciprofloxacin by zeolite 4 A followed the pseudo-second order kinetic model and the Langmuir isotherm. The maximum adsorption capacity (qmax) calculated with the Langmuir model was 87.72 mg/g with a value of the linear regression coefficient R2 of 0.9634. Positive ΔH values suggest an endothermic adsorption reaction. However the negative values for adsorption energy (Eads) and ΔG showed that adsorption was spontaneous. Experimental and theoretical results indicated the predominance of chemisorption during the adsorption. Zeolite 4 A had good stability and recyclability and achieved a high removal efficiency of 85.68 % for ciprofloxacin after seven consecutive adsorption cycles within optimal conditions. Zeolite 4 A could be recommended as an effective adsorbent for the removal of ciprofloxacin from wastewater.