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

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 degrees 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 Delta H values suggest an endothermic adsorption reaction. However the negative values for adsorption energy (Eads) and Delta G 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.