Microwave Synthesized Carbon Materials as Low-cost and Efficient Adsorbents for the Removal of Antibiotics in Single and Binary Systems

Carbon materials were prepared from eco-friendly pawpaw seeds and Kaolinite clay using green 'microwave' synthetic methods to give KPZ which was further activated with HCl (A-KPZ). The synthesized materials were employed in the removal of ciprofloxacin and tetracycline from water. Characterisation was carried out using Fourier Transform Infrared Spectroscopy and X-Ray Diffraction which confirmed the successful incorporation of the biomass into the clay. Adsorption performance of KPZ and A-KPZ was investigated with respect to time, solution pH, temperature, adsorbent mass and the presence of co-existing ions. Adsorption was found to be best suited to the Freundlich isotherm followed closely by Brouers-Sotolongo isotherm which shows that the adsorption was of a physical nature on heterogeneous surface sites of the adsorbents. Adsorption capacities were found to be 295, 229, 142 and 88 mg/g for CIP adsorption on KPZ and A-KPZ and TET adsorption on KPZ and A-KPZ, respectively. Intraparticle diffusion model studies showed that film diffusion was not negligible and adsorption mechanism involved both surface film diffusion and intraparticle diffusion. Electrostatic interactions and hydrophobic interactions were observed to significantly affect adsorption at different pH for both ciprofloxacin and tetracycline. An analysis of the production cost of the adsorbents as well as the cost of removal of 1 mg of pollutants shows that they are at least five times cheaper and more sustainable alternatives to activated carbon.