Catalytic transformation of coconut husk into single-crystal graphite and its application for the removal of antibiotics from wastewater

Abstract

Ciprofloxacin is a top-priority pollutant due to its hazardous effects and frequent detection in the environment. The objective of this study was to examine the adsorption capacity of graphite made from coconut husk (CHG) for the removal of the antibiotic, ciprofloxacin. Analytical techniques were used to characterize the material and the effects of operating conditions on the adsorption behaviour were investigated. In fixed-bed studies, the adsorbent's regeneration capacity was assessed. Maximum removal of ciprofloxacin was obtained at a pH of 10. Kinetic studies revealed that the adsorption was fast and experimental data best fit the pseudo second-order kinetic model (R2 = 0.99). Adsorption was found to follow the predictions of the Sips isotherm model with a maximum adsorption capacity of 124 mg g−1. The fixed bed system reached an adsorption capacity of 79 mg g−1 at saturation time and a mass transfer zone of 2 cm (flow rate of 5 mL min−1, a bed height of 5 cm, and a diameter of 1.9 cm). The Thomas model displayed the best fit to the experimental data (R2>0.9). Furthermore, regeneration studies revealed that after three cycles, CHG can retain up to 70% efficiency. The adsorption mechanism was investigated using desorption kinetic models, which supported the predictions that adsorption occurred via multilayer adsorption on heterogeneous active sites. The results obtained show that this adsorbent has the potential for the efficient removal of ciprofloxacin from aqueous solution on an industrial scale.