Heterogeneous carbon/apatite composite adsorbent: cooperative ciprofloxacin adsorption

This work aimed to evaluate the removal of ciprofloxacin (CIP) from aqueous solutions by adsorption onto a carbon/apatite composite (CApC) produced from fish scales. Initially, the adsorption of CIP was analyzed at different pH values, identifying pH 8 as the optimal condition (q_max = 79.09 mg g^-1-experimental). Subsequently, kinetics and equilibrium studies were conducted in a batch system. The CApC material was characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and separate adsorption tests of its carbonaceous and inorganic phases. The kinetic data were described using the pseudo-first-order model with two sites and diffusion in the pores, indicating limitation in the transport of the molecule. The Langmuir-Dubinin Radushkevich model (L-DR) provided the best fit to the data and predicted a total capacity of q_maxL-DR = 84 mg g^-1, suggesting monolayer surface adsorption followed by micropore filling. Moreover, the adsorption mechanism is controlled by both surface-chemical interactions (i.e., hydrogen bonding and π-π stacking) and textural properties, wherein a tailored micropores size allows the "pore filling effect" retention mechanism for the CIP molecule. In general, the CApC adsorbent material showed efficiency and desirable characteristics for the treatment of water contaminated with the CIP drug.