Comparative evaluation of biogenic hydroxyapatite derived from fish bones and synthetic hydroxyapatite for the removal of flucloxacillin sodium.

In this work, a comparative study of the adsorption of flucloxacillin sodium (FLCX-Na) from aqueous solution onto synthetic hydroxyapatite (Syn-CaHAp) and biogenic hydroxyapatite from fish bones (B-CaHAp) is reported. The adsorbents were prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric/differential thermal analysis (TGA/DTA), scanning electron microscopy coupled with energy-dispersive (SEM-EDS) and Transmission electron microscopy (TEM). The characterization results revealed that B-CaHAp possesses calcium-deficient carbonate-substituted apatite structure with heterogeneous morphology and higher density of accessible adsorption sites. Batch adsorption experiments indicated that the adsorbent dosage, contact time, initial concentration, and pH of the solution had a significant effect on the adsorption performance. The maximum experimental adsorption capacities of Syn-CaHAp and B-CaHAp were 15 and 26 mg·g- 1 with removal efficiencies of 62 and 77%, respectively, indicating the excellent adsorption performance of the biogenic material. The kinetic analysis showed that the adsorption process followed the pseudo-second-order model for both adsorbents. The equilibrium data were better fitted to the nonlinear Langmuir isotherm indicating that the monolayer adsorption was predominant under the studied conditions. The combined experimental and theoretical analyses imply that the adsorption of FLCX-Na occurs via specific interactions involving electrostatic attraction, hydrogen bonding and coordination between the functional groups of FLCX-Na and the calcium active sites of hydroxyapatite. Response surface methodology (RSM) indicated that the optimum conditions were approximately 0.10 g of adsorbent dosage, 25 mg·L- 1 of initial concentration, pH 6.5 and 160 min of contact time, yielding 83% maximum removal efficiency and approximately 20.8 mg·g- 1 of adsorption capacity. Additionally, B-CaHAp displayed high adsorption efficiency with rising NaCl concentrations, indicating its applicability in saline aqueous environments and its good tolerance to ionic strength. Furthermore, the regeneration experiments demonstrated that the adsorbent could retain ~ 92% of the initial adsorption capacity after five adsorption-desorption cycles with a slight decrease in removal efficiency from 83.0 to 76.1%, showing the excellent operational stability and reusability of the adsorbent. Finally, these results showed the great potential of B-CaHAp as an efficient, sustainable and reusable adsorbent for the removal of pharmaceutical contaminants from aqueous media.