Adsorption behavior and mechanisms of the emerging antibiotic pollutant norfloxacin on eco-friendly and low-cost hydroxyapatite: Integrated experimental and response surface methodology optimized adsorption process

In this study, hydroxyapatite derived from bovine bone (nat-HAp) was used to remove norfloxacin antibiotic (NOR) from an aqueous solution. The nat-HAp properties were interpreted by analysis of the structure, specific surface area, functional groups, morphology, and composition. The pseudo-second-order kinetic and Langmuir isotherm suit the experimental data on NOR adsorption very well. Maximum absorption was shown to be 166.01 mg g-1. Using a response surface methodology (RSM), the highest NOR elimination of 96.20 % was obtained under optimum conditions: NOR of 132.57 mg L-1, pH of 7.88, nat-HAp dose of 0.99 g L-1, and temperature of 25.06 degrees C. Thermodynamic studies demonstrated that the adsorption process was favorable, spontaneous, and exothermic. The value of standard enthalpy change (Delta H0) shows that physisorption controlled the adsorption, and for this purpose, a viable mechanism for the adsorption of NOR onto nat-HAp was suggested. Based on the reusability experiment, the nat-HAp remained stable after four cycling runs. These results show that nat-HAp effectively absorbed NOR and might be a cost-effective alternative adsorbent to eliminate fluoroquinolone antibiotics during wastewater treatment.