Efficient removal of emerging pollutant oxytetracycline by cost-effective biochar–hydroxyapatite composite

Biochar (BC) and hydroxyapatite (HAp) are widely used in environmental remediation due to their high adsorption capacity, porous structure, large specific surface area, chemical stability, non-toxicity, and low solubility. Combining BC and HAp is a green and effective strategy for creating new adsorbents (BCH) that have a synergistic impact on wastewater treatment. In this study, BCH composites derived from apatite ore and macadamia nut shells were synthesized by the wet impregnation method to remove oxytetracycline (OTC) from aqueous solutions. The BC-HAp composite with a ratio of 10:1 (by weight) was the most effective material for removing OTC. The Redlich–Peterson model achieved the highest correlation coefficient among the four models tested (Freundlich, Langmuir, Temkin, and Redlich–Peterson). The maximum adsorption capacity calculated with the Langmuir isotherm was 49.59 mg g−1. It was found that the adsorption process was significantly affected by the solution pH. The bipolar form of the drug was found to be OTC±, and the adsorption was most effective in solutions with a pH of 6. The OTC adsorption dominant mechanisms on nanocomposites could be electrostatic attraction, hydrogen bonding formation, surface complexation, or ion exchange. Therefore, the BCH composite showed great potential for removing OTC pollutants in a cost-effective, and environmentally friendly manner. © 2024 Curtin University and John Wiley & Sons Ltd.