Tuning the sorption ability of hydroxyapatite/carbon composites for the simultaneous remediation of wastewaters containing organic-inorganic pollutants

In this paper, we report on the rational design, synthesis, characterization, and application of eco-friendly hydroxyapatite/carbon (HAP/C) composites as effective sorbents for the simultaneous remediation of organic-inorganic pollution in wastewaters. Carbon content in composites ranged from ca. 4 to ca. 20 wt%. Structural and morphological features of the composites were studied by N2 adsorption/desorption analyses, electron microscopy (TEM and HAADF-STEM/EDX) and X-ray powder diffraction (XRPD). These features were correlated with the composition and the exposure of surface functional groups. Surface acid-base groups were assessed by liquid-solid acid/base titrations and results depended on the composition ratio of the two components. Batch adsorption tests, performed with various initial concentrations of pollutant species and dosages, proved that composites merged the sorption properties of the two moieties, being able to simultaneously adsorb organic (methylene blue) and inorganic (Cu(II) and Ni(II)) pollutants. On the optimal carbonaceous scaffold content (ca. 8 wt% carbon), kinetic tests revealed that this composite could almost completely remove high concentrations of co-present pollutants, namely, Cu(II), Ni(II), (300 ppm) and methylene blue (250 ppm) in ca. 1 h, with sorbent dosage of 10 g L−1. In addition, leaching tests proved the permanent retention of the hazardous species on the composites.