A facile microwave-assisted synthesis of mesoporous hydroxyapatite as an efficient adsorbent for Pb2+ adsorption

This study investigated the potential adsorption ability of microwave-assisted hydroxyapatite (MHAP) for the removal of metal ions (Pb2+) polluted water. The hydroxyapatite composite was synthesized by using CaCl2 and (NH4)(2)HPO4 powders as raw material through simple grinding, and then being assisted with microwave. Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses were applied to characterize the adsorbent sample. Pb2+ adsorption was performed by discussing the effects of various factors, such as initial pH, initial Pb2+ concentration, adsorbent dosage, and contact time. Co-existing ions (Na+ and Ca2+) showed little influence on Pb2+ adsorption, and were absorbed onto MHAP on the contrary. The adsorption kinetics of MHAP was well described by the pseudo-second-order model, and the equilibrium adsorption data showed a high correlation coefficient with the Langmuir isotherm model. Thermodynamically, the adsorption process of Pb2+ onto MHAP was spontaneous, endothermic and favorable in nature as Delta G degrees < 0, Delta H degrees > 0, and Delta S degrees > 0. The maximum adsorption capacity of synthesized MHAP for Pb2+ was 1438.85 mg/g according to the Langmuir adsorption model, significantly higher than many other adsorbents. It suggested that the mesoporous MHAP synthesized in this study was an effective and promising material for Pb2+ removal from aqueous solution.