Synthesis, characterization, and application of nano hydroxyapatite and nanocomposite of hydroxyapatite with granular activated carbon for the removal of Pb2+ from aqueous solutions

Abstract

Synthesis of neat nano hydroxyapatite (HAp) was carried out using wet chemical precipitation methods at low temperature and this resulted rod like HAp nanocrystals with a diameter around 50–80nm and length of about 250nm. Impregnation of nano HAp onto the granular activated carbon (GAC) to prepare hydroxyapatite granular activated carbon nanocomposite (C-HAp) was carried out using in situ synthesis of nano HAp in the presence of GAC. The samples of neat nano HAp and C-HAp composite were characterized using Fourier-Transformed Infrared Spectroscopy (FT-IR), powder X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Detailed adsorption studies of neat nano HAp, C-HAp and neat GAC were conducted for Pb2+ ions at room temperature at different pH levels. The adsorption data for Pb2+ ions was evaluated according to both Langmuir and Freundlich adsorption isotherm models for both neat nano HAp and C-HAp separately at ambient temperature, 298K. The equilibrium adsorption data were fitted well with Langmuir adsorption isotherm for neat nano HAp with an adsorption capacity in the range of 138–83mgg−1. For C-HAp nanocomposite the adsorption data were well fitted with Freundlich model and the calculated adsorption capacity was in the range of 9–14mgg−1. Leaching of Ca2+ ions by neat nano HAp and C-HAp were also analyzed as a function of pH. It was found that the leaching of Ca2+ was high in neat HAp than C-HAp. The leaching of Ca2+ by neat HAp and C-HAp during adsorption of Pb2+ ions were also investigated and revealed the lower percentage of leaching of Ca2+ from the C-HAp nanocomposite when compared to neat nano HAp.