Cation doped hydroxyapatite nanoparticles enhance strontium adsorption from aqueous system: A comparative study with and without calcination

The present study reports the synthesis of a biocompatible, eco-friendly, anisotropic cation doped hydroxyapatite nanoparticles (nHAp) for strontium removal from aqueous environment. The nHAp was modified by cation doping, characterized using suitable techniques like Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and, high resolution transmission electron microscopy (HRTEM) attached with selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDAX). nHAp based materials were investigated for its strontium adsorption property with and without calcination. Successful doping of the cations into the nHAp matrix was confirmed by X-ray photoelectron spectroscopy (XPS). The morphology and the particle size of the nHAp varied significantly with cation doping (Na, Mg and Al) and calcination. Calcination of nHAp decreased the dissolution rate when compared to uncalcined nHAp. The biocompatibility and toxicity studies of modified nHAp with human osteoblast (MG63) cell line indicated that the cation doping onto nHAp had considerable impact on its toxicity. In the initial screening studies, Al-nHAp and Mg-nHAp showed higher strontium adsorption percentage of 83.90 ± 3.03 and 70.98 ± 2.74 respectively. The adsorption capacity of the materials was much superior to many of the HAp based materials reported earlier. These studies clearly indicate that the cation doped, degradable (for efficient disposal of adsorbate saturated HAp beyond reuse), eco-friendly nHAp is suitable for removal of strontium from contaminated water.