LAUSR

Abstract In the present study, hydroxyapatite (HAP) nanoparticles were synthesized by a rapid microwave-hydrothermal method using calcium nitrate tetrahydrate and ammonium hydrogen phosphate as starting materials, and used as adsorbents for the removal of Brilliant blue FCF (BBF). The physicochemical properties of the obtained HAP were characterized by BET surface analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Batch adsorption experiments were performed to investigate the effects of various parameters including initial pH, adsorbent dosage, contact time, temperature, ionic strength, and the presence of humic acid on adsorption efficiency. Results showed that HAP nanoparticles possessed a good ability to adsorb BBF. The adsorption process was fast, and it reached a steady state after only 10 minutes. BBF adsorption increased with an increasing amount of adsorbent dosage but decreased as the pH increased. Increasing ionic strength and the presence of humic acid increased the adsorption of BBF by HAP. The adsorption isotherm studies showed that Sips models could fit the experimental data well, and the maximum adsorption capacity was estimated to be 14.51 mg/g. The thermodynamic parameters suggested that the adsorption of BBF on HAP was spontaneous and endothermic in nature. These experimental results demonstrated that such HAP nanoparticles are promising adsorbents for the efficient removal of BBF dye from water. Graphical Abstract