FAST REMOVAL OF METHYLENE BLUE FROM AQUEOUS SOLUTION BY ADSORPTION ONTO POORLY CRYSTALLINE HYDROXYAPATITE NANOPARTICLES

A novel poorly crystalline hydroxyapatite (HAP) nanomaterial was developed for methylene blue (MB) removal from aqueous solution. Surface functionality, crystallinity, and morphology of the synthetic adsorbent were characterized and the potential of poorly crystalline HAP nanoparticles for MB removal was evaluated. Results indicated that poorly crystalline HAP nanoparticles possessed good adsorption ability to MB. The adsorption process was fast, and it reached a steady state after only 2 min MB removal was increased with an increasing amount of adsorbent dosage but decreased as the ionic strength increased. It was worth noting that the presence of humic acid significantly promoted the adsorption of MB by poorly crystalline HAP. While the adsorption was favorable at higher pH and lower temperature, and the equilibrium data were well fitted by the Freundlich isotherm. The maximum adsorption capacity was estimated to be 14.27 mg/g. Thermodynamic parameters suggested that the adsorption was a typical physical process, spontaneous, and exothermic in nature. The mechanisms for the adsorption of MB on poorly crystalline HAP may include electrostatic attraction, hydrogen bonding, and Lewis acid-base interaction. Regeneration studies exhibited that HAP could be recyclable for a long term. The obtained results indicated that poorly crystalline HAP nanoparticles can be used as a biocompatible and effective adsorbent to remove MB from water.