Reed biochar supported hydroxyapatite nanocomposite: Characterization and reactivity for methylene blue removal from aqueous media

Adsorption ability of nanoscale hydroxyapatite (HAP) is compromised by aggregation of HAP particles. In this study, reed derived biochar (BC) was used as a supporting material to stabilize HAP to enhance the Methylene blue (MB) elimination from aqueous media, while the BC-supported HAP (BC-HAP) was synthesized by precipitating the nanoscale HAP on BC surfaces. Characteristics of BC-HAP and its roles in MB adsorption were systematically investigated in the lab. Results showed that HAP was well dispersed on the BC, and aggregation was dramatically reduced. The BC-HAP composite exhibited much higher surface area, pore volume, and superior adsorption ability than virgin BC or HAP, which was ascribed to the enhancement of colloidal stability and surface area, as well as reactivity of BC-HAP. MB adsorption amount was raised with an increasing in solution pH and temperature, while decreased with increasing ionic strength. Meanwhile, the addition of humic acid could improve MB adsorption by BC-HAP, and the equilibrium adsorption data and adsorption kinetics followed the Freundlich isotherm model and the Elovich kinetic model, respectively. Adsorption mechanisms of MB on BC-HAP might be governed by electrostatic attraction, hydrogen-bonding, Lewis acid-base interaction, and π-π dispersion interaction. Therefore, the BC-HAP nanocomposite could be an effective and promising adsorbent for MB removal from aqueous media owing to its high efficiency and excellent reusability.