Enhanced fluoride adsorption and regeneration efficiency of cross-linker-free mesoporous hydroxyapatite/chitosan nanocomposites

摘要

The presence of F- ions in water is either a helpful or harmful outcome, contingent upon the concentration level of the pollutant. In this work, hydroxyapatite/chitosan (HAp/CS) nanocomposites were prepared incorporating varying weight percentages of chitosan with HAp, using co-precipitation followed by lyophilization without employing any cross-linking agents for the adsorption of F- ions. An increase in the concentration of chitosan in the HAp matrix significantly enhanced the colloidal stability, F- ion adsorption capacity, and reduced the particle size (length 38 and width 86) when compared to HAp. The respective maximum F- adsorption capacity of HAp/CS1, HAp/CS2, HAp/CS3, and HAp/CS4 nanocomposites were 56 mg/g, 80 mg/g, 82 mg/g, and 100 mg/g at pH 7, which was considerably higher (10 times) than HAp when compared to other existing reports. The adsorption isotherm and kinetics of HAp and HAp/CS nanocomposite adsorbent confirmed the monolayer and strong chemisorption mechanisms. The surface morphology of the adsorbent after adsorption of F- ions changed from rod to sphere along with an increase in particle size, as confirmed by HR-TEM. Moreover, FTIR and XPS analysis revealed the surface interaction between the adsorbent and F- ions through ion exchange and electrostatic interaction, which lead to the formation of fluorapatite. HAp/CS4 showed 2.5 times higher sustainable regeneration efficiency (90 in 30 min) up to 7th cycle than HAp. Furthermore, the solution pH (5-7) of treated water was maintained at neutral pH after fluoride adsorption, rendering the water potable. Hence, these results demonstrate that chitosan plays a significant role in the removal of F- ions and this composite is ideal for F- ion adsorption applications. GRAPHICS .