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

Abstract

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 adsorption of F − ions. Increase in the concentration of chitosan with HAp matrix signi cantly enhanced the colloidal stability, F − ions adsorption capacity and reduced the particle size (length 38% and width 86%) compared to HAp. The maximum F − adsorption capacity of HAp/CS1, HAp/CS2, and HAp/CS4 nanocomposites are 56 mg/g, 80 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 con rm the monolayer and strong chemisorption. After adsorption of F − ions, the surface morphology of adsorbent changed from rod to sphere along with an increase in particle size, as con rmed by HR-TEM. Moreover, FTIR and XPS analysis revealed the surface interaction between adsorbent and F − ions through ion exchange and electrostatic interaction, which lead to formation of uorapatite. HAp/CS4 showed 2.5 times higher sustainable regeneration e ciency (90% in 30 mins) up to 7th cycle than HAp. Furthermore, the solution pH (5-7) of treated water was maintained at neutral after uoride adsorption, making the water potable. Hence, these results demonstrate that chitosan plays a major role in removal of F − ion and this composite is ideal for F − adsorption application. Highlights 1. First report on the synthesis and Fadsorption by the cross-linker-free mesoporous lyophilized HAp/chitosan nanocomposites 2. The HAp/CS4 exhibited signi cantly higher Fadsorption capacity (60%-98%) than the existing reports 3. Higher and sustained regeneration e ciency (90% up to7 th cycle) 4. Enhanced colloidal stability and along with signi cant reduction in the particle size (38% length and 86% width) with an increased chitosan incorporation.

Accelerating Cd2+ adsorption using hydroxyapatite nanoparticles engineered by combination of ultrasound and microwave treatment

“…09-0432 (Fig. 1a), indicating the polycrystalline nature of the hexagonal structure of the HAp phase [15][16][17]. This suggests that the hydrothermal, ultrasonication, microwave drying, and their combination significantly influence crystallinity and crystallite size.…”

“…6a). The adsorbent pHpzc was calculated from the pH drift method [16,17,30], as shown in Fig. 6b, and it found to be 6.9 ± 0.1, 7 ± 0.1, and 7 ± 0.1 of HAp-M, HAp-UM, and HAp-HUM, respectively.…”