Improved nanocomposite of montmorillonite and hydroxyapatite for defluoridation of water

M Shanika Fernando; A K D V K Wimalasiri; S P Ratnayake; J M A R B Jayasinghe; Gareth R William; D P Dissanayake; K M Nalin de Silva; Rohini M de Silva

doi:10.1039/c9ra03981c

Improved nanocomposite of montmorillonite and hydroxyapatite for defluoridation of water

RSC Adv. 2019 Nov 1;9(61):35588-35598. doi: 10.1039/c9ra03981c. eCollection 2019 Oct 31.

Authors

M Shanika Fernando¹, A K D V K Wimalasiri¹, S P Ratnayake², J M A R B Jayasinghe¹, Gareth R William³, D P Dissanayake¹, K M Nalin de Silva¹, Rohini M de Silva¹

Affiliations

¹ Centre for Advanced Materials and Devices (CAMD), Department of Chemistry, University of Colombo Colombo 03 Sri Lanka rohini@chem.cmb.ac.lk.
² Sri Lanka Institute of Nanotechnology (SLINTEC), Nanotechnology and Science Park Pitipana, Homagama Sri Lanka.
³ UCL School of Pharmacy, University College London 29-39 Brunswick Square London WCIN 1AX UK.

Abstract

A novel hydroxyapatite montmorillonite (HAP-MMT) nanocomposite system was synthesized using a simple wet chemical in situ precipitation method. Neat nano hydroxyapatite (HAP) was also synthesized for comparison. The characterization of the materials was carried out using Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) isotherms to study the functional groups, morphology, crystallinity and the surface area respectively. Batch adsorption studies and kinetic studies on fluoride adsorption were conducted for the HAP-MMT system and for neat HAP. The effect of parameters such as contact time, pH, initial concentration, temperature, and thermodynamic parameters and the effect of coexisting ions on fluoride adsorption by HAP-MMT were studied. Results of the isotherm experiments were fitted to four adsorption isotherm models namely Langmuir, Freundlich, Temkin and Dubinin Radushkevich. Fluoride adsorption over HAP-MMT fitted to the Freundlich adsorption isotherm model and showed more than two-fold improved adsorption capacity (16.7 mg g^-1) compared to neat HAP. The best-fitting kinetic model for both adsorbents was found to be pseudo second order. Calculated thermodynamic parameters indicated that the fluoride adsorption by HAP-MMT is more favorable compared to that on HAP within the temperature range of 27 °C-60 °C. Improved fluoride adsorption by HAP-MMT is attributed to the exfoliated nature of HAP-MMT. Gravity filtration studies carried out using a 1.5 ppm fluoride solution, which is closer to the ground water fluoride concentrations of Chronic Kidney Disease of unknown etiology (CKDu) affected areas in Sri Lanka, resulted in a 1600 ml g^-1 break through volume indicating the potential of HAP-MMT to be used in real applications.