Synthesis of bentonite clay based hydroxyapatite nanocomposites cross-linked by glutaraldehyde and optimization by response surface methodology for lead removal from aqueous solution

Abstract

A novel nanocomposite (BT–HAp) was developed by chemical synthesis using hydroxyapatite nanoparticles and bentonite clay and was further applied for toxic lead (Pb) removal from aqueous solution. Three types of bentonite clay based nanocomposites were prepared by varying the pH of the solution (3, 7 and 10) with the addition of glutaraldehyde as a cross-linking agent. The formation and performance of the prepared BT–HAps are described herein. Clear and sharp XRD peaks suggested the presence of hydroxyapatite and bentonite clay compounds in the composite. The FTIR spectra confirmed the existence of the functional groups required to develop the nanocomposite. The Bt–HAp nanocomposites were also characterized in terms of BET, FESEM and TEM etc. to establish their formation. The nanocomposite synthesized at pH 7 showed a higher sorption capacity than those at pH 3 and 10. A mathematical and statistical optimizing technique (response surface methodology) was applied to verify the interactive effects of various parameters on the sorption capacity. The analysis of variance was discussed for the factors and response and confirmed the significance of the predicted model (R² = 0.9906). The Langmuir isotherm model best represented the phenomenon having a sorption capacity of 346 mg g⁻¹ at 30 °C. The sorption mechanism was well described by the pseudo 2^nd order kinetic model indicating the coexistence of both physisorption and chemisorption. Moreover, a considerable amount of toxic Pb (∼99%) removal was observed for the synthesized nanocomposite via sorption.