Hydrothermal synthesis of environmentally-friendly hydroxyapatite using recycled waste for efficient Cd2+ removal from aqueous solutions

Abstract

This paper reports on the hydrothermal synthesis of environmentally–friendly hydroxyapatite (eco–HAp) using a cationic surfactant, cetyltrimethylammonium bromide, as a template agent with 1,3,5–trimethylbenzene as a pore expansion agent. Fourier transform infrared spectroscopy (FT–IR), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) revealed that the resulting product consists of rod–like structures.

In batch measurements, an adsorbent dose of 15 g/L was sufficient to eradicate roughly 99 % of the Cd²⁺ in solution within 60 min, resulting in a maximum calculated adsorption capacity of 13.44 mg/g. Kinetics analysis revealed that the rate of adsorption was governed by pseudo–second–order kinetics (i.e., chemical adsorption), reaching equilibrium within 60 min. Thermodynamic analysis revealed that Cd²⁺ adsorption on the eco–HAp was a spontaneous, energetically–favorable, exothermic reaction. Overall, this study demonstrated the effectiveness of the prepared eco–HAp for the elimination of Cd²⁺ from aqueous solutions.