Nano-hydroxyapatite as an efficient adsorbent for cadmium Removal: Experimental and theoretical insights

The presented work aims to investigate the cadmium adsorption on nano-crystalline hydroxyapatite (n-Hap). X ray diffraction (XRD), Fourier transform infra-red (FTIR), Scanning electron microscope (SEM), and Thermogravimetric analysis (TGA) techniques were applied to characterize the n-Hap. Adsorbent mass, pH value, and initial Cd2+concentration were varied to optimize the adsorption conditions. The best Langmuir adsorption isotherm provided equilibrium adsorption capacity of 52.79 mg/g. According to performed kinetic study, the surface reaction fits to the pseudo-second order model. Thermodynamic parameters of the adsorption (Delta G degrees, Delta H degrees and Delta S degrees ) were derived from the temperature dependence of the adsorption rates. We observed spontaneous endothermic chemisorption of Cd2+ ions. Density functional theory calculations confirmed the spontaneous chemisorption via formation of three Cd-O covalent bonds of about 2.1 & Aring; lengths.