Abstract:
The uptake of Zn(II) ions and reactive yellow 4 (RY4) dye from aqueous solutions onto synthesized
hydroxyapatite (HAp) nanoparticles was investigated under different experimental conditions such as
contact time, initial pollutants concentration, adsorbent dosage, temperature and solution pH, while the
structural elucidation of the prepared adsorbent before and after adsorption was achieved using Fourier
infrared spectroscopy (FTIR), X-Ray Diffraction (XRD), X-Ray Dispersed Spectroscopy (EDAX),
Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). XRD results
revealed the main characteristic peaks of single phase HAp powder, while the presence of PO43-, CO32-and OHfunctional groups corresponding to pure HAp were exhibited in the FT-IR analysis. The SEM
and TEM analyses confirmed the microscopic morphology of the synthesized apatites to be round shape
apatite. The correlation factors R2(0.992, 0.992, 0.992 and 0.976) for Zn(II) ions and (0.993, 0.990, 0.994
and 0.993) for RY4 dye obtained from Langmuir, Freundlich, Tempkin and Dubinin-Radushkavich
isotherms respectively confirmed the applicability of these models and suggest good agreement between
theoretical values and experimental results. Kinetic evaluations showed that the adsorption mechanism
obey the pseudo-first-order model with rate constant increasing with initial pollutant concentration. The
values of enthalpy change (ΔH) and entropy change (ΔS) as obtained are 4.92x106
kJ/mol and 51.123kJ/mol for Zn(II) ions and 3.99x106kJ/mol and 41.803 kJ/mol for RY4 dye respectively. The values of free energy and enthalpy changes revealed that the adsorption process was spontaneous and endothermic in nature. The present study thus concludes that HAp is a good adsorbent for zinc ions and RY4 dye removal from wastewater.
