AUTHOR=El Hammari L. , Hamed R. , Azzaoui K. , Jodeh S. , Latifi S. , Saoiabi S. , Boukra O. , Krime A. , Boukra A. , Saoiabi A. , Hammouti B. , Khan M. M. , Sabbahi R. , Hanbali G. , Berisha A. , Taleb M. , Dagdag O. 

TITLE=Optimization of the adsorption of lead (II) by hydroxyapatite using a factorial design: Density functional theory and molecular dynamics

JOURNAL=Frontiers in Environmental Science

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2023.1112019

DOI=10.3389/fenvs.2023.1112019

ISSN=2296-665X

ABSTRACT=<p>Hydroxyapatite (HAp) synthesized through a wet chemical procedure was used to adsorb lead (II) from an aqueous solution. HAp was characterized using Fourier transform infrared, X-ray diffraction, Brunauer–Emmett–Teller analysis, and scanning electron microscopy. The removal of Pb<sup>+2</sup> was investigated using the factorial design approach to investigate the efficiency of different Pb<sup>+2</sup> concentrations, adsorption contact time, and HAp mass. The greatest Pb<sup>+2</sup> removal (98.94%) was obtained at a starting concentration of 50 mg/L, a contact period of 15 min, and a pH of 8. At 323 K, the isothermal adoption module was fitted to the Langmuir isotherms with a regression coefficient (<italic>R</italic><sup>2</sup>) of 0.96. The thermodynamic calculations revealed that the adsorption process was exothermic, spontaneous, and predominantly dominated by chemisorption. Furthermore, the maximum adsorption capacity (<italic>Q</italic><sub>max</sub>) at equilibrium was 90.18 mg/g, and the adsorption kinetics was specified by a pseudo-second-order kinetic model. Density functional theory and theoretical studies showed that the results of the experiment were correlated by the observation of a much higher negative E<sub>ads</sub> value for the lead ion adsorbate molecules as they attached to the surface of the adsorbent. </p>