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

Abstract

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+2 was investigated using the factorial design approach to investigate the efficiency of different Pb+2 concentrations, adsorption contact time, and HAp mass. The greatest Pb+2 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 (R2) of 0.96. The thermodynamic calculations revealed that the adsorption process was exothermic, spontaneous, and predominantly dominated by chemisorption. Furthermore, the maximum adsorption capacity (Qmax) 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 Eads value for the lead ion adsorbate molecules as they attached to the surface of the adsorbent.

Adsorption of Methylene Blue Dye and Analysis of Two Clays: A Study of Kinetics, Thermodynamics, and Modeling with DFT, MD, and MC Simulations

“…These surfaces were immersed in an adsorption environment containing a single MB molecule along with 2500 water molecules. These simulations played a pivotal role in enabling us to thoroughly explore the dynamic behavior of molecules − and their binding characteristics with MB on both surface models. As a result, they provided invaluable insights into the intricate nature of these interactions, significantly advancing our understanding of how MB is adsorbed onto clay surfaces .…”

“…To quantitatively determine the adsorption energy ( E ads ), we can employ the following equation: ,− E ads = E total − ( E clay + E MB + E water ) where E ads represents the adsorption energy, E total is the total energy of the system, E clay signifies the energy of the clay surface, E MB denotes the energy of the MB molecule, and E water represents the energy of the surrounding water molecules. By solving this equation, we are equipped with a precise measure of the adsorption energy, which is instrumental in unraveling the intricate dynamics of the adsorption process. ,,, …”

“…These simulations played a pivotal role in enabling us to thoroughly explore the dynamic behavior of molecules − and their binding characteristics with MB on both surface models. As a result, they provided invaluable insights into the intricate nature of these interactions, significantly advancing our understanding of how MB is adsorbed onto clay surfaces . This knowledge serves as a foundation for further research in the field, enhancing our grasp of the underlying mechanisms at play.…”

“…As a result, they provided invaluable insights into the intricate nature of these interactions, significantly advancing our understanding of how MB is adsorbed onto clay surfaces. 52 This knowledge serves as a foundation for further research in the field, enhancing our grasp of the underlying mechanisms at play. The simulation's MC (Monte Carlo) and MD (molecular dynamics) computations made use of the well-established deriding force field, 55−58 renowned for its adaptability and proven reliability in scientific applications.…”

“…By solving this equation, we are equipped with a precise measure of the adsorption energy, which is instrumental in unraveling the intricate dynamics of the adsorption process. 52,64,69,70 The approach we employed, known as Monte Carlo (MC), to evaluate the intricacies of molecular interactions, entails the generation of a multitude of combinations involving species relevant to the simulation, such as molecules and ions. These combinations are generated randomly, allowing for a thorough exploration of a wide array of configurations, as elaborated in refs 60,66,71,72.…”