Molecular dynamics simulation of removal of heavy metals with sodium dodecyl sulfate micelle in water

Abstract

Sodium dodecyl sulfate is an anionic surfactant widely known for its remediation purposes in heavy metal pollution. Together with ultrafiltration membranes it can help the removal of heavy metals from wastewaters. In this work, we studied four different metallic ions Cd2+, Cu2+, Ni2+ and Zn2+ interacting with SDS molecules in water employing molecular dynamics simulations. We considered two different initial configurations, one with a SDS preassembled micelle and another in which every atom was randomly placed, all of them with 60 metallic ions and 60 SDS molecules in water. We could see that the addition of metallic ions into the solution causes the size and shape of the micelle to increase 25% in total volume and around 10% from its original radius, accessible surface areas results confirm this result. Radial distribution functions were calculated resulting in a preference for cadmium ions to be close to the sulfur headgroup atom of the micelle. Hydration numbers were calculated giving 5.0, 6.14, 6.05 and 6.04 for Ni, Cu, Zn and Cd ions, respectively, for the first shell. For the case in which the initial configuration was randomly placed, it takes more time to reach the equilibrium configuration, whereas if the micelle is pre-assembled it takes less time to relax but the radial distribution functions match finally, showing the same configuration. Besides we studied the effect of metal ion concentration on the size of the micelle, giving as a result that as there is an increase in metal concentration there is an increase in the size of the micelle.