Adsorption Efficiency of Carbon Materials for the Removal of Organic Pollutants: DDT from Aqueous Solution.

Carbon nanotubes (CNTs) are widely used to adsorb organic pollutants from wastewater due to their porous structure, large specific surface area, and unique physical and chemical properties. Examining the interactions between pollutant molecules and carbon nanotubes is an important topic in the applications of nanotubes for the removal of pollutants. In this study, molecular dynamics (MD) and metadynamics simulations were used to investigate the adsorption mechanism of Dichlorodiphenyltrichloroethane (DDT) pollutants on carbon nanotubes. Obtained results revealed that functionalized CNTs (f-CNTs) with active groups exhibited significantly enhanced performance compared to pristine CNTs. The adsorption isotherms were analyzed at different DDT concentrations, and it was found that increasing the concentration of DDT molecules led to a decrease in system energy and increased stability. The presence of biosurfactants as functional groups on the CNTs enhanced the interaction between DDT molecules and the nanotubes. In CNT, the addition of DDT increases the van der Waals energy from -176.83 kJ/mol for 3 DDT molecules to -2237.88 kJ/mol for 50 DDT molecules. In the case of f-CNT, the van der Waals energy in the system with 50 DDT molecules is about 2061.05 kJ/mol more negative than the system with 3 DDT molecules. The number of contacts between the adsorbent and DDT molecules increased over time, indicating increased adsorption interaction. The radial distribution functions (RDF) of DDT molecules around CNTs and f-CNTs showed the highest probability of finding DDT molecules at a distance of about 0.5 nm from the adsorbent surface. The study provided valuable insights into the adsorption process and can guide future experimental studies.