Molecular dynamics simulation and DFT calculations on the oil-water mixture separation by single-walled carbon nanotubes

Abstract

The treatment of oily wastewater has drawn much attention due to environmental and human health challenges. Among several techniques and materials developed to mitigate the contamination of oily wastewater, the nanostructured materials for effective adsorption and separation came into the limelight. Owing to their high specific area and nanosized structure, CNTs have demonstrated inclusive utilization as superior materials for selective adsorption. Here, we present molecular origin of oil-water mixture separation by SWCNTs. We used reactive MD simulation to explain scientifically the separation mechanism of considered mixture at molecular scale. It was shown that small hydrocarbons tend to migrate toward the nanotube surface faster than large counterparts do and whole components were adsorbed on the CNT surface up to 0.8 ns of simulation time. This is due to the different hydrophobicity tendency associated with each oil components that has also been addressed by MD simulation. DFT-D3 calculations showed that interaction nature of adsorbed oil molecules onto the nanotube surface was typical for the physisorption. Furthermore, the accuracy of current methods has been validated by experimental and theoretical data. Our simulation findings provide a well-founded understanding for adsorption and separation of oil-water mixture by carbon based nanostructured materials.