Water-ethanol separation with Janus tip charged carbon nanotubes

Ethanol is an important industrial substance, serving both as a solvent and fuel. In particular, from the perspective of producing bioethanol as an alternative fuel, there is a need for methods that can separate water and ethanol with lower energy consumption. Using molecular dynamics simulations, we investigate the selectivity for water and ethanol molecules with Janus tip charged carbon nanotubes (CNTs), where one tip is positively charged and the other negatively charged. These charges generate a non-uniform axial electric field within the CNT, which is strong enough to induce water structuring inside the CNT. Particularly, tip charged CNTs with diameters ranging from 1.6 to 2.8 nm exhibit high selectivity for water molecules, whereas those with diameters smaller than 1.6 nm preferentially select ethanol. As the CNT diameter exceeds 2.8 nm, the influence of the tip charges diminishes, leading to a gradual reduction in water selectivity. In this study, we demonstrated the feasibility of Janus tip charged CNTs as theoretical models, suggesting that ionized functionalization could enable their practical implementation for energy-efficient water-ethanol separation.