Investigation on dye separation mechanism in covalent-organic framework membranes with molecular dynamics simulation

Wastewater caused by textile and dyeing industry has become one of sources in water pollution. Membrane technology have been considered as the most promising method to deal with wastewater. Recently, Covalent organic frameworks (COFs) have been employed to construct membranes for dye separation. In this work, nonequilibrium molecular dynamics simulations are employed to investigate the transport and separation mechanism of dye. The effect of TpPa-1 membrane thickness and the structure of dye molecules on rejection rate is also discussed. It is found that the rejection rate of dyes is mainly determined by the adsorption on the surface of TpPa-1 membranes. The thicker TpPa-1 membrane is, the stronger π-π interactions become, which leads to better dye rejection. Particularly, dye molecules with better conjugate planar structures are prone to form π-π interactions with surface of TpPa-1 membrane, which results in the excellent rejection rate of dyes.