Fundamental Investigation on Osmotic Pressure and Phase Behavior of Novel pH-Responsive Draw Solute with Imine-Based Dynamic Covalent Chemistry

For the forward osmosis process, a draw solution (DS) with a high osmotic pressure and reusability is desirable. In this study, amine/aldehyde mixtures are proposed as novel pH-responsive draw solutes based on dynamic covalent chemistry. It has been demonstrated that the phase separation behavior of alkylamine/2-pyridinecarboxyaldehyde mixtures can be controlled via reversible imine formation. Moreover, the osmotic pressures of each aqueous solution of alkylamines and 2-pyridinecarboxyaldehyde were higher than those of conventional lower critical solution temperature-type ionic liquids (ILs). Additionally, the phase separation behavior was controlled by the reactivity of the amine, unlike the osmotic pressure, which is determined by hydrophilicity. The difference in the controlling factors would enable us to overcome the conventional trade-off relationship between the osmotic pressure and reusability. In summary, amine/aldehyde mixtures are potential draw solutes that exhibit better performance than conventional DS.