CO₂ and temperature dual-responsive dendrimer-based draw solutes for forward osmosis process

Forward osmosis (FO) is promising as an alternative to conventional pressure-driven membrane processes for water separation. Ideally, the draw solution (DS) for the FO process should have high osmotic pressure, easy reusability, and low reverse solute flux. In this study, novel CO₂/temperature dual-responsive dendrimers were prepared, and their performance as DSs were evaluated. Aqueous solutions of the synthesized dendrimers showed the lower critical solution temperature (LCST) type phase separation at moderate temperature. Therefore, the dendrimers could be easily recovered from the aqueous solution and reused as DS. Moreover, the dendrimer solutions showed high osmotic pressure after CO₂ absorption owing to the tertiary amine groups of the dendrimer, which could generate bicarbonate ions via neutralization reaction. Additionally, the dendrimer solution showed a low reverse solute flux through the FO membrane because of the branched structure of the dendrimers. Owing to the preferable properties of the CO₂/temperature dual-responsive dendrimers as the DS, the aqueous solution of the dendrimer showed high DS performance. This study demonstrated that CO₂/temperature dual-responsive dendrimers are potential candidates for constituting high-performance DSs.