Polyethylene Glycol-Coated Magnetic Nanoparticles-Based Draw Solution for Forward Osmosis

Abstract

Forward osmosis (FO) is a promising technology for urine volume reduction to ease the recovery of nutrients. Its efficiency is highly dependent on the draw solution. Hence, functionalization of novel draw solutions for forward osmosis (FO) has become a subject of intense investigation. Coated magnetic nanoparticles (MNPs) based solutions offer great potentials for their ability to generate osmotic pressure as well as their easy recovery. Since concentrated urine features high osmotic pressure, we aim to synthesize a high osmotic pressure generating draw solution. Polyethylene glycol (PEG), is an attractive coating agent as aqueous Polyethylene Glycol solutions are known to generate high osmotic Pressure. Moreover, PEG are hydrophilic and expected to have physical aggregation suppression. In this study, we adopted coprecipitation method to synthesize PEG 4000 coated MNPs as draw solution, and studied the influence of the initial coating agent amount and sonication effect on the coating ratio and the osmotic pressure generation of solutions made of the synthesized particles. We found that initial PEG to MNP ratio affects the coating ratio. Indeed, higher coating ratio is obtained with higher initial PEG to MNP ratio. A PEG to MNP ratio of 1 to 4 led to 31% coating ratio. This coating ratio can be slightly increased if the synthesized draw solution is treated with ultrasound for 30 minutes. Water flux data collected from forward osmosis experiment revealed that this novel draw solution generates osmotic pressure. The osmotic pressure obtained from a draw solution containing a given amount of PEG 4000, is larger than the osmotic pressure if the same amount of PEG 4000 is used alone. Fate of the osmotic pressure of the novel draw solution following recycling of the synthesized MNPs is also evaluated. It was found that the drop in osmotic pressure of the regenerated draw solution is insignificant, proving possibility to reuse this draw solution for many cycles.