Preparation of novel magnetic nanoparticles as draw solutes in forward osmosis desalination

Novel magnetic nanoparticles (MNPs), Fe 3 O 4 @SiO 2 and Fe 3 O 4 @SiO 2 @PEG-(COOH) 2 , were prepared by loading different amounts of SiO 2 or/and PEG-(COOH) 2 onto Fe 3 O 4 nanoparticles, and their feasibility to be used as forward osmosis (FO) draw solutes was investigated. The characterization of the materials showed that, compared to normal Fe 3 O 4 nanoparticles, the modified MNPs exhibited enhanced dispersity and high osmotic pressure in aqueous solution. The FO experiment indicated that the synthesized draw solutes could obtain a water flux as high as 10 L∙m −2 ·h −1 with an aquaporin FO membrane. The optimal concentration of the added tetraethyl orthosilicate was 30% during the synthesis. The novel MNPs could be easily recovered from draw solutions by magnetic field, and the recovery rate of Fe 3 O 4 @SiO 2 and Fe 3 O 4 @SiO 2 @PEG-(COOH) 2 was 83.95% and 63.37%, respectively. Moreover, after 5 recycles of reuse, the water flux of Fe 3 O 4 @SiO 2 and Fe 3 O 4 @SiO 2 @PEG-(COOH) 2 as draw solutes still remained 64.36% and 85.26%, respectively. The experimental results demonstrated that the synthesized core–shell magnetic nanoparticles are promising draw solutes, and the Fe 3 O 4 @SiO 2 @PEG-(COOH) 2 was more suitable to be used as draw solute in FO process.