Osmotic pressure regulated sodium alginate-graphene oxide hydrogel as a draw agent in forward osmosis desalination

Abstract

The freshwater shortage has become a global issue due to the population explosion. As an effective response to the water crisis, forward osmosis (FO) desalination technology is applied because of its comparatively low membrane fouling and low energy consumption. Hydrogels, as draw solutions in FO, have received increasing attention due to their properties of no reverse solute flux, and strong water recovery capability. However, the concentration in the feed solution is below 8000 ppm restricted by the lack of a clear mechanism for osmotic pressure regulation. In this work, a sodium alginate-graphene oxide (SA-GO) hydrogel was proposed with excellent performance in drawing water. The hydrogel has a homogeneous porous structure that enables easy water recovery through compression. When the SA-GO-1 hydrogel was used for the treatment of the simulated seawater (35,000 ppm NaCl solutions), the initial water flux achieved 0.4429 L m−2 h−1 (LMH), and the average water flux remained at 0.1783LMH. In contrast to conventional tactics, the osmotic pressure of hydrogel was regulated based on Flory-Rehner theory (FR). Moreover, the interaction energy was computed to reveal the mechanism of osmotic pressure regulation. This strategy provides a potential solution for the design of high-performance draw solutions for FO systems.