Hydrogel-driven salt fouling free FO-SIE integrated process for seawater desalination

Abstract

Solar-driven interfacial evaporation (SIE) is a low-energy, environmentally friendly seawater desalination technology with significant potential for water resource regeneration and resource recovery. However, challenges such as preventing salt crystallization fouling and maintaining high evaporation efficiency during prolonged seawater exposure persist. The Forward osmosis (FO) process can effectively reject salts in seawater, creating favorable conditions for the continuous operation of SIE. In this study, an integrated FO-SIE coupling process was developed using a custom-designed membrane module. A poly(acrylamide-co-isopropyl acrylamide) (PAM-NIPAM) three-dimensional double-network hydrogel evaporator was fabricated, with phlorizin (PHL) as a hydrophilic agent and graphene oxide (GO) as a photothermal agent. The system achieved an efficient evaporation rate of 3.05 kg m⁻² h⁻¹. Following FO pretreatment with sodium polyacrylate (PAAS) as the draw solution (DS), the reverse solute flux (RSF) remained consistently below 0.7 g m⁻² h⁻¹ throughout the process, effectively preventing salt ion fouling in the evaporator. During continuous seawater purification, no salt crystallization was observed, and the evaporation rate sustained an average of approximately 2.80 kg m⁻² h⁻¹. In contrast, in the separate FO process, the DS concentration gradually diluted over time. By integrating the SIE process and utilizing the hydrogel for continuous photothermal evaporation, the DS concentration was maintained, ensuring the sustained operation of FO. This study advances the development of energy-efficient membrane separation systems powered by solar energy and provides new insights into practical seawater desalination and anti-fouling strategies in SIE applications.