Solar-driven bifunctional hydrogel enables all-weather pure water and draw agent regeneration for forward osmosis

Abstract

Amid escalating global water scarcity, the efficient treatment of brackish water as a desalination source holds critical importance for ensuring water security and promoting sustainable development. In this study, we developed a novel photothermal hydrogel draw agent, CB-PNIPAM/SA, optimized for forward osmosis (FO) desalination. This hydrogel enables effective brackish water desalination and draw agent regeneration driven solely by solar irradiation. The CB-PNIPAM/SA hydrogel integrates sodium acrylate (SA), N-isopropyl acrylamide (NIPAM), and carbon black (CB), where SA provides high osmotic pressure, NIPAM offers pronounced thermosensitivity, and CB facilitating solar-driven photothermal conversion. This synergistic design supports freshwater recovery through evaporation while ensuring efficient regeneration of the draw agent. Under continuous solar irradiation, the 3 %CB-PNIPAM/SA hydrogel achieved a water flux of 9.46 L m⁻² per day and a freshwater recovery rate of 8.16 kg m⁻² per day over a five-day cycle, highlighting its potential for sustainable all-weather (continuous operation across diurnal cycles) desalination applications. This study offers a novel strategy for continuous brackish water desalination using solar energy, presenting a promising approach to mitigate global water scarcity and advance sustainable development.