State-of-the-art insights on applications of hydrogel membranes in water and wastewater treatment

Hydrogels have been used in various applications due to their superior wetness, softness, responsiveness and biocompatibility. Together with the rapid development of membrane technologies, hydrogel membranes are being intensively investigated for versatile functions in various fields. Unlike the huge literature focusing on biomedical applications, the environmental application of hydrogel membranes is not fully explored. This study aims at providing a comprehensive discussion on various categories of hydrogel membranes for treating typical aqueous pollutants. Firstly, the concept and current research status for hydrogel membranes are briefly described, highlighting the evolution of research topics based on bibliometric analysis on hydrogel membranes in water and wastewater treatment. Then, the raw polymers and strategies for preparing hydrogel membranes are discussed, focusing on cross-linking approaches. In the following sections, the state-of-the-art advances of hydrogel membranes in oil/water separation, filtration/desalination, adsorption and catalysis are systematically assessed, emphasizing the practical applications for aqueous pollutants removals. Finally, the challenges in practical application including membrane fouling, mechanical strength and stability, low-cost fabrication methods for scale-up and regeneration are proposed and further needs are carefully given. This review will give useful guide for the preparation and application of hydrogel membranes in water and wastewater treatment.