Role of divalent metal ions in the function and application of hydrogels

Hydrogels have been developed rapidly in recent years because of their great application prospects in biomedicine and intelligent devices. The excellent performance of hydrogels is very important for their applications. Introducing divalent metal ions (M 2+ ) into hydrogels is an effective method to improve the performance of hydrogels. M 2+ can interact with functional groups of polymers to affect the structures and properties of hydrogels. Here, we review the synthesis and theoretical simulation of M 2+ -hydrogels, the effect of M 2+ on hydrogels and their applications in energy storage, sensing, biomedicine, resource utilization and environmental remediation. The challenges of M 2+ -hydrogels are also discussed. We hope that this review can provide ideas for the preparation of multifunctional hydrogels and point out the important role of M 2+ in the development of hydrogels. Graphical Abstract. .