Hydrogel Network: A Dynamic Solution for Reversible Metal Ion Valence Switching

Efficient electron transfer between metallic active centers and cocatalysts is vital for sustainable catalysis. This work demonstrates a strategy using the dynamic contraction–rebound of hydrogels to promote the valence switch of metal ions in Fenton reactions. The key is to utilize low-valent Fe(II) to cross-link an alginate hydrogel network embedded with reducing nanoparticles, forming a macroporous structure composed of domains centered around nanoparticles. The hydrogel contracts when Fe(III) forms upon introduction of an electron acceptor. This contraction facilitates electron transfer from nanoparticles to nearby Fe(III) and causes the network to rebound. The dynamic contraction–rebound process among adjacent domains promotes the overall reduction efficiency of Fe(III) within the hydrogel. This approach allows the flexible combination of different metal ion pairs with reducing nanoparticles. Moreover, this system can efficiently conduct Fenton oxidation of methane in a neutral environment under ambient conditions, achieving a significant 28-fold increase in activity compared to the nonassembled system.