Plasmolysis-Inspired Nanoengineering of Functional Yolk–Shell Microspheres with Magnetic Core and Mesoporous Silica Shell

Yolk–shell nanomaterials with a rattle-like structure have been considered ideal carriers and nanoreactors. Traditional methods to constructing yolk–shell nanostructures mainly rely on multistep sacrificial template strategy. In this study, a facile and effective plasmolysis-inspired nanoengineering strategy is developed to controllably fabricate yolk–shell magnetic mesoporous silica microspheres via the swelling-shrinkage of resorcinol-formaldehyde (RF) upon soaking in or removal of n-hexane. Using Fe₃O₄@RF microspheres as seeds, surfactant-silica mesostructured composite is deposited on the swelled seeds through the multicomponent interface coassembly, followed by solvent extraction to remove surfactant and simultaneously induce shrinkage of RF shell. The obtained yolk–shell microspheres (Fe₃O₄@RF@void@mSiO₂) possess a high magnetization of 40.3 emu/g, high surface area (439 m²/g), radially aligned mesopores (5.4 nm) in the outer shell, tunable middle hollow space (472–638 nm in diameter), and a superparamagnetic core. This simple method allows a simultaneous encapsulation of Au nanoparticles into the hollow space during synthesis, and it leads to spherical Fe₃O₄@RF@void-Au@mSiO₂ magnetic nanocatalysts, which show excellent catalysis efficiency for hydrogenation of 4-nitrophenol by NaBH₄ with a high conversion rate (98%) and magnetic recycling stability.