Porous‐Carbon‐Confined Formation of Monodisperse Iron Nanoparticle Yolks toward Versatile Nanoreactors for Metal Extraction

: All-in-one architectures in which uniform nanoscale zero-valent iron nanoparticles are wrapped in hollow porous carbon shells are highly desirable for environmental applications such as wastewater treatment and for use as catalysts, but their preparation remains a significant challenge. Herein, a spatially confined strategy for the in situ preparation of uniform Fe0 @mC (mC=micro/mesoporous carbon) yolk-shell nanospheres, in which the iron nanoparticles are encapsulated in thin, porous carbon shells, is reported. The elaborately designed Fe0 @mC yolk-shell nanospheres were obtained by utilizing silica- and phenolic-resin-coated magnetite nanoparticle core-shell structures as templates by means of selective etching and in situ thermal reduction. The highly dispersed iron nanoparticles with superior reduction capability can effectively remove metal pollutants (e.g., AuIII , AgI , and CuII ), the carbon shell acts as protective cover and prevents aggregation of iron nanoparticles, and the void space in the capsules serves as a reactor for reduction and catalytic reactions.