One-pot synthesis of catalytically stable and active nanoreactors: encapsulation of size-controlled nanoparticles within a hierarchically macroporous core@ordered mesoporous shell system

) and tetramethyl orthosilicate (TMOS).Mostinterestingly,themethodofcore/shell-structuresynthesiswasprecisely applied to nanoreactor design, to generate new function-alitiesbyinsituencapsulationofmetaloxidenanoparticlesinsidethecore/shellstructure.Oneoftheultimateadvantagesofthisnewcore/shell structure is that a mesoporous shell allows the diffusion ofchemical reagents toward the inside of the structure, and preventsleachingofthemetaloxidenanocrystalsthatareformedinsidethemacroporouscore.Otheradvancedpropertiescanbeexploitedinthedesign of magnetic devices, sensors, and rechargeable lithiumbatteries. In addition, other active species, such as metallicnanoparticles, organometallics, and even biological species, canbeencapsulatedby this one-pot-synthesis strategy.Scanning electron microscopy (SEM) images of theas-synthesized sample show that the spheres are homogeneouslysized, with a diameter of around 500nm (Fig. 1a). Transmissionelectron microscopy (TEM) studies confirm the uniform sizes ofthese sub-micrometer spheres (Fig. 1b). Interestingly, foamlikehierarchicallymacroporous cagesofsizes50–80nmareobservedinside these spheres (Fig. 1b–d). A higher-magnification image(Fig.1dandinset)showsverygoodregularityinthedensershellsof the spheres, which were formed by the ordered 2D hexagonal(P6mm)mesostructurecoveringthefoamlikemacroporouscores.The thickness of the shells is around 80nm. More importantly,the TEM image shows that the macroporous cages areinterconnected with uniformly ordered mesopores, which wouldbe valuable for the fast diffusion of reactants and products incatalysis. Meanwhile, X-ray diffraction (XRD) pattern of theas-synthesized sample (Fig. 2a) clearly exhibits well-resolvedpeaks that can be indexed as the (100), (110), and (200)diffractions associated with the p6mm hexagonal symmetry witha lattice constant a