Fabrication of Bimodal Porous Silicate with Silicalite-1 Core/Mesoporous Shell Structures and Synthesis of Nonspherical Carbon and Silica Nanocases with Hollow Core/Mesoporous Shell Structures

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Abstract
In this work, an attempt has been made to modify the shape and nanostructure of core−shell materials, which have been usually generated on the basis of amorphous spherical cores. Novel core−shell silicate particles, each of which consists of a silicalite-1 zeolite crystal core and mesoporous shell (ZCMS), were synthesized for the first time. The ZCMS core−shell particles are unique because they are of pseudohexagonal prismatic shape and have hierarchical porosity of both a uniform microporous core and a mesoporous shell coexisting in a particle framework. The nonspherical bimodal porous core−shell particles were then utilized as templates to fabricate a new carbon replica structure. Interestingly, the pore replication process was carried out only through the mesopores in the shell, and not through the micropores due to the narrower micropore size in the core, resulting in nonspherical carbon nanocases with a hollow core and mesoporous shell (HCMS) structure. Nonspherical silica nanocases with HCMS structure were also generated by replication using the carbon nanocases as templates, which are not possible to synthesize through other synthetic methods. Interestingly, the pseudohexagonal prismatic shape of the zeolite crystals was transferred onto the carbon and silica nanocases.