Graphical Mesoporous ZIF-8 (PZIF-8) hollow microcages are prepared through synthetic wet-chemical etching by applying porous silicon microdisks (PSi) as hard templates. It is the property of ZIFs that promotes the formation of porous hollow structures on shells. On the basis of the mesoporous structure, the protein release behavior of PSi@PZIF-8 was investigated by applying BSA as a model protein. The results showed that ZIF-8 film can prolong protein release. Metal-organic frameworks (MOFs), with high crystalline and ordered pore structures, hold great potential for various applications. However, the small microporous structures of MOFs restrict their applications. MOFs with larger porous structure and dimensions can expand their functionality to integrate with other large active agents. By applying porous silicon microdisks (PSi) as hard templates, zeolitic imidazolate frameworks (ZIFs) were assembled on PSi to form PSi@ZIF-8 core-shell microdisks. A new porous structure of ZIF-8 microcages was obtained via a post-synthetic approach. The influence of PSi and reaction precursor for ZIF-8 were explored, and the formation mechanism of mesoporous ZIF-8 (PZIF-8) hollow microcages was also proposed. By applying bovine serum albumin (BSA) as a loading agent, the protein release behavior of PSi@PZIF-8 was investigated. It is noted that prepared PZIF-8 microcages could serve as new vectors for loading active agents.
Graphical In the bag : An optimized one-step pyrolysis strategy is used to design yolk–shell microcages (YS Co@C/BLCNTs), consisting of Co nanocrystals encapsulated in N-doped carbon framework and bridged by bamboo-like carbon nanotubes (BLCNTs).The yolk–shell microcage catalyst integrates the advantages of “micro-bag” and “cage effect” to realize effective nitrogen fixation. The electrocatalytic nitrogen reduction reaction (ENRR) under ambient conditions is considered as a promising process to produce ammonia. Towards highly efficient catalysts, here an optimized one-step pyrolysis strategy was tailored to design yolk–shell microcages (YS Co@C/BLCNTs), consisting of Co nanocrystals encapsulated in N-doped carbon framework and bridged by bamboo-like carbon nanotubes (BLCNTs). The cavity created between yolk and shell not only served as a “micro-bag” to store the reactant N 2 and enhance its dissolution, but also induced a “cage effect” to confine the diffusion of reaction intermediate, hence making the reaction proceed in the direction of producing NH 3 . This catalyst displayed excellent catalytic activities for ENRR: a high NH 3 yield of 12.87 μg mg cat −1 h −1 at a high faradaic efficiency of 20.7 % at −0.45 V (vs. reversible hydrogen electrode, RHE). After 5 cycles of consecutive ENRR process, the NH 3 yield rate was 11.29 μg mg cat −1 h −1 , indicating the excellent electrocatalytic stability. These results provide a structural engineering for ENRR catalyst with doped N, cooperating with non-precious metal to activate the inert triple bond of N 2 and achieve NH 3 fixation.
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