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This paper reports the novel design of shell-in-shell Ni3S4@Co9S8 double-shelled tube (DST) hierarchical structures with different shell compositions, and the subsequent attempt to fabricate these structures. We fabricated such unique shell-in-shell hierarchical structures through transition from isomorphic metal–organic framework core–shell structures of Ni-MOF-74@Co-MOF-74 in the presence of Na2S under solvothermal conditions. The as-prepared Ni3S4@Co9S8 DSTs demonstrated high specific capacity (up to 1257.4 F g−1 at a current density of 4 A g−1) with excellent charge–discharge reversibility (with 81.5% capacity retention after 1000 cycles), which is superior to that of the single-shelled Co9S8 tubes (337.8 F g−1 at 1 A g−1). The specific capacity of the prepared DST electrode also showed exceptional performance at a current density of 20 A g−1. Approximately 74.0% of the obtained value of the specific capacity was retained at 1 A g−1. This approach is a facile method to produce novel electrode materials for energy storage devices and a useful self-templated strategy for the preparation of multi-shelled hollow materials with different shell compositions for different functions. [ABSTRACT FROM AUTHOR]

This communication introduces a general approach toward the size/morphology-controlled synthesis of classical MOFs with 2-methylimidazole (2-MI) as a competitive ligand and a base to accelerate the nucleation of crystallization. A higher concentration of 2-MI and a suitable polarity and solubility of the solvent will accelerate the nucleation of the crystal, resulting in nanometer size particles. However, larger crystals can be obtained via the further growth of nanoparticles with prolonging the reaction time. Such a serendipitous discovery may inspire future researchers to design new MOF materials with desired structures. [ABSTRACT FROM AUTHOR]