| Calcium carbonate-based materials have the potential applications in fields of medicine, catalysis, environment and material synthesis and modification, with many advantages such as, nontoxicity, good biological compatibility and facile surface modification. It is difficult to control the size distribution, morphology and polymorph of product using traditional CO2 bubbling technology. As a novel inorganic material synthetic technology, biomimetic synthesis method using the principle of biomineralization can be used to fabricate biomimetic materials at the level of molecules as well as to obtain calcium carbonate particles with uniform size and various morphologies by adding additives and controlling experimental conditions. Biomimetic synthesis method can be further applied for the design and/or development of new materials and their mild-conditional preparation technologies and for the understanding of biomineralization occurring in nature.In this study, what we focus is the biomimetic syntheses of two metastable calcium carbonate polymorphs, monohydrocalcite and vaterite, and their physicochemical properties and the application of polycrystalline vaterite spherulites for the fabrication of lithium ion battery anode materials, shown as below.1. Crystallization and oriented attachment of monohydrocalcite (CaCO3·H2O). for the self-organization of dumbbell-like superstructures in the absence of any additives, as well as the crystalline phase transformation of CaCO3·H2O to anhydrous calcium carbonate, have been systematically described in this section. In Mg2+-containing artificial seawaters at 4℃, nanocrystalline CaCO3·H2O can be facilely obtained through a sudden transformation of initially formed amorphous calcium carbonate (ACC), and then the oriented attachment of CaCO3·H2O nanoparticles accounts for the formation of dumbbell-like superstructures using water hydrogen bonds localized at the particles’surface. These CaCO3·H2O superstructures can suffer a crystalline phase transformation to form anhydrous CaCO3 (calcite, aragonite and vaterite).As for the instability of CaCO3 H2O dumbbells in Mg2+-chelators (i.e., organic acetylacetone or inorganic NaOH) can induce the unique formation of cube-shaped or dumbbell-like superstructures of rhombohedral calcite. Therefore, CaCO3·H2O dumbbell-like supersturctures can applied as functionalized intermediates for biomimetic synthesis purposes.2. Crystalline vaterite is the most thermodynamically unstable polymorph of anhydrous calcium carbonate, and various morphologies can be controlled in the presence of organic additives. Constructing single-crystalline vaterite with minimal defects, determining its distinctive properties and understanding the formation mechanism behind a biomimetic process, are the main challenges in this field. In this study, a unique single-crystal-like vaterite tetrakaidecahedron with two hexagonal and twelve trapezoidal faces has been fabricated through a surfactant-assisted mineralization approach for the first time. Compared with the polycrystalline vaterite aggregates, these single-crystal-like tetrakaidecahedra clearly present a doublet for Raman v1 symmetric stretching mode, a low depolarizaiton ratio for carbonate molecular symmetry and a high structural stability. These indicate a dominant position of hexagonal phase in each crystallite and confirm the Raman v1 doublet characteristics of synthetic and biomineral-based vaterites. Our finding may provide evidence to distinguish vaterite with different structures and shed light on a possible formation mechanism of vaterite single crystals.3. Mn2O3 has been regarded as an appealing anode material for lithium ion batteries owing to its high theoretical capacity, low operating voltage, earth-abundance, nontoxicity and low processing cost. The slow ion-exchange reaction of solid-state vaterite (i.e., the instable polymorph of anhydrous CaCO3) with aqueous MnCl2 was firstly adopted to prepare cube-shaped MnC03, not the loose aggregates of tiny nanoparticles in case of the structural collapse occurring during the direct transformation of MnCO3 into oxides. Secondly, a well-known KMnO4-assisted wet-chemical oxidation of precursor MnC03 was used to produce amorphous MnO2 boxes. And then, a high-temperature calcination of intermediate MnO2 guarantees the final generation of Mn2O3 porous boxes. When evaluated as a lithium ion battery anode, the reversible capacity of Mn2O3 electrode initially expresses a routine downward trend owing to gradual capacity loss and thereafter exhibits an upward trend owing to the gradually outstood interfacial storage, reaching a high value of 712 mA h g-1 over 600 cycles at 1600 mA g-1. Insofar as the high reversible capacity of 1442 mA h g-1 over 600 cycles at 800 mA g-1 is concerned,65% of which originates from the gradually emerging interfacial storage contribution. Especially, the possible interfacial charge storage mechanism of Mn2O3 porous boxes is also investigated in this section. |
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