Abstract

Generating nanoand microstructured crystalline materials has become an important field in nanoscience, nanotechnology, and microtechnology for the practical processing of electronic, sensory, and optical devices. A wide range of biomineralization processes has been developed for creating hierarchical materials with exquisite structures and shapes at various range of length scales. In principle, an important requirement in the ‘synthesis with construction’ of biomimetic materials is control over crystallization, which can be guided by specific molecular recognition at interfaces. Although the morphogenetic foundations for the diversity and evolution of biomineralization remain largely unrealized, controlling crystallization processes can direct the unique shapes, sizes, patterns, polymorphs, and properties. Therefore, mimicking biomineralization may become a way of synthesizing crystalline materials with complexity of form and structure. Lee and White previously reported mineralization processes to give specific polymorphs and morphologies of carbonate derivatives at the air interface of aminosiloxane-based nanomatrixes under mild conditions. The nucleation and growth of crystalline materials were matrix-mediated on mesoporous poly(γ-aminopropyl triethoxysilane) (PAPS), where CO2 (0.03%) from air was utilized as a carbon source in the mineralization process under relative humidity 50%~ 60%. Mineralization from the matrixes (ca. 40-μm thick) of NaOH-catalyzed PAPS, denoted as Na/PAPS, led to the formation of crystalline Na3(CO3HCO3)·2H2O with exquisite floral shape. White et al. also reported self-organized fibrous nanostructures at the interface with air of the thin film (ca. 50-nm thick) of PAPS matrix spin-cast on sodalime glass substrates. The phenomenon was related to dissolved CO2 (aq) from air and Na ions leached out from the substrates. The growth of fibrous nanonetworks was directly dependent on the Na concentration segregated at the air interface of PAPS matrixes. It was explained that the selfassembly of nanofibers was attributed to hydrogen bonding and electrostatic interaction between Na and carbamate (-NHCO2) ions. While, when replacing NaOH with KOH, the growth of HCO2K-filled fibrous KHCO3 microtubes was mediated from the thick film (ca. 40-μm thick) of K/ PAPS deposited on boron-doped SiO2/Si(100) wafers. The proposed mineralization mechanism involved both a catalytic cycle via the reproduction of potassium carbamate (-NHCO2K) as a key intermediate for growing KHCO3 microtubes at the exposed interface with air and the photoelectrochemical reduction of CO3 to HCO2 at the buried interface with the substrate, e.g., a p-type SiO2 semiconductor, followed by the capillary action of the microtubes to collect ionic HCO2. Here, this research presents the results from the further exploration in the thin film version (ca. 50nm thick) of the K/PAPS matrix system, leading to the growth of trigonal micropyramids composed of crystalline carbamates matrix-mediated at the air-matrix interface.

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