Controlled Fabrication And Properties Of Regularly Morphological Porous CaCO₃ And MgO

Nano/microstructured inorganic materials with specific (e.g., fiber-, layer-, plate-, rod-, tube-like, etc.) morphologies have been utilized extensively in the modification of functional materials and the synthesis of high-performance composite materials. The controlled fabrication of inorganic compounds with desired crystalline structures and well-defined shapes is an attractive and challenging hot topic in the research of modern materials chemistry. Conventional calcium carbonate and magnesia are inorganic materials useful in the fields of physics and chemistry, however, their counterparts with specific morphologies and porous structures possess better physicochemical properties. Therefore, it is of significance to explore controllable making strategies and to clarify the physicochemical properties of high-surface-area porous CaCO3 and MgO with specific morphologies. The present thesis was focused on the surfactant-assisted solvo- or hydrothermal fabrication of CaCO3 and MgO nano/microparticles that possessed well-defined morphologies and/or porous structures, and on the physicochemical property characterization of these materials by means of the techniques, such as X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption-desorption measurements (BET). The results obtained are as follows:1. Hexagonally crystallized CaCO3 nano/microparticles with flower-, belt-, coralloid-, network-like, hexagonal, and rectangular parallelepiped morphologies were fabricated by adopting the solvo- or hydrothermal strategy with cetyltrimethylammonium bromide (CTAB), triblock copolymer EO20PO70EO20 (Pluronic P123), poly(N-vinyl-2-pyrrolidone (PVP), sodium dodecyl sulfate (SDS) or polyethylene glycol (PEG) as surfactant, irregularly morphological CaO powders as Ca source, oleic acid (OA)/ethanol (EtOH) (or ethylene glycol (EG)), oleylamine (OAM) or H2O as solvent. Cubically crystallized MgO nano/microparticles with flower-like, hexagonal, and hexagonal prism morphologies and mesopores were generated by adopting the solvo- or hydrothermal strategy with P123, triblock copolymer EO106PO70EO106 (Pluronic F127), CTAB, PVP or PEG as surfactant, irregularly morphological MgO powders as Mg source, and OA, decylamine (DA) or H2O as solvent. It is found that the morphologies of the CaCO3 and MgO nano/microparticles were dependent upon the nature of the surfactant and solvent and the solvo- or hydrothermal temperature.2. Increasing the solvo- or hydrothermal temperature favored the enhancement in surface area of the as-fabricated CaCO3 product. The surfactant-assisted solvothermally derived CaCO3 samples possessed higher surface areas (8?21 m2/g) in an OA/EtOH or OA/EG medium than those (2?6 m2/g) in an OAM medium. The mesoporous CaCO3 sample generated hydrothermally with PEG at 240 oC for 72 h exhibited hexagonal and rectangular parallelepiped morphologies and the highest surface area of 134 m2/g.3. Cubic MgO nanoparticles with higher surface areas (122?161 m2/g) were fabricated solvothermally with P123, F127 or OAM as surfactant and OA as solvent, in which the OAM-assisted derived MgO sample possessed the highest surface area (161 m2/g), the surfactant-free derived MgO sample displayed the lowest surface area (122 m2/g), and the P123- or F127-assisted derived MgO samples with hexagonal and rectangular parallelepiped morphologies exhibited surface areas between those of the above MgO samples. The hexagonal prism-like MgO sample obtained hydrothermally with PEG at 240 oC for 72 h possessed the highest surface area of 201 m2/g.4. The high-surface-area (134 m2/g) mesoporous CaCO3 nano/microparticles with hexagonal and rectangular parallelepiped morphologies generated hydrothermally with PEG at 240 oC for 72 h could decompose below 800 oC to similarly morphological mesoporous CaO nano/microparticles with a higher surface area (110 m2/g). The excellent reversible adsorption and regeneration behavior at lower temperatures between CaO and CaCO3 with well-defined particle shapes and mesoporous architectures makes such materials useful in the applications of acidic gas adsorption and separation as well as catalysis.