Biomimetic Synthesis And Morphology Control Of Oxalates Materials

In recent years, the controllable synthesis of inorganic particle materials with specific size and morphology has attracted more and more attention due to in the development of new materials in many fields such as, advanced materials, catalysis, medicine, electronics, ceramics, pigments, cosmetics, etc. Compared with the particle size control, the morphology control of particles is more difficult to achieve. Biological systems, however, use bio-macromolecules as nucleators, cooperative modifiers, and matrixes or molds to exert exquisite control over the processes of biomineralization. This results in the formation of unique inorganic-organic composites (e.g., seashells, bones, teeth, and many others) with various special morphologies and functions. The strategy of using organic additives and/or templates to control the nucleation, growth, and alignment of inorganic particles has been universally applied for the biomimetic synthesis of inorganic materials with unusual and complex form. In this thesis, oxalates particles exhibiting different shapes and phase structures were fabricated by a simple precipitation reaction using poly-(styrene-alt-maleic acid) (PSMA) or poly(sodium 4-styrene-sulfonate) (PSSS) as a crystal modifiers at room temperature.Firstly, calcium oxalate (CaOx) particles exhibiting different shapes and phase structures were fabricated by a simple precipitation reaction of sodium oxalate with calcium chloride in the absence and presence of poly-(styrene-alt-maleic acid) (PSMA) as a crystal modifier at room temperature. The as-obtained products were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of reaction conditions including pH, [Ca²+]/[C₂O₄² ] ratio and concentration of PSMA and CaC₂O₄ on the crystal forms and morphologies of the as-obtained calcium oxalate were investigated. The results show that various crystal morphologies of calcium oxalate, such as, parallelograms, plates, spheres, bipyramids etc. can be obtained depending on the experimental conditions. Higher polymer concentration favors the formation of the metastable calcium oxalate hydrate (COD) crystals. Lower pH is beneficial to the formation of plate-like CaOx crystals. Especially, the monodispersed parallelogram-like CaOx crystals can be produced by PSMA as an additive at pH 2.Secondly, poly(sodium 4-styrene-sulfonate) (PSSS) was employed as a new organic template for the control of morphology and phase structure of calcium oxalate (CaOx) particles by a facile precipitation reaction of sodium oxalate with calcium chloride at different temperature. The influences of experimental conditions including pH, temperature, concentration of PSSS and CaC₂O₄ on the morphologies and phase structures of the prepared calcium oxalate particles were investigated. It was found that variations in the concentration of PSSS and CaC₂O₄, temperature, and pH significantly influenced the crystal structure, morphology and particle size of the samples. Various crystal morphology of calcium oxalate such as plates leaf-shaped, bi-pyramids, and cylinders etc. could be fabricated depending on the experimental conditions. Higher PSSS concentration and reaction temperature favored the formation of the meta-stable calcium oxalate dihydrate (COD) crystals and stable calcium oxalate monohydrate (COM), respectively.Finally, we investigated the crystallization of strontium oxalate in the presence of PSMA under similar reaction conditions. The effects of pH, aging time and concentration of PSMA on the phase structures and morphologies of the as-prepared strontium oxalate particles were investigated and discussed. The results showed that strontium oxalate particles with various morphologies, such as bipyramids, rods, peanuts, and spherical particles etc. could be obtained by varying the experimental conditions. PSMA promoted the formation of strontium oxalate dihydrate (SOD) phase. Suitable pH values (pH 7⁸) favor the formation of the peanut-shaped SrC₂O₄ particles.