The Extraction And Structure Of Rice Biosilica

Biomineralization is an active research field. Biosilica is present in all living organisms. To many life forms, silicon is considered as an essential element, being required for the production of structural materials and for major metabolic processes. In this thesis, we extracted pure biosilicas from rice and studied their structures. Furthermore, oligo-lysine was employed to catalysis and template the formation of nanostructural silica. The details are as follows:1. Compared with other extraction methods, the wet oxidation method is the most feasible one to extract biosilica from higher plants. This method allows the extraction of biosilica quickly without destroying the physicochemical characters of the biosilca. Pure dumbbell-like silica, fan-like silica and papilla-like silica were extracted from rice by the wet oxidation method. EDXA data show that there are abundant silicon and oxygen elements and little nitrogen, phosphor and carbon elements in dumbbell-like silica. The papilla-like silica extracted from rice shells is classified into acute and obtuse types and each of them includes single- and double-peak papilla. A few silicified hairs were also to be extracted from rice shells. Although the structural motifs of the biosilica in rice are intricate and specific, all types of the biosilca are amorphous as indicated by the XRD data.2. Structural characters of the papilla-like silica were studied by TEM, BET and SAXS analyses. The experimental results reveal that the papilla-like silica is typical lamellar mesoporous materials composed of SiO2 nanoparticles withdiameter of 4 2 nm. Furthermore, we studied the structural characters of biosilica extracted by different methods. The papilla-like silica extracted by the wet oxidation method is a kind of amorphous mesoporous silicon material. The papilla-like silica remains its morphology and mesopore size after the heating treatment. However, the biosilica obtained by the dry ashing method from rice shells directly is cristobalite silica. The element analysis and the colorimetric reaction data indicate suggest that only a few biological organisms exist within the papilla-like silica and neither amino acids nor proteins can be identified in the biosilica.3. We investigate the formation of silica structure from silicic acid precursor as facilitated by oligo-lysine acting as catalyst/template at neutral pH. The results show that oligo-lysine could facilitate the polymerization of silicic acid and the more the amino acid residues contained in the oligo-lysine, the stronger the catalytic effect. When the oligo-lysine contains three or less lysine residues, it can only increases the polymerization rate of the silcic acid and can't direct the formation of silica with defined morphology. When the oligo-lysine containing four lysine residues was employed, the silicic acid solution becomes instantly turbid and results in the formation of silica nanoparticles with a diameter of 200-250 nm. Therefore, it is determined that the oligo-lysine containing four lysine residues is the smallest functional unit to catalysis and template the formation of defined silica nanoparticles.In summary, this work will be helpful to further understand the structural characters and the mechanisms of biosilica formation in higher plants and provide new strategy for construction of biomimetic materials.