Understanding molecular interactions in the precipitation and dissolution of silica and silicates under ambient conditions

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Tilburey, G.E., 2007. Understanding molecular interactions in the precipitation and dissolution of silica and silicates under ambient conditions. PhD, Nottingham Trent University.

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Abstract

The bio-geo-chemical silicon cycle provided the inspiration for investigations to be carried out into the formation and dissolution of silica. This thesis is concerned with understanding the molecular interactions occurring between silicon species and small organic molecules with emphasis on the dissolution and formation of silica in vitro. Three model systems have been employed to investigate molecular interactions occurring during silica formation; two supersaturated orthosilicic acid containing solutions generated from dipotassium tris(l,2-benzenediolato-0,0)silicate (KSiCat), an unbuffered tetramethoxysilane (TMOS) system and globally undersaturated silicon systems. The later two were developed in this thesis. These model systems enabled use to investigate the molecular interactions between bioinspired additives and different silicon species. Bioinspired polyelectrolytes and small organic molecules were investigated and shown to interact in a completely differently manner with similar silicon species.

The role of hydroxyl groups in silica formation was investigated using alkanediols. It has been hypothesised in the literature that Si-O-C bonds may template silica formation in vivo. Investigation into the interactions between hydroxyl functionalised molecules and supersaturated solutions of orthosilicic acid. No evidence was found for the formation of Si-O-C bonds and it was found that hydrogen bonding does not have a significant effect on the formation of silica.

Finally, an investigation was carried out into the effect of azamacrocyclic molecules in silica formation. Two supersaturated silica forming systems which utilised; KSiCat and TMOS were used. Inorganic-organic hybrid needle-like tetragonal prisms were formed when KSiCat was used which was shown to be a displacement reaction of the potassium ions by cyclam to form a 1:1 cyclam:SiCat layer like structure. In the unbuffered TMOS system azamacrocyclic molecules with >14 atoms were found to have a significant effect on the kinetics of silica formation. Through the control of pH, mono-dispersed solutions of silica spheres of different sizes could be stabilized through a charge neutralization mechanism.

Item Type:

Thesis

Creators:

Tilburey, G.E.

Date:

2007

ISBN:

9781369314380

Identifiers: