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Crystal engineering of tungsten (VI) oxide composite materials using hydro(solvo)thermal method
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Type
Thesis
Author
Yan, Bangbo
Supervisor
Goh, Ngoh Khang
Yan, Xu
Abstract
There has been much recent interest in preparing new transition metal oxide materials using hydrothermal method. The aqueous chemistry of polyoxotungstates has been extensively studied due to their rich chemical reactivity and structural complexity. However, the hydrothermal chemistry of tungsten polyoxoanions remains largely undeveloped. Synthesis and characterization of tungsten polyoxoanions are the focus of this work. Crystal engineering of tungsten polyoxoanion based materials using hydrothermal method has been investigated. The effects of templates, pH value of the initial reaction media, and heteroatoms on the crystallization of the polyoxoanions were studied. The hydrothermal reactions of tungsten oxides and/or heteroatom compounds with structure-directing agents such as en, bpy, and dpd yield interesting new products including clusters, chains, layers and open frameworks. Characterization was done using crystal X-ray analysis, as well as IR spectroscopy, CHN and thermogravimetric analysis (TGA) methods.
A brief review of porous materials and chemistry of tungsten oxides has been given. The impacts of pH, temperature, organoamines, heteroatoms and mineralizers on the crystallization are discussed. The investigation suggests that acid reaction mixture favorite the crystallization of tungsten polyoxoanions. The organoamines were used as structure-directing agents in the synthesis and they may function as ligands as well. The ditopic organoamine ligands presented unusual structure versatility and their roles are discussed. The heteroatoms are essential in certain cases; they may provide charge compensation or function as linkages as part of the inorganic framework itself.
A brief review of porous materials and chemistry of tungsten oxides has been given. The impacts of pH, temperature, organoamines, heteroatoms and mineralizers on the crystallization are discussed. The investigation suggests that acid reaction mixture favorite the crystallization of tungsten polyoxoanions. The organoamines were used as structure-directing agents in the synthesis and they may function as ligands as well. The ditopic organoamine ligands presented unusual structure versatility and their roles are discussed. The heteroatoms are essential in certain cases; they may provide charge compensation or function as linkages as part of the inorganic framework itself.
Date Issued
2001
Call Number
QD951 Yan
Date Submitted
2001