Author: Chee Ling Tong
Tong, Chee Ling, 2015 Synthesis of Siliceous Materials Using Vortex Fluidic Devices (VFDs), Flinders University, School of Chemical and Physical Sciences
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Santa Barbara Amorphous, SBA-15, has a hexagonally ordered array of mesoporous silica, discovered at the University of California Santa Barbara in 1988. SBA-15 exhibits high surface area, large and controllable pore sizes, and better hydrothermal stability over Mobil Crystalline Materials, MCM-41. In consequence SBA-15 has attracted much attention for developing the materials for a variety of applications such as separation, catalysis, drug delivery, adsorption, and biosensors.
Over the decades, research on SBA-15, has focused either on improving the synthesis methods or to use it as a support in different applications. However, the synthesis has not diverted much from the original hydrothermal process, which is a very successful and mature process. This is despite the process is lengthy and is highly temperature dependent, which represent some disadvantages.
This dissertation focuses on the formation of SBA-15 using a novel vortex fluidic device (VFD) without the need for hydrothermal treatment, under room temperature and atmospheric pressure. The vortex fluidic device enables the synthesis to be performed in a continuous mode, at ambient conditions, and reduces the processing time by at least half relative to the conventional method. Moreover, by fine-tuning the processing controls such as rotational speed, there is the ability to control the pore size of the periodic mesostructure which is without precedent.
In situ incorporation of palladium oxide (PdO) within the pore channels of SBA-15 was successfully achieved using the VFD. The resulting material served as a heterogeneous catalyst and was tested for its catalytic performance in Suzuki cross-coupling reactions. In addition, this VFD processing can be set up to operate under a hydrogen gas environment which results in spontaneous reduction of metal oxides to metal. This allowed a one-pot synthesis of Pd(0)/SBA-15 material, which is effective in the removal of 41% of the initial nitrate-nitrogen ions [NO3-N] from aqueous media with good recyclability, yielding 36% removal efficiency after being recycled.
The research was extended further in preparing silica hydrogel using the VFD, effectively creating a new paradigm in sol-gel technology. A benign aqueous synthesis of silica hydrogel can be achieved under continuous processing, without the need for a solvent or the addition of an acid or base, and under ambient conditions. The simplicity of this process greatly enhances the applicability of the use of silica as a drug delivery vehicle, in minimising the use of chemicals involved throughout the process. This was established for the in situ incorporation of curcumin within the silica network, which greatly enhanced its bioavailability, improving the bacterial growth inhibition of gram-positive bacterium Staphylococcus aureus.
Overall the work has established a breakthrough in process enhancement in making functional siliceous materials. It defies the orthodox process and the ability to make silica under more benign processing conditions, presumably involving less energy input, while significantly reducing the processing time and the generation of waste. The work establishes the ability of VFD processing in improving the green chemistry metrics of silica manufacturing in general.
Keywords: VFD, SBA-15, Hydrogel, Mesoporous silica
Subject: Chemistry thesis
Thesis type: Doctor of Philosophy
Completed: 2015
School: School of Chemical and Physical Sciences
Supervisor: Prof. Colin Raston