Photocatalytic treatment has the potential to become a cost effective method of organic contaminant removal from water. Photocatalytic materials are semiconductors that enhance chemical reactions such as the breakdown of organic molecules in the presence of light. One of the most studied photocatalysts for water purification is titanium dioxide (TiO2). Variations in the composition of photocatalysts can affect the outcome of the experiments, the detection of the change in behaviour of the photocatalyst is of significant scientific interest. It requires minimisation of the impact of all other factors affecting the photocatalytic process, such as temperature, light intensity, wavelength and uniformity. Repeatability of the experiments is also affected by these factors. If their impact is not considered and addressed the outcome of multiple seemingly identical experiments with a single sample of the photocatalyst will produce different results. Light is one of the most important factors in a photocatalytic process. The undoped TiO2 has a sharp drop in its light absorbtion characteristics between UV and visible spectral regions. It is theregion of the spectrum where most efficient UV LEDs radiate. As the characteristics of the light produced by LEDs are temperature dependent, heat management is important in achieving light with stable characteristics and prolonged lifetime of the LEDs. One of the contributions of this thesis is a novel method of not only stabilisation of the LED radiation parameters, namely optical output power and wavelength, but also the independent control of these parameters. The importance of LED calibration is also a significant contribution as commercial LEDs have dierent radiation parameters between devices. Possibility of independent control of optical power and wavelength of the LEDs has allowed to demonstrate the importance of radiant flux (total spectral power) over the peak spectral flux (power of a single wavelength component) for TiO2 activation, which is another significant contribution of this work. Uniformity of the produced light is another factor that needs to be addressed when a light source for the photocatalytic experimentation is designed. Non-uniform light distribution in a photocatalytic reactor will result in bright spot formation that will affect the overall performance of the photocatalytic sample. This together with the temperature control of the photocatalyst and the water sample are key issues that need to be addressed for achieving ecient and repeatable experimentation outcomes. Photocatalytic reactors developed from simulation to the working prototypes and tested during the work described in this thesis address the problem of light distribution uniformity. They have been designed to remove as many sources of uncertainty usually present in photocatalytic reactors as possible, such as for example temperature stability of the liquid sample, dierent sizes or of the photocatalytic samples and same volume of the liquid sample. As such, these novel reactors together with LED light sources provide a contribution of having a potential of becoming a photocatalytic experimentation standard for achieving the repeatable and comparable results.
|Date of Award||29 Jan 2018|
|Supervisor||Christopher Clarke (Supervisor), Duncan Allsopp (Supervisor) & Chris Bowen (Advisor)|