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1.4 CHEMICAL SCIENCES
This thesis is focused on the development of a novel ambient pressure microwave synthesis of ZnS based materials for photocatalytic and anti-bacterial technologies. Chapter 1 introduces the problems with anti-biotic resistant bacteria and the impact that these species are causing within healthcare systems. One of the approaches to tackling these problems is the development of self-cleaning materials to replace the harsh cleaning agents currently in use to sterilize the surfaces of buildings and materials used in healthcare environments. Chapter 1 also introduces semiconductors, semiconductor photocatalysis and the mechanism of action, improving photocatalytic action and how to semiconductor photocatalysts have been used for anti-bacterial activities. Chapter 1 discusses zinc sulfide and its various properties that make it attractive as a platform for photocatalytic materials with its wide band gap that can be modified to make it work in an indoor environment where UV light is not present. Chapter 2 describes the synthesis techniques employed in developing ZnS and doped ZnS materials using an ambient pressure aqueous method. This chapter also explores the techniques employed to characterise the materials prepared by the microwave technique. Chapter 3 covers to development of the ambient pressure aqueous microwave synthesis method including the variation of reagents, microwave irradiation power, irradiation time and volume of reagents and how these factors impacted the characteristics of the material. These characteristics include the crystallinity, size of the material, absorbance profile and its photocatalytic and antibacterial properties. The work of this chapter was published in Applied Catalysis B: Environmental in 2013 and was the subject of a talk which won the best Applied Chemistry talk at the Irish Universities Chemistry Colloquium at Queens University Belfast in 2010. Chapter 4 is a study on effect of metal doping of the Group 13 metals – aluminium, gallium and indium – on ZnS. The optimum conditions for microwave synthesis established in chapter 3 were used with varying amounts of dopant levels to determine the optimum doping concentration to enhance the photocatalytic activity and antibacterial activity under indoor light conditions. Luminescence spectroscopy and X-ray photoelectron spectroscopy were employed to determine the mechanism of doping by the three different metals and the difference of the ionic radii of the metals was shown to affect how the metals interact with the ZnS crystal. The work of this chapter is prepared for publication and will be submitted in late 2018. Chapter 5 presents a study of silver and indium co-doped ZnS prepared by microwave synthesis. The materials were characterised and shown to have a slight improved photocatalytic activity in comparison to indium doped ZnS and a greatly improved activity toward undoped ZnS prepared under the same conditions. There is also a study on the effect of silver doping concentrations on the crystallisation of ZnS and how the level of silver determines whether cubic blende or wurtzite phase material is formed. The work in chapter 5 was published in the Nanotechnology in 2013.
Synnott, D.W. (2019) Microwave Synthesis and Characterisation of Zinc Sulfide Nanomaterials for Photocatalytic and Anti-Bacterial Applications, Doctoral Thesis, Technological University Dublin.