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Title: Picosecond laser generation and modification of Ag-TiO2 nanoparticles for antibacterial application
Author: Hamad, Abubaker
ISNI:       0000 0004 6499 1894
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2017
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Despite the wide success of antibiotics against infectious diseases, bacterial infections continue to threaten mankind and animals. A major concern is that certain bacteria have developed resistance to drugs. This has been associated with the widespread use of antibiotics. Recent investigations have demonstrated that certain type of nanoparticles (NPs) can kill bacteria without causing bacterial resistance. A number of methods can be used to generate nanoparticles. One method is to use a laser. The expected advantages of laser generation of nanoparticles include high purity of the nanoparticles, special surface charge characteristics and ease of preparation in comparison with other methods particularly chemical methods. Although laser production of nanoparticles has been investigated for several decades, there is still a considerable knowledge gap. This includes the need to control nanoparticle properties such as energy gap, shape, size, surface charges, as well as combination of nanoparticles. Ag nanoparticles are widely used for antibacterial purposes such as medical dressings. However, they are also highly toxic to human cells. There is a great interest to develop next generation antibacterial nanoparticles that are as effective as Ag nanoparticles for antibacterial functions, while having less toxicity to human cells. The purpose of the present study was to generate and modify novel Ag-TiO2 nanoparticles by laser ablation in liquid and ice media and to understand their characteristics including antibacterial activities, energy gaps, and particle size distributions. Both Ag and TiO2 nanoparticles are antibacterial. TiO2 nanoparticles only work when exposed to ultra violet (UV) light due to their high energy gap. In this investigation, silver-titania nanoparticles (Ag-TiO2 NPs) were synthesised by picosecond (ps) laser ablation in ice water, and bimodal Ag-TiO2 NPs were generated in deionised water by hybrid ultrasonic vibration and ps laser ablation of Ag and Ti bulk targets. In addition, a bulk Ti/Ag alloy was used, to produce Ag-TiO2 compound NPs using ps laser ablation in deionised water, and TiO2@Ag core-shell NPs were produced via ultrasonic treatment of the compound NPs. The antibacterial activities of these new NPs were evaluated in comparison to those of standard Ag and TiO2 NPs. The toxicity study of these nanoparticles to human cells was carried out by another PhD student and the results were not reported in this thesis. The present PhD project was focused on nanoparticle production and their basic characteristics. The characteristics of Ag-TiO2 NPs were compared in the case of generation by nanosecond (ns), picosecond (ps) and femtosecond (fs) pulse lasers in deionised water. In this work, to show the effects of the different laser wavelengths (532 nm and 1064 nm) of a picosecond laser on the characteristics of Au, Ag, Ag-TiO2, TiO2, ZnO and iron oxide NPs, a comparison study was reported. The nanoparticle generation was carried out in deionised water. Finally, production of hollow and porous TiO2 NPs in a single step via high-repetition rate ps laser ablation in deionised water is presented. The significance of this work is the development and demonstration of a number of new ways of producing nanoparticles. The benefits of these new nanoparticle manufacturing methods include a decrease in the energy gap, Eg, of TiO2 NPs by using Ag NPs, effective combination of Ag and TiO2 NPs and extension of optical absorption spectra of the Ag-TiO2 NPs. Reduction of energy band gap of TiO2 nanoparticles is important to improve their photoactivation because a smaller Eg allows longer light wavelength, such as visible light, instead of UV light to initiate photoactivation. In addition, shifting the spectra to a longer wavelength would also lead to the enhancement of photoactivation of TiO2 and Ag-TiO2 nanoparticles. The reduction of the energy gap of nanoparticles is a major contribution from this research.
Supervisor: Li, Lin ; Liu, Zhu Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available