Environmental Applications of Magnetron Sputter Coated Coal Fly Ash

Gaddah, Abdul Hadi (2023) Environmental Applications of Magnetron Sputter Coated Coal Fly Ash. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Fly ash, also known as pulverised fuel ash, is made from fine particles, spherical in shape, which vary in size, ranging from 0.5 to 2500 m. Fly ash is a residue of coal combustion used in thermal energy generation; it is collected via a particle filtration method or using an electrostatic precipitator. Coal fly ash (CFA) consists of several elements including silicon, aluminium, and iron. The toxicity level of CFA is dependent on the grade of coal used in the energy generation. Electricity is mainly generated using coal as a source of energy in power plants, thus CFA is readily available in substantial quantities and this project has investigated routes to producing environmentally useful products from this waste material. Specifically, CFA has been coated with thin films of TiO2 ¬and Bi2O3 by means of the physical vapour deposition technique of magnetron sputtering. Thin films of TiO2 ¬and Bi2O3 have been known to be utilised for antimicrobial uses, organic waste degradation and fluorine uptake. Thus, combining the coatings of TiO2 ¬and Bi2O3 would in return enhance the use of the CFA for multiple purposes including photocatalytic degradation, desalination, and defluorination. Coated CFA should be able to degrade organic compounds that have been disposed of in industry, like textile effluent containing dyes that have been used. Coated CFA may be used to help regulate fluoride levels in water treatment process. Deposition of thin films of bismuth oxide and titanium oxide have been a research focal point, using two alternative magnetron sputtering set ups. Unbalanced magnetron sputtering is the method of choice, because of the high quality of the coatings produced. Two set ups have been utilised in this research: a single target magnetron sputtering and a dual twin magnetron sputtering arrangement. Studying the results obtained from XPS, XRD and EDX analysis indicated that the TiO2 ¬and Bi2O3 coatings were successfully deposited on to the CFA particles. TiO2 coated CFA, achieved by the dual twin magnetron sputtering arrangement, was deposited under a range of operating conditions. The best performing samples demonstrated strong results with dye degradation, achieving up to 89.1% decrease in absorbance. Other samples performed exceptionally well compared to TiO2 bulk particles in absorbing fluorine at 32.20mg/kg and 35.59mg/kg, respectively. The single target magnetron was utilised for the deposition of Bi2O3 onto the CFA, which demonstrated photocatalytic activity in dye degradation tests. The findings of the study shows that indeed coated CFA with either TiO2 or Bi2O3 can be utilised for environmental purposes such as for dye degradation and defluorination.