Matharu, Rupy Kaur; (2020) Production of Antimicrobial Filters for Water Systems using Novel Gyratory Techniques. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Diseases caused by the direct and indirect exposure to waterborne pathogens, pose a serious threat to human health. Such microorganisms spread in a non-uniform manner in water supplies and are extremely difficult to eradicate. This research focuses on the manufacture of antimicrobial fibrous membranes to be used in water filtration systems at the point-of-use. In this thesis a cross-disciplinary approach was taken, using knowledge from material science and microbiology, to investigate the antimicrobial activity of tellurium, tungsten, tungsten oxide, tungsten carbide, copper-silver, copper-zinc, graphene oxide nanosheets and graphene nanoplatelets against bacterial and viral microorganisms. By varying the nanomaterial concentration, the agents showed dose-dependent microbicidal characteristics. Carbonaceous based nanomaterials exhibited the strongest potency with a minimum inhibitory concentration of 2 w/v%. At this concentration graphene oxide nanosheets and graphene nanoplatelets killed 96.1 ±4.4% and 63.1 ±4.4% of Escherichia coli populations, respectively, 99% of Staphylococcus aureus populations and 100% of bacteriophage T4 populations. Both copper-based intermetallic materials also showed antimicrobial activity, with copper-silver nanoparticles deactivating 99.0 ±2.2% of E. coli, 75.4 ±1.0% of S. aureus and 100% of bacteriophage T4 populations at 2 w/v%, and copper-zinc nanoparticles deactivating 98.1 ±1.7 % of E. coli, 90.1 ±3.8% of S. aureus and 96.9 0.3±% of bacteriophage T4 populations at 2 w/v%. The solubility and spinnability of poly(methyl methacrylate) (PMMA) in seven different organic solvents was investigated using theoretical and experimental techniques. The effect of applied pressure on the formed fibres was also investigated. Halogenated solvents were identified as the most favourable for the dissolution of PMMA. Increasing the applied pressure was shown to alter fibre morphology and surface pore size as a trade-off between pore formation and solvent evaporation was identified. Pressurised gyration of 20 w/v% PMMA in chloroform at maximum speed and 0.1 MPa applied pressure was outlined as optimal as it yielded fibres with a diameter of 3.3 ±1.2 µm and average surface pore size of 126 ±18 nm. Graphene oxide nanosheets and graphene nanoplatelets were incorporated into PMMA fibres at four different concentrations and their antimicrobial properties were assessed. Fibre morphology was found to be influenced by nanoparticle concentration, as a positive correlation between nanoparticle loading and fibre diameter was observed. Of the prepared composite fibres, 8 wt% graphene oxide/PMMA fibres were found to have the strongest antimicrobial activity as they deactivated 85 ±20% of the E. coli, 95 ±3% of the S. aureus and 39 ±1% of the bacteriophage T4 populations following 24 hours of exposure. These fibres were characterised using Scanning Electron Microscopy, Raman mapping, Fourier Transform Infrared and Stimulated Raman Spectroscopy to confirm the presence of graphene oxide nanosheets on the fibre surface. Microbial cytotoxicity was attributed to oxidative stress, as demonstrated by reactive oxygen species studies. The microbial filtration efficiency of 8 wt% graphene oxide/PMMA fibrous membranes to decontaminate water at the point-of-use was studied. Results showed the membranes to deactivate 83.8 ±1.2% of Gram-negative bacteria, 95.0 ±2.5% Gram-positive bacteria and 32.1 ±2.9% of virions. This thesis shows the implementation of nanocomposite fibrous filter membranes as a viable solution to waterborne diseases.

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