Development of photosensitiser functionalised electrospun nanofibre for water sterilisation.

Waste water treatment is highly energy consuming in both developed and developing countries. Thus energy efficient water treatment techniques are continuously being sought. Ensuring microbiological safety of water is one of the utmost importance. However conventional disinfection processes produce toxic by-products which are difficult and costly to remove and photodynamic inactivation may provide a cheap and eco-friendly alternative. Photosensitisers kill microorganisms by a process known as photodynamic inactivation (PDI). In PDI, photosensitisers transfer energy to O2 to yield highly reactive singlet oxygen and its products. These reactive oxygen species cause PDI of bacteria with no toxic by-products and without chemical alteration of the photosensitiser which allows its re-use. In the work presented covalent immobilisation of photosensitiser onto electrospun nanofibre mats prevented photosensitiser release into the water during PDI and allowed continued use of the photosensitiser loaded mats. The synthesis and characterisation of antibacterial tetra cationic photosensitisers; tetra allyl pyridyl porphyrin (TAllylPyP) and tetra amine pyridyl porphyrin (TAminePyP) is reported and also the preparation and characterisation of water resistant polyacrylic acid cross-linked with polyvinyl alcohol (PAA-PVA) and ethylene glycol (PAA-EG) electro spun nanofibre (ENF) mats. Protocols for covalent immobilisation of photosensitises TAllylPyP and TAminePyP onto the mats and their characterisation is described. Successful PDI of E.coli by these nanofibres were carried out using 32 mW/cm2 white light which is around 3% of bright mid-day time sunlight under clear sky conditions in sub-Saharan Africa to study a graded PDI response. The PDI data imply that this system could be operated by using direct natural sunlight, to rapidly kill water borne bacteria. Both Gram-positive and Gram-negative bacteria were killed and this sunlight driven water disinfection system could be an economical and efficient solution to provide clean water to some of the world’s poorest people.