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Photosensitizer Impregnated Electro Spun Nanofibre: Environment Friendly, Low Cost Water Sterilizer.

Congress: 2015
Author(s): Kaniz Chowdhury (Leeds, UK), Paul Millner
University of Leeds1

Keyword(s): Sub-theme 13: Non-conventional sources of water,

Introduction: Water, the most valuable natural resource on earth, is continuously polluted because of undesirable human activities. Every day in industrial sector mass amount of waste water is produced. To convert waste water into non-conventional water resource, energy consumption is too high. Nowadays water security is not only the problem for third world countries but also the developed countries. Because waste water treatment is one of the largest energy consuming sectors. Water specialists are continuously seeking for techniques for water treatment that is affordable to everyone. Thus to ensure cost effective safe water supply several techniques have been employed for water treatment: nanoparticles, polymers, clay materials as thin film, membranes or powder etc. Among these membrane technology plays a crucial role in water treatment.

Electrospinning is a versatile and low cost simple technique to fabricate one dimensional membrane called electrospun nanofibre. Photodynamic inactivation (PDI) of micro-organism by photosensitizer (PS) is already an established approach. The small diameters of the PS loaded nanofibres allow the diffusion of 1O2 outside of the fibres, where it photo-oxidizes biological targets. It is also well established that photo chemically generated 1O2 acts as a primary oxidant in the photosensitized transformation of organic substances (1-5) and antimicrobial, antifungal activity (6-8) in waters. The polycyclic aromatic hydrocarbons, chlorophenols and pesticides are organic pollutants found to be vulnerable to oxidative stress (9-11), that occurs due to the energy transfer from the photochemically excited natural organic material (NOM) to oxygen. It was demonstrated that in natural waters under sunlight illumination MS-2 coliphage was inactivated by the production of singlet oxygen upon irradiation of NOMs (12). That occurs due to the high reactivity of singlet oxygen and its widespread occurrence in the naturally-occurring photo-oxidation reactions, the part of Paul Millner group is keen to photochemical remediation approaches and to exploit the oxidizing capacity for water treatment and disinfection processes. As electrophilic singlet oxygens are able to oxidize electron-rich olefins, dienes, sulfides, and aromatic hydrocarbons (13,14), the capability of photosensitizer singlet oxygen production enables oxidation of photochemical organic pollutant such as macro cyclic dyes, aromatic hydrocarbons, and transition metal complexes as well as caring microbial disinfection (12).

In broad view, the overall objective of this study is construct low cost water sterilisation devices that use visible light, to achieve a high sterilization reduction efficacy for microorganisms in waste water. This study involves PDI mechanisms of Photosensitisers immobilized onto electro-spun nanofibres for industrial waste water sterilization. The potential to recover and reuse photosensitizers makes environmental and economic sense. In the case of photochemical synthesis, immobilization of the photosensitizers offers easy isolation of the reaction products and reuse of photosensitisers from the treated water.

Materials/ Method: Fine electrospun nanofibres mats with an aminated surface were used in this study. Porphyrin based photosensitiser was used for photodynamic inactivation of gram negative bacteria.This study involved characterisation of electrospun nanofibres. Immobilisation of photosensitisers on to nanofibres. Study of photodynamic inactivation (PDI) of gram negative bacteria with photosensitisers was carried out with and without immobilization onto electrospun nanofibres. Result and Discussion: At first Photodynamic inactivation was carried out in solution without photosensitiser immobilisation. The survival fraction of gram negative bacteria (108 CFU/ml) was measured after exposure to photosensitiser in the dark or after irradiation with visible light for 30 min. The change in CFU/ml indicated no significant cell death due to PDI as expected. In comparison, the PDI of Gram positive bacteria. was significantly successful. This demonstrated that in Gram negative bacteria the negatively charged photosensitiser was probably not able to adhere or penetrate in to bacterial cell wall. The Gram negative bacteria contain a highly organised outer bacterial membrane structure with a highly negatively charged lipid layer, which prevents the cellular attachment with PS and thus interrupts 1O2 (15). When photosensitiser was immobilised onto electrospun nanofibre the initial result showed successful photodynamic inactivation of Gram negative bacteria with different concentration of photosensitisers.

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2011 IWRA - International Water Resources Association - - Admin