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Detoxification of waters for their recycling and potabilisation by solar photocatalysis in semi-arid countries

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Use of singlet oxygen for disinfecting drinking water

The AQUACAT project created a water disinfection treatment which used singlet oxygen as a bactericide. The team also developed a new family of photosensitisers to help produce singlet oxygen.

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The majority of cases of gastrointestinal illness occur in rural areas of developing nations where a supply of clean drinking water may not be readily available. In order to help solve this problem the AQUACAT project has developed a low-cost, low maintenance system for purifying drinking water by photocatalysis. The technology is based on sunlight, which generates hydroxyl radicals and singlet oxygen, a highly reactive type of oxygen molecule which can kill bacteria. In this way sunlight can be used to purify contaminated drinking water. The AQUACAT project developed new forms of photosensitisers. These chemical compounds undergo photoexcitation before transferring their energy to other molecules, thereby making the reaction mixture more sensitive to light. The photosensitisers are based on polyazaheterocyclic Ru(II) complexes. Researchers incubated water samples in the presence of visible irradiation and in the dark. The samples contained the microorganisms E. coli and E. faecalis as well as different forms of photosensitisers. The data showed that the photosensitiser RSD4 was not effective in removing microorganisms from water in the homogeneous phase. This was due to the anionic (negatively charged) nature of the biological membrane and the RSD4 photosensitiser. These factors were responsible for restricting interaction between the bacterium and the sensitiser molecule. In contrast it could be seen that even at very low concentrations in the homogeneous phase, the complex RDP2+ resulted in highly efficient disinfection. The cationic (positively charged) photosensitiser RDP2+ interacted with the negatively charged membrane of the bacterium, resulting in highly effective disinfection.

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