Principle of the Method

This method is based on the destruction of bacteria and decomposition of toxins by nanophotocatalysts (NPC) that are dispersed in water. Under natural ultraviolet radiation, these nanophotocatalysts form OH-radicals in water which destroy bacteria and decompose toxins. In brief, the photocatalytic reactions of aqueous NPC suspension system can be described as follows:

where hv is the UV irradiation, hVB+ is valence band holes, and eCB- is the conduction band electrons. The active oxygen and radical species existing in the presence of oxygen and water take part in the oxidation-reduction reaction and destroy bacteria and decompose toxins.

The nanophotocatalysts must be harmless; their concentration in water must be lower than the permissible level; and nanoparticles must form agglomerates during a specified period of time, coagulate, and precipitate. Many semiconductor metal compounds are used as photocatalysts; the most commonly known photocatalyst is TiO2. The reaction efficiency of TiO2 photocatalyst decreases in water and its performance deteriorates when the surface of photocatalyst particles becomes fouled up. For this reason, it is necessary to develop a new type of nanophotocatalyst which can meet all of the necessary requirements.

Nanocomposites combine the properties of two or more different materials with the possibility of novel mechanical, physical, or chemical behavior arising [20]. Nanocomposites of conjugated materials and metal nanoparticles are prepared from different metals, different types of conjugated polymers and oligomer linkers [21-28]. Other types of nanoscale materials are formed as composites of carbon nanoparticles and polymers. For example, electrolytically generated nano-carbon colloids (NCC) have functional groups such as carbonyl, hydroxyl and carboxyl groups formed on the surface of carbon nanoparticles [29-32]. These nanocomposites can be modified by attaching different cations. On the other hand, most polymers can react with different ions and molecules, and participate in modification of nanocomposites. For example, nanocarbon-polymer nanocom-posites (NCPC) prepared with electrolytically generated NCC and polyethylen-imine PEI [33]. A similar method can be used to prepare nanocarbon-metal nanocomposites (NCMC) as the nanophotocatalysts to control cyanobacteria.

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