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Stability of conducting polymer poly(3, 4-ethylenedioxytiophene) in water suspension under simulated solar irradiation

Conducting polymers are today used in fuel cells, computer displays, microsurgical tools and are now finding applications in the field of photocatalysis. Common photocatalysts such as TiO2, ZnO and other semiconducting metal oxides have low activity under visible irradiation due to their wide band gap. Conducting polymers with extended  conjugated electron systems have high absorption coefficient in the visible light region. Conducting polymers are also attributed with valence and conduction bands but they have lower band gap energy so visible light irradiation can easily excite sufficient number of electrons which occupy the conduction band and stimulate the e–/h+ generation. In that way, when combined with metal oxide photocatalysts, they act as their activators and enhance their photocatalytic activity in the visible part of spectrum. In order to be used in photocatalysis of wastewaters conducting polymers need to have high chemical stability under UV and visible irradiation. For that reason in this study poly(3, 4-ethylenedioxytiophene) (PEDOT) was synthesized by chemical oxidative polymerization at two temperatures (25 and 40 °C) and at three polymerization times (24, 48 and 72 h). Obtained samples were subjected to 90 min of simulated solar irradiation in water suspension, simulating one photocatalytic cycle. Stability was tested by thermogravimetric analysis (TGA) before and after simulated photocatalysis and by measuring total organic carbon (TOC) after photocatalysis to determine the amount of possible low molecular products which could indicate polymer degradation. From TOC results it was evident that although all samples have stable structure, samples synthesized at 25 °C showed somewhat higher stability. TGA results showed that samples retain the same level of thermal stability after simulated photocatalysis. It was also evident that washing procedure after polymerization needs to be improved as excess oxidant and non-reacted monomer were present in all samples. Acknowledgements

conductive polymers, poly (3, 4-ethylenedioxythiophene), photocatalysis, solar irradiation

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