Mechanistic investigation of the photocatalytic activity of PEDOT for aqueous contaminant removal: the role of iron and hydroxyl radicals

In this study, the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was successfully polymerised through electrochemical (E-PEDOT) and chemical oxidative (C-PEDOT) polymerisation techniques. The photocatalytic reaction mechanism of PEDOT in removing aqueous contaminants, including hexazinone and methylene blue, was investigated with and without the use of Fe(iii). An increase in iron concentration during PEDOT irradiation resulted in enhanced degradation of the contaminants. Moreover, E-PEDOT showed up to similar to 90% removal of contaminants by a combination of adsorption and photocatalysis effects. Hydroxyl radicals played a critical role in the photocatalytic degradation of contaminants using PEDOT, in the presence and absence of iron. This mechanism was proved through coumarin degradation. When evaluating reusability, E-PEDOT showed a decrease in its adsorption behaviour but a consistent photocatalytic activity. Finally, it was revealed that the addition of iron externally or during chemical polymerisation could boost PEDOT performance. Therefore, it is worth considering the implementation of the UV/Fe(iii)/PEDOT system, exhibiting remarkable efficacy in eliminating organic contaminants from aqueous solutions. Conducting polymers can be used as photocatalysts for aqueous contaminant remediation; however, if prepared using an iron source as an oxidant and/or dopant, they may suffer from leaching of iron during photocatalysis and misinterpretation of the results.