Conducting polymers (CPs) have shown great potential as effective photocatalysts for the removal of emerging contaminants in water. This study aimed to investigate the photocatalytic activity of CPs, including poly(3, 4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPY), and polyaniline (PANI). The immobilization of CPs on carbon fibre cloth substrate involved electrochemical polymerization of PEDOT and brush deposition method for PPY and PANI.
The effectiveness of the CPs-based photocatalysts was evaluated by studying the photodegradation of two emerging contaminants resistant to photolysis, hexazinone (a herbicide) and trimethoprim (an antibiotic). In the absence of the photocatalysts, an insignificant photodegradation of the contaminants was observed under visible and UV irradiation. Moreover, in the dark, PANI and PPY exhibited higher adsorption for trimethoprim (~20% and 27%) compared to that for hexazinone (<8% and <14%), respectively. However, when subjected to 1 hour UV irradiation at semi-neutral pH, PPY exhibited superior photocatalytic activity towards hexazinone and trimethoprim (~95%), compared to PANI.
Additionally, PEDOT demonstrated approximately 53% adsorption and 75% photocatalytic activity for hexazinone at semi-neutral pH after 6 hours of UV exposure. The reaction mechanism also showed the important role of hydroxyl radicals (•OH) in photodegradation. To confirm the involvement of •OH, the photocatalytic activity of PEDOT was further examined using coumarin as a probe. The degradation of coumarin and the formation of its by-product, 7-hydroxycoumarin, increased with longer exposure time, demonstrating •OH formation from PEDOT under UV irradiation. However, the study observed negligible concentrations of 7-hydroxycoumarin, likely due to its degradation after 5 minutes of irradiation.
Overall, this study highlights the remarkable photocatalytic capabilities of CPs in emerging contaminants removal from water.