Treatment of Polyaniline Wastewater by Coupling of Photoelectro-Fenton and Heterogeneous Photocatalysis with Black TiO2 Nanotubes

In this study, mineralization of organic pollutants in polyaniline (PANI) wastewater was achieved by a combination of photoelectro-Fenton (PEF) and heterogeneous photocatalysis with black TiO2 nanotubes. Organics were decomposed by the (OH)-O-center dot radicals and SO4-center dot radicals formed on the black TiO2 nanotube photocatalyst and at the IrO2/Ti anode during water oxidation and from the Fenton's reaction between Fe2+ and generated H2O2. Poor chemical oxygen demand (COD) removal was obtained utilizing visible light/TiO2, anodic oxidation with generated H2O2 (AO-H2O2), visible light/black TiO2/AO-H2O2, and electro-Fenton. The mineralization was strongly increased by the PEF/black TiO2 process because of the photolysis of products under visible light irradiation; it was improved by coupled heterogeneous photocatalysis due to the additional (OH)-O-center dot radicals at the black TiO2 nanotube surface. The results demonstrated that about 96.4% COD and 85% total organic carbon of PANI wastewater were removed after 360 min by the PEF/black TiO2 process under the optimal conditions. The black TiO2 nanotubes exhibited good stability as the mineralization ratio in 360 min which was still above 80% after 10 cycles' degradation, showing that the black TiO2 nanotubes are powerful and promising photocatalysts for improving the removal efficiency of PANI wastewater.