Combination of Photocatalytic and Photo-Fenton Oxidations Using Visible Light-Activated Photocatalyst for Decomposing Synthetic Chemical in Water

Heterogeneous photo-Fenton oxidation using CdS/multi-walled carbon nanotube-TiO₂ (CdS/MWCNT-TiO₂) under visible light relied on combination of the photocatalytic, photo-Fenton and photo-sensitizing oxidation. Heterogeneous photo-Fenton oxidation of methylene blue (MB), a model synthetic compound found in wastewater, was carried out in the CdS/MWCNT-TiO₂ aqueous suspension under visible light irradiation. The photo-Fenton reaction resulted in faster and higher removal of MB and the total organic carbon (TOC) (98% and 83 % in 30 min, respectively) than the dark Fenton oxidation and the photocatalytic degradation alone at the selected conditions. The optimum molar ratio of [MB]:[H₂O₂]:[Fe³⁺] (1:12:3.4) in the photo-Fenton oxidation showed that the process would be a cost-effective solution to degrade aqueous methylene blue. The photocatalytic activity of the CdS/MWCNT-TiO₂ was maintained effectively even after several cyclic experiments. Besides, this study assessed the potential of using the CdS/MWCNT-TiO₂ to degrade more toxic emerging contaminants from aqueous solutions under visible light and solar light irradiation. Degradation of bisphenol A (BPA), an endocrine disruptor was evaluated using the CdS/CNT-TiO₂ under solar and visible light irradiation. Nearly 95% BPA with initial concentration of 20 ppm in a solution with pH 3, and 0.5 g/L of catalyst was removed after solar and visible light irradiation in 5 min and 4 h, respectively. Further works will include identification of intermediate formation and possible mechanisms associated with the photo-Fenton oxidation of BPA, evaluation of cytotoxicity and estrogenic activity of BPA oxidation products and process modeling of the photo-reactor.