Cobalt-mediated activation of peroxymonosulfate (PMS) has been widely investigated for the oxidation of organic pollutants. Herein, we employ cobalt-doped Black TiO₂ nanotubes (Co-Black TNT) for the efficient, stable, and reusable activator of PMS for the degradation of organic pollutants. Cobalt-doped Black TNTs induce the activation of PMS by itself and stabilized oxygen vacancies that enhance the bonding with PMS and provide catalytic active sties for PMS activation. A relatively high electronic conductivity associated with the coexistence of Ti⁴⁺ and Ti³⁺ in Co-Black TNT enables an efficient electron transfer between PMS and the catalyst. As a result, Co-Black TNT is an effective catalyst for PMS activation leading to the degradation of selected organic pollutants when compared to other TNTs (TNT, Co-TNT, and black TNT) and other Co-based materials (Co₃O₄, Co-TiO₂, CoFe₂O₄, and Co₃O₄/rGO). The observed organic compound degradation kinetics are retarded in the presence of methanol and natural organic matter as sulfate radical scavengers. These results demonstrate that sulfate radical is the primary oxidant generated via PMS activation on Co-Black TNT. The strong interaction between Co and TiO₂ through Co-O-Ti bonds and rapid redox cycle of Co²⁺/Co³⁺ in Co-Black TNT prevents cobalt leaching and enhances catalyst stability over a wide pH range and repetitive uses of the catalyst. Electrode-supported Co-Black TNT facilitates the recovery of the catalyst from the treated water.

Peroxymonosulfate activation on cobalt-doped TiO₂ nanotubes (Co-TNTs) as applied for the degradation of organic pollutants in the absence of light and under solar light irradiation is investigated. Co-TNTs generate SO₄˙⁻via PMS activation in the dark, while they result in SO₄˙⁻ formation via PMS activation and, at the same time, produce ˙OH via photocatalytic water oxidation under simulated solar light illumination. Radical generation is explored using electron paramagnetic resonance (EPR) spectroscopy. The catalytic activity is maintained over multiple catalytic cycles with negligible Co(II) leaching. The nanotube catalysts are easily recovered without loss of activity after water treatment. The Co-TNT/PMS reaction system can be used for wastewater treatment during the day and at night.