Tribocatalytic activation of peroxymonosulfate by TiO₂ nanoparticles for powerful degradation of organic pollutants

Sulfate radical (SO₄·⁻)-based advanced oxidation processes have received increasing interest for the treatment of organic wastewater, and various methods are being intensively investigated to activate peroxydisulfate (PDS) or peroxymonosulfate (PMS) to generate SO₄·⁻. Presently, we have explored the activation of PMS via tribocatalysis for the first time. In glass beakers with polytetrafluoroethylene (PTFE) disks coated on the bottoms, solutions of organic pollutants suspended with TiO₂ nanoparticles were subjected to magnetic stirring to realize tribocatalytic degradation. To our great surprise, the addition of 200 mg/L PMS was found to greatly enhance the tribocatalytic degradation of 50 mg/L rhodamine B (RhB), methylene blue (MB), and methyl orange (MO) solutions and 20 mg/L bisphenol A (BPA) and phenol solutions, which were all degraded rather thoroughly in quite short periods of time, and their total organic carbon removals were substantially improved. Electron paramagnetic resonance spectroscopy analyses showed that the addition of PMS not only led to the formation of SO₄·⁻ but also dramatically increased the amount of ·OH, O₂·⁻, and ¹O₂ when TiO₂ nanoparticles were stimulated through magnetic stirring. It is proposed that electron–hole pairs are excited in TiO₂ nanoparticles by mechanical energy absorbed through friction, which react with PMS to generate SO₄·⁻ and other radicals. These findings demonstrate an energy-efficient paradigm for PMS activation, and many more studies on tribocatalytic activation of PDS/PMS are highly desirable.