Contact-Electrocatalytic Degradation of Organic Pollutants Driven by Stirring-Type Low-Frequency Mechanical Energy

Environmental chemical effects of low-frequency mechanical energy deserve attention, yet its role has been traditionally regarded as a physical process. Using a remarkably simple beaker-stirrer system without any external catalyst, we demonstrated the contact-electro-catalysis (CEC) degradation of various organic pollutants via mechanical stirring. Specifically, malachite green (20 μmol L^-1) was completely degraded within 5 h (k = 0.68 h^-1), while a series of emerging contaminants could also be removed to varying extents within 12 h. The organic pollutant degradation was attributed to the reactive oxygen species (·OH, ·O₂^-, and ¹O₂) generated at the reactor wall-solution interface by CEC. Furthermore, degradation performance depended on triboelectric properties of reactor materials (polytetrafluoroethylene > polystyrene > stainless steel > glass) and hydrodynamic conditions (rotation rate and impeller diameter). Increasing rotation rate or impeller diameter enhanced mechanical energy input (Reynolds number and turbulent kinetic energy), then increased the average interfacial mechanical force (resultant traction force), and thereby promoted CEC. This work proposed that low-frequency mechanical energy provided by the prevalent hydraulic processes in nature may drive degradation of organic pollutants at natural solid/liquid catalytic interfaces, thus providing an innovative explanation of natural water self-purification through a chemical process.