In recent years, more and more metal oxides have been finding critical tribo-catalytic applications. Presently, we have explored the tribo-catalytic conversion of H₂O and CO₂ using Co₃O₄ nanoparticles and obtained some surprising results. In an as-received 150 mL glass reactor enclosed with 10 mL of H₂O, 0.10 g of Co₃O₄ nanoparticles, 1 atm of CO₂, and a Teflon magnetic rotary disk, we observed the production of as much as 57.41 µmol/L of H₂, 0.15 µmol/L of CH₄, and 0.21 µmol/L of CO after 5 h of magnetic stirring. Metallic coatings of Cu, Ni, SUS316, Ti, Nb, Mo, and W were further introduced on reactor bottoms separately. For those coatings of Ni, SUS316, Ti, and Nb, the reduction of CO₂ was dramatically enhanced, and C₂₊ products of C₂H₆ and C₂H₄ were observed. Especially for the Ti coating, the amounts of H₂ and CH₄ were increased by 2 and 26 times from those for the glass bottom, respectively, and the amounts of C₂H₆ and C₂H₄ were very impressive. The Co₃O₄ nanoparticles were proven chemically stable under magnetic stirring in water, and hydroxyl radicals and superoxide radicals have been detected for the Co₃O₄ nanoparticles under magnetic stirring through fluorescence spectroscopy and electron paramagnetic resonance spectroscopy analyses. These findings not only reveal outstanding capability of Co₃O₄ to generate multicarbon products from H₂O and CO₂ through tribo-catalysis but also highlight a promising potential of tribo-catalysis as a whole to harness mechanical energy for addressing energy shortages and environmental pollution.

The TiO₂-H₂O₂ system possesses excellent oxidation activity even under dark conditions. However, the mechanism of this process is unclear and inconsistent. In this work, the binary component system containing TiO₂ nanoparticles (NPs) with single electron-trapped oxygen vacancy (SETOV, V_O·) and H₂O₂ exhibit excellent oxidative performance for tetracycline, RhB, and MO even without light irradiation. We systematically investigated the mechanism for the high activity of the TiO₂-H₂O₂ under dark condition. Reactive oxygen species (ROS) induced from H₂O₂ play a significant role in improving the catalytic degradation activities. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) results firstly confirm that H₂O₂ is primarily activated by SETOVs derived from the TiO₂ NPs through direct contribution of electrons, producing both ·O₂^-/·OOH and ·OH, which are responsible for the excellent reactivity of TiO₂-H₂O₂ system. This work not only provides a new perspective on the role of SETOVs playing in the H₂O₂ activation process, but also expands the application of TiO₂ in environmental conservation.