Mechanical friction energy is a ubiquitous green energy that can be collected and transformed into electrical energy for water treatment, a concept theoretically referred to as tribocatalysis. The efficient removal of organic pollutants from wastewater by tribocatalysis still faces challenges. Employing doping technology to introduce metallic elements into materials is anticipated to enhance tribocatalytic performance by improving material properties. In this work, NiO and x wt% Co-doped NiO (x = 3, 5, 7, and 9) nanocatalysts are prepared using a coprecipitation method. The incorporation of Co effectively reduces the bandgap of NiO, enhancing tribocatalytic decomposition performance through the synergistic effects of charge transfer and electron transition. Notably, the optimized 7 wt% Co–NiO nanoparticles demonstrate the leading performance in the decomposition of rhodamine B (RhB), with a decomposition ratio of 96.7% after 120 min, representing a 23.1% increase over pure NiO. Electrochemical impedance spectroscopy (EIS) demonstrates that Co doping reduces the charge transfer resistance of NiO, resulting in the production of more reactive species. Radical trapping experiments and electron paramagnetic resonance spectroscopy (ESR) reveal that both superoxide radicals (·O₂⁻) and holes (h⁺) are key active radicals in dye decomposition. Furthermore, the 7 wt% Co–NiO nanocatalyst exhibits excellent stability and magnetic recyclability, retaining an 87.1% decomposition ratio after five cycles. The Co–NiO nanocatalyst, with these advantages of excellent tribocatalysis performance, low cost, and magnetic recyclability, has potential for application in wastewater treatment through harvesting and utilizing environmental mechanical friction energy in the future.

The development of a high-performance ferroelectric piezo-photocatalyst is an efficient strategy for advancing sustainability within the environmental and energy sectors. Yet, a major challenge lies in the creation of a strong polarized electric field that can effectively hinder charge recombination, both within the bulk and on the surface of catalysts. Herein, we synthesize a series of Nb-doped Bi₄Ti₃O₁₂ nanosheets via a facile one-pot hydrothermal method to achieve synergistically enhanced piezo-photocatalytic performance in CO₂ reduction and pollutant degradation. The optimized doped Bi₄Ti₃O₁₂ demonstrates remarkable efficiency in the conversion of CO₂ into CO, with a high production rate of 72.7 μmol∙g⁻¹∙h⁻¹ without using co-catalysts or any sacrificial agent, surpassing the performance of unmodified Bi₄Ti₃O₁₂ by up to 4.69 folds. Additionally, our catalyst demonstrates ultra-fast piezo-photocatalytic degradation of organic pollutant Rhodamine B (RhB) at low concentrations and exceptional piezo-photocatalytic activity at high concentrations, outperforming most previously reported state-of-the-art catalysts. The systematic corroboration of catalyst characterization and experimental analysis reveals that the synergistic effect arises from the amplified macroscopic polarization induced by lattice distortion caused by the larger Nb ions, thereby improving piezo-photocatalytic efficiency. This research thus offers valuable insights into the direct design and fabrication of versatile catalytic systems, with applications spanning CO₂ valorization and beyond.

The BiFeO₃/g-C₃N₄ heterostructure, which is fabricated via a simple mixing-calcining method, benefits the significant enhancement of the pyrocatalytic performance. With the growth of g-C₃N₄ content in the heterostructure pyrocatalysts from 0 to 25%, the decomposition ratio of Rhodamine B (RhB) dye after 18 cold-hot temperature fluctuation (25-65 ℃) cycles increases at first and then decreases, reaching a maximum value of ~94.2% at 10% while that of the pure BiFeO₃ is ~67.7%. The enhanced dye decomposition may be due to the generation of the internal electric field which strengthens the separation of the positive and negative carriers and further accelerates their migrations. The intermediate products in the pyrocatalytic reaction also have been detected and confirmed, which proves the key role of the pyroelectric effect in realizing the dye decomposition using BiFeO₃/g-C₃N₄ heterostructure catalyst. The pyroelectric BiFeO₃/g-C₃N₄ heterostructure shows the potential application in pyrocatalytically degrading dye wastewater.