Tailored aluminum coordination in metakaolin: A defect-engineering strategy for high-performance tribocatalysis

Contact electrification, the charge exchange phenomenon occurring upon contact between dissimilar materials, is ubiquitous yet often underappreciated. Tribocatalysis, which harnesses this process to convert mechanical energy into chemical energy for degrading wastewater pollutants, has recently gained attention for its potential. In this study, we transformed natural kaolin into amorphous metakaolin (MK) tribocatalysts via a single-step calcination process, optimizing their performance through structural modulation. Solid-state NMR spectroscopy and degradation experiments revealed that MK-800, enriched with unsaturated Al[IV] and Al[V] sites, achieved a degradation rate constant of 0.1607 h ⁻¹ —64 times higher than that of raw kaolin. Density functional theory calculations confirmed that unsaturated aluminum coordination enhances electron mobility and reduces electron escape energy. We further refined tribocatalytic efficiency by optimizing parameters such as friction area, solution environment, and atmospheric conditions. Electron paramagnetic resonance spectroscopy identified positive charges (q ⁺), hydroxyl radicals ( OH), and superoxide anions ( O ₂ ⁻) as key reactive species driving pollutant degradation. This work introduces a novel, cost-effective approach to pollutant remediation and lays a theoretical foundation for advancing structural control in tribocatalysis.