Salt-Assisted Air-Purification of Detonation Nanodiamonds

The widespread application of detonation nanodiamonds (DNDs) is limited by surface-coated non-diamond sp² carbon impurities. In this work, an efficient salt-assisted catalytic purification strategy is developed to achieve selective oxidation removal of sp² carbon. DND black powder was mixed with various chloride, carbonate, and bicarbonate salts and thermally treated in air to systematically investigate the effects of anions and cations on purification efficiency. Thermogravimetric analysis reveals that all tested salts significantly reduce the oxidation onset temperature of sp² carbon and exhibit distinct catalytic trends: for anions, bicarbonates > carbonates > chlorides; for cations, Cs⁺ ≈ K⁺ > Na⁺. Among them, KHCO₃ introduced via a wet-wrapping method shows the optimal performance, lowering the oxidation temperature by approximately 160 °C. Moreover, the wet-wrapping process effectively suppresses particle sintering and agglomeration during purification, resulting in purified DNDs with reduced average particle size and markedly improved dispersibility. Mechanistic investigations demonstrate that free alkali metal cations act as active sites, preferentially catalyzing sp² carbon oxidation through a synergistic oxygen spillover-electron transfer mechanism. This study provides an effective and highly selective approach for DND purification. The proposed salt-assisted strategy, integrating catalytic oxidation and dispersion control, also offers valuable insights for the preparation of high-performance nanomaterials.