Silicon-Mediated Laser Shock Synthesis of Nanocrystalline Diamonds from Low-Rank Coal

Coal is traditionally regarded as a primary energy resource for combustion. However, its high carbon content renders it an ideal precursor for the synthesis of carbon nanomaterials. The valorization of low-value coal into high-value nanocrystalline diamonds (NDs) offers a promising strategy. In this work, we developed a facile and rapid strategy for the synthesis of NDs from low-rank long-flame coal via silicon-mediated laser-induced shockwave high pressure within a water-confinement layer. The as-synthesized products show an average crystallite size of ∼5 nm and exhibit features consistent with cubic diamond, including the (111), (220), and (311) reflections and ∼0.20 nm lattice fringes with a ∼70° intersection angle. C 1s X-ray photoelectron spectroscopy indicates an enhanced sp³-bonded carbon contribution after laser shock treatment. Raman spectra of the coal/Si pellet surfaces demonstrate that the laser-induced coal-to-ND transformation is a kinetically controlled process. Molecular dynamics (MD) simulations reveal that the chemical reaction between coal-derived carbon and active Si additives may locally provide an additional chemical driving force, which promotes C-C bond activation and accelerates the formation of sp³-like, diamond-like structural motifs. These findings provide a sustainable route for the synthesis of NDs from abundant and inexpensive coal, advancing the clean and high-value-added utilization of coal resources.