Nanodiamond Synthesis from Coal via Flash Joule Heating

As the coal industry transitions toward cleaner production,
it
demands advanced coal utilization strategies. Converting low-value
coal into high-value nanodiamonds (NDs) is a promising approach. NDs
exhibit exceptional properties with broad potential applications.
NDs are typically synthesized from high-purity graphite, whereas coal
serves as a lower-cost alternative. However, existing coal-based NDs
(C-NDs) are synthesized in low purity and low efficiency, restricting
their applicability and scalability. To address these challenges,
a fluorine (F)-assisted flash Joule heating (FJH) method is developed
using coke as a feedstock to synthesize C-NDs within 1 s. After post-treatment,
C-NDs achieve ∼ 100% purity with an 8% yield and exhibit thermal
stability comparable to commercial NDs. Theoretical calculations indicate
that F atoms induce electronic rearrangement and promote the formation
of interlayer C–C bonds. The application of C-NDs as seed crystals
was demonstrated to produce a high-quality diamond film. Life cycle
assessment (LCA) shows that C-NDs perform better than the high-pressure
high-temperature (HPHT) method in cost, carbon emissions, water consumption,
and electricity usage. Given their economic and environmental benefits,
a coal-to-diamond production system is proposed that may contribute
to cleaner coal utilization and the advancement of the coal industry.