posted on 2021-11-30, 18:14authored byItisha Dwivedi, Chandramouli Subramaniam
Soft graphitizable
carbon-based multifunctional nanomaterials have
found versatile applications ranging from energy storage to quantum
computing. In contrast, their hard-carbon analogues have been poorly
investigated from both fundamental and application-oriented perspectives.
The predominant challenges have been (a) the lack of approaches to
fabricate porous hard-carbons and (b) their thermally nongraphitizable
nature, leading to inaccessibility for several potential applications.
In this direction, we present design principles for fabrication of
porous hard-carbon-based nanostructured carbon florets (NCFs) with
a highly accessible surface area (∼936 m2/g), rivalling
their soft-carbon counterparts. Subjecting such thermally stable hard-carbons
to a synergistic combination of an electric field and Joule heating
drives their transformation to free-standing macroscopic monoliths
composed of onion-like carbons (OLCMs). This represents the first
such structural transformation observed in sp2-based hard-carbon
NCFs to sp2-networked OLCMs. Micro-Raman spectroscopy establishes
the simultaneous increase in the intensity of D-, 2D-, and D + G-bands
at 1341, 2712, and 2936 cm–1 and is correlated to
the reorganization in the disordered graphitic domains of NCFs to
curved concentric nested spheres in OLCMs. This therefore completely
precludes the formation of a nanodiamond core that has been consistently
observed in all previously reported OLCs. The Joule heating-driven
formation of OLCMs is accompanied by ∼5700% enhancement in
electrical conductivity that is brought about by the fusion of outermost
graphitic shells of OLCs to result in monolithic OLC structures (OLCMs).
The porous and inter-networked OLCMs exhibit an excellent adsorption-based
capture of volatile organic compounds such as toluene at high efficiencies
(∼99%) over a concentration range (0.22–1.86 ppm) that
is relevant for direct applications such as smoke filters in cigarettes.