Joule Heating-Driven Transformation of Hard-Carbons to Onion-like Carbon Monoliths for Efficient Capture of Volatile Organic Compounds

[Image: see text] 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 m(2)/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 sp(2)-based hard-carbon NCFs to sp(2)-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.