Turbostratic Carbon: Synthesis via Magnesium Self-Propagating Combustion and Microstructural Characterization

Turbostratic carbon constitutes a graphitic phase characterized by the disordered stacking of graphene layers, lacking the ABAB stacking sequence typical of crystalline graphite. This rotational and translational disorder between adjacent planes is manifested in an increased interplanar spacing (0.344–0.380 nm compared to 0.335 nm in crystalline graphite), which promotes ionic diffusion and confers a high specific surface area to the material [1]. Various synthetic routes enable its production, including the rapid pyrolysis of carbonaceous precursors (biomass or polymers at 600–1500 °C), thermal reduction of graphene oxide, low-temperature chemical vapor deposition, and methods based on solid CO2 have also been reported [2]. Its distinctive properties a high density of active edge sites, moderate electrical conductivity with low anisotropy, and low-cost scalability position it as a promising material for applications in Li/Na-ion battery anodes, supercapacitors, catalytic supports, and CO2 capture. Unlike monolayer graphene (a 2D material with ballistic conductivity), turbostratic carbon exhibits a three-dimensional architecture with diffusive charge transport, compatible with large-scale industrial processes [3]. In the present study, the synthesis of turbostratic carbon via the self-propagating combustion reaction of magnesium in a controlled CO2 atmosphere is reported. Compacted discs of metallic magnesium (70 mm in diameter × 20 mm in thickness) were introduced into a semihermetic stainless-steel reactor and subjected to a continuous CO2 flow of 250 cm³ min−¹. Ignition was induced by a localized electrical discharge, triggering a self-sustaining exothermic reaction that reached temperatures exceeding 2000 °C, according to thermographic estimation. Structural characterization was performed by X-ray diffraction (XRD) using a Panalytical X’Pert PRO diffractometer, operated at 40 kV and 30 mA with CuKα radiation (λ = 0.15406 nm) in Bragg–Brentano geometry. Scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS, HITACHI SU3500) at 30 kV was employed to examine both morphology and elemental composition. The microstructure of the turbostratic carbon was also investigated using high-resolution transmission electron microscopy (HR-TEM, JEOL JEM2200FS) operated at 200 kV. Figure 1a presents a SEM micrograph showing irregular agglomerates of 10–50 µm with a stacked laminar morphology. This material exhibits a matrix composed of turbostratic carbon intercalated with magnesium oxide (MgO) particles. Panels b–c display the energy-dispersive X-ray spectroscopy (EDS) analysis, confirming a residual Mg content below 3 at. %, attributable to remnants of unremoved MgO. Figure 2a shows a representative HR-TEM image in which the particle morphology appears as agglomerates of nano-onion–like structures. In this micrograph, a region of interest (ROI) was selected (panel b), and a Fast Fourier Transform (FFT) [4] was applied to index the interplanar spacings (panel c). These interplanar spacings were confirmed through indexing of the XRD pattern using the X’Pert HighScore Plus software and card 01-075-1621 ICSD [5]. This result confirmed that the turbostratic carbon structure exhibits a hexagonal phase with space group P63mc (186). The average crystallite size was 8 nm. Characteristic diffraction reflections of turbostratic carbon were identified at 2θ = 26.0° (002), 44.0° (100), and 54.5° (004), with a calculated d(002) spacing of 0.35 nm, consistent with stacking disorder. The results demonstrate the viability of autonomous magnesium combustion as a scalable synthetic route for producing turbostratic carbon with structural properties suitable for advanced electrochemical applications. (a) SEM micrograph showing irregular clusters of stacked sheets, (b) EDS measurement displaying an agglomerate of turbostratic carbon particles. (c) Elemental mapping for C, Mg and O, respectively. (a) HR-TEM image of carbon turbostratic nanoparticles. (b) Magnification of HR-TEM image showing nano-onions-like morphology. (c) Interplanar spacing indexation associated to the characteristic d(002).