Binary nanocomposite materials comprised of cobalt oxide (Co₃O₄) nanocrystals embedded in reduced graphene oxide (RGO) sheet were fabricated using one-pot hydrothermal synthetic route without using any structure guiding surfactant. We succeeded to visualize a 1/8 corner of a single cubic shape Co₃O₄ crystal under transmission electron microscopy (TEM). Shape and size of Co₃O₄ crystals varies from particle-type (size ∼10 nm), octahedral (size ∼20 nm) and aggregates of particles (size in the range of 50–80 nm) with increase in concentration of Co₃O₄ in the Co₃O₄/RGO composite. Cyclic voltammetry and charge/discharge measurements in aqueous KOH electrolyte (2 M) revealed that the Co₃O₄/RGO composite material exhibits electrochemical supercapacitive performance giving specific capacitance of 487 F g⁻¹ at scan rate of 5 mV s⁻¹ followed by outstanding cyclic stability sustaining 96.6% of capacitance after 2000 cycles.

Heat-treatment of crystalline fullerene C₇₀microtubes at a high temperature of 2000 °C yielded mesoporous graphitic carbon microtubes having a robust framework, which showed enhanced supercapacitive performance.

High surface area and large pore volume carbon materials having hierarchical nanoporous structure are required in high performance supercapacitors. Such nanoporous carbon materials can be fabricated from organic precursors with high carbon content, such as synthetic biomass or agricultural wastes containing cellulose, hemicellulose, and lignin. Using recently developed unique concept of materials nanoarchitectonics, high performance porous carbons with controllable surface area, pore size distribution, and hierarchy in nanoporous structure can be fabricated. In this review, we will overview the recent trends and advancements on the synthetic methods for the production of hierarchical porous carbons with one- to three-dimensional network structure with superior performance in supercapacitors applications. We highlight the promising scope of accessing nanoporous graphitic carbon materials from: (i) direct conversion of single crystalline self-assembled fullerene nanomaterials and metal organic frameworks, (ii) hard- and soft-templating routes, and (iii) the direct carbonization and/or activation of biomass or agricultural wastes as non-templating routes. We discuss the appealing points of the different synthetic carbon sources and natural precursor raw−materials derived nanoporous carbon materials in supercapacitors applications.

Iodine and methylene blue adsorption properties of the high surface area nanoporous carbon materials derived from agro-waste and rice husk is reported. Rice husk was pre-carbonized at 300 °C in air followed by leaching out the silica nanoparticles by extraction with sodium hydroxide solution. The silica-free rice husk char was mixed with chemical activating agents sodium hydroxide (NaOH), zinc chloride (ZnCl₂), and potassium hydroxide (KOH) separately at a mixing ratio of 1:1 (wt%) and carbonized at 900 °C under a constant flow of nitrogen. The prepared carbon materials were characterized by scanning electron microscopy (SEM), Fourier transformed-infrared spectroscopy (FT-IR), powder X-ray diffraction (pXRD), and Raman scattering. Due to the presence of bimodal micro- and mesopore structures, KOH activated samples showed high specific surface area ca. 2342 m²/g and large pore volume ca. 2.94 cm³/g. Oxygenated surface functional groups (hydroxyl, carbonyl, and carboxyl) were commonly observed in all of the samples and were essentially non-crystalline porous particle size of different sizes (<200 μm). Adsorption study revealed that KOH activated samples could be excellent material for the iodine and methylene blue adsorption from aqueous phase. Iodine and methylene blue number were ca. 1726 mg/g and 608 mg/g, respectively. The observed excellent iodine and methylene blue adsorption properties can be attributed to the well-developed micro- and mesopore structure in the carbon material. This study demonstrates that the agricultural waste, rice husk, and derived nanoporous carbon materials would be excellent adsorbent materials in water purifications.