Carbon nano-onions (CNOs) were synthesized at ambient conditions using the wick-pyrolysis technique with ghee as a precursor. A high-purity copper substrate produced unique CNOs, differing from those obtained with other metals. To purify the nanoparticles, they underwent treatment with a solvent mixture of acetone and deionized water or were pyrolyzed at 1000 °C under nitrogen without a catalyst. Various characterization techniques, including X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), High-Resolution Transmission Electron Microscopy (HR-TEM), and Raman Spectroscopy, confirmed the successful formation of CNOs. Energy Dispersive Spectroscopy (EDS) and Elemental analysis (CHN) indicated the presence of oxygen in treated CNOs. X-ray photoelectron spectroscopy (XPS) revealed binding energies linked to C-O and C=O bonds. The average particle size was found to be 30–50 nm, with some agglomeration in pyrolyzed samples. A significant increase in surface area from 79.7 m2/g to 261.8 m2/g was observed, along with changes in pore radius and volume via Brunauer–Emmett–Teller (BET) analysis. Water contact angles on the CNO surface were measured at 125° and 138°, indicating hydrophobicity. Electrochemical tests on CNO-based composite electrodes yielded a specific capacitance of 109.7 F/g with 96% capacity retention over 5000 cycles.
Srinivasan et al. (Fri,) studied this question.