Formation of carbon nano-balls and carbon nano-tubes from northeast Indian Tertiary coal: Value added products from low grade coal

The paper reports the presence of carbon nano-balls and nano-tubes in the clean coal product during our experiments on desulfurization and deashing of northeast Indian high-sulfur Tertiary coal by molten caustic leaching (MCL) method. The Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HR-TEM), X-ray Diffraction (XRD), Raman and Fourier Transform Infrared (FT-IR) spectroscopy analyses revealed the formation of varied sizes of carbon nanomaterials in the clean coal product (MCL product). The nano-balls are in the range of 5–10 nm with nominal areas in the range of 40–100 nm², 160–220 nm², and 550–650 nm². The diameters of the carbon nano-tubes (CNTs) formed are in the range of 18–24 nm. The diameters of the branch carbon nano-tubes (BCNTs) are in the range of 35–92 nm. It is further observed that the alkaline treatment followed by acid treatment favored the formation of the carbon nano-balls, carbon nano-tubes (CNTs), and branch carbon nanotubes (BCNTs) in the coal product. The low-grade coals could also be used for the preparation of nano-carbon-based high value added products.