Formation of onion-like fullerene and chemically converted graphene-like nanosheets from low-quality coals: application in photocatalytic degradation of 2-nitrophenol

The formation of coal-derived carbon nanomaterials (CNMs) consisting of onion-like fullerene and chemically converted graphene-like nanosheets from the low-quality coals were observed during an oxidation-cum-extraction (OCE) process. Detailed characterization of these CNMs was examined by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), solid-state C-13 NMR, UV-visible spectroscopy, and fluorescence spectroscopy (FL) techniques. The size of the coal-derived onion-like fullerenes was found to be in the size range of 5-20 nm and composed of 5-20 nm concentric shells. The outer diameter of the onion-like structures was estimated to be in the range of 3-15 nm. The presence of clusters of chemically converted graphene-like nanosheets was also observed in the coal-derived CNMs obtained by this novel OCE process. The method reported in this paper could be an inexpensive and simple chemical process for the preparation of CNMs from coals. These low-quality coal-derived CNMs were utilized as an efficient photocatalyst for the degradation of hazardous 2-nitrophenol under natural sunlight irradiation.