Surface Modifications of Sub‐Bituminous Coal for Preparing Carbon Nanofibers

ABSTRACT This study proposes two novel approaches to modify the surface properties of sub‐bituminous coal for its use as a precursor in the production of carbon nanofibers to energy storage applications. Sub‐bituminous coal is coded as raw coal (RC) in this study. Departing from conventional methods reported in the literature, this work introduces a thermal reduction process to synthesize reduced coal oxide (ROC) from oxide coal (OC). In addition, modified coal oxide (MOC) were prepared via noncovalent functionalization using a cationic surfactant. Fourier transform infrared (FTIR) analysis reveals the presence of −NO 2 , C = O, −OH, and −COOH functional groups on the surfaces of the OC, ROC, and MOC samples. These findings are further supported by energy dispersive spectrometer (EDS) and x‐ray diffractometer (XRD) analyses, which confirmed changes in the at. %O and at. %C contents and interlayer distance values, respectively. The surface charge values consistent with the contact angle changed with surface modifications. Overall, a linear correlation is observed between surface roughness and contact angle. The structure of the carbon nanofibers obtained from the ROC sample via electrospinning was characterized using XRD and TGA analyses. Field emission scanning electron microscopy (FE‐SEM) analysis revealed an average nanofiber diameter of 41.6 nm, while Brunauer–Emmett–Teller (BET) analysis indicated a specific surface area of 596.78 m 2 /g.