Synthesis of Carbon Nanofibers Film from Coal Liquefaction Residues: Effect of HNO₃ Pretreatment

Abstract

Preasphaltene derived from coal liquefaction residues (CLRPA) has a high carbon content and is easily graphitized, making it an excellent precursor for obtaining carbon nanofibers. In this work, carbon nanofibers film (CLRPACF) was obtained by electrospinning CLRPA and polyacrylonitrile (PAN) composites, HNO3 pretreatment, air stabilization, and carbonization. During the process, HNO3 pretreatment is crucial in maintaining morphology and regulating physicochemical properties. The effect of HNO3 pretreatment on as-spun and stabilized nanofibers was investigated. The characteristics of changes occurring at various temperatures and reaction times were evaluated via Fourier transform infrared and X-ray photoelectron spectroscopy. The results show that HNO3 pretreatment introduces −NOx groups into as-spun nanofibers, thereby promoting polymerization reactions at low temperatures. The cyclization cross-linking reaction of PAN molecules and oxidative polymerization reactions of CLRPA, along with the conversion of oxygen-containing functional groups from hydroxyl oxygen to carbonyl oxygen, mainly occur during the stabilization process. Our findings show that HNO3 pretreatment can improve the oxidative stability of low softening point pitch-based carbon nanofibers.