Panma

Poly (acrylonitrile-co-methyl acrylate) (PANMA) (acrylonitrile weight percentage: ~94%) and polyvinylpyrrolidone (PVP) (360,000 g/mol) were purchased from Sigma–Aldrich (St. Louis, MO, USA). PANMA acted as C- and N- source precursor, and PVP acted as a sacrificial material. Standard Reference Material^® 2682c subbituminous coal (referred as 2682 coal) from Wyodak–Anderson coal seam (powder river basin, PRB Coal), and Standard Reference Materials^® 2684c bituminous coal (referred as 2684 coal) from Pittsburgh coal seam were purchased from National Institution of Standards and Technology (NIST) (Gaithersburg, MD, USA). Figure 1 lists four ILs (>98.0% HPLC and <1.0% H₂O impurity) used in coal extraction: 1-butyl-2,3-dimethylimidazolium chloride (C₄m₂imCl), 1-ethyl-3-methylimidazolium chloride (C₂mimCl), 1-Hexyl-3-methylimidazolium chloride (C₆mimCl) and 1-Butyl-3-methylimidazolium chloride (C₄mimCl), which were purchased from Sigma–Aldrich (St. Louis, MO, USA) and used as extraction solvents without further purification. 1-Methyl-2-pyrrolidinone (NMP) (99.5%) (Sigma–Aldrich) was used as a solvent to obtain coal char from coal/ILs solution through a centrifuge. N,N-Dimethylformamide (DMF, 99.8%) (Sigma–Aldrich) was used as an organic solvent to dissolve PANMA, PVP and coal precursors for electrospinning process.