ARTICLE pubs.acs.org/EF
Reductive Alkylation of Anthracite: Edge Functionalization Yanqiu Sun, Oleksandr Kuznetsov, Lawrence B. Alemany, and W. E. Billups* Department of Chemistry and The Richard E. Smalley Institute for Nanoscale Science and Technology, Rice University, 6100 Main Street, Houston, Texas 77005, United States
bS Supporting Information ABSTRACT: Reduction of anthracite by electron transfer from either lithium or sodium in liquid ammonia yields a salt that can be alkylated by 1-iodododecane to yield nanocoal that is partially soluble in common organic solvents. NMR indicates that the dodecyl groups are attached to the edges of the aromatic ring systems, with many of the dodecyl groups extending into void spaces. Thermal gravimetric analysis shows that sodium gives a slightly higher level of functionalization. Atomic force microscopy (AFM) images of soluble dodecylated anthracite reveal nanoparticles that vary from 3 to 12 nm high. Scanning electron microscopy (SEM) and bright field high-resolution transmission electron microscopy (HRTEM) of the raw anthracite reveal a layered structure with dislocations. Inorganic materials that occur in the raw anthracite were identified by energy dispersive X-ray spectroscopy (EDS). Simple alkenes were found to react with the coal salt to give oligomers of the alkene that are grafted onto the surface of the coal.
1. INTRODUCTION Coal is an organic rock-like material that results from the decay and maturation of floral remains and plants over 50 to 100 million years. It is an abundant energy source and forms a major part of the earth’s fossil fuel resources.1,2 International reservoirs of coal are greater than any other fossil fuel, including oil and gas. Anthracite is the highest ranking coal, with a carbon content as high as 98%. Anthracite forms from bituminous coal when great pressures are developed in folded rock strata during the creation of mountain ranges. A major impediment in the handling and characterization of carbon-rich materials is their low solubility in organic solvents or water. Although early attempts to prepare soluble coal by reductive alkylation met with remarkable success when lower rank coals were studied,2 12 reductive alkylation of anthracite failed to yield a soluble product.5 A series of elegant experiments demonstrated that electron transfer from naphthalene anion to anthracite was comparable to a bituminous coal, but only one alkyl group for every 100 carbon atoms could be added to the anthracite and this proved to be insufficient to affect solubility. A detailed structural characterization of three Chinese anthracites was carried out by Tomita and his co-workers using a temperature programmed oxidation method to determine the hydrogen content of these anthracites.13 The accurate determination of the C/H ratio and a determination of the heteroatom content using information from the literature allowed the elemental composition, and thus the size of the graphenic sheets that form the anthracite, to be determined. It was suggested that the hetero atoms were located along the edges of the sheets and that no defects occur along the basal plane of the graphene sheets. HRTEM images were also used to determine the size of the graphenic sheets using a method developed earlier in this laboratory.14 It is interesting, however, that numerous dislocations can be seen in the HRTEM images that were published.13 In view of current interest in the synthesis of soluble carbon-rich materials, and the knowledge that anthracite consists mainly of polycyclic aromatic hydrocarbons, we have investigated routes to r 2011 American Chemical Society
soluble anthracite using methods described earlier for carbon nanotubes, graphite, and charcoal.15 19 Salient features of this study are the use of longer chain (dodecyl) solubilizing groups, the synthesis of anthracite grafted by polydodecene, and the use of microscopy for characterization.
2. EXPERIMENTAL SECTION Materials. A sample of anthracite was obtained from J. Crelling (Southern Illinois University). The anthracite came from the Mammoth seam that is located in Schuylkill county Pennsylvania. The composition of the sample was determined by XPS to be 92% carbon and 6.4% oxygen. Nitrogen, silicon, and sulfur were each present in
