Adsorption of Four Representative Biological Compounds onto Graphite Nanofibers Dorothy W. Skaf,* ,† Michael A. Smith, † Kevin C. Brodwater, † Maulin N. Gandhi, † Anthony R. DeBiase, † and Alexander J. Zoelle † † Department of Chemical Engineering, Villanova University, 800 East Lancaster Avenue, Villanova, Pennsylvania 19805, United States * S Supporting Information ABSTRACT: The present study investigates the adsorption of four compounds important in carbon adsorption hemoperfusion. Graphite nanofibers (GNFs) having different carbon plane orientations have structural features that make them potentially attractive in this application compared to activated carbon. Generally, adsorption capacity increased in the order of ribbon > herringbone > platelet fiber types. All fibers were poor adsorbents for creatinine. Herringbone and platelet fibers had sorption capacities less than 25% of activated carbon for all adsorbates on a mass basis. Except for vitamin B12, behavior of ribbon fibers was similar; vitamin B12 adsorption was nearly 50% greater than activated carbon on a mass basis. In contrast, on the basis of surface area, all of the fibers were comparable to or outperformed activated carbon for the adsorption of all adsorbates. This suggests that in addition to BET surface area, interactions between adsorbate and exposed basal planes in carbon are important in determining adsorption capacity. Chemical treatment with hydrochloric acid or with urea followed by thermal treatment did not significantly change the fiber surface area, micropore volume, or equilibrium adsorption. Nitric acid treatment of herringbone and ribbon fibers slightly decreased the surface area but did not enhance adsorption, whereas this treatment degraded platelet fibers. 1. INTRODUCTION The availability of carbon-based materials with different structures provides an avenue for tailoring the materials for specific applications. Hemoperfusion, the direct contact of blood with adsorbent, has application for removal of adsorbates with molecular weights between 500 and 6000 Da, which are too large to pass through dialysis membranes. 1 Activated carbon is the adsorbent of choice; however, there have also been ongoing efforts to design improved carbon-based adsorbents for hemoperfusion. 2 Graphite nanofibers (GNFs) have a unique combination of moderate surface area, electrical conductivity within the carbon planes, and surface function- alities that may prove advantageous in separations and purifications, specifically hemoperfusion. However, one of the disadvantages of GNFs is that they do not provide the very high pore volume and surface area afforded by microporous materials such as activated carbons and zeolites. Despite this disadvantage, the favorable characteristics of GNFs warrant investigation of their performance in removing uremic toxins. Several investigators have evaluated the hemoperfusion- related adsorption properties of various forms of carbon using vitamin B12, creatinine, and other model compounds. Yang et al. 3 made phenolic-resin-derived activated carbon spheres with various pore sizes through the addition of pore-forming agents and tested these with vitamin B12 and creatinine. The best sorption capacity for vitamin B12 was approximately 9 mg vitamin B12/gram of carbon for an initial vitamin B12 concentration of 25 mg/L. For creatinine, the best sorption capacity was approximately 45 mg creatinine/gram of carbon for an initial creatinine concentration of 100 mg/L. Carbon nanotubes (CNTs) from Ni-catalyzed pyrolysis of propylene have been studied as adsorbents for creatinine and vitamin B12 by Ye et al. 4,5 They found that the CNTs had a sorption capacity (24 mg creatinine/gram of carbon) slightly lower than that of an activated carbon sorbent used in a commercial Received: August 11, 2011 Revised: May 23, 2012 Accepted: May 25, 2012 Published: June 8, 2012 Figure 1. Sketches of (a) platelet, (b) herringbone, and (c) ribbon fibers. Sketches adapted from Bessel et al. 13 Article pubs.acs.org/IECR © 2012 American Chemical Society 8286 dx.doi.org/10.1021/ie201788j | Ind. Eng. Chem. Res. 2012, 51, 8286-8292