Detection of low concentration oxygen containing functional groups on activated carbon fiber surfaces through fluorescent labeling Xue Feng a,b , Nikolay Dementev b , Wenguo Feng a , Radisav Vidic a , Eric Borguet b, * a Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15260, USA b Chemistry Department, Temple University, 1901 N. 13th Street, Philadelphia, PA 19122, USA Received 14 June 2005; accepted 30 October 2005 Available online 7 February 2006 Abstract Covalent fluorescent labeling of surface species (FLOSS) was used to detect relatively low concentrations of surface functional groups (OH, COOH and CHO) on activated carbon fiber surfaces. The chromophores were attached to the surface through a reaction specific to each type of surface functional group. FLOSS indicated the presence of 8.7 · 10 11 COOH groups/cm 2 and 1.3 · 10 12 CHO groups/cm 2 on the ACF 25 fiber surface. Neither the infrared spectrum nor the X-ray photoelectron spectrum showed evidence of the existence of those low concentration groups. The concentration of OH groups on the fiber surface was lower than the detection limit (10 10 /cm 2 ) of FLOSS under the present conditions. The FLOSS results for CHO and COOH groups were compared with the concentrations deter- mined by Boehm titration (3.11 · 10 13 /cm 2 for CHO and 1.05 · 10 13 /cm 2 for COOH). The limited accessibility of the ACF surface to relatively large chromophores is one of the main reasons for the discrepancy between these two methods. FLOSS detects only exposed functional groups as opposed to functional groups hidden in small pores. This apparent limitation, however, highlights the surface sen- sitivity and specificity of FLOSS technique. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Carbon fibers; X-ray photoelectron spectroscopy; Infrared spectroscopy; Spectrophotometry; Functional groups 1. Introduction Many applications of carbon materials, including acti- vated carbon, activated carbon fibers and carbon nano- tubes, are based on the presence of oxygen containing surface functional groups [1–6]. For example, the dynamic adsorption of hexane by activated carbons under humid conditions was found to be mainly governed by the quan- tity of acidic surface functional groups [7]. It is reported that oxygen surface complexes, possibly lactone and car- bonyl groups, were the active sites for Hg-0 capture [8]. An increase in the number of some acid functional groups and the surface wetting quality was helpful to enhancing microorganism fixing [9]. Several methods have been applied to detect and quan- tify oxygen functional groups on carbon surfaces [10–13]. Infrared spectroscopy (IR) [14–20], X-ray photoelectron spectroscopy (XPS) [2,7,14,15,20,21], thermal desorption spectroscopy (TPD) [14,17,22], elemental analysis [2,23,24] and Boehm titration [14,15,24–26] are the most frequently used methods. Although the Boehm titration is a valuable technique, it is limited to special functional groups [13,27]. TPD only provides the total number of groups without detailed information about their types. Quantitative analysis of XPS and IR is not straightforward [13]. The time-consuming titration [10], the difficulty in assigning the peaks, and the influence of experimental parameters (such as the heating rate in TPD) highlight the need for new methods. Furthermore, these techniques 0008-6223/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2005.10.057 * Corresponding author. Tel.: +1 215 204 9696; fax: +1 215 204 9530. E-mail address: eborguet@temple.edu (E. Borguet). www.elsevier.com/locate/carbon Carbon 44 (2006) 1203–1209