Detection of low concentration oxygen containing functional groups on activated carbon fiber surfaces through fluorescent labeling

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 × 1011 COOH groups/cm2 and 1.3 × 1012 CHO groups/cm2 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 (∼1010/cm2) of FLOSS under the present conditions. The FLOSS results for CHO and COOH groups were compared with the concentrations determined by Boehm titration (3.11 × 1013/cm2 for CHO and 1.05 × 1013/cm2 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 sensitivity and specificity of FLOSS technique.