IDENTIFICATION OF SURFACE FUNCTIONAL GROUPS ON ACTIVE CARBON BY INFRARED INTERNAL REFLECTION SPECTROPHOTOMETRIC

Previous efforts (I-5) to obtain infrared spectra for carbon black, activated carbon, and coal have involved transmission measurements on prepared KBr pellets or Nujol mulls. Although some information regarding structure of the bulk materials has been gained in this manner, such techniques have proved rather unsatisfactory for identification of the surfaces of carbon materials because of invariably poor resolution. Ergun (4) has shown that the extinction coefficient of graphite in the infrared spectral range is very high, approaching that of a metal. The average extinction coefficient, k, is about 0.66 in the visible region, and little variation is observed through the short wavelength region of the infrared (4). Common organic compounds or functional groups exhibit extinction coefficients approximately two orders of magnitude smaller than that of graphite, and therefore transmit sufficient radiation to give infrared spectra of reasonable contrast. From the present spectral studies of active carbon, it appears that the bulk extinction coefficient of this material is approximately that of graphite. On this basis it is reasonable to conclude that light cannot be transmitted through particles of carbon unless they are extremely thin, in fact, light of 5-µ, wavelength will decay to 1 % of its initial value after passing through 3.7 µ of graphite. Thus, infrared light incident upon most micro-crystals of active carbon will be totally absorbed, unless it hits at a sufficiently grazing angle to allow the light to be reflected from the particle. © 1969, American Chemical Society. All rights reserved.