Many applications of carbonaceous adsorbents are strongly influenced by their surface
chemistry. The characterization of surface oxygen groups is very often done by chemical or
spectroscopic methods such as acid-base titration, FTIR, TPD, XPS etc. The aim of this work
was to modify the surface chemistry of the commercial granular active carbon AG-5, using as
oxidizing agent concentrated nitric acid. The surface chemistry characteristics of unmodified
(AG-5) and oxidized (AG-5ox) active carbon samples were evaluated by using the Boehm
titration method, pH of carbon suspension and IR spectral analysis.
The results of Boehm’s titration method and pH value of the carbon surface are given in Table 1.
Significant differences existed on the amount of acidic and basic functional groups of the active
carbons. After oxidation process the amount of total acidic groups (titrated with NaOH) on active
carbon surface AG-5ox increases by about 6 times in comparison with initial sample AG-5. The
concentration of the acidic groups on the oxidized active carbon surface AG-5ox followed the
order weak acidic > strong acidic > phenolic.
Table1. Surface chemistry of carbons evaluated by Boehm method and pH of suspension.

The FTIR spectral analysis is an important tool to identify some characteristic functional groups
on the active carbons surface. Bands in the 1000-1200 cm-1 region are difficult to assign because
there is a superposition of a number of broad overlapping bands. They could be assigned to C-O
as in phenols/ethers/esters (1200 cm). The shoulder at 1164 cm-1 together with two absorptions
of low intensity (1385 and 1399 cm-1), confirm the presence of phenolic groups on the oxidized
active carbon surface (AG-5ox). The bands in the region of 1500-1600 cm, presented in the
spectrum of AG-5ox at 1521, 1562 and 1625 cm-1, and in the spectrum of AG-5 at 1490 and
1560 cm-1, can be assigned to aromatic ring stretching (C=C) coupled to highly conjugated
carbonyl groups (C=O). The band between 1700 and 1730 cm-1, that can be assigned to the
stretching vibration of C=O bonds, characteristic of carboxylic, ketone and aldehyde groups, is
much higher in AG-5ox than in AG-5 spectrum.
Generally, both used methods to quantify the surface characteristic groups on active
carbon samples show an increase of acidic surface groups on oxidized sample, presented as
strong acidic – carboxylic groups, weak acidic – ketones and aldehyde groups, and phenolic
groups.