Chromatographic Studies Of The Active Carbon Surface Gradual Thermally Decomposed
CHROMATOGRAPHIC STUDIES OF THE ACTIVE CARBON SURFACE GRADUAL THERMALLY DECOMPOSED
OXYGEN COMPLEXES
H. Grajek1, Z. Witkiewicz1, A. Swiatkowski1, S. Biniak2, M. Pakula3
1Military Technical Academy, Institute of Chemistry,
Kaliski Str. 2, 00-908 Warsaw, Poland
2N. Copernicus University, Faculty of Chemistry,
Gagarin Str. 7, 87-100 Torun, Poland
3Naval Academy, 81-919 Gdynia, Poland
Inverse gas chromatography was applied to investigate of activated carbon samples which were oxidized in the liquid phase to increase the concentration of oxygen surface complexes, and next heated in an inert atmosphere (or under vacuum) to selectively remove some of these functions.
In the present work, previously oxidized activated carbon was modified by gradual heating under vacuum in order to obtain materials with different surface properties. A variety of experimental techniques were used to characterize the changes in surface chemistry.
An activated carbon obtained from plum stones was demineralized with concentrated HF and HCl acids (ash content 0.08%wt.) and subsequently oxidized with concentrated HNO3 (800C, 4 h). Several samples of activated carbon with different quantities of chemically bound oxygen were obtained by heat treatment of oxidized carbon at various temperatures (HTT) from 1800C to 9000C. The surface chemistry of these modified materials was analysed in various ways: elemental analysis, pH of carbon suspension measurement, acid-base titration. The elemental analysis (oxygen content) was done on a CHNS-O model 1108 analyser (Carlo Erba, Milan). The pH of the carbon slurries was determined for 1g of carbon sample in 100 cm3 of 0.1 M NaCl. The content of surface acidic oxygen functional groups was determined by neutralization with bases of various strength - the Boehm method; in the case of the basic groups, this was done with hydrochloric acid.
The thermal treatment of the oxidized carbon leads to changes in the chemical nature of the carbon surface, e.g. a stepwise decrease in the total
oxygen content and an increase in the pH of the carbon slurry. The thermal decomposition of the oxygen complexes reduced the total number of acidic functional groups, and increases the overall number of basic groups.
Table. Selected physicochemical properties of the samples investigated
HTT
Numbers of functional groups; mmolg-1
Total O
wt %
oC
pH
>COOH
>COO
>C-OH
>C=O
basic
180
500
900
2.97
5.87
10.25
1.017
0.227
0.000
0.288
0.262
0.000
0.783
0.484
0.109
0.204
0.148
0.109
0.072
0.311
0.636
10.34
5.49
0.95
Acknowledgments
This work was partly supported by the Polish State Committee for Scientific Research, Grant No. 3 T09B 036 16.
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