Fourier Transform Infrared Spectra of Activated Carbons

Fourier transform infrared spectroscopy (FT-IR) was applied to the study of the chemical surface structures of activated carbons and the carbons oxidized with air (400°C, 3hr) and nitric acid (3N HNO3, 100°C, 2hr).A FT-IR instrument used in this study is Digilab FTS-20C/D.KBr pellets of the carbons were prepared at a concentration of about 0.1 wt% and dried at 65°C for 3hr in vacuo.IR spectra were obtained by accumulating 800 scans (interferograms) at a resolution of 4 cm-1. The activated carbon prepared from wood by ZnCl2 activation method gave the aliphatic (alicyclic) C-H bands at 2960, 2920, 2860, 1450 and 1380 cm-1, the aromatic C-H bands at 3060, 870, 820 and 760 cm-1, the aromatic nucleus band at 1590 cm-1, and the carboxyl group bands at 1710 and 1260 cm-1.When the carbon was treated with KOH or Ca (OH) 2 aqueous solution, the band at 1710 cm-1 disappeared and the new band at 1400 cm-1 appeared, demonstrating that a carboxyl group (COOH) was converted into an ionized carboxyl group (COO-).It is, therefore, clear that carboxyl groups are present on activated carbon as surface acidic oxides. The activated carbons prepared from wood, coconut shell and coal by a steam activation method gave the aromatic nucleus band at 1590 cm-1 and the carboxyl group band at 1710 cm-1.The hydrogen contents of these carbons are so small that the absorption bands due to C-H bonds scarcely appeared.The band intensity at 1710 cm-1 was increased by oxidation of the carbon with air or nitric acid, indicating that the carboxyl groups were formed on the carbon by oxidation. It was very difficult in the past to obtain the IR spectra of activated carbons.The high resolution IR spectra of activated carbons were obtained by the use of FT-IR as shown in this paper.FT-IR is considered to be a very useful technique in the studies of chemical structures of carbons.