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Structural Study of Humic Acids by X-ray, Electron Spin Resonance, and Infrared Spectroscopy¹

ABSTRACT

Composts and soil humic acid structures were examined by X-ray, ESR, and IR methods. X-ray diffraction showed three bands at 3.6, 2.1, and 1.2Å for the studied humic acids. These bands occured on the same position as the (002), (10), and (11) of carbon black and were ascribed to aromatic structure or graphite-like layers. The presence of a 7.5Å band in the X-ray diffraction of the examined humic acids indicate to nonaromatic fraction too. IR spectra confirm the presence of aromatic and aliphatic fractions associated with various types of functional groups including quinone groups. The nature of these groups are discussed. ESR signal G 2 indicates the presence of free radicals within the humic substances, whereas very little is known about the ESR signal at G 4.125 observed in the studied humic acids. This signal was attributed to Fe³⁺ chelated to humic substances. Compost and soil humic acids showed some structural differences.

¹ Contribution of the Department of Soil and Agric. Chemistry, Univ. of Mansoura, Egypt.

² Associate Professor, Head, Department of Soil and Agric. Chemistry, Univ. of Mansoura, Egypt; and Prof., ENSIC, Nancy, France, respectively.

Received for publication June 19, 1978. Accepted for publication August 9, 1978.