Raman spectroscopy of urea and urea-intercalated kaolinites at 77 K

Ray L. Frost, J. Kristóf, Llewellyn Rintoul, J. Theo Kloprogge

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Abstract

The Raman spectra of urea and urea-intercalated kaolinites have been recorded at 77 K using a Renishaw Raman microprobe equipped with liquid nitrogen cooled microscope stage. The NH2 stretching modes of urea were observed as four bands at 3250, 3321, 3355 and 3425 cm-1 at 77 K. These four bands are attributed to a change in conformation upon cooling to liquid nitrogen temperature. Upon intercalation of urea into both low and high defect kaolinites, only two bands were observed near 3390 and 3410 cm-1. This is explained by hydrogen bonding between the amine groups of urea and oxygen atoms of the siloxane layer of kaolinite with only one urea conformation. When the intercalated low defect kaolinite was cooled to 77 K, the bands near 3700 cm-1 attributed to the stretching modes of the inner surface hydroxyls disappeared and a new band was observed at 3615 cm-1. This is explained by the breaking of hydrogen bonds involving OH groups of the gibbsite-like layer and formation of new bonds to the C double bond O group of the intercalated urea. Thus it is suggested that at low temperatures two kinds of hydrogen bonds are formed by urea molecules in urea-intercalated kaolinite.

Original languageEnglish
Pages (from-to)1681-1691
Number of pages11
JournalSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Volume56
Issue number9
DOIs
Publication statusPublished - Aug 2000

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ureas
Urea
Raman spectroscopy
Kaolin
kaolinite
Kaolinite
Hydrogen bonds
Liquid nitrogen
liquid nitrogen
Stretching
Conformations
hydrogen bonds
Siloxanes
Defects
siloxanes
defects
Intercalation
intercalation
Hydroxyl Radical
Amines

ASJC Scopus subject areas

  • Spectroscopy

Cite this

Raman spectroscopy of urea and urea-intercalated kaolinites at 77 K. / Frost, Ray L.; Kristóf, J.; Rintoul, Llewellyn; Kloprogge, J. Theo.

In: Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy, Vol. 56, No. 9, 08.2000, p. 1681-1691.

Research output: Contribution to journalArticle

Frost, Ray L. ; Kristóf, J. ; Rintoul, Llewellyn ; Kloprogge, J. Theo. / Raman spectroscopy of urea and urea-intercalated kaolinites at 77 K. In: Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy. 2000 ; Vol. 56, No. 9. pp. 1681-1691.
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AB - The Raman spectra of urea and urea-intercalated kaolinites have been recorded at 77 K using a Renishaw Raman microprobe equipped with liquid nitrogen cooled microscope stage. The NH2 stretching modes of urea were observed as four bands at 3250, 3321, 3355 and 3425 cm-1 at 77 K. These four bands are attributed to a change in conformation upon cooling to liquid nitrogen temperature. Upon intercalation of urea into both low and high defect kaolinites, only two bands were observed near 3390 and 3410 cm-1. This is explained by hydrogen bonding between the amine groups of urea and oxygen atoms of the siloxane layer of kaolinite with only one urea conformation. When the intercalated low defect kaolinite was cooled to 77 K, the bands near 3700 cm-1 attributed to the stretching modes of the inner surface hydroxyls disappeared and a new band was observed at 3615 cm-1. This is explained by the breaking of hydrogen bonds involving OH groups of the gibbsite-like layer and formation of new bonds to the C double bond O group of the intercalated urea. Thus it is suggested that at low temperatures two kinds of hydrogen bonds are formed by urea molecules in urea-intercalated kaolinite.

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