The effect of synthesis temperature on the FT-Raman and FT-IR spectra of saponites

• Published in: Vibrational spectroscopy 2000-04, Vol.23 (1), p.119-127
• Main Authors: Kloprogge, J.T., Frost, R.L.
• Format: Article
• Language: English
• Subjects: Crystallisation; FT-IR spectroscopy; FT-Raman spectroscopy; Saponite; Smectite; Synthesis
• ISSN: 0924-2031; 1873-3697
• DOI: 10.1016/S0924-2031(00)00056-4

Saponites hydrothermally synthesised between 125°C and 280°C were studied by Fourier transform (FT)-Raman and FT-infrared (IR) spectroscopy and compared to natural saponite. FT-IR spectra with increasing synthesis temperature showed saponite crystallisation and disappearance of amorphous material. The 457 cm −1 gel band developed at higher temperatures in two components at 447 cm −1 and 465 cm −1 ascribed to e 1 2 of SiO 2 and AlOH translation modes of saponite. Above 150°C, minor octahedral sheet vibrations appeared at ±530 cm −1 (MgOH perpendicular mode) followed by a band around 750 cm −1 (AlOH deformation mode) above 200°C. At this temperature, two bands due to the a 1 2 SiO 2 and apical AlO bond of AlO 4 in the tetrahedral sheet became visible at 691 and 837 cm −1, respectively. The strongest SiO 2 band showed a continuous shift from 1043 to 1013 cm −1 with increasing synthesis temperature. Two overlapping bands around 660 and 690 cm −1 appeared almost simultaneously before the wide amorphous material band around 1240 cm −1 had disappeared, indicating that in the saponite structure, the octahedral and tetrahedral layers form almost simultaneously. Sharpening of other bands associated with various SiO modes was not observed up to 200°C. The FT-Raman spectra only revealed the formation of internal tetrahedral vibrational modes. Upon increasing temperature, the first band observed was at 683 cm −1 at 150°C followed by the 360 cm −1 band at 175°C. Around 240–280°C, two bands around 430–465 cm −1 were observed. The increase in intensity of these bands with temperature confirmed the concept that the silica in the gel rapidly changes its configuration.