Laponite-derived porous clay heterostructures: II. FTIR study of the structure evolution

A comprehensive study in the middle infrared (MIR) and near infrared (NIR) regions aimed at characterizing materials obtained during the successive steps of Laponite-derived porous clay heterostructure (PCH) synthesis is presented. It is found that the exchange of hydrated Na+ with hexadecyltrimethylammonium cations (HDTMA+) affects the vibrations of structural groups of Laponite with perpendicular orientation to the basal oxygens plane. The vibrating dipoles are more aligned with one another and related absorption bands become more narrow and intensive. Upon addition of co-surfactant (dodecylamine – DDA) and Si-source (tetraethylorthosilicate – TEOS) to HDTMA-Laponite a broad complex Si–O band at 1070 cm−1 appears, evidencing the hydrolysis of TEOS and development of silica network in the PCH-precursor. The NIR spectrum shows characteristic O–H and C–H bands of HDTMA-Laponite and the N–H overtones (6523 and 6478 cm−1) and combination (4935 cm−1) band of dodecylamine. Only this region permits identification of NH2 groups because the N–H bands in the MIR region are overlapped with absorption bands of water molecules. No C–H or N–H vibrations relating to organic template could be recognized in the NIR spectrum after PCH-precursor calcination. Laponite component in the calcined PCH-precursor retains its layered structure, as evidenced by the presence of Mg3OH and Si–O bands. The only thermal damage consists in the removal of OH groups bonded to both Mg and Li. The NIR spectrum of PCH after pyridine adsorption demonstrates that the Laponite-derived PCH contains SiOH groups of different local environment.