Adsorption of cetyltrimethylammonium bromide on parent and molybdenum-modified silica gels in the solid state

The adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) on silica gel and on molybdenum-modified silica gel substrate, in the solid state, was studied by differential scanning calorimetry and Fourier transform IR photoacoustic spectroscopy (FTIR-PA) techniques. Examination of the solid state IR spectra of CTAB absorbed onto molybdenum—silica substrate, as a function of temperature, shows a new band at 938 cm −1 shifted to 961 cm −1 (during the temperature flow), representing a chemisorption via the interaction of the head group of the surfactant (CH 3 ) 3 N + and MoO stretching vibration species. In the presence of NaCl, shifting of the high temperature exothermic peak at 411°C to 451°C was obtained, providing an enhancement of cetyltrimethylammonium chloride adsorption onto molybdenum—silica substrate and a considerable reduction in the Δ H value is observed. This decrease in the Δ H value was obtained as a result of the interference of the less reactive site Na + ions in the adsorption, because of substitution of Na + for Mo 6+ ions.