ADSORPTION OF CETYLTRIMETHYLAMMONIUM BROMIDE ON PARENT AND MOLYBDENUM-MODIFIED SILICA-GELS IN THE SOLID-STATE

The adsorption of the cationic surfactant cetyltrimethylammonium bromi de (CTAB) on silica gel and on molybdenum-modified silica gel substrat e, in the solid state, was studied by differential scanning calorimetr y and Fourier transform IR photoacoustic spectroscopy (FTIR-PA) techni ques. 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 (CH3)3N+ and Mo=O stretching vibration species. In the presence of NaCl, shifting of the high temperature exothermic peak at 411-degrees-C to 451-degrees-C was obtained, providing an enhancement of cetyltrimethylammonium chloride adsorption onto molybdenum-silica s ubstrate and a considerable reduction in the DELTAH value is observed. This decrease in the AH value was obtained as a result of the interfe rence of the less reactive site Na+ ions in the adsorption, because of substitution of Na+ for Mo6+ ions.