Phyllosilicate-like structure anchored silylating agents: calorimetric data on divalent cation-aminated centre interactions in the lamellar cavity

Nanocomposites with phyllosilicate-like structure containing silylating age nts have been synthesized by using metal ions to aid the formation of the i norganic matrix, giving a structure similar to that of talc. Two distinct s ilicates were prepared by treating magnesium chloride with 3-aminopropyltri methoxysilane or 6-amino-4-azahexyltrimethoxysilane, catalysed by sodium hy droxide, to give SILMg1 and SILMg2, with lamellar distances of 1731 and 205 3 pm, respectively. Adsorption isotherms were obtained by suspending the so lid with M(NO3)(2) solutions (M=Cu, Zn, Ni or Co), which gave the number of moles adsorbed as 7.70 +/- 0.050, 6.10 +/- 0.04 and 3.81 +/- 0.01, 2.20 +/ - 0.01 mmol g(-1) for SILMg1 and SILMg2 with Cu2+ and Zn2+, respectively. T hese data obtained from a batch method were adjusted to the Langmuir model. The adsorption process was also followed by microcalorimetry, by suspendin g the mass of material in 2.0 cm(3) of water and titrating with aqueous sol utions of the cations. From these values, the respective thermal effects of dilution were subtracted to give the net thermal effects, which enabled th e determination of Delta H and K values and from them Delta G and Delta S v alues. The exothermic enthalpic values for Cu2+, Zn2+, Ni2+ and Co2+ were - 8.62 +/- 0.56, -8.20 +/- 0.48, -3.78 +/- 0.03 and 8.86 +/- 0.81 for SILMg1 and -8.40 +/- 0.50, -9.29 +/- 0.55, -20.12 +/- 0.67 and -61.55 +/- 0.06 for SILMg2. The entropic values varied from 27 to 143 J K-1 mol(-1). The exoth ermic values for all free energies indicated that the cations are favourabl y bonded to the pendant groups disposed in the lamellar cavities.