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

Abstract

Nanocomposites with phyllosilicate-like structure containing silylating agents have been synthesized by using metal ions to aid the formation of the inorganic matrix, giving a structure similar to that of talc. Two distinct silicates were prepared by treating magnesium chloride with 3-aminopropyltrimethoxysilane or 6-amino-4-azahexyltrimethoxysilane, catalysed by sodium hydroxide, to give SILMg1 and SILMg2, with lamellar distances of 1731 and 2053 pm, respectively. Adsorption isotherms were obtained by suspending the solid 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. These data obtained from a batch method were adjusted to the Langmuir model. The adsorption process was also followed by microcalorimetry, by suspending the mass of material in 2.0 cm³ of water and titrating with aqueous solutions of the cations. From these values, the respective thermal effects of dilution were subtracted to give the net thermal effects, which enabled the determination of ΔH and K values and from them ΔG and ΔS values. 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 exothermic values for all free energies indicated that the cations are favourably bonded to the pendant groups disposed in the lamellar cavities.