Thermodynamic features associated with intercalation of some n-alkylmonoamines into barium phosphate

Elemental analysis for the synthesized crystalline lamellar compound conforms to the formula Ba(H2PO4)2 and the X-ray diffraction patterns is in agreement with the lamellar structure for this compound. The precursor host was intercalated with a series of n-alkylmonoamines of the general formula H3C(CH2)n-NH2 (n = 1 to 4) in aqueous solution. The lamellar host was calorimetrically titrated with an aqueous amine solution at T = (298.15 ± 0.02) K and the enthalpy, Gibbs free energy and entropy were calculated. The enthalpic values increased, although not uniformly, with the number of carbon atoms is the amine chain, to give (−13.96 ± 0.12, −14.00 ± 0.48, −15.75 ± 0.23, −16.05 ± 0.11) kJ · mol−1, from n = 1 to 4. The exothermic enthalpy, the negative Gibbs free energy and positive entropic values are in agreement with the favourable energetic process of intercalation for this system.