Thermodynamics of the nickel and cobalt removal from aqueous solution by layered crystalline organofunctionalized barium phosphate

The available hydroxyl groups inside the lamellar cavity of barium phosphate (BaP) reacted with the silylating agents (RO)3Si(CH2)3Lx (L1 = NH2, L2 = NH(CH2)2NH2, and L3 = NH(CH2)2 NH(CH2)2NH2), to yield organofunctionalized BaPSiL1, BaPSiL2 and BaPSiL3 nanomaterials. The amounts of organofunctional groups covalently attached to the inorganic layer were (1.24, 1.46, and 1.23) mmol · g−1, respectively. The basic nitrogen atoms attached to the distinct pendant organic chains adsorb divalent nickel and cobalt from aqueous solutions, as represented by well-established isotherms. The energetic effects caused by metallic cation interactions were determined through calorimetric titration at the solid/liquid interface and gave a net thermal effect that enabled enthalpy and equilibrium constant calculations. Complete thermodynamic results composed of exothermic enthalpy, negative free Gibbs energy and positive entropy result in a set of favourable cation/basic centre interactions, to indicate that these nanomaterials could be useful tools to eliminate undesirable cations from aqueous systems.