Pendant chains containing thiopropanamide groups inside talc-like phyllosilicate galleries as thermodynamically favorable agents for cation removal

Abstract

A lamellar inorganic–organic talc-like magnesium phyllosilicate has been synthesized through a single step sol–gel route under mild conditions, using a newly synthesized [3-(3-trimethoxysilylpropyl)thiopropanamide] silylating agent, obtained from acrylamine and 3-mercaptopropyltrimethoxysilane. Elemental analysis data based on the sulfur atom showed an incorporation of 3.66 mmol g−1 of the thiopropanamide group inside the galleries of the hybrid. Infrared spectroscopy and nuclear magnetic resonance (NMR) in the solid state for the 13C nucleus confirmed the thiopropanamide moiety covalently bonded inside the lamellar structural galleries. Solid state 29Si NMR showed the presence of Tn silicon species in the backbone in agreement to the hydrolysis and condensation reactions during the sol–gel process. X-ray diffractions gave a basal distance of 1.854 nm, near twice that of the natural talc and the 060 reflection confirmed a structure similar to natural talc. The basic centers on pendant chain coordinate divalent nickel, cadmium and lead cations from aqueous solution at the solid/liquid interface. Based on the Langmuir model, the maximum sorption capacity of the hybrid for these cations was 0.70, 1.10 and 2.71 mmol g−1, respectively. The thermodynamic data for cation/basic center interactions were determined through calorimetric titration, demonstrating spontaneous interactions, ΔG, exothermic enthalpic ΔH and positive entropy ΔS values. These favorable results for removal these toxic cations in a heterogeneous system may be useful for remove ions from wastewaters.