Inorganic–organic hybrids derived from lamellar acidic kenyaite immobilizations for cation removal at the solid/liquid interface

Abstract

Synthesized crystalline sodium lamellar kenyaite exchanges the original cation on the surface to yield silanol groups when exposed to hydrochloric acid solution. The silanol groups successfully favour the formation of covalent bonds with the silylating agents 3-aminopropyltriethoxysilane, N-propyldiethylenetrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide, after expanding the interlayer distance with polar organic solvents such as dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF). These new organofunctionalized nanomaterials were characterized by elemental analysis, infrared spectroscopy, X-ray diffraction, carbon and silicon nuclear magnetic resonance in the solid state, surface analysis, porosity, thermogravimetry, electronic scanning and transmission electron microscopies. The amounts of sililyating agents incorporated into the nanospace were 0.60 ± 0.02, 0.90 ± 0.04 and 0.96 ± 0.01 mmol g−1, by expanding the interlayer distance of 1633 pm for the original polysilicate to 1933, 1847 and 1828 pm for the sequence of anchored nanocompounds. Nuclear magnetic resonance for 13C and 29Si nuclei confirmed the covalent attachment of the organosilyl groups inside the inorganic layered structures, as shown by carbon chemical shifts of the pendant organic chains, with distinguishable 3Q and 4Q species, followed by 2T and 3T species that correspond to the carbon to silicon bond originating from the precursor silylating agents covalently incorporated in the acidic kenyaite structure. These three new synthesized nanomaterials have the ability to remove divalent cations from aqueous solution. The adsorption isotherms were adjusted using a modified Langmuir equation, whose values enable calculation of the equilibrium constants and negative Gibbs free energies. The favourable values corroborate with the cation/basic centre interaction at the solid/liquid interface in a spontaneous process for these three new nanomaterials.