Preparation, characterization and adsorption properties of tetraalkylphosphonium organobeidellites

Abstract

New intercalated clay materials based on the combination of four systematically selected alkylphosphonium organocations and beidellite (Bd) were prepared. Particularly, tetraethyl-, tetrabutyl-, tetrahexyl- and tetraoctyl- phosphonium cations were used in the synthesis. The samples were characterized by X-ray diffraction, thermal analysis, infrared spectroscopy and elemental carbon analysis. Further, calculations based on density functional theory method including dispersion corrections (DFT-D3) were carried out in a prediction of stability and detailed characterization of the structure and interactions of the beidellite intercalated models corresponding to four tetraalkylphosphonium cations used in experiment (4PX-Bd; X = 2, 4, 6, 8 / ethyl-, butyl-, hexyl-, octyl-). Calculated interlayer distances (d001) for all four models agreed well with experimental data continuously growing with a length of the alkyl chains of the 4PX cations. The structural stability of 4PX-Bd intercalates also increased with the size of the 4PX cations. Calculated vibrational spectra obtained from ab initio molecular dynamics were in a good agreement with experimental IR spectra. Further, a sorption capacity of synthetized organobeidellites was probed by loading sulfamethoxazole drug and quantified by liquid chromatography method. Adsorption of sulfamethoxazole was the most effective using tetraoctylphosphonium-modified beidellite.