Adsorption of anionic food azo dyes from aqueous solution by silica modified with cetylpyridinium chloride

摘要

A silica modified by cetylpyridinium cations for the effective preconcentration of azo dyes from dilute aqueous solutions was proposed. The morphology of the modified silica was studied by SEM and it was shown that the modified silica surface has a 3D framework structure. The fixation of cetylpyridinium cations on the silica surface was confirmed by the diffuse reflectance infrared Fourier-transform spectroscopy method. Using the mathematical planning of the experiment via the method of Latin squares; the conditions for the adsorption of dyes have been optimized. It was found that the maximum dye adsorption occurs at pH 1.5-2.5 where azo dyes are in the ionic form with dissociated sulfo groups. The formation of ion pairs of azo dye anions and cetylpyridinium cations in solution was proved by spectrophotometry and on the surface by diffuse reflection spectroscopy. It is shown that adsorption isotherms are of the H-type and they are well described by the Langmuir equation. The maximum adsorption capacity of the modified silica with respect to azo dyes ranges from 2 to 9mol/g and depends on the geometric dimensions and spatial configuration of the dyes molecules. Thermodynamic studies have made it possible to establish the endothermic nature of adsorption. It is shown that the most effective eluent is 1.0x10(-3)moldm(-3) solution of sodium dodecylsulfate in 0.1moldm(-3) solution of NH3H2O, and desorption itself occurs due to the destruction of ion pairs of dye anions with cetylpyridinium cations fixed on the surface.