PROCESSES OF ADSORPTION OF CONGO RED FROM AQUEOUS SOLUTIONS BY THE SURFACE OF COPPER-YTTRIUM GARNET

Abstract

In this work, the synthesis of copper-yttrium garnet with a spinel structure was carried out by the Pechini method and its morphology was studied using a set of physicochemical methods. X-ray fluorescence spectral analysis was performed to determine the structure of the obtained copper-yttrium garnet and the quantitative ratio between the components. According to the X-ray fluorescence spectral analysis, it was found that the copper-yttrium garnet has a composition of: 9.4% Copper, 67.5% Yttrium and 23.1% Oxygen, which corresponds to the simplest formula CuY5O10. IR-Fourier spectroscopy methods showed that at 1600-1400 cm-1, stretching vibrations of Cu – OH bonds of the surface of copper-yttrium garnet with a spinel structure occur. At 800-700 cm-1, stretching vibrations of Y – O bonds of coordinated Yttrium dodecahedra (unit cell of yttrium garnet) were detected, which is typical for garnets with a spinel structure.In the process of studying the adsorption activity of the surface of copper-yttrium garnet with respect to the Congo red dye from solutions, it was found that the maximum degree of extraction of 54.6% is achieved for an adsorbent mass of 0.08 g. It was shown that the degree of extraction of the dye of 43.5% is achieved in the first 30 minutes from the beginning of adsorption, and reaches its maximum value after 120 minutes from the beginning of interaction at the adsorbate-adsorbent interface. The nature of the curve indicates non-equilibrium adsorption processes, in which the adsorption processes at the phase interface prevail over the processes of desorption of the dye from the surface. It was established that the adsorption capacity is 1.59 mg/g, and the distribution coefficient at the maximum concentration of the dye (Со = 10 mg/l) is 432.06 ml/g. This means that the affinity of this dye to the surface of copper-yttrium garnet is insignificant.The character of the isotherm curve resembles the rectilinear Henry isotherm curves according to the Giles classification. This type of isotherm indicates that the intermolecular interaction of the adsorbate-adsorbent prevails over the intermolecular interaction in the solution between the Congo red molecules. The adsorption isotherm of Congo red is satisfactorily described by the Tiomkin model, in comparison with other models, as evidenced by the correlation coefficient (R2 = 0.854), i.e. the adsorption of the dye occurs on potentially inhomogeneous surfaces, on which there is a uniform distribution of adsorption centers in terms of energy. The calculated value of the adsorption energy is 2.162 kJ/mol, which indicates a purely physical adsorption of the dye molecules on the garnet surface.