ADSORPTION OF CONGO RED FROM A NICKEL-YTTRIUM GARNET SURFACE SOLUTION

Abstract

At the current stage of development of nanochemistry and nanotechnology, complex oxide materials with a spinel structure are of great interest to researchers. Such materials include yttrium garnets. Thanks to the isomorphic substitutions widely allowed in the structure of garnets, it is possible to obtain materials with a unique set of physicochemical properties by incorporating new elements, such as Ni. To study the processes of adsorption of Congo red from aqueous solutions, nickel-yttrium garnet sol-gel was synthesized by the self-combustion method (Pechini). The obtained samples were investigated by the methods of X-ray fluorescence and IR-Fourier spectroscopy. On the basis of elemental analysis, it was established that the formula of nickel-yttrium garnet is Ni2Y9O14, and the formed particles are prone to aggregation. In the work, the adsorption of Congo red from aqueous solutions on the surface of nickel-yttrium garnet was carried out. It was established that the degree of dye extraction of more than 78% at a temperature of 293 K is achieved in the first 30 minutes from the beginning of adsorbate-adsorbent contact. The adsorption equilibrium at the separation boundary is satisfactorily described by the pseudo-second-order model. It was determined that the adsorption capacity is 3.14 mg/g, and the character of the isotherm curve resembles the Langmuir isotherm curves (L3-type) according to the Giles classification, without reaching saturation. This type of isotherm is typical for adsorbents with low energy of adsorbent-adsorbate interaction. It is shown that the adsorption isotherms are satisfactorily described by the Freundlich monomolecular adsorption model, compared to other models, as evidenced by the correlation coefficient (R2 = 0.973). This means that dye adsorption occurs on heterogeneous (unequal) centers of the surface, on which there is an uneven energy distribution. It was calculated that for the adsorption of Congo red, the value of the adsorption energy is 2.06 kJ/mol, which indicates a purely physical adsorption of dye molecules on the surface.