Coordinating Polymers Based on Nickel(II) and Cobalt(II) Trimesinates as Promising Adsorbents of Organic Dyes

Abstract

Metal-organic frameworks (MOFs) are crystalline compounds consisting of metal ions coordinated by bridging organic ligands. Depending on the coordination geometry of the metal and the direction of the bond of donor atoms, as well as on the geometry of the bridging ligand, 1D, 2D, or 3D polymer structures are formed. The characteristic features of metal-organic frameworks are low density, high porosity and crystallinity, and large specific surface. Wide attention is paid to the technological aspects of creating such materials and their integration into various devices. To obtain MOFs, various synthetic approaches have been developed based on precipitation reactions at room temperature and under convective heating, including hydrothermal and solvothermal syntheses. In this work, metal organic framework structures based on nickel and cobalt trimesinates were synthesized by a modified procedure by reacting nickel acetate and cobalt nitrate with trimesic acid in the presence of alkali. The obtained compounds were used to study the adsorption of Congo Red and Methylene blue organic dyes from their aqueous solutions. The degree of adsorption depends on temperature and reaches a value of 97% for Congo Red, while for Methylene blue it is 83%. The mechanisms and characteristic parameters of the adsorption process were analyzed using empirical models of Langmuir, Temkin, and Freundlich isotherms, of which the adsorption process was optimally described by the Freundlich model. The calculated thermodynamic parameters indicate the spontaneity of the process and its insignificant endothermic character.