Polímeros de coordenação e seus óxidos derivados: da preparação a aplicação na descolorização de águas contaminadas com corantes orgânicos

Abstract

Coordination polymers (CP) are a new class of hybrid materials consisting of species or metal clusters connected by organic linkers and forming structures along one, two, or three dimensions. In this research, the use of CPs and their derived oxides in the discoloration of water contaminated with organic dyes is proposed. Three Cu2+ coordination polymers were prepared by an electrochemical method using the following linkers: 1,3-H2BDC, 1,4-H2BDC, and 5-NH2-H2BDC. The samples obtained were calcined in air at 923 K yielding porous CuO. The synthesis of Ca-MOFs was performed using a sonochemical method. The main synthetic parameters were studied, and the factorial planning was employed to reduce the total number of samples produced. All the prepared samples were characterized by X-ray powder diffraction (PXRD), Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (ATRFTIR), Thermal Analysis (TGA-DTA) and Scanning Electron Microscopy (SEM). The results confirmed both the crystallization of the Cu2+ coordination polymers and the formation of the copper oxide after the heat treatment. The porous CuO was tested for the catalytic degradation of methylene blue in the presence of H2O2, and the effect of reaction parameters such as catalyst mass and H2O2 volume were studied. The optimum reaction conditions were established, with discoloration reaching about 94 and 100% at 308 and 311 K, respectively, after only 120 minutes of reaction. Regarding the Ca-MOFs samples were applied in the adsorption of the methylene blue dye at pH 5.6, obtaining maximum adsorption of 60.241 μmol.g-1 and high efficiency in the reuse, reaching 97% of the initial adsorption capacity in the second reuse cycle. The results suggest that the presence of the Ca(BDC) phase does not increase the adsorption capacity when compared to the other obtained crystalline phase, Ca(BDC)(H2O)3. Both materials are promising in the discoloration of water contaminated with organic dyes.