Desenvolvimento de nanoadsorventes (ZIF-8 E ZIF-67) para remoção de óleo em emulsão o/a: regeneração e reutilização.

Abstract

This work aimed to evaluate ZIF-8 and ZIF-67 nanoadsorbents in emulsified oil/water separation. In addition, regenerating the nanoadsorbents used in oil/water separation, also seeking to determine the number of consecutive batches supported by the nanoadsorbents. For this purpose, the nanomaterials were obtained by the solvothermal synthesis method, using the metals zinc and cobalt, respectively, with the organic ligand 2-methylimidazole (IM) in the presence of methanol. The ZIFs were characterized by a combination of techniques such as X-Ray Diffraction (XRD), Infrared (IR) Spectroscopy, Physical N2 Adsorption, Scanning Electron Microscopy (SEM) and Thermal Analysis (TG). Chemical stability tests were carried out in the presence of water, with a temperature of 25 °C, varying the time from 1 to 7 days and thermal stability in a muffle furnace in the temperature range of 200 to 500 °C for 1 hour, in order to evaluate the structural strength of nanomaterials. After these tests, XRD analyzes were performed. In batch studies, the influence of pH, kinetic evolution and equilibrium isotherms were evaluated. The regeneration was carried out with ethanol and the ZIFs were reused in three adsorption cycles. In view of the XRD results obtained, the structures of ZIF-8 and ZIF-67 were confirmed. The textural analysis of the synthesized ZIF-8 and ZIF-67 metalorganic structures showed high specific surface areas, 1033 and 1143 m²/g, respectively. The SEM analyzes confirmed the morphology of the nanocrystals corroborating the other characterization analyses. Chemical stability tests, using water, confirmed that despite the dissolution of the crystalline structure, the amorphous phase of the ZIFs was not obtained, as all the characteristic peaks that form the structure of the nanomaterials were maintained. The thermal resistances of nanomaterials found were 400 °C for ZIF-8 and 300 °C for ZIF-67, respectively. The oil removal tests showed greater adsorption capacity at pH 7 (neutral) of 1064.4 mg/g for ZIF-8 and 1292.07 mg/g for ZIF-67. The pseudo-second order kinetic model and the Langmuir isotherm fit the experimental data. The adsorption process occurred spontaneously and of an endothermic nature with high disorder of the solid-liquid interface. The regenerated ZIFs adsorbed the emulsified oil in the third removal cycle. The IR spectra of the ZIFs after adsorption revealed peaks referring to mineral oil, showing the incorporation of oil molecules on the surfaces of the ZIFs.