O uso de resíduos vegetais amazônicos (Euterpe) na obtenção de compósitos baseados em carvão ativado/óxidos de ferro para a remoção de contaminantes ambientais

Abstract

The development of agroindustrial activity has increased the amount of waste generated that is normally discarded. In this sense, the açaí fruit residues (Euterpe), which is found in abundance in the Amazon rainforest, is an alternative in the production of materials with adsorptive properties for remediation of environmental contaminants. In this work, they prepared composite iron oxide / activated carbon using the waste of acai berry to removal the acid herbicide 2,4-D. The materials were prepared by pyrolysis and simultaneous activation with FeCℓ3 and pyrolysis with subsequent activation with FeCℓ3 400, 500 and 600 °C in muffle furnace. The composites were then prepared at temperatures of 400 to 500 °C, respectively, from activated carbon simultaneously at 400 °C (CD4). Elemental Analysis, Specific Surface Area (SSA) estimated by Methylene Blue method, Infrared Spectroscopy (FTIR), X-Rays Diffraction (XRD) Thermogravimetric Analysis, Scanning Electron Microscopy (SEM) and Zero Charge Point (ZCP) were characterized. Adsorption tests were carried out using methylene blue dye and the anionic herbicide 2,4-D by varying the pH, temperature and concentration of the initial solution. Commercial carbon (CA-C) was used for comparison purposes. The materials had yields ranging from 21.4 to 28.5 % for the materials prepared by pyrolysis and simultaneous activation, 39.4 to 46.0 % for the materials prepared by pyrolysis with subsequent activation and 82.5 to 76.5 % for composites. The SSA ranged from 47 to 155 m2 g-1, below SSA CA-C. The Elemental Analysis showed an increase of the C/H, indicating increased aromaticity. The materials showed similar active modes in FTIR spectra corresponding to the functional groups -OH, -CH3 and -CH2, and ethers and iron oxides. The study by XRD, with the aid of ReX software confirmed the formation of the single phase of hematite in materials prepared by pyrolysis and simultaneous activation, different from these, the materials prepared by pyrolysis with subsequent activation showed mixing phase of hematite and magnetite in 500 and 600 °C. All materials were thermal stability at around 230 °C. The ZCP of materials treated with HCℓ 0.1 mol L-1 was close to 3. For the adsorption tests, the materials had higher efficiency at pH≈11 for methylene blue dye and pH≈2 for the acid 2,4-D. For the tests depending on the temperature, values of ∆Hand ∆Swere positive indicating endothermic nature and increasing degree of disorder at the interface. The ∆G values decrease with increasing temperature indicating the spontaneity of the adsorption process. Regarding the effect of the initial concentration, samples were adjusted to the Langmuir model with qo in the range of 19.1 to 64.0 mg g-1 for methylene blue dye and 9.9 to 80.0 mg g–1 for 2,4-D acid. Compared with CA-C, the material showed reduced efficiency, however it is important to note that the material resembled with other activated carbons produced from agro-industry waste but need further investigation when the methodology used in the activation these materials.