BIOCARVÕES FUNCIONAIS DE CARCAÇA DE TILÁPIA (Oreochromis niloticus) PARA REMOÇÃO DE OXITETRACICLINA EM SOLUÇÕES AQUOSAS

Abstract

Anthropogenic activity generates a huge amount of air pollution, soil protection and water pollution. Emerging contaminants, such as antibiotics, are compounds present in bodies of water that have persistent effects and are difficult to remove from the environment. These substances are extremely harmful to human health, leading to the development of resistant microorganisms and causing possible environmental imbalances. The current demand for environmental remediation brings a notable interest among humanity, mainly in sustainable technologies. Recently, various remediation systems using heterogeneous materials for adsorption and photocatalytic degradations have been extensively trained and applied in different fields. Due to their low cost, high ecological availability, high surface area, porous structure and surface functional groups, biochars have been extensively used as adsorbents in water and soils. The present research project aims to develop functional biochars (BC) from tilapia carcass (Oreochromis niloticus) through the use of materials as a remedial agent for the antibiotic oxytetracycline (OTC) in the aquatic environment. The biochars were synthesized in an inert nitrogen atmosphere at three different pyrolysis temperatures (400, 600 and 800°C), generating samples BC400, BC600 and BC800, respectively. After this process, they were subjected to a particle size reduction process in a high-energy ball mill. The biochars were magnetized in an alkaline solution of FeSO4.7H2O by the co-precipitation method, forming the semiconductor magnetite (Fe3O4) under the surface of the pyrolyzed biomass. The morphological, structural and thermal stability characterization of biochars was carried out using TG/DTG, Raman, FTIR, XRD, XPS, SEM, BET and pHPCZ techniques and pH study. SEM micrographs showed the presence of microparticles measuring between 11 and 180 µm. The BET surface area of BCNM600 (24.3970 m2/g) was 1.75 times greater than the area of BCT600 (13.9158 m2/g). In FTIR spectroscopy, absorption bands associated with hydroxyapatite (1450 cm-1 and 1030 cm-1) and collagen (2930 cm-1 and 1620 cm-1) present in biochars were found. The band at 584 cm-1 present in BCNM600 and BCNM600 + OTC can be attributed to the Fe=O bond of the samples. The Fe 2p orbitals of these last samples, containing peaks located at 725.0 and 711.3 eV, are related to the Fe2+ (2p1/2) and Fe3+ (2p3/2) cations. The XPS C 1s orbitals of BCT600 present binding energy peaks at 285.3 eV, 284.4 eV, 287.1 eV and 289.1 eV that correspond to the C-C/C-H, C-N, C-O and C=O groups, respectively. These three orbitals (N 1s, O 1s and C 1s) are certainly involved in the connection between the functional groups of collagen present in biochars with the ketone group (electron acceptor) of its surface structure. The characteristic diffraction peaks of hydroxyapatite present in biochars are found at 25.9º, 31.9° and 49.6° and the crystalline phase of magnetite at 29.2º, 35.7º and 43.4º. The adsorption isotherm presented a type III curve, with H3 hysteresis (macroporous solid). In Raman spectroscopy, the relative intensity ratios (ID/IG) for BCT600 and BCNM600 were 1.139 and 1.059, respectively, suggesting a smaller structural defect and a higher degree of graphitization for BCNM600. In the pH influence study, the value of 7.50 was chosen as ideal. The pHZPC for BCT600 and BCNM600 was 8.58 and 4.35, respectively. A concentration of 50 mg L-1 of OTC was optimized in the adsorbate dosage study. In the biochar dosage study, 100 mg of biochar was the quantity chosen. For both bioadsorbents, the kinetic model that presented the best fit to experimental data was Elovich. Considering the results obtained by the nonlinear adjustment of experimental data, the adsorption isotherm that presented the best fit for biochars was the Sips model. In the reuse study, BCT600 and BCNM600 biochars showed a similar %R, of 52.2% and 54.4%, respectively. The adsorption thermodynamics of OTC to biochars were evaluated. Due to the negative values of ∆Gº, it was assumed that the adsorptive process was favorable and spontaneous. Negative values of ∆Hº between 20 – 30 kJ mol-1 classified OTC adsorption, for both materials, as a physical and exothermic process. The negative values of ∆Sº for BCT600 and positive values for BCNM600 revealed a decrease and an increase in randomness at the solid-solution interface, respectively. In the heterogeneous photocatalysis study, BCT600 showed a %R and qe of 72.47% and 52.47 mg g-1, respectively, and BCNM600 had a %R and qe of 70.1% and 66.50 mg g-1. The biochars chosen from the project didn’t show a significant influence on the toxicity test of zebrafish embryos, and the colloidal fractions of BCT600 and BCNM600 in suspension provided (in EPA medium, 96 hours) a zeta potential and hydrodynamic size of -22.35 mV and -14.91 mV and 528,34 nm e 856,60 nm, respectively. These results suggest the viability of these biochars to adsorptive and photocatalytic removal of oxytetracycline in aqueous solutions.