In this work, cobalt ferrite (CoFe 2 O 4) was synthesized by solvothermal route for application as a catalyst in the ozonation reaction for the decolorization and mineralization of melanoidin from aqueous solution. The structural properties of CoFe 2 O 4 sample were investigated by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, Fourier-transform infrared spectroscopy (FTIR), particlesize distribution, scanning electron microscopy (SEM) and X-ray dispersive energy spectroscopy (EDS). Single-phase CoFe 2 O 4 particles with a predominantly mesoporous structure containing a high specific surface area were obtained. Results showed that the CoFe 2 O 4-catalyzed ozonation reaction has higher activity for the decolorization and mineralization of melanoidin when compared with the ozonation reaction without the presence of catalyst. Therefore, this material can be very promising for the application in catalytic ozonation systems for the melanoidin removal from liquid effluents.

The treatment of colored effluents containing Procion Red dye (PR) was investigated using HSO and HNO modified avocado shells (Persea americana) as adsorbents. The adsorbent materials (AS-HSO and AS-HNO) were properly characterized. The adsorption study was carried out considering the effects of adsorbent dosage and pH. Kinetic, equilibrium, and thermodynamic aspects were also evaluated. Finally, the adsorbents were tested to treat simulated dye house effluents. For both materials, the adsorption was favored using 0.300 g L of adsorbent at pH 6.5, where, more than 90% of PR was removed from the solution. General order model was able to explain the adsorption kinetics for both adsorbents. The Sips model was adequate to represent the isotherm data, being the maximum adsorption capacities of 167.0 and 212.6 mg g for AS-HSO and AS-HNO, respectively. The adsorption processes were thermodynamically spontaneous, favorable (- 17.0 < ΔG < - 13.2 kJ mol), and exothermic (ΔH values of - 29 and - 55 kJ mol). AS-HSO and AS-HNO were adequate to treat dye house effluents, attaining color removal percentages of 82 and 75%. Avocado shells, after a simple acid treatment, can be a low-cost option to treat colored effluents.

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The chalcogenide composite FeIn 2 S 4 was prepared by hydrothermal route and, for the first time, investigated as a heterogeneous catalyst in the photo-Fenton treatment for Ponceau 4R dye (C 20 H 11 N 2 Na 3 O 10 S 3 ) under visible irradiation. The composite was characterized by X-ray diffraction (DRX), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDS) and elemental mapping, band gap energy and X-ray photoelectron spectroscopy (XPS). The optimal experimental conditions were investigated and determined to be pH 3.0, 0.5 g L −1 of catalyst and 2.5 mmol L −1 of H 2 O 2 . A decolorization efficiency of 93.3% was achieved in 60 min of reaction and a TOC removal of 92.3% was reached in 180 min. The stability and recycle capacity of FeIn 2 S 4 indicated that the catalyst can be used more than four times without considerable loss of efficiency. Free radicals investigation revealed that • OH and O 2•− radicals were the major oxygen reactive species involved on Ponceau 4R degradation. The lower-mass intermediates from Ponceau 4R degradation were identified, and a mechanism for the photo-Fenton treatment was suggested. Therefore, the composite showed a performance that makes it a promising catalyst for removing emerging contaminants in water.

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