Estudo da eletro-oxidação de poluentes sobre ânodos dimensionalmente estáveis comerciais (ADE® ) modificados com platina

Abstract

Currently, there is a great concern with different compounds with great potential to pollute the environment, among them drugs and dyes stand out. These pollutants have different sources of origin, both industrial and domestic effluents. For many effluents, treatment is still carried out by conventional methods, which have proven to be ineffective and costly to eliminate these pollutants. Electrochemical Advanced Oxidation Processes (EAOPs), which consist of a set of techniques capable of oxidizing different pollutants, have been shown to be an efficient alternative for this purpose. Furthermore, this class of methods can be combined with other techniques in order to increase the efficiency of the degradation process. Therefore, this work aims to evaluate the applicability of electrooxidation in the treatment of simulated effluents containing drugs (tetracycline and diclofenac) and the dye Reactive Yellow 145 (AR-145). The first pollutant to be evaluated was tetracycline hydrochloride (TC) in acidic medium using commercial DSA® (Ti/Ru0.3Ti0.7O2) and commercial DSA® modified by platinum electrodeposition (DSA®/Pt) as anodes. The DSA® were modified by platinum electrodeposition with constant potential at different times (1,200, 2,400 and 4,800 s) and the electrochemical and morphological characterization showed that, with increasing electrodeposition time, there is an increase in the active electrochemical area. For TC electrooxidation, higher current densities and higher amounts of platinum in the electrodes showed that they are more efficient in TC removal, reaching 100% degradation. However, the materials showed slow efficiency in TC mineralization (TOC reduction <15%). The DSA®/Pt electrodes showed greater stability and efficiency to TC oxidation, indicating that they are a promising material for the oxidation of organic pollutants. The photoelectrochemical study suggests that the degradation efficiency is higher for the DSA®/Pt anode with 68.9% degradation of the initial concentration of the pollutant, with 27.75% of COD abatement. The use of photoelectrochemistry combined with sodium persulfate as a mediator species proved to be more efficient when the DSA® anode was used, where we achieved a 69.39% decrease in the initial concentration and 31.62% in the reduction of the COD. The results obtained with the electrochemical treatment combined with the biological treatment suggest that there is the formation of intermediates that are biodegradable. In the study of diclofenac sodium (DCF) electrooxidation, using commercial and modified DSA® anodes (DSA®/Pt), for both electrodes, the increased applied current density (j = 25, 50 and 100 mA cm-2) decreases the DCF concentration, however, the efficiency of the DSA® electrode was higher with removal of 82.15%, 95.40% and 90.46%, respectively, after 60 minutes of electrooxidation. Pollutant mineralization was evaluated by reducing COD, which reached 75.09%, 82.83% and 80.15%, for j = 25, 50 and 100 mA cm-2, respectively. The lower efficiency at 100 mA cm-2 than at 50 mA cm-2 is associated with parallel reactions such as oxygen evolution reaction (OER) that consumes part of the applied energy. With pseudo-first order reaction kinetics, the Total Current Efficiency (TCE) was 59.75% and the Specific Energy Consumption (ECDQO) was 0.0056 kWh(g COD)-1 for the DSA®. Taking into account all the studied parameters, the best current density was 25 mA cm-2 because it presented a reduction in DCF and CO D close to the other current densities used, but reached the best values of TCE and ECDQO. In the study of the electrooxidation of the dye AR-145 with commercial DSA® and DSA®/Pt, the determination of the pollutant degradation rate was performed as a function of different electrolyte compositions, with the composition Na2SO4 0.1 mol L-1 + NaCl 6.25 mmol L-1, with a current density of 25 mA cm-2, which presented the best result of 100% reduction in the concentration of AR-145, 60.8% reduction in COD and energy consumption 0.568 kWh (g COD)-1, for the unmodified DSA® electrode. For the same conditions, the DSA®/Pt electrode showed 100% reduction in dye concentration, 75.1% reduction in COD, 0.232 kWh(g COD)-1, that is, the modified electrode showed greater efficiency than not modified, indicating a possible synergistic or changing effect of the electronic properties of the commercial DSA®. In the second part of the work of electrooxidation of AR-145 was studied with a lower concentration of chloride in the medium (Na2SO4 0.1 mol L-1 + NaCl 0.05 mol L-1) with the DSA® anode and in this composition the results for the parameters evaluated were superior, that is, 100% reduction in the concentration of AR-145, 88.94% reduction in COD and energy consumption 0.227 kWh(g COD)-1 with a current density of 25 mA cm-2.