Short communicationRuthenium–tin oxides-coated graphite felt: Enhanced active area and improved efficiency for the electrochemical generation of hydrogen peroxide
Introduction
The advanced oxidation processes are applied in the removal of organic compounds restrained in polluted water. These clean technologies are based in the generation of the hydroxyl radical, •OH, (E°=2.80 V) [1], producing CO2 and H2O as final products [2]. Among them, advanced electrochemical oxidation processes are used to increasing the efficiency of organic pollution decontamination, because they produce large amount of •OH under control of the current׳s intensity applied [3].
According to Bertazolli et al. [4] the cathodic electro-generation of H2O2 (E°=0.682 V/SHE), from dissolved O2, occurs without generation of contaminants, and depends on pressure and temperature, where the advantages are the simplicity in the operation, efficiency of pollutants degradation and high reactivity of •OH. A disadvantage is the low time of •OH half-life, making necessary its production in situ [5].
Porous carbonaceous materials with high surface area have been extensively used as electrodes for several applications, from sensors to fuel cell catalysts substrates [6]. In particular, graphite felt, with good electronic conductivity, is an appropriate material to provide abundant reaction sites. However, due to its hydrophobic surface nature, its wettability and electrochemical activity needs to be improved. In this sense, the development of chemically modified electrodes with metallic oxides is an interesting way to improve carbon properties [7]. RuO2 is commonly used as an active catalyst. SnO2, which is a semiconductor with a band gap 3.0–3.2 eV at room temperature [8], [9], possess its conductivity based on O2 vacancies. Its deactivation occurs with the addition of O2 to the oxide layer, when applied anodic potentials, resulting in a more stoichiometric and less conductive material. So, the solution is to add a dopant like RuO2 to increase its conductivity and stability.
Thus, we developed chemically modified electrodes, made from reticulated vitreous graphite felt (RVG 4000) covered with (RuO2)0.9–(SnO2)0.1, by Pechini method, for the electro-generation of H2O2 in situ, in a filter-press reactor for future use in the decontamination of liquid effluents by the Electro-Fenton process.
Section snippets
Materials and methods
The precursor solutions were prepared, according Wang et al. report [8], by dissolving of RuCl3 (Sigma Aldrich, 98.0%) and SnCl2 (Synth®, 98.0%) salts (9:1) in citric acid (C.A., Synth®, 99.5%) and ethylene glycol (E.G., Vetec® 99.5%) at molar ratios EG:AC:RuCl3–SnCl2 (1.0:4.6:0.3) at 60 °C. The RVG 4000 (volume 12 cm3) was immersed in the precursor solution and thermally treated initially at 130 °C/30 min, then at 250 °C/10 min (for the adhesion layer) and finally at 350 °C for 5 min to remove organic
Results and discussion
The SEM image of the uncoated graphite felt Fig. 1(a) exhibit a clean and smooth surface with carbon randomly oriented in a 2D plane, also forming a porous 3D network. Similar characteristics were also previously observed for the same material by Vilar et al. [11]. The surface morphology characterization of the modified graphite felt is displayed in Fig. 1(b), and shows that the carbon surfaces were totally and uniformly coated by ceramic deposits as they become significantly rougher. Besides,
Conclusions
The deposition of (RuO2)0.9–(SnO2)0.1 in the graphite felt RVG 4000 by the Pechini method, resulted in a material with electroactive area ~250 times higher than the bare RVG 4000, electrochemically stable, with homogenous deposits on the whole matrix of the felt and with the desired stoichiometric composition. So, the use of this material increased the yield of H2O2, by electro-generation, in 72.2%. Thus, the material developed is promising for use in efficient sewage treatment systems using an
Acknowledgments
The authors thank to CNPq (grants: 303630/2012-4 and 310282/2013-6), FINEP, CAPES and LNNano/LNLS.
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