This paper presents a comparative study about the oxygen reduction reaction (ORR) catalyzed by nanoparticles of Fe 2 O 3 and Co 3 O 4 applied on the surface of glassy carbon electrodes (GCE). The nanoparticles were synthesized using the modified polymeric precursor method (Pechini). These two nanomaterials were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. The estimated average particle sizes were 21 and 31 nm for Fe 2 O 3 and Co 3 O 4 , respectively. Electrochemical impedance spectroscopy (EIS) showed that Fe 2 O 3 /GCE has lower charge transfer resistance than Co 3 O 4 /GCE. The surface electrochemistry of both Fe 2 O 3 /GCE and Co 3 O 4 /GCE was studied in the solution free of O 2 , and their corresponding reaction mechanisms were analyzed. The electrocatalytic ORR activities of these two catalysts were studied by cyclic voltammetry (CV) and rotating disk electrode (RDE) in acidic solution. The results obtained by RDE indicated that both Fe 2 O 3 /GCE and Co 3 O 4 /GCE can catalyze the ORR with a dominating 2-electron transfer process to produce H 2 O 2 , using a potential of −0.8 V. These kinetic results indicate that Fe 2 O 3 /GCE is more efficient than Co 3 O 4 /GCE in terms of ORR. Considering the low cost of these two non-noble metal catalysts, they may be used as viable alternatives for ORR electrocatalysts.
Square-wave adsorptive stripping voltammetry (SWAdSV) was used to determine iron in ethanol and biodiesel using a bismuth-film electrode (BiFE) prepared onto the surface of a glassy carbon electrode (GCE) by electrochemical deposition to promote the reduction of Fe (III) previously complexed with 1-(2-pyridylazo)-2-naphthol (PAN) directly in the electrochemical cell. The supporting electrolyte was composed by mixture of acetate buffer (0.1 mol L À1 , pH 4.5) and ethanol (40/60% v/v) into which 500 mL of a 0.1 mmol L À1 stock solution of PAN was added as complexing agent. The Fe (III)-PAN complex presented a well-defined current peak at À0.7 V. For biodiesel, a treatment with tetramethylammonium hydroxide (TMAH) was proposed as an efficient mean to minimized matrix interferences. A limit of detection of 6.0 Â 10 À8 mol L À1 (0.06 mmol L À1 ) and limit of quantification of 2.0 Â 10 À7 mol L À1 (0.2 mmol L À1 ) were obtained for Fe(III). Under the optimized conditions, there were no significant interferences from Cu(II), Al(III), Mn(II), Cr(III), Cd(II), Zn(II) and Ni(II) and Pb(II) while Ni(II) interfered significantly. The analytical curves produced linear responses with equations I (mA) ¼ (-1.315 Â 10 À7 ± 5.158 Â 10 À8 ) þ (-0.238 ± 0.01) [Fe (III)] (mmol L À1 ), R 2 ¼ 0.992 and I (mA) ¼ (-6.836 Â 10 À7 ± 1.124 Â 10 À8 ) þ (-0.408 ± 0.013) [Fe (III)] (mmol L À1 ), R 2 ¼0.998 for pure ethanol and biodiesel, respectively. The method produced satisfactory results in quantifying original quantities of Fe(III) in fuel ethanol (5.65 ± 0.71 mmol L À1 ) and biodiesel (1.28 ± 0.25 mmol L À1 ) at a 95% confidence limit (n ¼ 3).
The contamination of water and soil by petroleum hydrocarbons is reported quite frequently, mainly due to accidents involving transport and storage of fuels. Among the most toxic compounds the most volatile benzene, toluene, ethylbenzene and xylene (BTEX). Residues of these compounds can cause serious environmental and public health troubles. Thus, more sensitive, selective and low-cost techniques, focused on the analysis and monitoring of these contaminants are being developed in order to establish operational control and to comply with local laws, but the intellectual property of such technologies is still unknown. The present study shows the panorama about patents, thesis and dissertations which have been already published on this theme. Together, the United States and China hold the largest number of patents, and most of thesis/dissertations describe methodologies for BTEX detection in water, although numerous environmental problems caused by oils in the soil had been reported. Also, the methods based on chromatographic techniques stand out in relation to the other techniques. It was possible to verify important advances in the field of sensors, especially the electrochemical ones, in order to solve the analytical gaps.
As a result of anthropogenic action, an increasing amount of toxic organic compounds has been released into the environment. These pollutants have adverse effects on human health and wildlife, which has motivated the development of different types of technologies for the treatment of effluents and contaminated environments. The electrochemical degradation of organic pollutants has attracted the interest of research centers around the world for its environmental compatibility, high efficiency and affordable cost. In the present study, a bibliometric analysis was performed using the Web of Science database in order to assess the progress of publications related to electrochemical degradation of organic pollutants between the years 2001 and 2021. The data retrieved showed a significant increase in publications related to the topic in the last 20 years. Electrochimica Acta was the magazine responsible for the largest number of publications (230, 7.22%). The studies mainly included the areas of chemistry, engineering and electrochemistry. China with a total of 1004 (31.49%) publications dominated research in this area, followed by Spain (282, 8.85%) and Brazil (255, 8.00%). The institutions with the highest number of contributions were the University of Castilla-la Mancha and the Chinese Academy of Sciences, and the most productive authors were Rodrigo MA and Martines-Huitle CA. The results of this study provide important references and information on possible research directions for future investigations on electrochemical degradation of organic pollutants.
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