Metal oxide-coated anodes in wastewater treatment.
ABSTRACT Electrochemical oxidation is an effective wastewater treatment method. Metal oxide-coated substrates are commonly used as anodes in this process. This article compiles the developments in the fabrication, application, and performance of metal oxide anodes in wastewater treatment. It summarizes the preparative methods and mechanism of oxidation of organics on the metal oxide anodes. The discussion is focused on the application of SnO2, PbO2, IrO2, and RuO2 metal oxide anodes and their effectiveness in wastewater treatment process.
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ABSTRACT: The Ce-doped modified porous nanocrystalline PbO(2) film electrode prepared by electrodeposition technology was used for electrochemical mineralization of environmentally persistent perfluorinated carboxylic acids (PFCAs) (∼C(4)-C(8)), i.e., perfluorobutanoic acid (PFBA), perfluopentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoheptanoic acid (PFHpA), and perfluorooctanoic acid (PFOA) in aqueous solution (100 mL of 100 mg L(-1)). The degradation of PFCAs follows pseudo-first-order kinetics, and the values of the relative rate constant (k) depend upon chain length k(PFHpA) (4.1 × 10(-2) min(-1); corresponding half-life 16.8 min) ≈ 1.1k(PFOA) ≈ 2.5k(PFHxA)≈ 6.9k(PFPeA) ≈ 9.7k(PFBA). The carbon mineralization indices [i.e., 1 - (TOC(insolution)/TOC(inPFCA,degraded))] were 0.49, 0.70, 0.84, 0.91, and 0.95 for PFBA, PFPeA, PFHxA, PFHpA, and PFOA, respectively, after 90 min electrolysis. The major mineralization product, F(-), as well as low amount of intermediate PFCAs with shortened chain lengths were detected in aqueous solution. By observing the intermediates and tracking the concentration change, a possible pathway of electrochemical mineralization is proposed as follows: Kolbe decarboxylation reaction occurs first at the anode to form the perfluoroalkyl radical, followed by reaction with hydroxyl radicals to form the perfluoroalkyl alcohol which then undergoes intramolecular rearrangement to form the perfluoroalkyl fluoride. After this, the perfluoroalkyl fluoride reforms perfluorinated carboxylic with shorter chain length than its origin by hydrolysis. This electrochemical technique could be employed to treat PFCAs (∼C(4)-C(8)) in contaminated wastewater.Environmental Science & Technology 08/2012; 46(18):10191-8. · 5.26 Impact Factor
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ABSTRACT: Elecrtochemical degradation of phenol was evaluated at five typical anodes for mineralization to carbon dioxide or for being a pre-treatment method in toxic aromatic compounds. Three kinds of RuO(2)-base electrodes were prepared by thermal deposition, which were coated by the oxides of Ru or by Ru, Sn and Sb or by Ru, Sn, Sb and Gd on Ti metal surface, respectively. Another electrode Ti/ PbO(2) was prepared by electro-deposition method with PbO(2) coated on Ti. A Pt electrode was chosen for comparison. Characteristics of the typical five electrodes were investigated by cyclic voltammetry, SEM and its degradation ability for phenol. Performance for phenol degradation of the three RuO(2) electrodes lie in: Ti/Sb-Sn-RuO(2)-Gd> Ti/Sb-Sn-RuO(2)> Ti/RuO(2) and the electrode with beta-PbO(2) coating was superior to RuO(2)-based electrodes and Pt electrode. Aromatic ring opening take place at all researched electrodes and it is supposed that electrolysis run stop at different intermediates, such as benzoquinone, maleic acid, etc. Under the present experimental conditions, whole mineralization to CO(2) takes place only in the beta-PbO(2) anode. A pathway of electrochemical degradation of phenol was suggested based on the experimental analysis.Water Research 05/2003; 37(10):2399-407. · 4.66 Impact Factor
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ABSTRACT: Characterization of RuO(2) and TiO(2) sols of different aging times, obtained by forced hydrolysis of appropriate chloride salts, was performed by transmission electron microscopy (TEM). The aging time of TiO(2) sols was observed to affect the size of particles as well as the crystallinity of the solid phase of the sols. The surface morphology of RuO(2)-TiO(2) coatings on titanium, obtained by the sol-gel procedure using TiO(2) sols of different aging times and RuO(2) sol of fixed aging time, was investigated by scanning tunneling microscopy (STM) at three different scan sizes. The STM data indicated uniform microdistribution of the coating material (small microroughness) and an increase in nanoroughness with the aging time of the TiO(2) sol. The observed increase in real coating surface area with increasing TiO(2) particle size confirms the earlier cyclic voltammetry results.Journal of Colloid and Interface Science 08/2003; 263(1):68-73. · 3.17 Impact Factor