ABSTRACT
In this work we have studied the treatment of imazapyr by electrochemical oxidation with boron-doped diamond anode. Electrochemical degradation experiments were performed in a one-compartment cell containing 0.45 L of commercial formulations of herbicide in the pH range 3.0-10.0 by applying a density current between 10 and 150 mA cm(-2) and in the temperature range 25-45 °C. The maximum current efficiencies were obtained at lower current densities since the electrochemical system is under mass transfer control. The mineralization rate increased in acid medium and at higher temperatures. The treatment was able to completely degrade imazapyr in the range 4.6-100.0 mg L(-1), although the current charge required rises along with the increasing initial concentration of the herbicide. Toxicity analysis with the bioluminescent bacterium Vibrio fischeri showed that at higher pollutant concentrations the toxicity was reduced after the electrochemical treatment. To clarify the reaction pathway for imazapyr mineralization by OH radicals, LC-MS/MS analyses we performed together with a theoretical study. Ions analysis showed the formation of high levels of ammonium in the cathode. The main final products of the electrochemical oxidation of imazapyr with diamond thin film electrodes are formic, acetic and butyric acids.
Subject(s)
Diamond/chemistry , Imidazoles/chemistry , Niacin/analogs & derivatives , Titanium/chemistry , Waste Disposal, Fluid/methods , Water Pollutants, Chemical/chemistry , Chromatography, Liquid , Electrodes , Electrolysis , Herbicides/chemistry , Hydrogen-Ion Concentration , Niacin/chemistry , Oxidation-Reduction , Tandem Mass SpectrometryABSTRACT
The thiadiazolylurea derivative tebuthiuron (TBH) is commonly used as an herbicide even though it is highly toxic to humans. While various processes have been proposed for the removal of organic contaminants of this type from wastewater, electrochemical degradation has shown particular promise. The aim of the present study was to investigate the electrochemical degradation of TBH using anodes comprising boron-doped (5000 and 30,000 ppm) diamond (BDD) films deposited onto Ti substrates operated at current densities in the range 10-200 mA cm(-2). Both anodes removed TBH following a similar pseudo first-order reaction kinetics with k(app) close to 3.2 × 10(-2) min(-1). The maximum mineralization efficiency obtained was 80%. High-pressure liquid chromatography with UV-VIS detection established that both anodes degraded TBH via similar intermediates. Ion chromatography revealed that increasing concentrations of nitrate ions (up to 0.9 ppm) were formed with increasing current density, while the formation of nitrite ions was observed with both anodes at current densities ≥ 150 mA cm(-2). The BDD film prepared at the lower doping level (5000 ppm) was more efficient in degrading TBH than its more highly doped counterpart. This unexpected finding may be explained in terms of the quantity of impurities incorporated into the diamond lattice during chemical vapor deposition.
Subject(s)
Boron/chemistry , Diamond/chemistry , Electrodes , Herbicides/chemistry , Methylurea Compounds/chemistry , Water Pollutants, Chemical/chemistry , Herbicides/analysis , Kinetics , Methylurea Compounds/analysis , Oxidation-Reduction , Waste Disposal, Fluid/methods , Water Pollutants, Chemical/analysisABSTRACT
Boron-doped diamond (BDD) films grown on the titanium substrate were used to study the electrochemical degradation of Reactive Orange (RO) 16 Dye. The films were produced by hot filament chemical vapor deposition (HFCVD) technique using two different boron concentrations. The growth parameters were controlled to obtain heavily doped diamond films. They were named as E1 and E2 electrodes, with acceptor concentrations of 4.0 and 8.0 × 10(21)atoms cm(-3), respectively. The boron levels were evaluated from Mott-Schottky plots also corroborated by Raman's spectra, which characterized the film quality as well as its physical property. Scanning Electron Microscopy showed well-defined microcrystalline grain morphologies with crystal orientation mixtures of (111) and (100). The electrode efficiencies were studied from the advanced oxidation process (AOP) to degrade electrochemically the Reactive Orange 16 azo-dye (RO16). The results were analyzed by UV/VIS spectroscopy, total organic carbon (TOC) and high-performance liquid chromatography (HPLC) techniques. From UV/VIS spectra the highest doped electrode (E2) showed the best efficiency for both, the aromaticity reduction and the azo group fracture. These tendencies were confirmed by the TOC and chromatographic measurements. Besides, the results showed a direct relationship among the BDD morphology, physical property, and its performance during the degradation process.
