EC(EE) process in the reduction of the herbicide clopyralid on mercury electrodes

Corredor, M.C.; Mellado, José Miguel Rodríguez; Montoya, Mercedes Ruiz

doi:10.1016/j.electacta.2005.12.010

Cited by 32 publications

(25 citation statements)

References 16 publications

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“…1 shows the cyclic voltammograms of picloram in the absence and in the presence of Triton X-100. In the absence of the surfactant, and at concentrations higher than 2 · 10 À4 m, two prepeak systems were found in the voltammogram: in the potential range À 0.6 to À 0.8 V, close to the main reductions peak (in the following, peak 1), appears a system named system I, and in the potential range 0 to À 0.4 V, which is far from both peak 1 and system I, appears a system named system II [8]. Under these conditions, these prepeak systems can be attributed to the weak adsorption of reactant and the strong adsorption of the product at the electrode surface.…”

Section: Methodsmentioning

confidence: 97%

“…were purged with purified N 2 and the temp. was kept at 298 AE 0.1 K. All other experimental conditions are given in [8] [12].…”

Section: At Concentrations Higher Than 2 · 10mentioning

confidence: 99%

“…For picloram, a pK value of dissociation of the carboxylic acid group of 2.20 AE 0.03 was determined [8], and the pK corresponding to the protonation of the pyridine ring was found to be 3.4 [8 -11] (Scheme 1).…”

Section: At Concentrations Higher Than 2 · 10mentioning

confidence: 99%

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On the Adsorption and Reduction of the Herbicide Picloram on Mercury and Carbon Electrodes

Mellado

Pintado

Montoya

2008

Helvetica Chimica Acta

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At concentrations higher than 2 · 10À4 m, and below pH 3, the cyclic voltammograms of picloram (¼ 4-amino-3,5,6-trichloropyridine-2-carboxylic acid) on Hg electrodes show two prepeak systems (named I and II attending to the proximity to the main reductions peak), which can be attributed to the weak adsorption of reactant and the strong adsorption of the product at the electrode surface. The system II is due to the uncharged form of picloram, and system I to the picloram protonated at the pyridine Natom. Small amounts of the surfactant Triton X-100 (¼ a-[4-(1,1,3,3-tetramethylbutyl)phenyl]-whydroxypoly(oxyethane-1,2-diyl)) cause the disappearance of system I, the shift of system II, and also affect the intensities and widths of anodic and cathodic peaks but not the charge passed in each peak. Thus, the adsorption process responsible for the appearance of system I is inhibited by the presence of Triton; by contrast, the process corresponding to system II is only modified by the surfactant, becoming an electrochemical process occurring at the potentials corresponding to system II, which is more reversible than that observed in the absence of Triton. The addition of Triton permitted the analysis of the main reduction process. Convolution voltammetry of the main reduction peak is consistent with the loss of a Cl-atom in equilibrium which occurs after a reversible electron transfer and is followed by the reductions of both species present in the equilibrium (Scheme 2). This is also the reduction mechanism on a glassy carbon electrode but the electron transfer on the carbon electrode increases with respect to the mercury electrodes; in addition, the loss of the Cl-atom does not take place on the electrode surface. From the recording of differential capacity -potential curves, it was concluded that picloram is adsorbed on the carbon electrode; but this adsorption is too weak to induce the appearance of prepeak systems.

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Section: Methodsmentioning

confidence: 97%

“…were purged with purified N 2 and the temp. was kept at 298 AE 0.1 K. All other experimental conditions are given in [8] [12].…”

Section: At Concentrations Higher Than 2 · 10mentioning

confidence: 99%

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On the Adsorption and Reduction of the Herbicide Picloram on Mercury and Carbon Electrodes

Mellado

Pintado

Montoya

2008

Helvetica Chimica Acta

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“…Thus, the TiO 2 surface will be positively charged ( 2 TiOH  ) in acidic media (pH  pH pzc ) and negatively charged (TiO  ) in alkaline media (pH  pH pzc ). On the other hand, the pK a values for CLP are 1.4±0.1 and 4.4±0.1 (Corredor et al, 2006), so that at pH < 1.4 the herbicide is mainly present in its protonated form, and at pH > 4.4 in the anionic form. In the pH interval from 2.4 to 3.5, one can expect a great increase in the photodegradation rate, arising as a consequence of the dissociation of the carboxylic group and deprotonation of the pyridine nitrogen (to a significantly smaller extent).…”

Section: Effect Of the Initial Phmentioning

confidence: 99%

Comparative Assessment of the Photocatalytic Efficiency of TiO2 Wackherr in the Removal of Clopyralid from Various Types of Water

Abramović¹,

Despotović²,

Šojić³

et al. 2012

Herbicides - Properties, Synthesis and Control of Weeds

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“…Namely, under the visible light, clopyralid is practically not degraded in the presence of any of the mentioned catalysts (Figure 6a), whereas under UV irradiation (Figure 6b) some degradation takes place, but at a rate which is by about three times lower than in the case of mecoprop. The photocatalytic degradation of mecoprop and clopyralid seems to be related to the difference in pK a values (for mecoprop pK a = 3.11-3.78 [20] and for clopyralid pK 1 = 1.4 and pK 2 = 4.4 [21]) [22] and to the difference in molecular structure of these compounds. The larger rate of clopyralid photodegradation under UV than under visible irradiation is in agreement with results of other authors [22], who explain it by the difference in the mechanism of the process.…”

Section: Photocatalytic Activitymentioning

confidence: 99%

Photocatalytic Degradation of Mecoprop and Clopyralid in Aqueous Suspensions of Nanostructured N-doped TiO2

et al. 2010

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Abstract:The work describes a study of the oxidation power of N-doped and undoped anatase TiO 2 , as well as TiO 2 Degussa P25 suspensions for photocatalytic degradation of the herbicides propionic acid (mecoprop) and 3,6-dichloropyridine-2-carboxylic acid (clopyralid) using visible and UV light. Undoped nanostructured TiO 2 powder in the form of anatase was prepared by a sol-gel route. The synthesized TiO 2 , as well as TiO 2 Degussa P25 powder, were modified with urea to introduce nitrogen into the structure. N-doped TiO 2 appeared to be somewhat more efficient than the starting TiO 2 (anatase) powder when visible light was used for mecoprop degradation. N-doped TiO 2 Degussa P25 was also slightly more efficient than TiO 2 Degussa P25. However, under the same experimental conditions, no degradation of clopyralid was observed in the presence of any of the mentioned catalysts. When the kinetics of mecoprop degradation was studied using UV light, more efficient were the undoped powders, while in the case of clopyralid, N-doped TiO 2 Degussa P25 powder was most efficient, which is probably a consequence of the difference in the molecular structure of the two herbicides. OPEN ACCESSMolecules 2010, 15 2995

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EC(EE) process in the reduction of the herbicide clopyralid on mercury electrodes

Cited by 32 publications

References 16 publications

On the Adsorption and Reduction of the Herbicide Picloram on Mercury and Carbon Electrodes

On the Adsorption and Reduction of the Herbicide Picloram on Mercury and Carbon Electrodes

Comparative Assessment of the Photocatalytic Efficiency of TiO2 Wackherr in the Removal of Clopyralid from Various Types of Water

Photocatalytic Degradation of Mecoprop and Clopyralid in Aqueous Suspensions of Nanostructured N-doped TiO2

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