ELECTROOXIDATION OF 2,4,6-TRICHLOROPHENOL ON GLASSY CARBON ELECTRODES MODIFIED WITH COMPOSITE Ni(OH)2-Co(OH)2 FILMS

Abstract

Glassy carbon electrodes coated with a film of electrodeposited cobalt and nickel hydroxides were prepared in order to determine its activity to the 2,4,6-trichlorophenol (TCP) oxidation. The modified electrodes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy and Scan Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS). The results indicate that both hydroxides are homogeneously distributed in the electrode surface. From the viewpoint of electrochemical oxidation of TCP, the presence of cobalt and nickel hydroxides on the electrode surface (i) promotes a more complete oxidation of TCP and (ii) decreases the fouling of the electrode surface in comparison with GC and GC modified with Ni or Co separately. Keywords:Modified electrodes, (Ni-Co) hydroxides, chlorophenol oxidation e-mail: soledad.ureta@usach.cl 1.-INTRODUCTIONWaste from domestic, agricultural and industrial activities such as cellulose treatment and the manufacturing of plastics, adhesives and petrochemicals may pollute watercourses [1]. The widely used halogenated compounds are not amenable to biological degradation, and can accumulate in living organisms, this being the reason why they are used as wood preservatives, antibacterial agents, fungicides, insecticides and herbicides [2,3].Au and Pt show high catalytic activity for the electrooxidation of chlorophenols (CP) over short times, but they are quickly fouled up by small oligomers, generated by the coupling of two phenoxy radicals or by reaction of a radical with unreacted CP molecules [4,5]. Electrodes modified with redox mediators could increase the activity and specificity for a given reaction and avoid fouling [6]. So, glassy carbon (GC) electrodes modified with Co(II) phthalocyanine (CoPc) show higher currents and less fouling in the oxidation of 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) in 1 M NaOH [7]. Also Alatorre et al. [8] found that GC electrodes modified with electropolymerized nickel complexes showed less fouling in the oxidation of 4-CP and 4-nitrophenol in 1 M NaOH. Our laboratory has some experience in this field [4,5,9,10,11]. The goal is to decrease the oligomerization rate and to promote full oxidation of the phenolic compound.The redox mediator activity in alkaline media of electrodes modified with Ni(II) compounds is due to the quasi reversible properties of the Ni(III)/Ni(II) process [9,10,11],which may be represented as follows [12]:Actually nickel hydroxide can have more than one stable structure [13,14,15]. Van der Ven et al. [16] reported the formation of two types of nickel hydroxide, α -and β-Ni(OH) 2 , and two kinds of nickel oxyhydroxides, α -and γ-NiOOH, which, due to their different structures and degrees of hydration, have different electrochemical properties.Other hydroxide, Co(OH) 2 , has been widely used as an additive to Ni(OH) 2 in order to improve alkaline secondary batteries [17,18,19], these improvements being attributed to an increase of bot...

Exceptional Lithium Storage in a Co(OH)2 Anode: Hydride Formation

“…The most intense ∼530.9 eV peak is characteristic of a metal Co–OH bond, and the binding energy at ∼529.5 eV is a characteristic of a metalO double bond that may be due to CoOOH possibly formed by air oxidation of Co­(OH) 2 , particularly during the synthesis. Mostly, the peak at ∼532.4 eV is related to the adsorbed water during the synthesis process . During the discharge process, a peak at ∼531.0 eV appears in the high-voltage region, which corresponds to LiOH, ,, formed by conversion reaction, and a Li 2 O peak (∼528.6 eV) , and a Li 2 CO 3 peak (∼532 eV) arise in the low-voltage region due to reaction products derived from a combination of hydride formation between LiOH and lithium and side reactions with electrolyte.…”

“…Mostly, the peak at ∼532.4 eV is related to the adsorbed water during the synthesis process. 88 During the discharge process, a peak at ∼531.0 eV appears in the high-voltage region, which corresponds to LiOH, 79,80,82 formed by conversion reaction, and a Li 2 O peak (∼528.6 eV) 79,82 and a Li 2 CO 3 peak (∼532 eV) 83 arise in the low-voltage region due to reaction products derived from a combination of hydride formation between LiOH and lithium and side reactions with electrolyte. From all these results, the overall reaction mechanism of CS-Co(OH) 2 is summarized in Figure 10, and the lithiation of CS-Co(OH) 2 can be described by the following processes: reversibility of conversion and hydride formation.…”

Metal–Organic Coordination Network Thin Film by Surface-Induced Assembly

“…The peaks of Co 2p 3/2 and Co 2p 1/2 were located at 781.1 and 796.9 eV, respectively, , along with the presence of the two strong satellite peaks of cobalt at 784.9 and 802.2 eV, representing the oxidation state of cobalt ion as +2 (Figure ). − Furthermore, no difference in Co 2p spectra was observed, indicating that the cobalt oxidation number was not changed during fabrication process. The results show the coordination network between cobalt ion and H 2 TCPP.…”

Nonenzymatic Electrochemical Detection of 2,4,6-Trichlorophenol Using CuO/Nafion/GCE: A Practical Sensor for Environmental Toxicants

“…17,18 In contrast, the electroanalytical methods got a clear edge over the conventional analytical methods in terms of high sensitivity, fast response, low cost, miniaturization, and most importantly, in-situ analysis. 19−21 Until now, different electrochemical sensors have been reported for the detection of 2,4,6 TCP such as HS-β-cyclodextrin, 22 graphene-bromocresol purple, 23 composite sensor based on rhodamine B/platinum nanoparticles/carbon nanotubes, 24 film composite of Ni-(OH) 2 −Co(OH) 2 , 25 and SWCNTs/poly-3,4-ethylenedioxothiophen. 26 However, the electrochemical activity of 2,4,6 TCP is very weak, and it requires a large amount of activation energy that results in poor sensitivity.…”

“…There are several traditional analytical methods reported for the quantification of CPs in the environmental samples, for example, gas chromatography/mass spectrometry, high performance-liquid chromatography, and capillary electrophoresis. , Surely, these analytical methods offer influential trace analysis and can detect CPs at very low concentration levels. However, there are certain serious factors that limit the practices of these analytical tools, as these techniques require tedious sample treatment, extensive purification, expensive equipment, and demand well-qualified personnel. , In contrast, the electroanalytical methods got a clear edge over the conventional analytical methods in terms of high sensitivity, fast response, low cost, miniaturization, and most importantly, in-situ analysis. − Until now, different electrochemical sensors have been reported for the detection of 2,4,6 TCP such as HS-β-cyclodextrin, graphene-bromocresol purple, composite sensor based on rhodamine B/platinum nanoparticles/carbon nanotubes, film composite of Ni­(OH) 2 –Co­(OH) 2 , and SWCNTs/poly-3,4-ethylenedioxothiophen . However, the electrochemical activity of 2,4,6 TCP is very weak, and it requires a large amount of activation energy that results in poor sensitivity. , …”