Synthesis and electrochemical properties of copper(II), manganese(III) phthalocyanines bearing chalcone groups at peripheral or nonperipheral positions

In this study, new chalcone compound 1 , new phthalonitrile derivatives 2 and 3, new copper(II), manganese(III) phthalocyanines bearing chalcone groups at peripheral or nonperipheral positions were synthesized. Electrochemistry of tetra-(4-{(2 E )-3-[2-fluoro-4-(trifluoromethyl)phenyl]prop-2-enoyl}phenoxy) substituted Co(II)Pc and Mn(III)Pcs were studied with cyclic voltammetry (CV) to determine the redox properties of the phthalocyanines. According to the results, while the CuPcs 2a and 3a showed two Pc based reduction reactions and one Pc based oxidation reaction, MnPcs 2b and 3b gave two metal-based reduction reactions. All the redox processes are shifted toward positive potentials as a result of the increased electron-withdrawing ability of the trifluoromethyl substituents.     

Antioxidant behaviour of 2′‐hydroxy‐chalcones: a study of their electrochemical properties

The electrochemical behaviour of 13 chalcone analogues was systematically studied by means of cyclic voltammetry and chronoamperometry at a glassy carbon (GC), gold and platinum working electrodes using two different supporting electrolyte/solvent combinations. It was found that chalcone analogues can be easily oxidized at both GC and gold working electrodes, but not at a platinum electrode. Principal component analysis was further employed to reveal similarities/dissimilarities between oxidation potentials, chronoamperometric signals and ability of the compounds to scavenge the reactive oxygen species H₂O₂. The study reveals the inverse proportional relationship between the scavenging ability of H₂O₂, expressed as IC₅₀, and chronoamperometric signal at 800 mV using gold as working electrode. Copyright © 2012 John Wiley & Sons, Ltd.     

Cyclic voltammetry study of electrodeposition of CuGaSe2 thin films on ITO-glass substrates

The electrodeposition mechanism of CuGaSe₂ (CGS) thin films on ITO substrates has been investigated using cyclic voltammetry technique. The cyclic voltammetric study was performed in unitary Cu, Ga and Se systems, binary Cu–Se, Ga–Se systems and ternary Cu–Ga–Se system. The electrodeposition metallic Ga from Ga unitary electrolytes is impossible due to its low reduction potential. No reduction peak was found for the reduction of Ga³⁺ to Ga in the cyclic voltammogram of unitary system. However, in the cyclic voltammogram of ternary Cu–Ga–Se system, reduction peak at −0.6 V was observed with addition of GaCl₃. Also, current density of the peak was increased with increasing concentration of GaCl₃. It is corresponded to the formation of gallium selenides and/or copper–gallium–selenium compounds. The contents of Ga in the films were significantly changed from −0.4 V to −0.6 V. SEM and XRD analysis also showed that surface morphology and crystalline phase of films were significantly changed with increasing Ga content.     

Developing On-Site Trace Level Speciation of Lead,Cadmium and Zinc by Stripping Chronopotentiometry (SCP): Fast Screening and Quantification of Total Metal Concentrations

Electrochemical stripping techniques are interesting candidates for carrying out onsite speciation of environmentally relevant trace metals due to the existing low-cost portable instrumentation available and the low detection limits that can be achieved. In this work, we describe the initial analytical technique method development by quantifying the total metal concentrations using Stripping Chronopotentiometry (SCP). Carbon paste screen-printed electrodes were modified with thin films of mercury and used to quantify sub-nanomolar concentrations of lead and cadmium and sub-micromolar concentrations of zinc in river water. Low detection limits of 0.06 nM for Pb(II) and 0.04 nM for Cd(II) were obtained by the standard addition method using a SCP deposition time of 180 s. The SCP results obtained for Pb(II) and Cd(II) agreed with those of inductively coupled plasma mass spectrometry (ICP-MS). The coupling of SCP with screen-printed electrodes opens up excellent potential for the development of onsite speciation of trace metals. Due to the low analysis throughput obtained for the standard addition method, we also propose a new, more rapid screening Cd(II) internal standard methodology to significantly increase the number of samples that can be analyzed per day.     

Free‐Standing Membranes to Study the Optical Properties of Anodic TiO2 Nanotube Layers

In the present work we investigate various optical properties (such as light absorption and reflectance) of anodic TiO₂ nanotube layers directly transferred as self‐standing membranes onto quartz substrates. This allows investigation in a transmission geometry which provides significantly more reliable data than measurements on the metallic Ti substrate. Light transmission and reflectance measurements were carried out for layers of thickness varying from 1.8 to 50 μm, and the layers were investigated in their amorphous and crystalline forms. A series of wavelength‐dependent light attenuation coefficients are extrapolated and found to match the photocurrent versus irradiation wavelength behavior. A feature specific to anodic nanotubes is that their intrinsic carbon contamination content causes a proportional sub‐bandgap response. Overall, the extracted data provide a valuable basis and understanding for the design of photo‐electrochemical devices based on TiO₂ nanotubes.     

Electroreduction of cationic fluorene complexes of manganese

Using cyclic voltammetry method, the reduction of cationic η⁶-fluorene complexes of manganese [(η⁶-9-R-C₁₃H₉)Mn(CO)₂L]PF₆ (L = CO, R = H (1 ⁺); L = CO, R = CH₃ (2 ⁺); L = PⁿBu₃, R = H (3 ⁺); L = CO, R = ^tBu (4 ⁺)) is studied. It is shown that, depending on the nature of a substituent in the position 9 of the fluorene ligand, the reduction occurs either with the detachment of an H atom from position 9 to give zwitterion compounds (complexes 1 ^±, 2 ^±, 3 ^±) or with the attachment of an H atom into the coordinated ring of the fluorene ligand to given η⁵-cyclohexadienyl complex (η⁵-9-^tBu-C₁₃H₉)Mn(CO)₃ (5).     

Use of hydrogen peroxide to achieve interference-free stripping voltammetric determination of copper at the bismuth-film electrode

In this work, a new approach is presented to allow interference-free determination of Cu (II) by stripping voltammetry using the bismuth-film electrode. The addition of hydrogen peroxide to the electroanalytical cell has promoted complete resolution between re-dissolution peaks of Bi (III) and Cu (II). The absence of interference could be evaluated by the correlation coefficient (r > 0.99) between Cu (II) concentration and its shifted current peak (at +212 mV) while achieving a slightly fluctuation of the bismuth current peak at −180 mV. Studies were performed aiming towards the optimum conditions for trace determination of Cu (II) using hydrogen peroxide. The methodology was applied to a real sample (sugarcane spirits) and the results were compared to those from graphite furnace atomic absorption spectrometry. The analytical parameters of merit and the results of the analysis indicated that the analytical methodology could be readily used for trace determination of Cu (II).     

Formation of negative oxidation states of platinum and gold in redox ionic liquid: Electrochemical evidence

The electrochemical reduction of noble metal electrodes in the presence of redox ionic liquid, 1-ferrocenylethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [FcEMIM][TFSI], was investigated by cyclic voltammetry. Our experiments suggest the formation of metal with negative oxidation states, in the cases of platinum and gold electrodes [M_n⁻, FcEMIM⁺]. By analogy with the previous work, the formation of these phases is concomitant with the insertion of the supporting electrolyte; which correspond in our experimental condition to the redox cation of the ionic liquid. As an exciting result, the electrochemical investigations of the reduced electrode in electrolytic solution, containing solvent and supporting electrolyte, evidence the presence of the ferrocene groups at the electrode surface. Moreover, the reduced electrode exhibits the presence of the ferrocene even after, contact with air, after ultrasound, and after physical polishing, highlighting the large stability of this organo-metallic phases formed in this media. The AFM investigations demonstrate the morphological change of the platinum surface after the reduction process. Finally, our works bring a formal electrochemical proof of the presence of the ionic liquid cation inside the electrode material after the cathodic treatment in this media.     

Electrochemical and Spectroscopic Properties of Fly Ash–Polyaniline Matrix Nanorod Composites

Polyaniline (PANI) nanocomposites were prepared with fly ash (FA) either by aging the starting materials (aniline and FA) before oxidative polymerisation or by including poly(styrene sulphonic acid) (PSSA) eliminating the aging step. The aging procedure formed polymer nanotubes that have cross-sectional diameters of 50–110 nm. The procedure involving PSSA produced nanorods and nanofibres composites that have diameters of 100–500 nm and length of up to 10 μm attributed to the presence of metal oxides and silica in FA. The electrochemical analysis of the PANI–PSSA–FA nanorod composites shows three redox couples with formal potentials, , values of 105 mV, 455 mV and 670 mV, and conductance, C, value of 1.21 × 10⁻² S. The UV-Vis spectroscopy of the polymeric nanorod shows absorption maxima at 340 and 370 nm (due to π–π^* transition of the benzoid rings), and 600–650 nm (due to charge transfer excitons of the quinoid structure), which are characteristic of emeraldine base.     

Reactivity of 2,2′‐Bis(2N‐(1,1′,3,3′‐tetramethyl‐guanidino))diphenylene‐amine with CuI and [Cu(MeCN)4][PF6]: Benzimidazole Formation vs. Cu Oxidation

The reaction of 2,2′‐Bis(2N‐(1,1′,3,3′‐tetramethyl‐guanidino))diphenylene‐amine (TMG₂PA) ( 1 ) with CuI in MeCN results in the formation of [Cu^II(TMG₂PA^amid)I] ( 2 ) indicatingthat Cu^I is the target of an oxidative attack of the N‐H proton of the ligand which itself is converted to molecular hydrogen. In contrast, if [Cu(MeCN)₄][PF₆] is used as the Cu^I source, [Cu^I₂(TMGbenz)₂][PF₆]₂ ( 3 ) is obtained instead. The use of the non‐coordinating counterion [PF₆]^– apparently prevents Cu^I from oxidation but induces itself a cyclisation reaction within the ligand which results in the formation of a benzimidazole‐guanidine ligand.