Methanol In Alkaline Solution Research Articles

ChemInform Abstract: Direct Oxidation of Methanol on Self‐Supported Nanoporous Gold Film Electrodes with High Catalytic Activity and Stability.

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Controlled Synthesis of Gold Nanobelts and Nanocombs in Aqueous Mixed Surfactant Solutions

Well-defined gold nanobelts as well as unique gold nanocombs made of nanobelts were readily synthesized by the reduction of HAuCl4 with ascorbic acid in aqueous mixed solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium dodecylsulfonate (SDSn). Single-crystalline gold nanobelts grown along the <110> and <211> directions were prepared in mixed CTAB-SDSn solutions at 4 and 27 degrees C, respectively. Furthermore, single-crystalline gold nanocombs consisting of a <110>-oriented stem nanobelt and numerous <211>-oriented nanobelts grown perpendicularly on one side of the stem were fabricated by a two-step process with temperature changing from 4 to 27 degrees C. It was proposed that the mixed cationic-anionic surfactants exerted a subtle control on the growth of gold nanocrystals in solution due to the cooperative effect of mixed surfactants. This synthetic strategy may open a new route for the mild fabrication and hierarchical assembly of metal nanobelts in solution. The obtained gold nanobelts showed good electrocatalytic activity toward the oxidation of methanol in alkaline solution; in particular, the electrode modified with the nanobelts obtained at 27 degrees C exhibited an electrocatalytic activity considerably higher than normal polycrystalline gold electrode. Moreover, the gold nanobelts were used as the surface-enhanced Raman scattering (SERS) substrate for detecting the enhanced Raman spectra of p-aminothiophenol (PATP) molecules, and the gold nanobelts obtained at 4 degrees C exhibited an unusual larger enhancement of the b2 modes relative to the a1 modes for the adsorbed PATP molecules.

Direct Oxidation of Methanol on Self-Supported Nanoporous Gold Film Electrodes with High Catalytic Activity and Stability

A novel self-supported nanoporous gold film electrode with ultrahigh surface area shows excellent electrocatalytic activity and stability toward the direct oxidation of methanol in alkaline solution. The activity of NPGF electrode was about 400 times that of the smooth gold electrode and did not decrease after 100 cycles of activity test.

The corrosion and electrochemical behaviour of pure aluminium in alkaline methanol solutions

The corrosion and electrochemical behaviour of pure aluminium in alkaline methanol solutions has been investigated. The results of hydrogen collection experiments showed that aluminium has a lower corrosion rate in alkaline methanol solutions compared to water based solutions and that the corrosion rate increases with increasing water content of the solution. Polarization and galvanostatic discharge experiments showed that there is a wide potential window of electrochemical activity and a better discharge performance in the alkaline methanol solutions with a certain amount of water. Scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDAX) showed that the passivation in the later stages of discharge in alkaline methanol solutions at relatively high current densities is due to the formation of a dense Al(OH)(3) layer on the surface of the anode.

Synthesis of Flower-like Gold Nanoparticles and Their Electrocatalytic Activity Towards the Oxidation of Methanol and the Reduction of Oxygen

This article describes the synthesis of branched flower-like gold (Au) nanocrystals and their electrocatalytic activity toward the oxidation of methanol and the reduction of oxygen. Gold nanoflowers (GNFs) were obtained by a one-pot synthesis using N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid (HEPES) as a reducing/stabilizing agent. The GNFs have been characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and electrochemical measurements. The UV-visible spectra show two bands corresponding to the transverse and longitudinal surface plasmon (SP) absorption at 532 and 720 nm, respectively, for the colloidal GNFs. The GNFs were self-assembled on a sol-gel-derived silicate network, which was preassembled on a polycrystalline Au electrode and used for electrocatalytic applications. The GNFs retain their morphology on the silicate network; the UV-visible diffuse reflectance spectra (DRS) of GNFs on the silicate network show longitudinal and transverse bands as in the case of colloidal GNFs. The GNFs show excellent electrocatalytic activity toward the oxidation of methanol and the reduction of oxygen. Oxidation of methanol in alkaline solution was observed at approximately 0.245 V, which is much less positive than that on an unmodified polycrystalline gold electrode. Reduction of oxygen to H2O2 and the further reduction of H2O2 to water in neutral pH were observed at less negative potentials on the GNFs electrode. The electrocatalytic activity of GNFs is significantly higher than that of the spherically shaped citrate-stabilized Au nanoparticles (SGNs).

Electro-oxidation of methanol and ethylene glycol on platinum in alkaline solution: Poisoning effects and product analysis

The electrochemical oxidation of ethylene glycol on platinum was investigated and compared with that of methanol in alkaline solution by using various electrochemical and analytical measurements. Ethylene glycol showed much less significant electrode poisoning than methanol at low potential (400mV). This phenomenon was clarified by analyzing the products of ethylene glycol oxidation. In ethylene glycol oxidation, partial oxidation to glycolate was much faster than complete oxidation to CO2. In addition, there were two paths for ethylene glycol oxidation: poisoning and non-poisoning paths. The poisoning path led to the production of C1 compounds and the non-poisoning path gave oxalate. The non-poisoning path prevented the formation of poisonous species on platinum.

Highly dispersed Ag nanoparticles on functional MWNT surfaces for methanol oxidation in alkaline solution

Silver (Ag) nanoparticles were electrocrystallized on 4-aminobenzene monolayer-grafted multi-walled carbon nanotubes (MWNTs) by a potential-step method. The structure and nature of the resulting Ag/MWNT composite were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD), the results show that the electrochemically synthesized Ag nanoparticles were homogeneously dispersed and well-separated from one another on the modified MWNT surfaces. The electrocatalytic properties of the Ag/MWNT electrode for oxidation of methanol in alkaline solution have been investigated by cyclic voltammetry (CV), and excellent electrocatalytic activity was observed. This may be attributed to the small particle size of the silver particles. The results imply that the Ag/MWNT composites have a good application potential in fuel cells.

Electrocatalytic Properties of Electrolytic Ni/Ru and Fe/Ru in the Methanol Oxidation

Electrocatalytic activity of electrolytic alloys Ni/Ru and Fe/Ru in anodic oxidation of methanol in alkaline solutions is higher than that of Ni and Ru and rises with the Ru content increasing to 80% and with the coating weight.

New beta cis folded organocobalt derivatives with a salen-type ligand.

The reduction of [Co(III)(tmsalen)py(2)](+)ClO(4)(-), where tmsalen = 4,4',7,7'-tetramethylsalen, with NaBH(4)/PdCl(2) in alkaline methanolic solution, followed by the oxidative addition of CH(2)ClI, leads to the expected trans organometallic dimeric species 1, [CH(2)ClCo(tmsalen)](2), provided that the product is recovered from the reaction mixture immediately after the completion of the reaction. If 1 is left for longer time in contact with the reaction mixture, the intramolecular reaction of the axial chloromethyl group with the equatorial chelate leads to the formation of the monocationic complex 2, containing a seven-membered ring. In this complex the novel tetradentate ligand coordinates Co in a cis fashion, the other two positions being occupied by one py and one water molecule. The resulting complex is chiral, even if the reaction product is a racemic compound. The unidentate ligands of 2 have been exchanged quantitatively for N-MeIm, and the resulting complex 3 still maintains the beta cis geometry. Therefore, 2 may be considered the precursor of a new class of organocobalt derivatives with a folded tetradentate ligand and two adjacent exchangeable sites. On the basis of the geometry of the tetradentate Schiff bases in complexes, where they adopt a planar geometry, it was suggested that there is a significant electron density delocalization involving the metal center over the two chemically equivalent moieties of Co(chel). Comparison of the geometry of the planar salicylaldiminate (sal) moiety with that of the cyclized methoxy-iminate one (imi) in 2 and 3 strongly supports that the delocalization, still present in sal, is essentially either lost or strongly reduced in imi.

A study of the electro-catalytic oxidation of methanol on a cobalt hydroxide modified glassy carbon electrode

Cobalt hydroxide modified glassy carbon electrodes (CHM/GC) prepared by the anodic deposition in presence of tartrate ions have been used for the electro-catalytic oxidation of methanol in alkaline solutions where the methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (IS) have been employed. In CV studies, in the presence of methanol the peak current of the oxidation of cobalt hydroxide increase is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of methanol is being catalysed through the mediated electron transfer across the cobalt hydroxide layer comprising of cobalt ions of various valence states. A mechanism based on the electro-chemical generation of Co(IV) active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. In this context the charge transfer resistance accessible both theoretically and through the IS studies have been used as a criteria. Under the CA regimes the reaction followed a Cottrellian behaviour.

Routes of degradation of β- O-4 syringyl and guaiacyl lignin model compounds during photobleaching processes

The photolysis of guaiacyl and syringyl β- O-4 lignin model compounds (I, II, III and IV) with a phenol or α- O-4 substituted in the phenacyl moiety was done by three different methods, designed to perform the photobleaching of lignocellulosics. The photolysis systems were carried out in alkaline methanolic solution (pH∼11), and consisted in: (a) H 2O 2, (b) methylene blue (MB)/O 2 and (c) TiO 2. The fragments produced in the reactions were analyzed by mass spectrometry–gas chromatography technique. The results show that the reaction is dependent on the substituent in the phenacyl moiety. The most important route for the degradation mechanism seems to be the incorporation of the hydroxyl radical in the aromatic rings. Semi-empirical calculations of the charge distribution over the atoms in the model compounds show that this parameter is important to decide the reaction mechanisms. For the unprotected phenolic model compound the production of phenolic fragments is higher than in the labile substituted α- O-4 model compound. On the other hand, the photodegradation of the model compound (IV) using method (a) yielded coniferyl alcohol as the principal product. The processes (a) and (c) showed to be the most aggressive for the studied compounds.

Protective effect of electropolymerized 2-mercaptobenzimidazole upon copper corrosion

The electrochemical oxidation of 2-mercaptobenzimidazole (MBIH) on a copper substrate in alkaline methanol solution was investigated by cyclic voltammetry, chronoamperommetry, and quartz crystal microbalance. Cyclic voltammograms indicated that the polymer film (pMBIH) is formed anodically and this film cannot be reduced by cathodic potential scan. However, one potential cycle is not sufficient to form a good barrier layer, and the anodic current peak is observed on subsequent cycles, though its height decreases for each cycle. If the film formations were performed at a constant potential, an EQCM showed the adsorption of MBIH before the anodic oxidation of this monomer leading to the film formation. The film forming efficiency was maximum at ca. 0.8 V SCE though the film thickness increased up to 1.2 V SCE. A thicker film was obtained by potential scan method. From a long period impedance measurement, it was shown that the polymer film thus obtained on copper exhibited a high protective effectiveness.

Protective effect of electropolymerized 3-amino 1,2,4-triazole towards corrosion of copper in 0.5 M NaCl

The electro-oxidation of 3-amino 1,2,4-triazole on a copper substrate in alkaline methanol solution produces a homogeneous and adherent polymer film. The formation kinetics of the film was investigated using cyclic voltammetry, chronoamperommetry and quartz crystal microbalance. The protection of poly-amino 1,2,4-triazole (pATA) films obtained by different electropolymerization conditions was determined by electrochemical impedance spectroscopy in 0.5 M NaCl solutions. These results were compared with those obtained with bare copper electrodes immersed in this corrosive medium. The protection of ATA reaches 99% after one month immersion test.

Isolation and characterization of Mn(III) tartrate from Phanerochaete chrysosporium culture broth

High initial Mn(II) concentration results in accumulation of a Mn(III) tartrate complex in the growth medium of Phanerochaete chrysosporium. Since Mn(III) is the major oxidant in ligninolysis by manganese peroxidase, the role of accumulated complex should not be neglected when degradation experiments by a crude culture filtrate are performed. To study the Mn(III) complex oxidative potential it was isolated by absorption to polyamide followed by desorption with an alkaline methanol solution. High performance liquid chromatography analysis and atomic absorption spectroscopy confirmed that the isolate was Mn(III) tartrate. Oxidation of 2,2′-azino-bis(3-ethylbenz-thiazoline-6-sulfonate) was used for testing the temperature and pH stability of the isolate that also intensively oxidized 2,6-dimethoxyphenol. In comparison with the non-isolated complex in the culture filtrate, the isolate showed increased temperature and pH stability. The oxidative potential of the isolated Mn(III) tartrate was additionally tested by decolorization of the synthetic dye Indigo carmine.

Isolation and characterization of Mn(III) tartrate from Phanerochaete chrysosporium culture broth.

High initial Mn(II) concentration results in accumulation of a Mn(III) tartrate complex in the growth medium of Phanerochaete chrysosporium. Since Mn(III) is the major oxidant in ligninolysis by manganese peroxidase, the role of accumulated complex should not be neglected when degradation experiments by a crude culture filtrate are performed. To study the Mn(III) complex oxidative potential it was isolated by absorption to polyamide followed by desorption with an alkaline methanol solution. High performance liquid chromatography analysis and atomic absorption spectroscopy confirmed that the isolate was Mn(III) tartrate. Oxidation of 2,2'-azino-bis(3-ethylbenz-thiazoline-6-sulfonate) was used for testing the temperature and pH stability of the isolate that also intensively oxidized 2,6-dimethoxyphenol. In comparison with the non-isolated complex in the culture filtrate, the isolate showed increased temperature and pH stability. The oxidative potential of the isolated Mn(III) tartrate was additionally tested by decolorization of the synthetic dye Indigo carmine.

Highly efficient polypyridyl-ruthenium(II) photosensitizers with chelating oxygen donor ligands: β-diketonato-bis(dicarboxybipyridine)ruthenium

A series of mono-cationic polypyridyl-ruthenium complexes with strongly electron donating β-diketonate ligands {(dcbp) 2Ru(L)}Cl, where dcbp=4,4′-dicarboxy-2,2′-bipyridine; L=acetylacetonate ( 1), 3-methyl-2,4-pentanedionate ( 2), 1,3-diphenyl-1,3-propanedionate ( 3), have been synthesized as molecular photosensitizers for a nanocrystalline TiO 2 electrode. In alkaline methanol solution, these complexes exhibit intense visible light absorption with low energy MLCT maxima above 517 nm which accompany a significantly enhanced band tail, improving red light absorptivity beyond 600 nm. The photoelectrochemical properties of these three diketonate complexes on a TiO 2 semiconductor have been compared to cis-dithiocyanate complex, (dcbp) 2Ru(NCS) 2, which is one of the most efficient sensitizers reported to date. The diketonate complexes show quite high performances in photoelectrochemical cells containing I −/I 3 − electrolyte. The overall solar light-to-electrical energy conversion efficiencies are in the range of 6.0–3.9% while the dithiocyanate complex yields 5.7% efficiency in our experiments.

Neutral ‘3 + 1’ mixed-ligand oxorhenium(V) complexes with tridentate [S,N,S] chelates and aminoalkanethiols: synthesis, characterization and structure determination ‡

‘3 + 1’ Oxorhenium(V) complexes [ReO(SN(R′)S)(SR)] (R′ = Me, Et, Pr or Bu; SR = aminoalkane thiolate) have been synthesized by ligand exchange at trans-trichloromonooxo-bis(triphenylphosphine)rhenium(V) with a mixture of HSN(R′)SH and RSH in alkaline methanolic solution. The complexes were purified by column chromatography and characterized by elemental analysis, mass and IR spectroscopy and for selected compounds by 1H NMR spectroscopy. The structures of those complexes have been determined by X-ray diffraction analysis and revealed a change in the co-ordination geometry from square pyramidal to trigonal bipyramidal, depending on the chelating (SN(R′)S) moiety. The alkyl group (R′) was found to be arranged “syn” to the oxorhenium group.

Infrared spectroelectrochemistry of the oxidation of absolute methanol at a platinum electrode

Abstract Infrared spectroelectrochemistry has been used to identify the products of the oxidation of methanol at a polycrystalline platinum electrode in absolute methanol solutions. A spectroelectrochemical cell, with potential control under ambient conditions and optical path under vacuum, provided spectra which were free of H 2 O and CO 2 vapour absorptions. The SNIFTIRS potential step technique was used to obtain absorbance difference spectra which indicated that methyl formate was the major methanol oxidation product in acidic, neutral, and alkaline methanol solutions. CO 2 and formate ion were also shown to be significant products under alkaline conditions. Spectra recorded with different infrared polarisations gave no evidence of adsorbed intermediates or adsorbed oxidation products.

Spectrofluorimetric determination of anthranilic acid derivatives based on terbium sensitized fluorescence.

Terbium sensitized fluorescence was used to develop a sensitive and simple spectrofluorimetric method for the determination of the anthranilic acid derivatives furosemide and mefenamic and tolfenamic acids. The method makes use of radiative energy transfer from anthranilates to terbium ions in alkaline methanolic solutions. Optimum conditions for the formation of the anthranilate-Tb3+ complexes were investigated. Under optimized conditions, the detection limits are 6 x 10(-9), 1.4 x 10(-8) and 9.0 x 10(-9) mol l-1 for furosemide, mefenamic acids and tolfenamic acid, respectively. The range of application is 2.5 x 10(-8)-5.0 x 10(-5) mol l-1 for all three drugs. The method was successfully applied to the determination of furosemide and mefenamic and tolfenamic acids in serum after extraction of the samples with ethyl acetate, evaporation of the organic layer under a stream of nitrogen at 40 degrees C and reconstitution of the residue with alkaline methanolic terbium solution prior to instrumental measurement. The mean recoveries from serum samples spiked with furosemide (5.0 x 10(-7), 2.0 x 10(-6) and 8.0 x 10(-6) mol l-1), mefenamic acid (3.0 x 10(-6), 9.0 x 10(-6) and 3.0 x 10(-5) mol l-1) and tolfenamic acid (3.1 x 10(-6), 12.5 x 10(-6) and 2.5 x 10(-5) mol l-1) were 96 +/- 8, 101 +/- 5 and 98 +/- 7%, respectively. The within-run precision (RSD) for the method for two serum samples of each drug varied from 2 to 8% and the day-to-day precision for two concentration levels varied from 2 to 13%.

Effects of incorporation of Cu and Ag in Pd on electrochemical oxidation of methanol in alkaline solution

Pd fine particles were prepared by heterogeneous reaction of PdOx with dry methanol as well as by the NaBH4 reduction method. The former method was found to give Pd nanoparticles (~5nm). Similarly f.c.c. structured, single phase nanoparticles of alloy compositions Pd0.8Cu0.2, Pd0.5Cu0.5, Pd0.8Ag0.2 and Pd0.5Ag0.5 were prepared by the heterogeneous reaction of dry methanol with intimate mixtures of PdOx+CuOx and PdOx+AgNO3. The electrochemical properties of the porous unsupported electrodes, prepared from these materials, in alkaline solutions, were investigated by cyclic voltammetry and steady-state polarization measurements. Various processes taking place during potential scanning in the presence and absence of methanol in 6m KOH solution are␣discussed. Steady-state polarization data indicate that the methanol oxidation reaction (MOR) activity decreases with incorporation of Cu and Ag into the Pd lattice. The extent of decrease in the MOR activity is less for Cu ad dition than for Ag addition.