Oxidation In Alkaline Solution Research Articles

Vanadium oxide nanotubes as the support of Pd catalysts for methanol oxidation in alkaline solution

Well-dispersed Pd nanoparticles were prepared on the surface of vanadium oxide nanotubes (VO x -NTs) through a simple reductive process. The morphology and structure of the resulting Pd/VO x -NTs composites were characterized by transmission electron microscopy (TEM), electron diffraction (ED) and X-ray diffraction (XRD), the results showed Pd nanoparticles were well dispersed with the size distribution from 7 to 13 nm. The electrocatalytic properties of Pd/VO x -NTs composites for methanol oxidation were investigated on the corresponding modified glassy carbon (GC) electrode in alkaline solution. The results indicated the prepared Pd/VO x -NTs composites had an excellent electrocatalytic activity and stability.

DMAB Oxidation for Electroless Deposition from Alkaline Solutions

Dimethylamine borane (DMAB) has been used as a reducing agent in electroless baths for many years. There has been an increased interest in DMAB-based electroless baths recently for applications in microelectronics such as barrier/capping layers for copper IC interconnect. To optimise the plating baths a thorough understanding of the role of each of the bath constituents is required. To this end we have employed microelectrodes to investigate the oxidation mechanism of boranes in alkaline solutions. In this paper we present data for DMAB and the simpler ammonia borane (AB) to assist in the analysis of borane oxidation in alkaline solutions. Both DMAB and AB are shown to oxidise in two steady state mass transport- controlled oxidation waves for specific concentration ranges. The potential range for oxidation, the optimum concentration and a suggested mechanism for oxidation are shown.

Macroporous conducting matrix: Fabrication and application as electrocatalyst support

Conducting carbon matrix with macroporous and mesoporous bimodal pore structure has been fabricated by combining the templating and sol–gel methods. The further surface modify by Pt–Co catalyst results in a high activity towards the ethanol oxidation in alkaline solution. The high-performance is believed due to the reduction of the liquid sealing effect. The materials with bimodal structure have the advantages that the reagents and products can transfer not only through macropores but also from mesopores. These electrodes are potentially used in liquid fuel cells. The anode electrode with such highly porous structure will reduce the liquid sealing effect, in consequence, improves the cell performance.

A new oscillatory mechanism for the electro-oxidation of iodide involving two phase transitions and a disproportional reaction

Oscillations have been first observed during iodide oxidation in alkaline solution on a static platinum electrode, where phase transitions at the interface of electrode/solution are essential. The film formation of solid iodine acts as a negative nonlinear feedback slowing down the iodide oxidation due to its poor conductivity, and oxygen evolution as a positive nonlinear feedback by destroying the iodine film mechanically and by promoting its dissolution through convection mainly via a disproportional reaction. Based on the results of electrochemical experiments and in situ Raman spectroscopy, a tentative mechanism is given concerning the interfacial phase transitions and the disproportional reaction.

The influence of pyrite pre-oxidation on gold recovery by cyanidation

The influence of pyrite pre-oxidation in alkaline solutions on gold recovery by cyanidation from Twin Creek refractory gold ore in which pyrite was identified as the major sulfide mineral has been investigated with the aid of electrochemical measurements, leaching experiments, and direct analysis of reaction products for selected residues. It was found that gold recovery by cyanidation in bottle roll experiments mainly depended on the extent of pyrite pre-oxidation. The rate of pyrite oxidation in alkaline solutions measured by electrochemical measurements, including chronoamperometry and linear sweep voltammetry, increased with an increase in pH, potential, and temperature. All alkaline reagents used for the electrochemical measurements, NaOH, NH 4OH, Na 2CO 3 and Ca(OH) 2, showed a similar effect on pyrite oxidation kinetics. However, the results of alkaline pre-oxidation for pyrite of the Twin Creek refractory gold ore suggested that NaOH and Na 2CO 3/Ca(OH) 2 were superior to Ca(OH) 2. Without pre-oxidation, cyanide leachable gold was found to be only 20% which could be increased to 70% under appropriate pre-oxidation conditions. At the same time, cyanide consumption decreased from 2.5 kg/t ore to 1.5 kg/t ore. Selected residues after pre-oxidation and cyanidation were examined by X-ray diffraction. Backscattered electron images of pyrite particles in these residues were taken. The reaction products at the surface of pyrite particles were found to be iron-, silicon-, and calcium-bearing compounds with variable amounts of sulfur as determined by X-ray energy dispersion analysis. Additionally, some mineral fines, such as aluminum and/or potassium-bearing minerals, were found to be present at the partially oxidized pyrite surface.

Structure sensitivity of CO oxidation on gold single crystal surfaces in alkaline solution: Surface X-ray scattering and rotating disk measurements

A combination of in situ surface X-ray scattering (SXS) and cyclic voltammetry (CV) measurements have been performed to determine the effect that the surface atomic structure of the low-index faces of Au single crystals has on carbon monoxide (CO) oxidation in alkaline solution. For the (1 1 1), (1 0 0) and (1 1 0) surface orientations, potentiodynamic measurements of the scattered X-ray intensity at key reciprocal lattice points have been employed to determine the potential window of stability for the reconstructed surfaces. By saturation of the electrolyte with CO, the effect that adsorbed CO has on the stability of the reconstructed surfaces has been investigated. The presence of CO acts to stabilize the surface reconstructions over a wider potential range, causing a positive shift in the potential for the lifting of the Au(1 1 1) surface reconstruction of ∼200 mV. In the case of the (1 0 0) and (1 1 0) orientations, the adsorption of CO stabilizes the reconstruction over the entire potential range studied. The oxidation of dissolved CO was found to be structure-sensitive, with the activity decreasing in the order Au(1 1 0)-(1 × 2) > Au(1 0 0)-“hex” > Au(1 1 1)-(23 × √3). The structure-sensitivity is correlated with the surface density of low coordinated sites.

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.

In situ rapid-scan time-resolved microscope FTIR spectroelectrochemistry: study of the dynamic processes of methanol oxidation on a nanostructured Pt electrode

In this paper we report the development of an electrochemical in situ rapid-scan time-resolved microscope infrared reflection spectroscopy (RS-TR-MFTIRS), which consists of a FTIR spectrometer with rapid-scan facility, an infrared microscope in combination with a nanostructured Pt microelectrode, and a versatile external reflection (or thin-layer) spectroelectrochemical flow cell. It has been demonstrated that the RS-TR-MFTIRS can successfully overcome the disadvantages in mass transport, transient response and uniformity of current flow that arise from a conventional external reflection infrared cell. The dynamic process of methanol oxidation on a nanostructured platinum microelectrode in alkaline solution was employed as a test reaction to characterize the performance of the newly developed technique. The results illustrate that cyclic voltammograms (CVs) and infrared spectra within a potential interval of 2.6 mV can be simultaneously recorded at a potential scan rate up to 200 mV s −1. The dynamic processes of the poisoning intermediate (adsorbed CO species) and reactive intermediate (formate ions) involved in methanol oxidation in alkaline solutions were studied intensively. It has been revealed that the bridge-bonded CO (CO B) species and formate ions are generated preferentially at the onset potential (−0.54 V vs SCE) of methanol oxidation, while the linearly bonded CO (CO L) species originate at more positive potentials that are close to the anodic current peak potential (−0.17 V vs SCE) of methanol oxidation.

Electrocatalytic properties of supported platinum–cobalt nanoparticles with uniform and controlled composition

Platinum–cobalt nanoparticles were prepared from water/Triton X-100/propanol-2/cyclohexane reverse microemulsions. The Pt:Co ratio in the nanoparticles was well controlled by the initial concentrations of Pt and Co in the precursor solution. The nanoparticles were characterized by transmission electron microscopy, X-ray diffractometry and energy dispersive X-ray analysis. The Pt–Co nanoparticles supported on a carbon electrode possessed high dispersion and high catalytic activity for methanol oxidation in alkaline solution at room temperature. The optimum Pt:Co ratio for methanol oxidation was determined to be 1:0.5.

Electrooxidation of phenol at exfoliated graphite electrode in alkaline solution

The present paper reports on exfoliated graphite (EG) used for the cyclic electrochemical process of phenol oxidation in alkaline solution. It is shown that the electrochemical activity of anode-produced EG decreases considerably in the second cycle due to the deposition of an oligomer film, composed of the products of phenol oxidation, on the EG surface. Thermal treatment of the inactive graphite anode in air at 500 °C provided a regenerated material of activity three times higher for the first cycle and 2.6 times higher for three cycles as compared to the original anode. The reason for such a behavior is assigned to a carbon film formed on the EG surface during the carbonization/oxidation processes involving the products of phenol oxidation. Comparative studies showed that electroactivity of the original EG can also be enhanced if before the process of phenol oxidation the original EG is activated by heat treatment. Unfortunately, the electrochemical activity of the product of such a treatment is higher only for the first cycle of phenol oxidation and drops dramatically in the following cycles.

Mineralization of 4‐Chlorophenol under Visible Light Irradiation in the Presence of Aluminum and Zinc Phthalocyaninesulfonates

AbstractPhotosensitized oxidation of 4‐chlorophenol (4CP) by the title complexes (AlPcS and ZnPcS) in aerated aqueous solution upon visible light irradiation (δ ≥ 450 nm) has been investigated using methanol as a disassociating reagent. It is confirmed that the monomeric species of the sensitizer is more active than the corresponding dimer in singlet oxygen generation for 4CP oxidation. However, the monomer is also the main component found in the sensitizer's photobleaching. In this regard, AlPcS is much more stable than ZnPcS, and the photobleaching is observed to proceed via singlet and triplet oxygen, respectively. The final products of 4CP oxidation in alkaline solution are carbon dioxide and chloride ions, while at pH = 7 and pH = 3 the p‐benzoquinone is the product. The temperature is found to have influence on both the photosensitized degradation of methyl orange and ZnPcS photobleaching, with an activation energy of 15.8 and 24.2 kJ/mol, respectively.

Pyrite oxidation in alkaline solutions: nature of the product layer

The nature of the oxides formed during pyrite oxidation by molecular oxygen in alkaline solutions has been investigated with the aid of Eh–pH diagrams and direct analysis of the solid products. X-ray diffraction (XRD) and infrared analyses indicate that the products formed are determined by solution composition. In hydroxide medium, hematite, as the main phase, and small amounts of ferrihydrite are identified. In contrast, in carbonate medium, the main constituent is ferrihydrite, with some iron hydroxide carbonate phase also present. In calcium hydroxide medium, only calcium carbonate was detected on the surface of oxidized pyrite in an amount that increased when the system was opened to the atmosphere. Only by diffuse reflectance infrared spectroscopy (IR) was it possible to identify carbonate compounds among the products formed during pyrite oxidation in aqueous solutions. The morphology of the product layers was also affected by solution composition. In NaOH solutions, the particles are initially covered by a thin oxide layer that fractures after longer reaction times. Most of the oxide reports to the solution, where it remains as a stable suspension. Pyrite oxidation in Na 2CO 3/NaHCO 3 solutions results in particles that are initially covered by a discontinuous oxide coating that grows with reaction time, thus increasing the overall pyrite surface coverage. In this case, a precipitation confined to the solid/liquid interface is favored by the higher ionic strength of the sodium carbonate solutions.

Determination of thiamine in pharmaceutical preparations by sequential injection renewable surface solid-phase spectrofluorometry.

Fluorometric determination of thiamine requires the conversion of the analyte to fluorescent thiochrome by hexacyanoferrate(III) oxidation in alkaline solution and the isolation of the produced thiochrome from the reaction medium by solvent extraction. It was observed that thiochrome could be concentrated and separated from the reaction medium by solid-phase extraction. The thiochrome sorpted on the surface of octadecyl-alklylated poly[styrene/divinylbenzene] (C18-PS/DP) microbeads emitted strong fluorescence upon excitation, the maximum excitation and emission wavelengths being 385 nm and 433 nm, respectively. Based on this observation, a sequential injection renewable surface solid-phase spectrofluorometry was developed for the determination of thiamine. A sequential injection system on-line coupled to a chip-based flow-through cell was employed to handle the chemical reaction, bead injection and discharging, and adsorption of thiochrome. Solid-phase fluorometric detection was realized by coupling the chip-based flow-through cell to a spectrofluorometer with a multistrand bifurcated optical fiber. Under the optimized condition, a detection limit of 0.03 microg ml(-1) was achieved at the sample throughput of 30 h(-1) and consumption of 1 mg C18-PS/DP microbeads for each run. Eleven runs of a 2 microg ml(-1) thiamine standard solution gave a relative standard deviation of 1.0%. The developed approach was successfully applied for the determination of thiamine contents in pharmaceutical preparations.

Conversion of a Used Poly(ethylene terephthalate) Bottle into Oxalic Acid and Terephthalic Acid by Oxygen Oxidation in Alkaline Solutions at Elevated Temperatures

Chemical recycling of poly(ethylene terephthalate) (PET) flakes to terephthalic acid (TPA) and oxalic acid was investigated by simultaneous hydrolysis and oxygen oxidation in concentrated NaOH. PET flakes were hydrolyzed to sodium terephthalate and ethylene glycol (EG) in NaOH solutions before oxygen introduction. Because sparingly soluble sodium terephthalate in concentrated NaOH solutions was stable to the oxidation, the TPA yield was approximately 100 mol % under all conditions. In contrast, EG was oxidized to oxalate and CO2, and the maximum oxalic acid yields were 60.7 mol % using flakes from the bodies of transparent bottles and 65.9 and 71.4 mol % using commercial transparent flakes and a mixture of transparent and green flakes from PET, respectively. If the gate fee (83.3¢/kg of PET) can be obtained as a waste PET recycling subsidy from the Japanese government, this process will generate a profit of $1,134.20 for the treatment of 1000 kg of PET as a net profit for 70 mol % of oxalic acid yield.

Hydrogen evolution during the oxidation of formaldehyde on Au:: The influence of single crystal structure and Tl-upd

Hydrogen evolution during formaldehyde oxidation in alkaline solution has been monitored by Differential Electrochemical Mass Spectrometry on Au(111) and polycrystalline gold. The current efficiency for hydrogen evolution increases with higher concentration and is in the same range on both, polycrystalline Au and Au(111) electrode. The onset potentials and half-wave potentials are higher on Au(111). Reaction orders for the faradaic current on the bare gold electrodes have been determined as 0.21 for higher and 0.76 for lower concentrations. Reaction orders for hydrogen evolution during formaldehyde oxidation are 1.4 times higher in each case. Tafel slopes in the range of 140–160 mV are found. This signifies that the first reaction step involving the formation of adsorbed hydrogen is largely determining the overall reaction rate. In the presence of thallium adlayers hydrogen evolution from formaldehyde oxidation is largely suppressed. On the thallium modified polycrystalline Au, formaldehyde oxidation is shifted for 100 mV to higher potentials where Tl is partially desorbed and hydroxide is coadsorbed on the modified surface. On thallium modified Au(111), a similar process takes place, but in the same potential region as the onset of formaldehyde oxidation on the bare surface and therefore the formaldehyde oxidation is only slightly shifted. Tafel slopes are decreased to 80 mV/dec in the presence of thallium. In the presence of adsorbed thallium, the first reaction step is in equilibrium, the coverage with adsorbed hydrogen is smaller and its recombination to H 2 is largely suppressed.

Anodic Oxidation of Polyhydric Alcohols on a Pt Electrode in Alkaline Solution

The electrochemical oxidation of various polyhydric alcohols, ethylene glycol, glycerol, meso-erythoritol, and xylitol, on a platinum electrode was investigated systemematically in acidic H2SO4, and in alkaline KOH and K2CO3 solutions to evaluate the potential of these polyhydric alcohols as fuels in micro-fuel cells for portable electronic devices. All polyhydric alcohols tested in the present study showed high reactivities in both alkaline solutions. Ethylene glycol showed the highest reactivity. Although the reactivity of ethylene glycol was lower in K2CO3 than in KOH, the carbonate solution is a potential candidate as an electrolyte solution due to its resistance to solution carbonation. Furthermore, ethylene glycol showed much less significant electrode poisoning by adsorbed CO upon oxidation in alkaline solution.

Electrochemical SHG at a Ag (111) single-crystal electrode using the hanging meniscus configuration

We combine in situ electrochemical second-harmonic generation (SHG) with voltammetry measurements using the hanging meniscus configuration. This setup is used to investigate the interface between a Ag (111) electrode and an alkaline electrolyte. The study offers a new in situ insight into the electrochemical processes at the Ag (111) electrode during OH adsorption and subsequent oxidation. The behavior of SHG isotropic and anisotropic contributions as a function of potential is discussed and related to the interfacial electric field. Comparison of the results with previous investigations of the Ag underpotential oxidation in alkaline solutions shows that submonolayer oxidation is followed by bulk oxidation.

Study of photoelectrochemical corrosion of lead oxide in alkaline solution by the rotating ring-disk electrode technique

Photoelectrochemical corrosion of n-type α-PbO electrodes in aqueous Fe(CN)63−/4− and I−/I3− electrolytes using the rotating ring-disk electrode technique has been investigated. The α-PbO thin film is found to be more stable in I−/I3− (48%) than in Fe(CN)63−/4− electrolyte (10%). Preferential adsorption of iodide ions decreases the photocorrosion reaction of holes with α-PbO. Addition of CsI (0.4 mM) to the I−/I3− electrolyte decreases the photocorrosion from 48% to less than 10%. Cs+ ions perhaps nullify the effect of negatively charged surface states of α-PbO, thus minimizing the trapping of holes at the surface of α-PbO and hence decrease the possibility of photocorrosion of lead oxide with holes.

A photoelectrochemical study of anodic oxides on lead selenide surfaces in alkaline solutions

Lead selenide is a narrow gap semiconductor material. It finds applications in infrared emitting and detecting devices. Their performance is closely related to charge carrier recombination at the surface, which can be reduced by passivation, e.g. due to PbSeO3 formation by anodic oxidation in alkaline solutions. In dependence on the pretreatment of the surface, two different types of oxide formation were observed. To determine the electronic properties of the anodic oxide, the wavelength dependence of the photocurrent was investigated. The energy of the band gap of both types of anodic oxide on PbSe has been determined to be 2.4 eV for the direct and 1.8 eV for the indirect band gap. A weakening of the photocurrent generated in the bulk (PbSe) due to scattering or absorption within the oxide confirms the potential dependence of the oxide thickness for a high field growth mechanism.

Coating composition

A simple electrodeposition approach to grow multi-laminated copper particles on two conductive substrates is presented. Morphological and structural characterization was performed using SEM and XRD. The copper crystallites are preferentially oriented with {111} planes parallel to the substrate surfaces, providing an optimum interface for methanol oxidation. There are a large number of edges, corners, and atomic steps around individual multi-laminated nanostructured particles. The excellent electrocatalytic activity of the particles to methanol oxidation in alkaline solutions is demonstrated by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The presence of the conductive poly(2-amino-5-mercapto-1,3,4-thiadiazole) interlayer between the Cu particles and the carbon paste substrate results in larger specific surface areas of the particles and smaller charge-transfer resistances of methanol oxidation reaction in the lower potential range. Such an anisotropic laminated structure of non-noble metal nanomaterials deserves further investigation for finding a suitable alternative to noble metal-based anodic catalysts in fuel cells.