Oxygen Bubbling Research Articles

Mediator facilitated, laccase catalysed oxidation of granular potato starch and the physico-chemical characterisation of the oxidized products

The primary hydroxyl groups in potato starch were selectively oxidized to the corresponding aldehyde and carboxylic acid functionalities by mediators like TEMPO, using laccase from fungi as catalytic oxidant and oxygen as the primary oxidant. Oxidized starch products with degree of substitution (DS CHO ranging from 0.16 to 16.4/100AGU and DS COOH from 0.01 to 3.71 carboxyl groups/100AGU) were obtained with mediator facilitated enzymatic oxidation. Maximum conversion of the primary alcohol group was obtained at a pH of 5, with TEMPO as mediator, under oxygen bubbling and two step administration of Trametes versicolor laccase (200 + 200 nkat/g of starch). The oxidized products were characterised by IR spectroscopy, XRD and thermal studies. In the oxidized samples, the larger starch granules exhibited cracks and fractures in comparison to the smaller granules which were relatively unaffected, as observed from the microstructural studies.

Inactivation of Bacteria in Oil Field Injection Water by Non-thermal Plasma Treatment

Microbial pollution commonly causes serious pipe corrosion in oil field injection water system. This paper reports on the application of non-thermal plasma to inactivate bacteria in oil filed injection water. As an efficient inactivation technology, pulsed streamer discharge plasma method injects energy into solution through a plasma channel formed by discharge between electrodes and produces various active species in solution with physical effects (electric field, UV etc.) occurring. Saprophytic bacteria, iron bacteria and sulfate reducing bacteria are used as target. The effects of various gases bubbling (oxygen, nitrogen and air) as well as aeration intensity are investigated. Experimental results show that the inactivation efficiency is greatly enhanced by gas bubbling. After 150 s discharge with oxygen bubbling (667 m3 (m3 h)−1), the inactivation efficiencies of saprophytic bacteria, iron bacteria and sulfate reducing bacteria achieve 1.85, 4.51 and 5.70 log reduction, respectively. The possible mechanism of bacteria inactivation is also discussed.

Effect of pH and temperature on degradation of dilute dihydroxybenzene, in aqueous titanium dioxide suspension irradiated by UV light

The degradation of p-dihydroxybenzene in a batch photocatalytic reactor, irradiated by a high intensity UV lamp, was investigated. In this experimental work, commercial anatase titanium dioxide (degussa P 25) was used as a catalyst. Various operating conditions such as initial concentration, pH of the solution, temperature, addition of H 2O 2, bubbling of oxygen, and catalyst loading were examined. A pseudo-first-order kinetics was observed with a rate constant ranging between 17.1 × 10 −3 and 5.6 × 10 −3 min −1 which was decreasing with increasing initial concentration. H 2O 2 enhanced the degradation significantly. For the experimental conditions, there was no significant effect for the added catalyst dosage. The degradation rate of p-dihydroxybenzene increased to a certain amount with increasing temperature then decreased. Further experimentation is needed to verify this observation.

Laccase treatment of recycled blue dyed paper: physical properties and fiber charge

Recycled blue colored paper was treated with laccase under various combinations of physical and chemical parameters including enzyme concentration, temperature, oxygen, and reaction time. Laccase treatment of recycled dyed pulp increased acid group content, tear index, tensile index, and color removal in a dose-dependent manner. Lengthening the treatment time from 2 to 4 h was beneficial to acid group content (12% increase), dye removal, and tensile index but had a detrimental 8% decrease on the tear index. A higher reaction temperature (65 vs. 45 degrees C) had a beneficial effect on acid group content (+31%), and tensile index (+26%) and a slightly negative effect on tear index (-5%), but significantly reduced the ability of laccase to remove color. Comparison of reactions subjected to different levels of oxygen supplementation showed the greatest beneficial effect for laccase treatment with slow oxygen bubbling. The experimental results indicate that laccase treatment increases fiber carboxylic acid content and tensile strength, in addition to reducing the color of the enzyme treated paper.

Oxolinic acid photo-oxidation using immobilized TiO 2

This work studied the photocatalysed oxidation of the antibiotic oxolinic acid (OA) in an annular reactor operated with immobilized TiO 2 on sintered glass cylinders (SGC). Experiments were carried out in 1 l solution of OA (18 mg l −1) at pH 9 with oxygen bubbling. Irradiation was performed with black light (36 W). The reaction was monitored by COD, TOC and average oxidation state (AOS) calculations. The antibacterial activity of intermediates was followed using the inhibition halo technique on Escherichia coli cultures. The initial antibiotic concentration decreases in one order of magnitude after 60 min irradiation, and was completely eliminated at 100 min reaction. The TOC was reduced in 54% and the AOS reach values around +3 indicating the formation of low molecular weight carboxylic acids. The oxidation reaction fit well with the Langmuir–Hinshelwood kinetic model indicating the dependence of reaction rate with initial adsorption step. The antibacterial activity of the solution decreases with antibiotic removal, demonstrating that intermediates do not present antibiotic activity.

Chemical characterization of pulp components in unbleached softwood kraft fibers recycled with the assistance of laccase/HBT system

Oxidative treatments, without and with assistance of a Laccase-Mediator System (LMS), were characterized in relation to their effects on the chemical composition and strength properties of the fibrous fraction of an unbleached recycled softwood kraft pulp. The LMS, composed of a Trametes hirsuta laccase extract and 1-hydroxybenzotriazole (HBT), was applied on the fibrous fraction of a recycled pulp at low consistency under continuous stirring and oxygen bubbling. Control treatments adding neither the enzyme nor the mediator were also considered. The LMS treatment caused a partial reversion of the detrimental effects of hornification. A considerable increase in the amount of carbonyl groups on the lignin structure was observed as a result of the enzyme treatment. The amount of extractives in ethanol:toluene also increased after the enzymatic treatment, and the dioxane-soluble kraft lignin underwent a noticeable decrease in its apparent molecular mass. This latter effect was readily attributed to the hydrolysis of aryl-ether bonds that survived the severity employed in the pulping process. These observations were useful to explain why LMS-recycled fibers produce handsheets with 9.4% better tensile strength than the control pulps.

Electrodeposited zinc oxide thin films: Nucleation and growth mechanism

The nucleation and growth mechanism of the electrodeposited zinc oxide thin films on fluorine-doped tin oxide (FTO) coated (10–20 Ω/cm 2) glass substrates from acetate solution, without and with ex situ oxygen bubbling, has been studied by cyclic voltammetry (CV), chronoamperometry (CA) and scanning electron microscopy (SEM) techniques. Ethylene diamine tetra acetic acid (EDTA) was used as a complexing agent. The cyclic voltammograms exhibit crossover, a characteristic of nucleation process on FTO-coated conducting glass substrates for all the baths bubbled with oxygen. The current transients were analyzed by fitting chronoamperometric data into the Scharifker–Hills nucleation model. The plausible nucleation and growth mechanism is proposed. For mother bath and lower oxygen bubbling time, the nucleation and growth mechanism follows 3D progressive nucleation and growth, which became instantaneous in case of baths for higher oxygen bubbling time. The SEM study showed that the films become compact when the oxygen bubbling time was increased. The thin films were further characterized by X-ray diffraction technique for structural studies and the ZnO film formation was confirmed. With the increase in oxygen bubbling time, the shift in band gap energies from 3.2 to 3.3 eV is observed.

Photooxidation of Some Organic Sulfides under UV Light Irradiation Using Titanium Dioxide Photocatalyst

The photocatalytic oxidation of three organic sulfide compounds (thioethers); methyl phenyl sulfide (MPS), benzyl phenyl sulfide (BPS), and diphenyl sulfide (dPS) using titanium dioxide (TiO2) photocatalyst suspension under UV light irradiation in aqueous-acetonitrilic (5/95), was studied. Three types of experiments were carried out: (a) the solution was eliminated from atmospheric oxygen by a flow of argon before irradiation, (b) the solution was irradiated with continuous bubbling of oxygen, and (c) the irradiation was carried out at neutral atmospheric oxygen conditions. Results showed that the process will proceed in the presence of pure oxygen much better than atmospheric oxygen or in the absence of oxygen. In fact, no detectable products were observed in the presence of atmospheric oxygen or argon flux. Besides the main products such as methyl phenyl sulfoxide, benzyl phenyl sulfoxide, diphenyl sulfoxide, diphenyl disulfide, benzaldehyde, phenyl propyl sulfide, and n-buthyl phenyl sulfide, trace concentrations of dibenzyl, biphenyl, thiophenol, benzyl alcohol, benzene, benzyl phenyl sulfone, diphenyl sulfone, and methyl phenyl sulfone were detected. Thus in summary, this study provides an example of specific, controlled oxidative chemistry in organic substrates adsorbed on photoactivatedTiO2surface.

Degradation mechanisms of 4-chlorophenol in a novel gas–liquid hybrid discharge reactor by pulsed high voltage system with oxygen or nitrogen bubbling

The effect of gas bubbling on the removal efficiency of 4-chlorophenol (4-CP) in aqueous solution has been investigated using a novel pulsed high voltage gas-liquid hybrid discharge reactor, which generates gas-phase discharge above the water surface simultaneously with the spark discharge directly in the liquid. The time for 100% of 4-CP degradation in the case of oxygen bubbling (7 min) was much shorter than that in the case of nitrogen bubbling (25 min) as plenty of hydrogen peroxide and ozone formed in oxygen atmosphere enhanced the removal efficiency of 4-CP. Except for the main similar intermediates (4-chlorocatechol, hydroquinone and 1,4-benzoquinone) produced in the both cases of oxygen and nitrogen bubbling, special intermediates (5-chloro-3-nitropyrocatechol, 4-chloro-2-nitrophenol, nitrate and nitrite ions) were produced in nitrogen atmosphere. The reaction pathway of 4-CP in the case of oxygen bubbling was oxygen/ozone attack on the radical hydroxylated derivatives of 4-CP. However, in the case of nitrogen bubbling, hydroxylation was the main reaction pathway with effect of N atom on degradation of 4-CP.

The role of oxygen in thiosulphate leaching of gold

The role of oxygen in thiosulphate leaching of gold has been investigated in both pure gold and ore systems. The gold dissolution decreased in the presence of oxygen in the pure gold system. Air or oxygen bubbling caused higher consumption of thiosulphate and leaching passivation. Nitrogen bubbling largely increased gold dissolution and this beneficial effect appeared to be more noticeable at a higher nitrogen flowrate. Nitrogen bubbling stabilised thiosulphate and prevented the passivation of gold. The use of oxygen pre-saturated water had little effect on gold dissolution. The counter current leaching tests showed that both gold passivation and the products due to thiosulphate decomposition affected the gold dissolution. The leaching solutions could be re-used without any impact on gold dissolution under a nitrogen atmosphere. Mineralogy affected the thiosulphate leaching system under different atmospheres. The leaching behaviour of a sulphide ore with only a small amount of sulphides was determined by the leaching behaviour of gold. However, air bubbling gave a higher overall recovery in the leaching of a pyrite concentrate, while nitrogen bubbling only marginally increased the overall gold recovery. Oxygen injection enhanced the dissolution of sulphides, releasing more gold from the sulphide matrices. Nitrogen injection hindered the corrosion process of the sulphides, affecting the overall gold recovery. Nitrogen bubbling decreased the thiosulphate consumption in the leaching of the pyrite concentrate, while air bubbling increased the thiosulphate consumption. It is suggested that high sulphide containing ores should be pre-treated to fully or partially break down the sulphide matrices to liberate gold, followed by gold leaching under a nitrogen atmosphere.

Aerobic oxidation of benzyl alcohols by MoVI compounds

AbstractSelective and controlled aerobic oxidation of activated benzyl alcohols to the corresponding aldehydes is achieved in refluxing CH3CN using catalytic amounts of MoO2Cl2(L)2 where L is DMSO, DMF or THF. The catalysis reactions are possible under open air in the absence of any other external co‐oxidants. However, bubbling of oxygen to the reaction mixture is useful in making the catalysis reaction sustained. Both activated and deactivated varieties of α‐substituted benzyl alcohols (secondary alcohols) give ketones in the same reaction conditions. The inexpensive catalyst is selective towards activated primary benzyl alcohols and also, being mild, stops the oxidation at the aldehyde stage, making it synthetically useful. Copyright © 2006 John Wiley & Sons, Ltd.

Biochemical and photochemical degradation of the herbicide Lontrel

Degradation of Lontrel by activated sludge (AS) of purification works and UV irradiation was studied. 3,6-Dichloropicolinic acid (3,6-DCPA, the main active principle of Lontrel) was not degraded by the microbial association of the AS. AS treated with nitrosourea under various conditions did not oxidize Lontrel either. Hard UV radiation degraded 3,6-DCPA within 4-24 h at constant sparging (bubbling) of air, oxygen, or ozone. The rate of oxidation with oxygen or ozone bubbling was three to four times higher than with air bubbling. It was found that the products of photochemical degradation of Lontrel were also toxic; however, they were readily degraded by AS microorganisms without additional AS treatment.

Corrosion studies of a copper–beryllium alloy in a simulated polymer electrolyte membrane fuel cell environment

Bipolar plates play an important role in the performance, and cost of fuel cell. The properties of copper–beryllium alloy were studied in simulated fuel cell environment. Corrosion studies of the alloy were carried out by using Tafel extrapolation, and potentiodynamic polarization plots at various temperatures. The conditions selected were 0.5 M H 2SO 4 with varying pH in the range of 3–5 and 5% (v/v) HCl + 5% (v/v) Na 2SO 4 with the bubbling of oxygen, and argon. The corrosion rate for the alloy was found to be 0.05, and 0.28 μm year −1 at 25 and 70 °C, respectively. A similar range of corrosion rates was reported in literature for other copper alloys. Due to their good corrosion resistance and high conductivity the alloy can be considered as a candidate material for bipolar plates. Use of copper alloy in bipolar plate will reduce the contact resistance in cell stack due to their high conductivity.

Decoloration of Organic Dye in Water by Pulsed Discharge Plasma Generated Simultaneously in Gas and Liquid Media

AbstractA new process for decomposing organic contaminants in water was proposed. Pulsed discharge plasma was generated in the gas phase, and the produced plasma was permeated through a pinhole into the water phase. Water (upper) and gas (lower) were separated by an insulating plate, where a pinhole was perforated at the center of the plate. Gas was bubbled into the water phase through the pinhole. In the gas phase, the high voltage pulse was applied between the needle electrode and the ground electrode (immersed in the water phase). The high voltage pulsed discharge plasma was generated in the gas phase, simultaneously the plasma channel was permeated into the water phase accompanying by the gas bubbles. The water phase plasma produced a lot of active species, UV light, and high-energy electrons. Porous ceramic tube was tried to use for producing water phase plasma, instead of the insulating plate in a pinhole reactor. It was observed that the gas phase plasma also permeated through many small pores into the water and generated streamer discharge in water. Chicago sky blue aqueous solution was effectively decolored with oxygen gas bubbling than the cases of argon gas and air. With applying pulsed voltage of 20 kV and pulse frequency of 25 Hz with 500 mL/min oxygen bubbling, the dye aqueous solution with 10 ppm initial concentration was decolored about 95% in 10 min treatment. The decoloration rate increased with increasing electrical conductivity of the solution. This type of simultaneous discharge plasma reactor is expected to have high-energy efficiency degradation rate.

Development of less expensive process technologies for three-dimensional chip stacking with through-vias

Three-dimensional chip stacking with through-vias is a very promising technology in semiconductor system development. A major problem of this technology is the cost. We analyzed the costs of the fabrication process and identified the three processes of Cu plating, Cu-CMP, and back surface bumps as the high-cost processes. To address these problems, we studied the processes and the stacking structure to improve the productivity. The plating time for Cu plating was reduced by up to 1 hour by optimizing the plating fluid composition and the oxygen bubbling of the plating fluid. In Cu-CMP, 9-µm-thick Cu was polished for 8.7 minutes by using high-speed polishing slurry and the softlanding process. We evaluated a structure where the back surface bumps were removed, and the front surface Cu bumps were directly connected by Cu through-vias and Sn-Ag. We verified the reliability for up to 1000 temperature cycles of this structure which uses a low thermal expansion resin as the adhesive in two-step sealing. From these results, a substantial reduction in the cost of the three-dimensional chip stacking with through-vias has become possible. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(7): 50–60, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20150

Instantaneous impedance measurements on aluminium using a Schroeder multisine excitation signal

Time-varying phenomena, such as crystallographic pitting corrosion, can be investigated by electrochemical impedance spectroscopy (EIS). For this purpose, a stepped sine excitation is most frequently used. However, when the frequency ranges from 25 Hz down to 15 mHz this experiment takes at least 30 min. In this work a periodic Schroeder multisine excitation signal is presented, by which the measurement time can be reduced to 2 min for the same frequency range. To evaluate the correctness of the EIS results obtained with the multisine, data was acquired for aluminum (99.5 wt.%) immersed in 0.5 M NaCl with oxygen bubbling by means of a stepped sine, next a multsine and finally a stepped sine excitation. From the spectra obtained with both stepped sines a new virtual spectrum is calculated as if all excited frequencies would have been recorded at the moment when the multisine was imposed to the system. A comparison of the multisine spectrum with this interpolated spectrum was then used for validation. The results show that the instantaneous behaviour of a time-varying system, observed during EIS is better approximated by the use of a multisine excitation signal. Moreover, the approximation further ameliorates when the immersion time evolves.

Instantaneous impedance measurements on aluminium using a Schroeder multisine excitation signal

Time-varying phenomena, such as crystallographic pitting corrosion, can be investigated by electrochemical impedance spectroscopy (EIS). For this purpose, a stepped sine excitation is most frequently used. However, when the frequency ranges from 25 Hz down to 15 mHz this experiment takes at least 30 min. In this work a periodic Schroeder multisine excitation signal is presented, by which the measurement time can be reduced to 2 min for the same frequency range. To evaluate the correctness of the EIS results obtained with the multisine, data was acquired for aluminum (99.5 wt.%) immersed in 0.5 M NaCl with oxygen bubbling by means of a stepped sine, next a multsine and finally a stepped sine excitation. From the spectra obtained with both stepped sines a new virtual spectrum is calculated as if all excited frequencies would have been recorded at the moment when the multisine was imposed to the system. A comparison of the multisine spectrum with this interpolated spectrum was then used for validation. The results show that the instantaneous behaviour of a time-varying system, observed during EIS is better approximated by the use of a multisine excitation signal. Moreover, the approximation further ameliorates when the immersion time evolves.

Effect of Cavitation on Corrosion Behavior of 20SiMn Low-Alloy Steel in 3% Sodium Chloride Solution

The cavitation corrosion behavior of 20SiMn low-alloy steel in both distilled water and 3% sodium chloride (NaCl) solution was investigated using a magnetostrictive-induced cavitation facility. The micrographs of damaged surfaces were observed with a scanning electron microscope (SEM). The role of corro- sion was analyzed using polarization curves, electrochemical impedance spectroscopy (EIS), linear polarization resistance, and the corrosion potential with or without cavitation. Fur- thermore, the effect of cavitation on corrosion behavior of 20SiMn steel was compared to that of oxygen bubbling. The results showed that a fraction (0.05) of the damage arose from electrochemical corrosion and a fraction (0.59) arose from corrosion-induced erosion. Cavitation shifted the corro- sion potential in the positive direction and strongly enhanced the cathodic current density in the polarization curves. Cavi- tation also reduced the magnitude of impedance. The mor- phological examination revealed that the ferrite area and grain and ferrite-pearlite boundaries were preferential sites for cavitation attack as a result of the low hardness of ferrite. The mass loss came from the detachment of small pieces in the ferrite area in the early stage and from the removal of massive chunks by the propagation and connection of cracks in the following test period.

Simple and reliable preparation of pentavalent 99Tcm-dimercaptosuccinic acid at alkaline pH without oxygen bubbling.

We investigated a simple and reliable method for the preparation of 99Tcm-dimercaptosuccinic acid (99Tcm(V)-DMSA) without the addition of oxygen. The effect of pH, amount of reducing agent, and oxygen addition in the synthesis of 99Tcm(V)-DMSA were evaluated. At pH 9, we obtained a radiochemical yield of 95% +/- 1.2% within 10 min and a high stability until 7 h, with 92% +/- 1.5% radiochemical purity. However, at a pH lower than 9, the radiochemical yield was below 90% within 10 min, and a longer reaction time was needed to obtain a radiochemical yield above 90%. The addition of oxygen did not have an additional effect on the radiochemical yield or its stability at pH 9, whereas it increased the radiochemical yield of 99Tcm-(V)-DMSA at pH 7. It was noted that the smaller the amount of reducing agent used, the higher was the radiochemical yield obtained at pH 7. However, at pH 9, the radiochemical yield was not dependent on the amount of reducing agent. In conclusion, the synthesis of 99Tcm(V)-DMSA was more dependent on the pH of the reaction mixture than on the amount of reducing agent or the addition of oxygen. The adjustment of pH 9 was the easiest and most effective method for the synthesis of 99Tcm(V)-DMSA using a commercial kit for 99Tcm(III)-DMSA.

Photocatalytic degradation of lignin and lignin models, using titanium dioxide: the role of the hydroxyl radical

The role of hydroxyl radicals on the degradation of lignins during a cellulosic pulp bleaching process including a photocatalytic stage, was assessed using peroxyformic acid lignins EL1 and REL1 and two phenolic biphenyl lignin models 1 and 2 . The irradiations were performed in the absence of photocatalyst TiO 2 and H 2O 2 (condition a), in the presence of TiO 2 (condition b) and in the presence of H 2O 2 (condition c). The experiments were conducted in alkaline (pH ≈ 11) aqueous ethanol solutions with oxygen bubbling. The relative phenolic content of the irradiated solutions, which is indicative of the involvement of hydroxyl radicals, was determined by ionization absorption spectroscopy. The results obtained show that the catalyzed reaction involves both degradation of the phenolate groups by electron transfer and hydroxylation of the lignin aromatic structure. Benzyl alcohol structural elements in sodium borohydride reduced lignin REL1 and compound 2 were also found as good trapping agents for the hydroxyl radicals. The degradation of EL1 was studied by measuring its fluorescence emission by comparison to the fluorescence of compound 2 . The emission spectra indicate that some biphenyl phenolate anions in EL1 are reacting under UV/visible irradiation and some others, probably polyphenolic chromophores emitting less fluorescence, are formed.