Air-saturated Aqueous Solutions Research Articles

Chain Reaction of Fenton Autoxidation of Tartaric Acid: Critical Behavior at Low pH

Autoxidation of tartaric acid in air-saturated aqueous solutions in the presence of Fe(II) at low pH, 2.5, shows autocatalytic behavior with distinct initiation, propagation, and termination phases. With increasing pH, the initiation phase speeds up, while the propagation phase shortens and reduces to none. We show that the propagation phase is a chain reaction that occurs via activation of oxygen in the initiation stage with the production of hydrogen peroxide. The subsequent Fenton oxidation that regenerates hydrogen peroxide with a positive feedback is typical of a self-sustained chain reaction. The conditions for such a chain reaction are shown to be similar to those of a dynamical system with critical behavior; namely, the system becomes unstable when the kinetic matrix of pseudo-first-order reaction becomes negatively defined with a negative eigenvalue giving the rate of exponential (chain) growth of the reactive species.

γ–radiolytic degradation of rosuvastatin in the air–saturated aqueous solution

Widespread environmental occurrence and persistence of pharmaceuticals have attracted great concern due to their incomplete removal by conventional wastewater treatment technologies. The use of radiation technology has proven to be a good and successful alternative where highly reactive species lead to high degradation level of pharmaceuticals. Among the most commonly prescribed pharmaceuticals is rosuvastatin (ROSU), cholesterol-lowering agent, which has been detected as a contaminant in wastewater and natural waters. The aim of the present study was to investigate the γ-radiolytic degradation of ROSU in aqueous solutions under different conditions. The focus was given to the most applicable conditions, the degradation of ROSU in air, where dominant reactions of •OH radicals with ROSU are expected. Therefore, the reaction rate constant of ROSU with •OH radicals (2.15 ± 0.07 × 1010 M−1 s−1) was determined by laser flash photolysis. By combined γ-radiolysis and mass spectrometry study, the reaction mechanism of radiation degradation of ROSU was proposed and the radiolytic products were identified.

Catechin Photolysis Suppression by Aluminum Chloride under Alkaline Conditions and Assessment with Liquid Chromatography–Mass Spectrometry

Tea is rich in catechins and aluminum. In this study, the process of catechin photolysis was applied as a model for examining the effects of aluminum chloride (AlCl3) on the structural changes of catechin and the alteration of aluminum complexes under blue light irradiation (BLI) at pH 8 using liquid chromatography and mass spectrometry techniques. Additionally, the effects of anions on catechin upon the addition of AlCl3 and treatment with BLI were also studied. In this study, when 1 mM catechin was treated with BLI, a superoxide anion radical () was generated in an air-saturated aqueous solution, in addition to forming a dimeric catechin (proanthocyanidin) via a photon-induced redox reaction. The relative percentage of catechin was found to be 59.0 and 95.7 for catechin treated with BLI and catechin upon the addition of 1 mM AlCl3 treated with BLI, respectively. It suggested that catechin treated with BLI could be suppressed by AlCl3, while AlCl3 did not form a complex with catechin in the photolytic system. However, under the same conditions, it was also found that the addition of AlCl3 inhibited the photolytic formation of and reduced the generation of proanthocyanidin, suggesting that the disconnection of proanthocyanidin was achieved by AlCl3 acting as a catalyst under treatment with BLI. The influence of 1 mM fluoride () and 1 mM oxalate () ions on the photolysis of 1 mM catechin upon the addition of 1 mM AlCl3 and treatment with BLI was found to be insignificant, implying that, during the photolysis of catechin, the Al species were either neutral or negatively charged and the aluminum species did not form a complex with anions in the photolytic system. Therefore, aluminum, which is an amphoteric species, has an inherent potential to stabilize the photolysis of catechin in an alkaline conditions, while suppressing the and proanthocyanidin generation via aluminum ion catalysis in the catechin/Al system under treatment with BLI.

Nano Structured and Pyrolytic Deposited Carbon Electrodes for Detection of Nitroaromates – a Comparison

IntroductionNitroaromatics like 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT) are long-lasting organic pollutants in natural water and soil caused mainly by the military usage. Nano structured electrodes are established in detection of such compounds in water by linear sweep voltammetry (DP) [1]. On the other hand, it could be shown that screen printed carbon electrodes [2] and such made of pyrolytic deposited carbon are also suited for that purpose [3]. Both kind of electrodes were investigated regarding the determination of nitroaromatic compounds in aqueous solution. The aim of this paper is to compare the performance of both electrodes in comparison to commercial electrodes respecting sensitivity, selectivity and long-term stability.ExperimentalElectrodes using carbon nano-tubes and gold nano-particles on printed carbon are commercially available (DropSens, Spain DRP-110CNT-GNP). Screen printed electrodes (SPCE) of 3mm in diameter were industrially like produced on an alumina substrate with a commercial carbon ink (DuPont) carbon paste. Pyrolytic graphite layer were deposited by high temperature decomposition (1050 °C) of aromatic vapor for 15 min with high reproducibility (PyGE). Solid state analyses as XRD and SEM analysis show crystalline carbon with a sp2 hybridization (Fig. 1). The setup of the electrodes is seen in Fig. 2. All experiments were performed in a three electrode arrangement using platinum counter electrode and Ag/AgCl,Cl--reference electrode in a buffer solution. Voltammetric experiments were performed by a PalmSens potentiostate (Palm Instruments, NL). DRP-110CNT-GNP were investigated by linear sweep voltammetrie. SPCE and PyGE were measured in differential pulse voltammetry mode (DPV). The parameter for the DPV were selected as follows: scan rates of 15 mV∙s-1 to 20 mV∙s-1, amplitude of 50 mV and step height of 5 mVResults and discussionThe potentials of the single reduction peak of nitro-aromates can be clearly separated (Fig. 3) for both kind of electrodes, SPCE and PyGE. The nitroaromates trinitrotoluene (TNT) and dinitrotoluene (DNT) are reduced and dopamine is oxidized in DPV mode (Fig.4). The peak currents are proportional to the TNT concentrations with a sensitivity of 2.7 nA/ppb for SPCE (Fig.5) and 0.78 for PyGE (Fig. 6) at the characteristic peak potential of -0.59 V (R²=0.99). Commercial electrodes DRP-110CNT-GNP made of carbon with gold nano particles require a special treatment in cyclo-voltammertic mode up to stable measuring conditions. The sensitivity of 2.8 nA/ppb is high compared to PyGEs. The relative errors in measuring cycles (35 %) are very much higher than those for PyGEs (5 %). PyGE do not need a special pretreatment before use.Screen printed and pyrolytic deposited carbon electrodes can be applied in air saturated aqueous solutions like in field application. For both electrodes, SCPE and PyGE, the oxygen reduction peak do not interfere with the reduction of the nitro groups. The manufacturing tolerances become smaller in the row DRP-110CNT-GNP, SPCE, PyGE. PyGEs can be produced in few steps with very small deviations. They can stored in air or in water over years without a loss of performance. Commercial electrodes are very complex in setup and obviously not so easy to produce in proper quality. Furthermore, their signals are remarkably influenced by oxygen so that measurements in air are not possible.

Photochemical Processes in Molecular Polymethine Dye Probes in the Presence of Bile Salts

Primary photochemical processes in polymethine dye probes 3,3′-di(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine (DEC) and 3,3′,9-trimethylthiacarbocyanine iodide (Cyan 2) in micellar systems of bile-acid salts (BASs) sodium cholate, deoxycholate, and taurocholate and sodium dodecyl sulfate (SDS) as a reference are studied by flash photolysis. Signals due to photoisomerization of dye trans-isomers and dark reverse isomerization of the resulting cis-photoisomers are observed during pulse photolysis of air-saturated aqueous dye solutions in the presence of BAS and SDS micelles. The lifetimes of the photoisomers are 60–190 μs. Pulse photolysis of Cyan 2 and DEC solutions without oxygen and with BAS and SDS micelles induced photoisomerization and transition of the dyes into an excited triplet state followed by the reverse transition (intersystem crossing) into the initial singlet state. Triplet–triplet absorption spectra of these dyes isomers in polar (EtOH, i-PrOH) and nonpolar (dioxane) solvents were obtained for comparison using triplet–triplet energy transfer from anthracene. The conclusion was drawn that the photochemical behavior of the dyes in BAS and SDS micellar systems were similar.

A table-top PXI based low-field spectrometer for solution dynamic nuclear polarization.

We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation platform. The main purpose of the instrument is for study of 1 H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7mT, using a modified Alderman-Grant resonator at 241MHz for saturation of the electron transition. The solenoid for detection of the enhanced 1 H signal at 288kHz was constructed with Litz wire. The largest observed 1 H enhancements (ε) at 6.7mT for 14 N-CTPO radical in air saturated aqueous solution was ε~65. A concentration dependence of the enhancement is observed, with maximum ε at 5.5mM. A low resonator efficiency for saturation of the electron paramagnetic resonance transition results in a decrease in ε for the 10.3mM sample. At high incident powers (42W) and long pump times, capacitor heating effects can also decrease the enhancement. The core unit and program described here could be easily adopted for multi-frequency DNP work, depending on available main magnets and selection of the "plug and play" arbitrary waveform generator, digitizer, and radiofrequency synthesizer PCI eXtensions for Instrumentatione cards.

Degradation of Triton X-100 surfactant/lipid regulator systems by ionizing radiation in water

The radiolytic degradation of Triton X-100 surfactant was investigated at concentrations below and above the critical micelle concentration (CMC, ~ 0.23 mmol dm−3) in air saturated aqueous solutions. At low concentrations the degradation took place both on the aromatic head and on the polyethoxylates chain, while above CMC it was shifted towards the chain. The CMC was higher in irradiated solutions at 10 Gy by a factor of 2, at 20 kGy by a factor of 3 than in the un-irradiated solution. The degradation of clofibric acid in the presence of TX-100 was more effective outside the micelles than inside them.

Probing Co-Assembly of Supramolecular Photocatalysts and Polyelectrolytes Using Isothermal Titration Calorimetry.

The creation of renewable fuels to replace dwindling fossil energy resources is one of the greatest challenges facing the scientific community. Generating H2 fuel from water is a carbon-neutral strategy that demonstrates great promise. Photocatalysts of the molecular architecture [{(TL)2Ru(BL)}2RhX2]5+ (BL = bridging ligand, TL = terminal ligand, X = halide) catalyze the formation of H2 in deoxygenated organic solvents but are limited by poor performance in air-saturated aqueous solutions. Addition of the water-soluble polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) was recently shown as being a promising new strategy to increase efficiency and stability of H2 evolving photocatalysts in air-saturated aqueous solutions. Herein we investigate intermolecular interactions between Ru,Rh,Ru photocatalysts and water-soluble polyelectrolytes using isothermal titration calorimetry (ITC). ITC studies provide insight into the thermodynamic forces that drive assembly of PSS-photocatalyst aggregates and give new evidence for the intermolecular forces that lead to increased photocatalytic efficiency.

Hydrogen peroxide formation during radiolysis of aerated aqueous solutions of organic molecules

A large number of aromatic molecules were irradiated in 10−4moldm−3 concentration air-saturated aqueous solutions; the hydrogen peroxide production was followed. H2O2 formed with an initial yield of 2.5–3.5×10−7molJ−1, the concentration had a maximum (∼3×10−4moldm−3) due to the competition between the formation and decay. The H2O2 concentration increased with the dose rate in purified water samples, here the •OH+•OH reaction dominated in H2O2 production. In the presence of aromatic compounds the H2O2 concentration decreased with the increasing dose rate: the main source of H2O2 was the termination reaction of the O2•−/HO2• pair. This pair formed in the eaq−+ O2 and H•+O2 reactions and also in elimination from organic peroxy radicals. The dose rate dependence was attributed to the changes in the ratios of the different formation ways of H2O2. The main H2O2 consuming process was suggested to be the eaq−+H2O2 reaction. In the present study the Cu(II)/phenanthroline H2O2 test was used for concentration determination. The test was found to be applicable in wide concentration range, but it provided false results when the solutions contained phenol type compounds. To overcome such interferences the removal of these compounds by liquid-liquid extraction was suggested.

Fluorescence-based characterization of non-fluorescent transient states of tryptophan - prospects for protein conformation and interaction studies.

Tryptophan fluorescence is extensively used for label-free protein characterization. Here, we show that by analyzing how the average tryptophan fluorescence intensity varies with excitation modulation, kinetics of tryptophan dark transient states can be determined in a simple, robust and reliable manner. Thereby, highly environment-, protein conformation- and interaction-sensitive information can be recorded, inaccessible via traditional protein fluorescence readouts. For verification, tryptophan transient state kinetics were determined under different environmental conditions, and compared to literature data. Conformational changes in a spider silk protein were monitored via the triplet state kinetics of its tryptophan residues, reflecting their exposure to an air-saturated aqueous solution. Moreover, tryptophan fluorescence anti-bunching was discovered, reflecting local pH and buffer conditions, previously observed only by ultrasensitive measurements in highly fluorescent photo-acids. Taken together, the presented approach, broadly applicable under biologically relevant conditions, has the potential to become a standard biophysical approach for protein conformation, interaction and microenvironment studies.

Kinetics of Corrosion Process in H2SO4 and HNO3 Aqueous Solutions of Lead Free Sn-Ag-Cu Solder Alloys

Abstract This paper presents the results of the corrosion resistance of Sn-Ag-Cu alloys in air-saturated aqueous solutions containing NO3-, SO42- ions, whose concentration was equivalent to their contents in acid rains and in concentrations 10 - 100 times higher. The Ag, Cu and Sn concentrations in the corrosive media were determined using the Atomic Absorption Spectrometry. The specific dissolution rate and corrosion current were derived using the a rotating disc technique. The corrosion rate of Sn- Ag-Cu alloys depends on pH of the examined solutions and on the concentration of oxygen near the phase boundary. In the whole range of concentrations of the applied H2SO4 + HNO3 mixtures of acids, the pure Sn was more corrosion resistant than eutectic alloy as well as the near eutectic one, following the sequence: Sn>Sn3.66Ag0.91Cu>3.8Ag0.7Cu.

Photogeneration of H2O2 in Water-Swollen SPEEK/PVA Polymer Films.

Efficient reduction of O2 took place via illumination with 350 nm photons of cross-linked films containing a blend of sulfonated poly(ether etherketone) and poly(vinyl alcohol) in contact with air-saturated aqueous solutions. Swelling of the solid macromolecular matrices in H2O enabled O2 diffusion into the films and also continuous extraction of the photogenerated H2O2, which was the basis for a method that allowed quantification of the product. Peroxide formed with similar efficiencies in films containing sulfonated polyketones prepared from different precursors and the initial photochemical process was found to be the rate-determining step. Generation of H2O2 was most proficient in the range of 4.9 ≤ pH ≤ 8 with a quantum yield of 0.2, which was 10 times higher than the efficiencies determined for solutions of the polymer blend. Increases in temperature as well as [O2] in solution were factors that enhanced the H2O2 generation. H2O2 quantum yields as high as 0.6 were achieved in H2O/CH3CN mixtures with low water concentrations, but peroxide no longer formed when film swelling was suppressed. A mechanism involving reduction of O2 by photogenerated α-hydroxy radicals from the polyketone in competition with second-order radical decay processes explains the kinetic features. Higher yields result from the films because cross-links present in them hinder diffusion of the radicals, limiting their decay and enhancing the oxygen reduction pathway.

Robust Benzo[g, h, i]perylenetriimide Dye-Sensitized Electrodes in Air-Saturated Aqueous Buffer Solution.

Highly electron deficient benzo[ghi]perylenetriimide (BPTI) chromophores were persistently anchored to a metal oxide electrode surface and reversible formation of their radical anions was shown in air-saturated aqueous buffer solution. Our results show a very low reaction-rate constant of BPTI(.-) with O2 (k=1.92 ± 0.05 × 10(-2) s(-1)). BPTI is a robust chromophore that can be used as the electron acceptor in molecule-based artificial photosynthetic devices for direct water splitting in aqueous phase.

Increased Water Reduction Efficiency of Polyelectrolyte-Bound Trimetallic [Ru,Rh,Ru] Photocatalysts in Air-Saturated Aqueous Solutions.

The groundbreaking use of polyelectrolytes to increase the efficiency of supramolecular photocatalysts in solar H2 production schemes under aqueous aerobic conditions is reported. Supramolecular photocatalysts of the architecture [{(TL)2 Ru(BL)}2 RhX2 ](5+) (BL=bridging ligand, TL=terminal ligand, X=halide) demonstrate high efficiencies in deoxygenated organic solvents but do not function in air-saturated aqueous solution because of the quenching of the metal-to-ligand charge-transfer (MLCT) excited state under these conditions. The new photocatalytic system incorporates poly(4-styrenesulfonate) (PSS) into aqueous solutions containing [{(bpy)2 Ru(dpp)}2 RhCl2 ](5+) (bpy=2,2'-bipyridine, dpp=2,3-bis(2-pyridyl)pyrazine). PSS has a profound impact on the photocatalyst efficiency, increasing H2 production over three times that of deoxygenated aqueous solutions alone. H2 photocatalysis proceeds even under aerobic conditions for PSS-containing solutions, an exciting consequence for solar hydrogen-production research.

Effect of Temperature on Photophysical Properties of Polymeric Nanofiber Materials with Porphyrin Photosensitizers

Electrospun nanofibers possess large surface to volume ratios, high porosity, and good mechanical properties that are necessary for biological applications. We prepared different types of photoactive polymeric nanofiber materials with encapsulated or externally bound porphyrin photosensitizers. The kinetics of formation and the decay of both singlet oxygen O2((1)Δg) and porphyrin triplet states that are generated by irradiation of nanofiber materials in an air atmosphere or in an air-saturated aqueous solution were measured and evaluated by luminescence and transient absorption spectroscopy in the temperature range between 5 and 60 °C. We found shortening of the O2((1)Δg) lifetime and a significant increase in singlet oxygen-sensitized delayed fluorescence at higher temperatures. These photophysical data show an increase in the diffusion coefficient for O2((1)Δg) with temperature, and they are consistent with a stronger antibacterial effect of the nanofiber material on Escherichia coli at higher temperature.

Corrosion behavior of lead-free SAC-type solder alloys in liquid media

New lead-free solders are developed for electronic assemblies as a replacement for traditional Pb-containing alloys. The main goal of this study was to investigate the corrosion resistance of ternary Sn–Ag–Cu (SAC) alloys in the air-saturated aqueous solutions of NaCl (including sea water) and containing NO3−, SO42−, Cl− ions of concentration equivalent to those in acid rains. The Atomic Absorption Spectrometry (AAS) was used to determine Ag, Cu and Sn concentrations in the corrosive media. The corrosion potential and current were obtained using the potentiodynamic polarization technique. Corrosion resistance experiments of Sn–Ag–Cu alloys with the potentiodynamic method revealed that the solders were considerably resistant to corrosion in the liquid media used. The eutectic composition alloy was characterized by a higher resistance than the near eutectic one despite very small differences in the chemical composition. Corrosion rate during spontaneous dissolution was considerably lower than that derived from the potentiodynamic experiments because of blocking the reaction surface with corrosion products.

A Sono-Electrochemical Technique for Enhanced Particle Removal from Tantalum Surfaces

Low power megasonics is of interest to semiconductor cleaning community due to minimal feature damage. In this work, megasonic field at low power density in conjunction with electrochemistry is used for enhanced removal of silica particles from tantalum wafers. Cleaning studies were conducted in air or argon saturated aqueous solutions at 0.5 W/cm2 in the absence and presence of applied potentials of −1.5 V or −2.0 V to tantalum (vs Ag/AgCl). The improvement in particle removal efficiency is attributed to oscillating hydrogen bubbles formed from water reduction in vicinity of tantalum surface and grown to a resonant size under suitable acoustic conditions. © 2014 The Electrochemical Society. [DOI: 10.1149/2.008404ssl] All rights reserved.

Photogeneration of H2O2 in SPEEK/PVA Aqueous Polymer Solutions

Photolysis of air-saturated aqueous solutions containing sulphonated poly(ether etherketone) and poly(vinyl alcohol) results in the generation of hydrogen peroxide. Consumption of oxygen and H2O2 formation are initially concurrent processes with a quantum yield of peroxide generation of 0.02 in stirred or unstirred solutions within the range of 7 ≤ pH ≤ 9. The results are rationalized in terms of O2 reduction by photogenerated α-hydroxy radicals of the polymeric ketone in competition with radical-radical processes that consume the macromolecular reducing agents. Generation of H2O2 is controlled by the photochemical transformation that produces the polymer radicals, which is most efficient in neutral and slightly alkaline solutions. Quenching of the excited state of the polyketone by both H3O(+) and OH(-) affect the yields of the reducing macromolecular radicals and of H2O2. Deprotonation of the α-hydroxy polymeric radicals at pH > 9 accelerate their decay and contribute to suppressing the peroxide yields in basic solutions. Maxima in [H2O2] are observed when illuminations are performed with static systems, where O2 reduction is faster than diffusion of oxygen into the solutions. Under such conditions H2O2 can compete with O2 for the reducing radicals resulting in a consumption of the peroxide.

Spectral and luminescent investigations of ammonia cyclometalated Pt(II) complexes

A method of synthesis of ammonia cyclometalated Pt(II) complexes [Pt(NH3)2C∧N]ClO4, where C∧N is 2-phenylpyridinate or 2-phenylbenzothiazole ion, is developed. The electronic absorption and emission properties of the complexes are studied. It is found that the state responsible for intense long-lived luminescence is the excited charge-transfer state of the 3(d-π*) type, the π* orbital being localized at the corresponding cyclometalating ligand. Formation of platinum blue is observed in air-saturated aqueous solutions of ammonia cyclometalated complexes.

Degradation of organic molecules in advanced oxidation processes: Relation between chemical structure and degradability

Hydroxyl radical induced degradation of maleic acid, fumaric acid and 20 aromatic molecules was investigated in air saturated aqueous solutions. Hydroxyl radicals were generated by an advanced oxidation process (AOP), water radiolysis. Oxidation was followed by chemical oxygen demand (COD) and total organic carbon content (TOC) measurements. Up to ∼30–50% decrease of COD the dose dependence was linear. By the ratio of the decrease of COD and the amount of reactive radiolysis intermediates introduced into the solution the oxidation efficiencies were calculated. Efficiencies around 0.5–1 (O2 molecule built in products/OH) found for most of the compounds show that the one-electron-oxidant OH induces 2–4 electron oxidations. The high oxidation rates were explained by OH addition to unsaturated bonds and subsequent reactions of dissolved O2 with organic radicals. In amino substituted molecules or in Acid Red 1 azo dye, O2 cannot compete efficiently with unimolecular transformation of organic radicals and the efficiency is lower (0.2–0.5).