Sulfite Oxidation Research Articles

Molybdenum.

Molybdenum, a trace element essential for micro-organisms, plants, and animals, was discovered in 1778 by a Swedish chemist named Karl Scheele. Initially mistaken for lead, molybdenum was named after the Greek work molybdos, meaning lead-like. In the 1930s, it was recognized that ingestion of forage with high amounts of molybdenum by cattle caused a debilitating condition. In the 1950s, the essentiality of molybdenum was established with the discovery of the first molybdenum-containing enzymes. In humans, only 4 enzymes requiring molybdenum have been identified to date: sulfite oxidase, xanthine oxidase, aldehyde oxidase, and mitochondrial amidoxime-reducing component (mARC). Sulfite oxidase, an enzyme found in mitochondria, catalyzes oxidation of sulfite to sulfate, the final step in oxidation of sulfur amino acids (cysteine and methionine). Xanthine oxidase converts hypoxanthine to xanthine, and further converts xanthine to uric acid, preventing hypoxanthine, formed from spontaneous deamination of adenine, from leading to DNA mutations if paired with cytosine in place of thymine. Aldehyde oxidase is abundant in the liver and is an important enzyme in phase 1 drug metabolism. Finally, mARC, discovered less than a decade ago, works in concert with cytochrome b5 type B and NAD(H) cytochrome b5 reductase to reduce a variety of N-hydroxylated substrates, although the physiologic significance is still unclear. In the case of each of the molybdenum enzymes, activity is catalyzed via a tricyclic cofactor composed of a pterin, a dithiolene, and a pyran ring, called molybdenum cofactor (MoCo) (1).

Electrochemical Oxidation of Sulphite in Neutral Media on Platinum Anode

Electrochemical Oxidation of Sulphite in Neutral Media on Platinum Anode

Photoelectrochemical Activity of CdS/CdSe-Deposited TiO2 photoanodes Due to Electrolytes with and without Sacrificial Reagents

Literature on the photoelectrochemical (PEC) activity of TiO2 electrodes modified by CdS and or CdSe depositions are mostly performed using electrolytes with sacrificial reagents. The overall performance of a PEC system can vary significantly simply due to the use of different electrolytes, especially those with and without sacrificial reagents. In this paper, we have used a well-known TiO2 nanotube structure modified by CdS/CdSe nanoparticles deposited by successive ionic layer adsorption and reaction (SILAR) method to highlight the difference in PEC activities arising from sulfite oxidation and water oxidation. Linear Sweep Voltammograms measured under a standard AM1.5G simulated spectra, 1 sun (100 mWcm-2) exhibited a photocurrent density of 0.92 mAcm-2 at 1.23 V vs. RHE for the TiO2/CdS/CdSe photoactive electrodes using an aqueous alkaline electrolyte (1 M NaOH) for which water oxidation occurs. However, for the similar photoanode an 8-fold higher photocurrent of 7.4 mAcm-2 (at 1.23 V vs. RHE) was observed using an Na2S/Na2SO3 aqueous electrolyte where sulfite oxidation was the dominant mechanism for the enhanced photocurrent. A maximum STH efficiency of 0.71% and water splitting efficiency of 12.4% was determined for water oxidation. The STH efficiency parameter is more relevant to water splitting systems and to report such device efficiencies we propose that the ‘water splitting efficiency’ parameter is much more meaningful since it correlates the PEC activity specifically to water splitting and not to other pathways that produce an artificially enhanced photocurrent through the use of sacrificial reagents. The incident photon-to-current conversion efficiency spectrum measured at 1.23 V (vs. RHE) bias for the TiO2 photoanodes modified by CdS/CdSe nanoparticles revealed that the current conversion efficiency is lower (~17% or less) when absorption occurs solely from the external CdSe layers indicating higher recombination during charge transport. The increase of dark current observed in the linear sweep voltammetry plots for the voltage range of -0.25 V to +0.15 V vs. RHE was attributed to anodic dissolution of the photoanodes in aqueous electrolytes containing no sacrificial reagents. The photocurrents and onset potentials for the CdS/CdSe modified TiO2 photoanodes were found to improve under acidic conditions showing a slightly increased PEC activity and faster reaction kinetics.

Electrodeposited Thin Conformal TiO2 Coating Enabling Stable Operation of BiVO4 Photoanodes in Basic Media

Producing hydrogen via solar water splitting using a photoelectrochemical cell (PEC) persists as one of the most exciting research topics in the field of solar fuels. The construction of efficient PECs requires the integration of multiple components including a photoanode, a photocathode, an oxygen evolution catalyst, and a hydrogen evolution catalyst. Therefore, the compatibility and stability of all of these elements in a given operating condition are crucial. When the stability of a semiconductor electrode used as the photoanode or photocathode is limited in an acidic or basic condition which is optimum for the operation of the other components, a thin protective layer has been deposited on the semiconductor surface to prevent its chemical dissolution. Surface coating of a thin and conformal TiO2 layer has been proven to be successful for protecting photoelectrodes since TiO2 is chemically and electrochemically stable in a wide range of pH conditions under both anodic and cathodic conditions. In order to prevent the semiconductor surface from coming into direct contact with the corrosive electrolyte, complete coverage of the photoelectrode with TiO2 is required. At the same time, the TiO2 layer should be thin enough not to interfere with the charge transport properties of the photoelectrode. As a result, atomic layer deposition (ALD) has been the only successful tool used to date to produce an effective protective layer. However, the slow processing time and economic viability of ALD methods motivated us to develop an inexpensive and facile solution-based synthesis method for the deposition of high quality TiO2 coating layers. In this presentation, we report a new electrochemical method to deposit a thin and conformal TiO2 layer on nanoporous BiVO4 that has an intricate, high surface area morphology. BiVO4 is a promising n-type photoanode material with a relatively low bandgap (2.4~2.5 eV). However, its usage has been limited to neutral and mildly basic conditions (pH 5~9) because it is chemically unstable in strongly acidic and basic conditions. Our method allows for the deposition of a 5~6 nm thick TiO2 layer on BiVO4 within 1 min and the resulting BiVO4/TiO2 electrodes exhibit chemical stability in basic solutions (pH 12~13). Sulfite oxidation measurements of BiVO4 and BiVO4/TiO2 electrodes show that the thin TiO2 protective layer does not significantly reduce the hole transfer to the electrolyte. Finally, we demonstrate the photoelectrochemical stability of the BiVO4/TiO2 electrode for photoelectrochemical water oxidation in basic solutions by coupling the BiVO4/TiO2 electrode with appropriate oxygen evolution catalysts.

Qualitative dependence of the electro-oxidation behavior of sulfite on solution pH

Electrochemical oxidation of sulfite at a platinum electrode was investigated, in which changing the pH of supporting electrolytes caused qualitative changes in the oxidation behavior. In an acidic environment, oscillations in current were found to occur; however, only transient behavior was observed without the incorporation of an external resistor. Electrochemical impedance spectroscopic measurements indicate that the system possesses a region of negative differential resistance (NDR) at acidic conditions. To gain insights into the influence of pH, electrochemical oxidation of bisulfite was also studied, in which NDR was found, suggesting that changes in the dominant species induced by pH is responsible for the observed phenomena. Perturbation experiments illustrate the presence of bistability under galvanostatic conditions, lending support that the observed instabilities belong to the N-NDR class of electrochemical oscillators. Mass spectroscopic analysis and precipitation with barium ion suggest that SO42− is a major product of the electro-oxidation of sulfite.

Electrochemical oxidation of sulfites by DWCNTs, MWCNTs, higher fullerenes and manganese

Different electrocatalysts were tested for oxidation of sulfites to sulfates, namely, manganese thin films deposited on fullerenes and carbon nanotubes. The results presented clearly show that electrodes containing HFs (higher fullerenes), DWCNTs (double-wall carbon nanotubes) and manganese acetate are effective catalysts in S/O2 fuel cells. HFs and DWCNTs have high catalytic activity and can be employed as standalone catalysts. Manganese was deposited on DWCNTs, HFs and fullerenes C60/C70 by a thermal process. The electrocatalysts were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical testing was carried out by plotting the E/V polarization curve. The polarization curves of the electrodes composed of pristine DWCNTs showed the lowest overpotentials.

Application and Research of High Molecular Carboxylates in Desulphurization System of Thermal Power Plant

The main components of polymer carboxyl group are introduced.The effects of macromolecular carboxyl groups on the limestone-gypsum wet flue gas desulfurization (FGD) system of coal-fired power plants in China were studied by test method. The results showed that the macromolecular carboxyl groups can accelerate the chemical absorption of SO2 under the action of active agents and crystallization agents, improve the desulfurization efficiency of about 2%, and shorten the limestone ablation time of more than 40%, catalytic calcium sulfite oxidation of calcium sulfate.

Enhanced charge separation and oxidation kinetics by loading Pt nanoparticles with hydrogenated TiO2 nanotubes

Charge separation and oxidation kinetics are both critical for solar energy conversion in photoelectrochemical cell, but it is difficult to enhance simultaneously by a semiconductor. Here, the hydrogenated TiO2 loaded by Pt nanoparticles with improved charge separation and oxidation kinetics photoanodes are developed, characterized, and tested. The TiO2 nanotubes are prepared by hydrothermal of Ti foils and used as substrates for hydrogenation and loaded by Pt through photodeposition. Ascribe to the synergetic of hydroxylated surface and Pt nanoparticles, the photocurrent of Pt/H:TiO2 is enhanced from 0.052 (TiO2) to 0.098 mA/cm2 at 1.0 V versus RHE for water oxidation and almost increased 1.3 times for sulfite oxidation. Further, the electrons’ transport time has been reduced 20%, and the incident photon-to-electron conversion efficiency for Pt/H:TiO2 has been increased by 2.5-fold for water oxidation under 350 nm illumination at 1.0 V versus RHE. The charge separation and oxidation kinetics efficiencies of Pt/H:TiO2 are improved to 62.2 and 39.9% compared with pristine TiO2 (54.2 and 27.6%) at 1.0 V versus RHE. The origin of the enhanced photoelectrochemical performances for Pt/H:TiO2 is due to the hydroxylated surface and the absorption of plasmon resonance by Pt nanoparticles.

Synthesis and characterization of NiO nanoplatelet and its application in electrochemical sensing of sulphite

Nanostructured NiO such as nanoplatelet, nanoflower, nanosheet and nanoflakes were prepared by simple precipitation and hydrothermal methods. Physical properties, morphology and porous nature were studied using several characterization techniques. The studies confirm the formation of NiO and its nano-porous morphologies. Nanostructured NiO was used as an electrocatalyst to detect sulphite. Electrocatalytic oxidation behaviour of sulphite on nanostructured NiO was evaluated using cyclic voltammetry and amperometric methods. All the synthesized materials display good electrocatalytic response towards sulphite oxidation. Amongst, NiO nanoplatelet acts as best sensitive and selective material for sulphite sensing with some other foreign interference ions in solution. The proposed sensor showed reliable linear response in the range from 16.2 μM to 610 μM with a detection limit (LOD) of 8.8 μM.

Hydrothermal Synthesis of Carbon Coated NiCo2O4 Nano flower for the Electrochemical Oxidation of Sulfite in Real Sample

Hydrothermal Synthesis of Carbon Coated NiCo2O4 Nano flower for the Electrochemical Oxidation of Sulfite in Real Sample

The role and mechanism of triethanolamine in simultaneous absorption of NOx and SO2 by magnesia slurry combined with ozone gas-phase oxidation

A novel absorption method was developed and used for the simultaneous removal of SO2 and NOx, whereby triethanolamine (TEA)-modified magnesia was utilized as an absorption slurry and combined with gas-phase oxidation by ozone. TEA was first used as the additive to magnesia slurry to facilitating the aqueous absorption of NOx and SO2. The injection of O3 increased the solubility of NOx considerably. Furthermore, the addition of TEA facilitated the absorption of NOx in wet combined desulfurization and denitrification processes. In addition, experiments on operating factors included initial pH, TEA concentration, and the effect of SO2 were performed in this study. The results show that after the addition of TEA to a magnesium-based slurry, the absorption efficiency of NO2 improved to almost 100% under alkaline conditions. However, the improvement effect of TEA was less evident in acidic conditions. Based on studies of operating factors and product analysis, the reaction mechanism of TEA-assisted magnesia slurry absorption was proposed. Under alkaline conditions, TEA served as the radical scavenger, terminated the excessive oxidation of sulfite, and then strongly promoted the reaction between NO2− and SO32−. Furthermore, TEA could react with NO2 and SO2 directly, and its alkalinity was beneficial for the absorption of NO2 and SO2. In acidic conditions, TEA reacted with H+ and formed +H-N(CH2CH2OH)3, and the antioxidant capability of TEA would be lost.

Ferrocene Tethered Polyvinyl Alcohol/Silica Film Electrode for Electrocatalytic Sulfite Sensing

AbstractFerrocene was linked to polyvinyl alcohol polymer via ethylene dioxi‐bis‐ethylamine (PV‐Fc) spacer and the synthesized redox polymer was characterised by FT‐IR and H1NMR spectroscopy. Aqueous solution of PVA‐Fc was used to prepare its silica composite with tetraethylorthosilicate (TEOS). The immobilized PVA‐Fc/silica film showed E0 about 0.245 V and apparent diffusion coefficient was measured to be 2.76×10−8 cm2 s−1. The ferrocene with flexible spacer in PVA‐Fc/silica film showed an excellent electrocatalytic activity towards the sulfite oxidation at 0.35 V, that was minimum 0.3 V negative shift of the overpotential than the bare electrode. The effect of the interfearing species like acetate, ammonium, carbonate, phosphate and sulfate has been checked for the sulfite detection. Under the optimized conditions the prepared composite showed sulfite oxidation in the linear range of 5×10−7 M to 1×10−4 M and lower detection limits of 1.5×10−7 M.

Efficient metoprolol degradation by heterogeneous copper ferrite/sulfite reaction

Metal/sulfite systems are currently used for SO 4 •− generation and oxidative removal of organic contaminants. However, homogeneous metal/sulfite systems are limited because their working pHs must be acidic and metal ions cannot be separated from the bulk reaction solution. As a consequence, these drawbacks have severely limited the application of metal/sulfite systems in real conditions. To address these issues, we tested the use of copper ferrite (CuFe2O4), a ferromagnetic nanoparticle, to catalyze sulfite oxidation for the degradation of the metoprolol drug. The reaction mechanism was investigated by electron spin resonance, X-ray photoelectron spectroscopy, and radical quenching assay. The effects of pH, CuFe2O4, and sulfite dosages were also assessed. Results show that SO 4 •− was the primary radical responsible for metoprolol degradation. Higher pHs induced more metoprolol degradation using CuFe2O4/sulfite. Moreover, CuFe2O4 remained morphologically intact and catalytically active after four batches of recycling. Overall, our findings show that CuFe2O4/sulfite can effectively degrade water contaminants in alkali pH and withhold catalyst activity after multiple reuses, therefore addressing the issues associated with homogeneous metal/sulfite systems.

Study of oxidation of calcium sulfite in flue gas desulfurization by pore-type surface dielectric barrier discharge

Novelty: a new pore-type surface dielectric barrier discharge (PSDBD) reactor was first applied in the oxidation of calcium sulfite in flue gas desulfurization.

Ultrasonic-assisted preparation of a pinhole-free BiVO4 photoanode for enhanced photoelectrochemical water oxidation

A pinhole-free BiVO4 electrode was successfully synthesized using an ultrasonic-assisted synthetic method on a conductive substrate. The pinhole-free BiVO4 electrode showed highly improved photoelectrochemical activity for both sulfite oxidation and water oxidation. The blocking recombination processes were examined to clarify the enhanced photoelectrochemical performances.

A glassy carbon electrode modified by a triply-fused-like Co(ii) polyporphine and its ability for sulphite oxidation and detection

An original Co(ii) porphyrin conductive polymer is electrosynthesized which efficiently catalyzes sulphite oxidation in water offering opportunities for sensor development.

Electrochemical Synthesis of Lutetium (III) Hexacyanoferrate/poly(taurine) Modified Glassy Carbon Electrode for the Sensitive Detection of Sulfite in Tap Water

The well-defined Lutetium (III) hexacyanoferrate microparticles were electrodeposited on poly(taurine) modified glassy carbon electrode (GCE), namely (LuHCF/poly(taurine)-GCE). The as-fabricated LuHCF/poly(taurine)-GCE possesses excellent electrochemical activities and high sensitivity toward the sensing of sulfite. The electrochemical oxidation of sulfite on LuHCF/poly(taurine)-GCE is studied by using Cyclic Voltammetry (CV), and Differential Pulse Voltammetry techniques (DPV). Remarkably, the reported modified electrode exhibits high sensitivity (448 μA mM−1 cm−2) and limit of detection (1.33 μM) toward the electrochemical oxidation of sulfite with superior selectivity and practicability.

Kinetics of sodium sulphite oxidation catalyzed by Co2O3 and inhibited by ethylene glycol

Kinetics of sodium sulphite oxidation catalyzed by Co₂O₃ and inhibited by ethylene glycol

Sulfite-induced protein radical formation in LPS aerosol-challenged mice: Implications for sulfite sensitivity in human lung disease

Exposure to (bi)sulfite (HSO3–) and sulfite (SO32–) has been shown to induce a wide range of adverse reactions in sensitive individuals. Studies have shown that peroxidase-catalyzed oxidation of (bi)sulfite leads to formation of several reactive free radicals, such as sulfur trioxide anion (.SO3–), peroxymonosulfate (–O3SOO.), and especially the sulfate (SO4. –) anion radicals. One such peroxidase in neutrophils is myeloperoxidase (MPO), which has been shown to form protein radicals. Although formation of (bi)sulfite-derived protein radicals is documented in isolated neutrophils, its involvement and role in in vivo inflammatory processes, has not been demonstrated. Therefore, we aimed to investigate (bi)sulfite-derived protein radical formation and its mechanism in LPS aerosol-challenged mice, a model of non-atopic asthma. Using immuno-spin trapping to detect protein radical formation, we show that, in the presence of (bi)sulfite, neutrophils present in bronchoalveolar lavage and in the lung parenchyma exhibit, MPO-catalyzed oxidation of MPO to a protein radical. The absence of radical formation in LPS-challenged MPO- or NADPH oxidase-knockout mice indicates that sulfite-derived radical formation is dependent on both MPO and NADPH oxidase activity. In addition to its oxidation by the MPO-catalyzed pathway, (bi)sulfite is efficiently detoxified to sulfate by the sulfite oxidase (SOX) pathway, which forms sulfate in a two-electron oxidation reaction. Since SOX activity in rodents is much higher than in humans, to better model sulfite toxicity in humans, we induced SOX deficiency in mice by feeding them a low molybdenum diet with tungstate. We found that mice treated with the SOX deficiency diet prior to exposure to (bi)sulfite had much higher protein radical formation than mice with normal SOX activity. Altogether, these results demonstrate the role of MPO and NADPH oxidase in (bi)sulfite-derived protein radical formation and show the involvement of protein radicals in a mouse model of human lung disease.

Water splitting vs. sulfite oxidation: An assessment of photoelectrochemical performance of TiO2 nanotubes modified by CdS/CdSe nanoparticles

A major portion of the existing literature on TiO2 nanotubes modified by CdS and CdSe report an enhanced photoelectrochemical (PEC) performance using electrolytes with inorganic sacrificial electron donors where a dominant sulfite oxidation occurs. In this study, we distinguish the PEC performance arising entirely from water splitting to that originated by sulfite oxidation in the TiO2 nanotube system modified by CdS/CdSe nanoparticle depositions. The photocurrent density measured under the AM1.5G simulated spectra, 1 sun (100 mWcm−2) intensity for the TiO2 nanotubes modified by CdS/CdSe nanoparticles and using an aqueous alkaline electrolyte (1 M NaOH) was observed to be 0.92 mAcm−2 at 1.23 V vs. RHE which was 8-fold lower than in the case for sulfite oxidation (Jph/SO = 7.4 mAcm−2 at 1.23 V vs. RHE) using an Na2S/Na2SO3 aqueous electrolyte. A maximum STH efficiency of 0.71% and water splitting efficiency of 12.4% was determined for water oxidation using an aqueous alkaline electrolyte. To rationalize such device efficiency, we propose that the ‘water splitting efficiency’ parameter is much more meaningful since it correlates the PEC activity specifically to water splitting and not to other pathways that produce an artificially enhanced photocurrent through the use of sacrificial reagents. The incident photon-to-current conversion efficiency spectrum measured at 1.23 V (vs. RHE) bias for the TiO2 photoanodes modified by CdS/CdSe nanoparticles revealed that the current conversion efficiency is lower (∼17% or less) when absorption occurs solely from the external CdSe layers indicating higher recombination during charge transport. The increase of dark current observed in the linear sweep voltammetry plots for the voltage range of −0.25 V to +0.15 V vs. RHE was attributed to anodic dissolution of the photoanodes in aqueous electrolytes containing no sacrificial reagents. The photocurrents and onset potentials for the CdS/CdSe modified TiO2 photoanodes improved under acidic conditions showing a slightly increased PEC activity and faster reaction kinetics.