Study of the Photodegradation Kinetics and Pathways of Hexaflumuron in Liquid Media

Hexaflumuron, one of the benzoylphenylurea insect growth regulators, can be leached into surface water and thus having a potential impact on aquatic organisms. In this study, the photodegradation processes of hexaflumuron under high‐pressure mercury lamp irradiation were assessed. The photodegradation kinetics were studied, as were the effects of pH, different light sources, organic solvents and environmental substances, including nitrate ions (NO₃^?), nitrite ions (NO₂^?), ferrous ions (Fe²⁺), ferric ions (Fe³⁺), humic acid, sodium dodecyl sulfate (SDS) and hydrogen peroxide (H₂O₂). Three photodegradation products in methanol were identified by gas chromatography‐mass spectrometry (GC‐MS). In general, the degradation of hexaflumuron followed first‐order kinetics. In the four media studied, the photodegradation rate order was n‐hexane > methanol > ultrapure water > acetone. Faster degradation was observed under high‐pressure mercury lamp irradiation than under xenon lamp irradiation. The pH had a considerable effect, with the most rapid degradation occurring at pH 5.0. The photodegradation rate of hexaflumuron was promoted in the presence of NO₃^?, NO₂^?, Fe²⁺, humic acid, SDS and H₂O₂, but inhibited by Fe³⁺. Moreover, the presumed photodegradation pathway was proposed to be the cleavage of the urea linkage.     

Grape tissue-based electrochemical sensor for the determination of hydrogen peroxide

The use of grape tissue as a source of catalase for the determination of hydrogen peroxide is reported. A slice of grape tissue attached to the membrane of a Clark-type oxgen sensor was used to monitor the oxidation of hydrogen peroxide by catalase. At the steady state, the sensor responds linearly to hydrogen peroxide in the concentration range 1 × 10^?5–5 × 10^?4 M. The response time (T₉₀) was of the order of 1 min for this sensor. No interference was observed from ethanol, amino acids, glucose and lactic acid. The long-term stability of the grape tissue sensor was much better than previously reported immobilized enzyme and liver tissue-based hydrogen peroxide sensors.     

Determination of itraconazole and its photodegradation products with kinetic evaluation by ultra‐performance liquid chromatography/tandem mass spectrometry

A simple and reproducible UPLC‐MS/MS method for the determination of itraconazole (ITZ) and its photodegradation products formed during exposure to UV‐A radiation was developed. Chromatographic separations were carried out using an Acquity UPLC BEH C₁₈ column (2.1 × 100 mm, 1.7 μm particle size). The column was maintained at 40°C, and eluted under gradient conditions from 100% to 50% of eluent A over 13 min, at a flow rate of 0.3 mL min^?1. Eluent A was 0.1% (v/v) formic acid in water; eluent B was 0.1% (v/v) formic acid in acetonitrile. The linear regression analysis for the calibration curve showed a good linear correlation over the concentration range 0.0066–0.15 mg mL^?1 with determination coefficient > 0.99. The activities of some photocatalysts during degradation process of ITZ were compared. It was found that indirect photodegradation of ITZ was more effective than direct photolysis. Under our experimental conditions the photodegradation rate constant depended on the applied catalysts with catalytic activity decreasing in the following pattern: FeCl₃ > TiO₂/FeCl₃ > TiO₂. The kinetic analysis of the photodegradation data revealed that the degradation of the ITZ follows first‐order kinetics. The photodegradation products of ITZ were identified, and their fragmentation pathways, derived from MS/MS data, were proposed. Copyright © 2016 John Wiley & Sons, Ltd.     

The kinetics of complex formation between Ti(IV) and hydrogen peroxide

The kinetics of the formation of the titanium‐peroxide [TiO²⁺₂] complex from the reaction of Ti(IV)OSO₄ with hydrogen peroxide and the hydrolysis of hydroxymethyl hydroperoxide (HMHP) were examined to determine whether Ti(IV)OSO₄ could be used to distinguish between hydrogen peroxide and HMHP in mixed solutions. Stopped‐flow analysis coupled to UV‐vis spectroscopy was used to examine the reaction kinetics at various temperatures. The molar absorptivity (ε) of the [TiO²⁺₂] complex was found to be 679.5 ± 20.8 L mol^?1 cm^?1 at 405 nm. The reaction between hydrogen peroxide and Ti(IV)OSO₄ was first order with respect to both Ti(IV)OSO₄ and H₂O₂ with a rate constant of 5.70 ± 0.18 × 10⁴ M^?1 s^?1 at 25°C, and an activation energy, E_a = 40.5 ± 1.9 kJ mol^?1. The rate constant for the hydrolysis of HMHP was 4.3 × 10^?3 s^?1 at pH 8.5. Since the rate of complex formation between Ti(IV)OSO₄ and hydrogen peroxide is much faster than the rate of hydrolysis of HMHP, the Ti(IV)OSO₄ reaction coupled to time‐dependent UV‐vis spectroscopic measurements can be used to distinguish between hydrogen peroxide and HMHP in solution. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 457–461, 2007     

Nanostructured Alpha‐Nickel Hydroxide Electrodes for High Performance Hydrogen Peroxide Sensing

Nanostructured alpha‐nickel hydroxide (α‐Ni(OH)₂) immobilized on a Fluorine‐doped Tin Oxide (FTO) surface was explored for the construction of hydrogen peroxide amperometric Flow Injection Analysis (FIA) sensors. Their notable electrocatalytic activity and heterogeneous electron‐transfer rate were confirmed by the appearance of a broad and intense peak associated with the oxidation of hydrogen peroxide and the enhancement of sensibility in hydrodynamic conditions. The α‐Ni(OH)₂ electrodes exhibited a broad dynamic range (5×10^?6 to 1×10^?3 mol L^?1), low detection limit (2×10^?7 mol L^?1), good repeatability (RSD=1.29 % for 20 successive analyses), and a sensitivity greater than 500 µA mmol^?1 L^?1 cm^?2.     

General Preparation of Heme Protein Functional Fe3O4@Au‐Nps Magnetic Nanocomposite for Sensitive Detection of Hydrogen Peroxide

Stable magnetic nanocomposite of gold nanoparticles (Au‐NPs) decorating Fe₃O₄ core was successfully synthesized by the linker of Boc‐L‐cysteine. Transmission electron microscope (TEM), energy dispersive X‐ray spectroscopy (EDX) and cyclic voltammograms (CV) were performed to characterize the as‐prepared Fe₃O₄@Au‐Nps. The results indicated that Au‐Nps dispersed homogeneously around Fe₃O₄ with the ratio of Au to Fe₃O₄ nanoparticles as 5–10/1 and the apparent electrochemical area as 0.121 cm². After self‐assembly of hemoglobin (Hb) on Fe₃O₄@Au‐Nps by electrostatic interaction, a hydrogen peroxide biosensor was developed. The Fe₃O₄@Au‐Nps/Hb modified GCE exhibited fast direct electron transfer between heme center and electrode surface with the heterogeneous electron transfer rate constant (Ks ) of 3.35 s⁻¹. Importantly, it showed excellent electrocatalytic activity towards hydrogen peroxide reduction with low detection limit of 0.133 μM (S /D =3) and high sensitivity of 0.163 μA μM⁻¹, respectively. At the concentration evaluated, the interfering species of glucose, dopamine, uric acid and ascorbic acid did not affect the determination of hydrogen peroxide. These results demonstrated that the introduction of Au‐Nps on Fe₃O₄ not only stabilized the immobilized enzyme but also provided large surface area, fast electron transfer and excellent biocompatibility. This facile nanoassembly protocol can be extended to immobilize various enzymes, proteins and biomolecules to develop robust biosensors.     

A new process for preparing dialdehyde by catalytic oxidation of cyclic olefins with aqueous hydrogen peroxide

A. novel peroxo-niobophosphate was synthesized for the first time and used as a catalyst in the oxidation reaction of cyclic olefins with aqueous hydrogen peroxide to prepare dialdehy-des. The catalyst was characterized by elemental analysis, thermographic analyses, IR, UV/vis, 31P NMR and XPS spectra as [ π-C5H5N(CH2 )13 CH3 ]2 [ Nb4O6 (O2 )2 (PO4 )2 ] ·6H2O (PTNP). It showed high selectivity to glutaraldehyde in the catalytic oxidation of cyclopentene with aqueous hydrogen peroxide in ethanol.     

Enhanced visible light photodegradation of water pollutants over N-, S-doped titanium dioxide and n-titanium dioxide in the presence of inorganic anions

The potential application of waste water treatment by photocatalysis is very likely to find its place in the near future. We have studied the photocatalytic degradation of three dyes (Eosin B, Rhodamine 6G, Rhodamine B) in the presence of doped n-TiO₂ in water and found that anchoring groups are favorable to the photodegradation of the pollutants. Taking Rhodamine B as a model pollutant, this study points out an alternative route to enhance photodegradation in invisible light, which consumes energy to synthesize, but addition of 0.1 mM of I⁻ or S₂O₃²⁻ increases the discoloration by up to three folds. For example, KI increased degradation to 36% while Na₂S₂O₃ enhanced it by 61%, which was higher than that of pure n-TiO₂ after sun light irradiation of 40 min. The enhancement of degradation by I⁻ and S₂O₃²⁻ may be linked to the scavenging of the holes by the inorganic anions, thus inhibiting recombination between h⁺/e⁻ after excitation of the semiconductor. The degradation is more effective in the presence of S₂O₃²⁻. In the presence of 0.1 mM KI, the rate constant increased from 0.0231 s⁻¹ to 0.0325 s⁻¹.Peroxodisulphate increases degradation, however, this is attributed to the sulfate radicals.     

Kinetics Study on Reaction of Atenolol with Singlet Oxygen by Directly Monitoring the 1O2 Phosphorescence

The pharmaceutically active compound atenolol, a kind of $\beta$-blockers, may result in adverse effects both for human health and ecosystems if it is excreted to the surface water resources. To effectively remove atenolol in the environment, both direct and indirect photodegradation, driven by sunlight play an important role. Among indirect photodegradation, singlet oxygen (¹O₂), as a pivotal reactive species, is likely to determine the fates of atenolol. Nevertheless, the kinetic information on the reaction of atenolol with singlet oxygen has not been well investigated and the reaction rate constant is still ambiguous. Herein, the reaction rate constant of atenolol with singlet oxygen is investigated directly through observing the decay of the ¹O₂ phosphorescence at 1270 nm. It is determined that the reaction rate constant between atenolol and ¹O₂ is 7.0×10⁵ (mol/L)$^{-1}\cdot$s^-1 in D₂O, 8.0×10⁶ (mol/L)$^{-1}\cdot$s^-1 in acetonitrile, and 8.4×10⁵ (mol/L)$^{-1}\cdot$s^-1 in EtOH, respectively. Furthermore, the solvent effects on the title reaction were also investigated. It is revealed that the solvents with strong polarity and weak hydrogen donating ability are suitable to achieve high rate constant values. These kinetics information on the reaction of atenolol with singlet oxygen may provide fundamental knowledge to the indirect photodegradation of $\beta$-blockers.     

Electrocatalytic Oxidation of Hydrogen Peroxide on Poly(m‐toluidine)‐Nickel Modified Carbon Paste Electrode in Alkaline Medium

The poly(m‐toluidine) film was prepared by using the repeated potential cycling technique in an acidic solution at the surface of carbon paste electrode. Then transition metal ions of Ni(II) were incorporated to the polymer by immersion of the modified electrode in a 0.2 M NiSO₄, also the electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)/Ni(II) couple. The electrocatalytic ability of Ni(II)/poly(m‐toluidine)/modified carbon paste electrode (Ni/PMT/MCPE) was demonstrated by electrocatalytic oxidation of hydrogen peroxide with cyclic voltammetry and chronoamperometry methods in the alkaline solution. The effects of scan rate and hydrogen peroxide concentration on the anodic peak height of hydrogen peroxide oxidation were also investigated. The catalytic oxidation peak current showed two linear ranges with different slopes dependent on the hydrogen peroxide concentration and the lower detection limit was 6.5 μM (S/N=3). The catalytic reaction rate constant, (k_h), was calculated 5.5×10² M^?1 s^?1 by the data of chronoamperometry. This modified electrode has many advantages such as simple preparation procedure, good reproducibility and high catalytic activity toward the hydrogen peroxide oxidation. This method was also applied as a simple method for routine control and can be employed directly without any pretreatment or separation for analysis cosmetics products.     

One‐Pot Fabrication of RGO–Ag3VO4 Nanocomposites by in situ Photoreduction using Different Sacrificial Agents: High Selectivity Toward Catechol Synthesis and Photodegradation Ability

Weak photon absorption and fast carrier kinetics in graphene restrict its applications in photosensitive reactions. Such restrictions/limitations can be overcome by covalent coupling of another photosensitive nanostructure to graphene, forming graphene‐semiconductor nanocomposites. Herein, we report one‐pot synthesis of RGO–Ag₃VO₄ nanocomposites using various sacrificial agents like ethanol, methanol, propanol and ethylene glycol (EG) under visible light illumination. The Raman spectral analysis and ¹³C MAS NMR suggest ethanol to be the best sacrificial agent among those studied. Thermal analysis studies, further, confirm the stability of the synthesized nanocomposite with ethanol as sacrificial agent. In view of this, the activity toward dye degradation was focused over the composites prepared via ethanol as sacrificial agent. It was observed and proved that cationic dyes could be degraded quantitatively and swiftly compared to anionic dyes (37.79%) in 1.5 h. This suggests that the surface of the nanocomposites is anionic as partial reduction takes place during synthesis process. In case of mixed dye degradation process, it was noticed that the presence of cationic dye doubles the degradation of anionic dye. The activity of these synthesized nanocomposites is more than five‐fold toward the phototransformation of phenol and photodegradation of textile dyes under visible light illumination.     

Photodegradation kinetics and byproducts identification of the Aflatoxin B1 in aqueous medium by ultra‐performance liquid chromatography–quadrupole time‐of‐flight mass spectrometry

A photodegradation study of Aflatoxin B₁ (AFB₁) in water solution was performed under UV irradiation at different AFB₁ initial concentrations and UV irradiation intensities. The effect of UV intensity on the AFB₁ photodegradation ratio is dominative, when compared with AFB₁ initial concentration. The photodegradation of AFB₁ was proved to follow first‐order reaction kinetics (R² ≥ 0.99). Three photodegradation products, i.e. P₁ (C₁₇H₁₄O₇), P₂ (C₁₆H₁₄O₆) and P₃ (C₁₆H₁₂O₇), were identified on the basis of low mass error and high matching property by ultra‐performance liquid chromatography–quadrupole time‐of‐flight mass spectrometry (UPLC–Q‐TOF MS), and the degradation pathway was proposed. This study first reports the appearance of these photodegradation products and the proposed degradation pathway in aqueous media. Copyright © 2010 John Wiley & Sons, Ltd.     

A Novel Fluorescent Reagent for Analysis of Hydrogen Peroxide

IntroductionTheoxidationofmanyclinicalsubstancesinbodyfluidsproducesaquantityofhydrogenperoxide ,sothedetermina tionoftracehydrogenperoxideisofconsiderableimportanceinclinicalchemistry .1Further,themonitoringofhydrogenperoxideisalsonecessarytoenvironmentalsciencesinceitisakeyspeciesinthereactionsofthetroposphere,beingin volvedinimportantreactionssuchasthecatalyzedoruncat alyzedaqueousphaseoxidationofSO2 andtheultraviolet en hancedaqueousphaseoxidationoforganicspecies.2 Uptonow ,variousmethods…     

SnFe2O4 Nanocrystals as Highly Efficient Catalysts for Hydrogen‐Peroxide Sensing

SnFe₂O₄ nanocrystals (NC), prepared with a simple one‐step carrier‐solvent‐assisted interfacial reaction process, were developed as highly efficient catalysts for hydrogen peroxide sensing. These NCs, with a size of around 7 nm, served as the sensing catalyst and were decorated onto the pore surfaces of a porous fluorine‐doped tin oxide (PFTO) host electrode, prepared from commercial FTO glass with a simple anodic treatment, to form the sensing electrode for hydrogen peroxide. The SnFe₂O₄ NCs‐loaded PFTO electrode exhibited an ultra‐high sensitivity of 1027 mA m ^?1 cm^?2 toward hydrogen peroxide, outperforming Pt NCs‐loaded PFTO electrodes. The SnFe₂O₄ NCs‐loaded PFTO electrode proved a promising relatively low cost, high performance sensing electrode for hydrogen peroxide.     

Effect of the Spacer Chain Length of Organic Dicarboxylic Acid on the Supramolecular Assembly of Two Ternary Zinc (II) Coordination Polymers Derived from Mixed Ligands

Two new Zn^II coordination polymers (CPs), [Zn₂(SA)₂(L)₂]_n ( 1 ) and [Zn(AA)(L)]_n ( 2 ) [L = 1,6‐bis(benzimidazol‐1‐yl)hexane, H₂SA = succinic acid, H₂AA = adipic acid], were synthesized via hydrothermal method and characterized by elemental analysis, infrared spectroscopy, and single‐crystal X‐ray diffraction. CP 1 possesses a sql network, which is further extended into a 3D supramolecular skeleton by non‐classical C–H ··· O hydrogen bonding interactions. CP 2 exhibits a 1D linear chain, which is further assembled into a 2D supramolecular layer by π ··· π stacking interactions. The solid state fluorescence properties of two Zn^II CPs were investigated. Both CPs present high photocatalytic activities for the degradation of methylene blue (MB) under UV light irradiation. The photodegradation efficiency using CP 1 as catalyst is 91.3 % and using CP 2 as catalyst is 85.0 %, respectively.     

Catalytic Adsorptive Stripping Voltammetry of Molybdenum: Redox Kinetic Measurements

The electrode mechanism of Mo(VI) reduction was studied under catalytic adsorptive stripping mode by means of square‐wave voltammetry (SWV). Mo(VI) creates a stable surface active complex with mandelic acid. The electrode reaction of Mo(VI)‐mandelic acid system undergoes as one‐electron reduction, exhibiting properties of a surface electrode process. In the presence of chlorate, bromate, and hydrogen peroxide, the electrode reaction is transposed into a catalytic mechanism. The experimental results are compared with the recent theory for surface catalytic reaction, enabling qualitative characterization of the electrode mechanism in the presence of different catalytic agents. Utilizing both the method of “split SW peaks” and “quasireversible maximum” the standard redox rate constant of Mo(VI)‐mandelic acid system was estimates as k_s=150±5 s^?1. By fitting the experimental and theoretical results, the following catalytic rate constants have been estimated: (8.0±0.5)×10⁴ mol^?1 dm³ s^?1, (1.0±0.1)×10⁵ mol^?1 dm³ s^?1, and (3.2±0.1)×10⁶ mol^?1 dm³ s^?1, for hydrogen peroxide, chlorate, and bromate, respectively.     

Chemical Oxidative Degradation of Acridine Orange Dye in Aqueous Solution by Fenton's Reagent

Degradation of acridine orange (AO) in aqueous solution by Fenton's reagent (Fe²⁺ and H₂O₂) was investigated. The effects of different reaction parameters such as initial AO concentration, pH value of solution, ferrous concentration, hydrogen peroxide concentration, and the presence of chloride ion on the oxidative degradation of AO were investigated. Under optimum conditions, 2 mM H₂O₂, 0.4 mM Fe²⁺ and pH 3.0, the initial 0.2 mM AO solution was reduced by 95.8% within 10 min. The primary intermediates of the degradation reaction of AO were identified. The analytical results indicated that the N‐de‐methylation degradation of AO dye took place in a stepwise manner to yield mono‐, di‐, tri‐, and tetra‐N‐de‐methylated AO species generated during the Fenton process. The probable degradation pathways were proposed and discussed.     

Electrocatalysis via Direct Electrochemistry of Myoglobin Immobilized on Colloidal Gold Nanoparticles

The direct electron transfer between immobilized myoglobin (Mb) and colloidal gold modified carbon paste electrode was studied. The Mb immobilized on the colloidal gold nanoparticles displayed a pair of redox peaks in 0.1 M pH 7.0 PBS with a formal potential of –(0.108 ± 0.002) V (vs. NHE). The response showed a surface‐controlled electrode process with an electron transfer rate constant of (26.7 ± 3.7) s ^?1 at scan rates from 10 to 100 mV s^?1 and a diffusion‐controlled process involving the diffusion of proton at scan rates more than 100 mV s^?1. The immobilized Mb maintained its activity and could electrocatalyze the reduction of both hydrogen peroxide and nitrite. Thus, the novel renewable reagentless sensors for hydrogen peroxide and nitrite were developed, respectively. The activity of Mb with respect to the pseudo peroxidase with a K_M^app value of 0.65 mM could respond linearly to hydrogen peroxide concentration from 4.6 to 28 μM. The sensor exhibited a fast amperometric response to NO₂^? reduction and reached 93% of steady‐state current within 5 s. The linear range for NO₂^? determination was from 8.0 to 112 μM with a detection limit of 0.7 μM at 3σ.     

A Multicommuted Flow‐based System for Hydrogen Peroxide Determination by Chemiluminescence Detection Using a Photodiode

Abstract

A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow‐cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III).

The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2–210 µmol l^?1 H₂O₂ with a LD of 1.8 µmol l^?1 H₂O₂ and coefficient of variations smaller than 0.8% for 1.0×10^?5 mol l^?1 and 6.8×10^?5 mol l^?1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 µg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved.     

Characterization and Catalytic Activity of New Metal‐organic Frameworks Resulted from Self‐assembly of Ph3SnCl,K[Cu(CN)2] and Nitrogen Donor Ligands

Five new metal‐organic frameworks (MOFs) of the general composition [Ph₃SnCu(CN)₂·L], where L=pyrazine (pyz) ( 1 ), methylpyrazine (mepyz) ( 2 ), 4,4′‐bipyridine (bpy) ( 3 ), trans‐1,2‐bis(4‐pyridyl)ethene (tbpe) ( 4 ) or 1,2‐bis(4‐pyridyl)ethane (bpe) ( 5 ), have been synthesized and characterized to test their potential applications as catalysts. The structures of the MOFs 1 – 5 mainly consist of Cu(CN)₂ building blocks connected by the Ph₃Sn cations and the bipodal ligand forming polymeric networks. They exhibit strong fluorescence in the solid state. Also, they are used as heterogeneous catalysts for the degradation of azo‐dyes, metanil yellow (MY) by diluted solution of hydrogen peroxide as oxidant. The reaction is first order with respect to MY dye, while the factors affecting the rate constant of the degradation reaction are investigated. The activation parameters of the reaction have been estimated and a possible mechanism has been proposed.