14C in spent ion-exchange resins and process water from nuclear reactors: A method for quantitative determination of organic and inorganic fractions

A method of separately quantifying organic and inorganic ¹⁴C compounds present in spent ion-exchange resins and process water from nuclear power reactors has been developed. Extraction of carbon compounds is accomplished by means of acid stripping (inorganic ¹⁴C) and subsequent wet oxidation (organic ¹⁴C) or by N₂ purging in combination with a catalytic furnace (oxidized and reduced gaseous compounds) with organic and inorganic ¹⁴C species collected separately. Recovery experiments on simulated samples spiked with ¹⁴C-labeled sodium carbonate, sodium acetate and sodium formate, showed extraction yields of 94–98%. The sample-specific procedures were also tested on authentic samples of spent resins and reactor water with good results. Validation and reliability of the procedures are presented and the method is compared to previous methods reported in the literature.     

Liquid chromatography/mass spectrometry stable isotope analysis of dissolved organic carbon in stream and soil waters

A commercial interface coupling liquid chromatography (LC) to a continuous‐flow isotope ratio mass spectrometry (CF‐IRMS) instrument was used to determine the δ¹³C of dissolved organic carbon (DOC) in natural waters. Stream and soil waters from a farmland plot in a hedgerow landscape were studied. Based on wet chemical oxidation of dissolved organics the LC/IRMS interface allows the on‐line injection of small volumes of water samples, an oxidation reaction to produce CO₂ and gas transfer to the isotope ratio mass spectrometer. In flow injection analysis (FIA) mode, bulk DOC δ¹³C analysis was performed on aqueous samples of up to 100 μL in volume in the range of DOC concentration in fresh waters (1–10 mg C.L^–1). Mapping the DOC δ¹³C spatial distribution at the plot scale was made possible by this fairly quick method (10 min for triplicate analyses) with little sample manipulation. The relative contributions of different plot sectors to the DOC pool in the stream draining the plot were tentatively inferred on the basis of δ¹³C differences between the hydrophilic and hydrophobic components. Copyright © 2011 John Wiley & Sons, Ltd.     

The determination of sulfoxide configuration in five-membered rings using NMR spectroscopy and DFT calculations

Cyclic five-membered ring sulfoxides and sulfones were prepared by a stepwise in situ oxidation of the corresponding sulfides with meta-chloroperbenzoic acid in an NMR tube. The oxidation was followed by NMR and both ¹H and ¹³C NMR data were collected. The geometries of all of the compounds were optimized using the DFT B3LYP/6-31G⁷ method and the ¹³C and ¹H chemical shifts were calculated for geometry-optimized structures with the DFT B3LYP/6-31++G⁷ method. The calculated ¹³C chemical shifts induced by oxidation (Δδ values) were in very good agreement with the experimental data and could be used to determine the oxidation state of the sulfur atom (–S–, –SO–, –SO₂–). The characteristic differences of the induced oxidation chemical shifts of the carbon atoms in the α-position and β-position to sulfur were successfully used to distinguish between the diastereoisomeric sulfoxides and allowed configuration determination.     

Wet oxidation of trichloroethylene over well-characterized CoO x /TiO2 catalysts

The 5% CoO _x /TiO₂ catalyst, well-characterized earlier, consisting of complete CoTiO _x overlayers on Co₃O₄ nano-particles (“Type A”) after calcination at 843 K but of clean Co₃O₄ particles (“Type B”) after a continuous wet oxidation of trichloroethylene (TCE) at 310 K forca. 6 h, has been used to investigate the influence of operating variables on the activity and the stability of the Type B Co₃O₄ particles during wet catalysis. At 310 K, the catalyst exhibited a 48% steady-state conversion with a transient behavior in activity up toca. 1 h on stream. As the reaction temperature increased, higher performances were achieved and the transient period disappeared, which might be due to easier decapsulation of the Type A Co₃O₄ particles at higher temperatures to form the Type B Co₃O₄ particles very active for this wet oxidation reaction. All wet activities were equal to those based on the concentration of Cl^? ions produced, implying the complete oxidation of TCE to HCl and CO₂, and significant decrease in pH occurred because of the HCl formation. The supported CoO _x was very stable for the wet oxidation at 310 K, even forca. 36 h, and XPS measurements of samples of the catalyst following the wet oxidation for desired hours were in good agreement with our earlier proposed model for CoO _x species.     

The determination of sulfoxide configuration in six-membered rings using NMR spectroscopy and DFT calculations

Cyclic six-membered ring sulfoxides and sulfones were prepared by a stepwise in situ oxidation of the corresponding sulfides with meta-chloroperbenzoic acid in an NMR tube. The oxidation was followed by NMR spectra and the ¹H and ¹³C NMR data were collected. The geometries of all of the compounds were optimized using the DFT B3LYP/6-31G^∗∗ method and the ¹³C and ¹H NMR chemical shifts were calculated for geometry-optimized structures with the DFT B3LYP/6-31++G^∗∗ method. The calculated ¹³C NMR chemical shifts induced by oxidation (Δδ values) are in very good agreement with the experimental data and can be used to determine the oxidation state of the sulfur atom (-S-, -SO-, -SO₂-). The characteristic differences of the induced oxidation chemical shifts of carbon atoms at the α- and β-position to sulfur were successfully used for distinguishing between the diastereoisomeric sulfoxides.     

纳米TiO2膜用于光催化氧化测定化学需氧量的研究

A photocatalytic oxidation method for determination of chemical oxygen demand （COD） using nano-TiO2 film, based on the use of a nano-TiO2-Ce（SO4）2 system and electrochemical detection, was proposed. The technique was originated from the direct determination of the Ce（Ⅲ） concentration change resulting from photocatalytic oxidation of organic compounds. Ce（Ⅲ）, which was produced by photocatalytic reduction of Ce（SO4）2, could be measured at a multi-walled carbon nanotubes （MWNT） chemically modified electrode （CME）. The COD values by this method were calculated from the differential pulse voltammetry （DPV） current of Ce（Ⅲ） at the CME. Under the optimal operation conditions, the detection limit of 0.5 mg·L^-1 COD with the linear range of 1-600 mg·L^-1 was achieved. This method was also applied to determination of various COD of ground water and wastewater samples. The resuits were in good agreement with those from the conventional COD methods, i.e., permanganate and dichromate ones.     

Determination of total nitrogen in atmospheric wet and dry deposition samples

A microwave-assisted persulfate oxidation method followed by ion chromatographic determination of nitrate was developed for total nitrogen determination in atmospheric wet and dry deposition samples. Various operating parameters such as oxidation reagent concentrations, microwave power, and extraction time were optimized to maximize the conversion of total nitrogen to nitrate for subsequent chemical analysis. Under optimized conditions, 0.012 M K₂S₂O₈ and 0.024 M NaOH were found to be necessary for complete digestion of wet and dry deposition samples at 400 W for 7 min using microwave. The optimized extraction method was then validated by testing different forms of organic nitrogen loaded to pre-baked filter substrates and NIST SRM 1648 (urban particulate matter), and satisfactory results were obtained. In the case of wet deposition samples, standard addition experiments were performed. The suitability of the method for real-world application was assessed by analyzing a number of wet and dry deposition samples collected in Singapore during the period of March-April 2007. The organic nitrogen content was 15% (wet) and 30% (dry) of the total nitrogen. During the study period, the estimated wet fluxes for nitrate (NO₃⁻), ammonium (NH₄⁺), organic nitrogen (ON), and total nitrogen (TN) were 16.1 ± 6.5 kg ha⁻¹ year⁻¹, 11.5 ± 5.7 kg ha⁻¹ year⁻¹, 3.8 ± 1.5 kg ha⁻¹ year⁻¹and 31.5 ± 13.2 kg ha⁻¹ year⁻¹, respectively, while the dry fluxes were 2.5 ± 0.8 kg ha⁻¹ year⁻¹, 1.4 ± 0.9 kg ha⁻¹ year⁻¹, 2.3 ± 1.4 kg ha⁻¹ year⁻¹ and 7.5 ± 2.6 kg ha⁻¹ year⁻¹, respectively.     

In-situ synthesis of N,S co-doped hollow carbon microspheres for efficient catalytic oxidation of organic contaminants

Metal-free heteroatom doped nanocarbons are promising alternatives to the metal-based materials in catalytic ozonation for destruction of aqueous organic contaminants.In this study,N,S co-doped hollow carbon microspheres（NSCs） were synthesized from the polymerization products during persulfate wet air oxidation of benzothiazole.The contents of doped N and S as well as the structural stability were maneuvered by adjusting the subsequent N₂-annealing temperature.Compared with the prevai...     

Mineralization of aqueous phenolate solutions: A combination of irradiation treatment and wet oxidation

Wet oxidation (high-temperature, high-pressure oxidation of organic wastes in aqueous solution) and radiation technology were combined in γ-ray and electron beam induced oxidation of 4×10^?4–1×10^?2 mol dm^?3 Na-phenolate solutions in a wide O₂ concentration (1–20 bar pressure) and absorbed dose (0–50 kGy) range. Most experiments were made in stainless steel high pressure autoclave equipped with magnetic stirrer. The rate of oxidation was followed by chemical oxygen demand and total organic carbon content measurements. The rate was similar in γ-ray and pulsed electron beam irradiation and increased with O₂ concentration in the liquid.     

Experimental determination of the effect of temperature and oxygen concentration on the production of birch wood main fire emissions

The combustion process (efficiency and toxicity of combustion generated emissions) depends on the chemical composition and physical characteristics of materials, the oxidizing agents, and the temperature. This article will determine the influence of temperature (450 and 600?°C) and the volume of oxygen concentration (9, 15, and 21%) in an oxidizing atmosphere on the main emissions of burning White Birch wood (Betula verrucosa Ehrh.) The examined samples weighed 3?±?0.05?g; the average density was 540?kg/m³; and the absolute humidity was 8%. The samples were thermally loaded in a Setchkin furnace specially modified to enable the thermal sample in an atmosphere with an adjustable oxygen concentration and the withdrawal of fire emissions by means of UniGas C440 analyzer probes and BERNATH ATOMIC Modell 3006 analyzers. At 450?°C, the concentration of oxygen in the oxidation mixture did not significantly influence the maximum concentration of carbon monoxide (CO) and the total organic carbon (TOC) in the fire emissions. At 600?°C, the decrease of the oxygen concentration in the oxidation atmosphere caused a significant increase of the maximum concentration of CO and TOC in the fire emissions. However, the generally accepted presumption of a maximum concentration increase of CO in the emissions as a result of the oxygen (O₂) concentration decrease in the oxidation atmosphere has not been confirmed. The highest concentration of CO and TOC were measured in the initiation phase or closely after it.     

A solid composite electrode for the determination of the electrochemical oxygen demand of aqueous samples

A composite electrode containing graphite, paraffin, AgO and CuO is described for the determination of the electrochemical oxygen demand (EOD) of waste waters. The oxidation of dissolved organic compounds at the electrode is based on a heterogeneous chemical reaction of AgO/CuO with the organic constituents of the waste water. This chemical reaction can be followed by a solid state electrochemical oxidation of the formed Ag₂O/Cu₂O. The method has been tested with various organic compounds and applied to real samples of sewage water. The EOD values correlate well to BOD and COD values.     

Photoelectrochemical water oxidation improved by pyridine N-oxide as a mimic of tyrosine-Z in photosystem II

Artificial photosynthesis provides a way to store solar energy in chemical bonds with water oxidation as a major challenge for creating highly efficient and robust photoanodes that mimic photosystem II. We report here an easily available pyridine N-oxide (PNO) derivative as an efficient electron transfer relay between an organic light absorber and molecular water oxidation catalyst on a nanoparticle TiO₂ photoanode. Spectroscopic and kinetic studies revealed that the PNO/PNO⁺˙ couple closely mimics the redox behavior of the tyrosine/tyrosyl radical pair in PSII in improving light-driven charge separation via multi-step electron transfer. The integrated photoanode exhibited a 1 sun current density of 3 mA cm⁻² in the presence of Na₂SO₃ and a highly stable photocurrent density of >0.5 mA cm⁻² at 0.4 V vs. NHE over a period of 1 h for water oxidation at pH 7. The performance shown here is superior to those of previously reported organic dye-based photoanodes in terms of photocurrent and stability.

Stable and high photocurrent for water oxidation was achieved by an organic dye-sensitized photoanode with a pyridine N-oxide derivative as an efficient electron relay between the chromophore and molecular water oxidation catalyst.     

Characteristics of a novel UV-TiO2-microwave integrated irradiation device in decomposition processes

The efficiency of oxidation in wet decomposition procedures for organic materials can be of great importance to the quality of the analytical data from various measurement techniques. A novel, microwave-assisted, high-temperature/high-pressure UV-TiO₂ digestion procedure was developed for the accelerated decomposition of various biological samples. The technique is based on a closed, pressurized, microwave digestion apparatus (MW). UV irradiation is generated by immersed electrodeless Cd discharge lamp operated by the focused microwave field in the single polymer vessel. To enhance oxidation efficiency, a photocatalyst TiO₂ was added to the microwave heated Teflon bomb. Measures of digestion completeness were provided by the appearance of carbon content and determination of trace and minor elements, enabling a comparison of different digestion procedures and sample types. Compared with other digestion systems, unusually low residual carbon contents were obtained. For the organic compounds and biological samples digested, the residual carbon content was 1-2%, corresponding to a decomposition efficiency of 98-99%. The potential of the MW-UV-TiO₂ system was illustrated by the decomposition of four certified reference materials (serum, urine, milk, arsenobetaine solution) and subsequent determination of trace and minor elements. Recoveries between 92% and 107% were found.     

Amperometric sensor for nitrite using a glassy carbon electrode modified with thionine functionalized MWCNTs/Au nanorods/SDS nanohybrids

A sensitive nitrite (NO₂^‐) biosensor was fabricated by using sodium dodecyl sulfate (SDS), Au nanorods, and thionine functionalized MWCNTs (TH‐f‐MWCNTs) nanohybrids modified glassy carbon electrode. TH was covalently immobilized on the MWCNTs via a carbodiimide reaction. Comparing with MWCNTs/GCE, TH‐f‐MWCNTs/GCE displays higher catalytic activity toward the oxidation of NO₂^‐, since TH not only promoted the electronic transmission but also could improve the concentration of NO₂^‐ at the surface of the modified electrode in acidic solutions. The Au nanorods (AuNRs) were prepared through a simple wet chemical method and were characterized by TEM. The extremely high surface‐to‐volume ratios associated with one dimension nanostructures make their electrical properties extremely sensitive to species adsorbed on surfaces and result in excellent sensitivity and selectivity. SDS displays excellent film forming ability, which made the electrode stable. Under optimal conditions, the linear range for the detection of nitrite was 0.26 to 51 μM, and the low detection limit was 20 nM. In addition, the modified electrode was successfully applied to determine nitrite in real water samples. Copyright © 2012 John Wiley & Sons, Ltd.     

Highly Oriented Nitrogen-doped Carbon Nanotube Integrated Bimetallic Cobalt Copper Organic Framework for Non-enzymatic Electrochemical Glucose and Hydrogen Peroxide Sensor

The hierarchical three-dimensional nitrogen-doped carbon nanotube anchored bimetallic cobalt copper organic framework (NCNT MOF CoCu) is successfully synthesized by the direct growth approach using the high-temperature carbonization of bimetallic cobalt copper organic framework (MOF CoCu-500). The as-prepared NCNT MOF CoCu nanostructure possesses high-level activity for both glucose and hydrogen peroxide (H₂O₂) sensing molecules. The cyclic voltammetry (CV) and chronoamperometry (CA) studies demonstrate excellent electrocatalytic performance for the oxidation of glucose with a linear range of 0.05 to 2.5 mM, high sensitivity of 1027 μA mM⁻¹cm⁻², and the lowest detection limit of 0.15 μM. Similarly, the NCNT MOF CoCu nanostructure showed significantly higher H₂O₂ activity with a linear range of 0.05 to 3.5 mM, high sensitivity of 639.5 μA mM⁻¹cm⁻², and the lowest detection limit of 0.206 μM. Thanks to its special hierarchical nanoarchitecture, homogeneous nitrogen-doped carbon nanotubes, and highly graphitized carbon, which may be increased the synergistic effect between bimetallic CoCu and NCNT in the organic framework. The potentially effective fabricated sensor was also used as a suitable probe for the detection of glucose and H₂O₂ in the analysis of the real samples.     

Oxidation States of Iron in Doped TiO2-SiO2 Sol-Gel Powders: A 57Fe Mössbauer Study

Ceramic coatings obtained by sol-gel routes are more and more attractive for protective purposes. Improved resistance against wet corrosion of steels can be obtained by doping the covering layer with elements like for instance transition ones. It is of major importance to have a clear-cut knowledge of the oxidation state of the doping element, especially after different heat treatments which usually follow the deposition process. Here we report about the oxidation states of 5 wt.% iron doped TiO₂, SiO₂ and mixed sol powders obtained by the sol-gel method with alkoxide precursors added with FeSO₄, 7 H₂O in organic medium. The evolution of the Fe oxidation state versus various heat treatments is followed by ⁵⁷Fe Mössbauer spectrometry supplemented by XRD data. As-dried samples are amorphous and contain ferric Fe cations, with a local distorted oxygen environment. After heating at 500°C during 3 min, ferrous and ferric oxides are evidenced together solely for silica and mixed silica-titania powders, in marked contrast with titania powders where only ferric species exist. The complete ferric state is restored for all samples after annealing at 900°C for one hour.     

Cleaning of Porous Aluminium Titanate by Oxygen Plasma

The removal of organic contaminants from porous Al₂TiO₅ during treatment in oxygen plasma was studied by optical emission spectroscopy (OES). The samples of Al₂TiO₅ were immersed into water emulsion of mineral oil for 3 h to get soaked. Then, they were thoroughly cleaned in ultrasound to remove oil from the surface. Samples were later exposed to RF oxygen plasma at the pressure of 75 Pa. The plasma density was about 2 × 10¹⁶ m⁻³, the electron temperature was about 6 eV and the density of neutral oxygen atoms was about 2 × 10²¹ m⁻³. Optical emission spectra between 200 and 1,000 nm were measured continuously during plasma treatment. The CO peak resulting from oil oxidation reached a well-pronounced maximum between 100 and 150 s of plasma treatment. The maximum in CO corresponded well with a minimum in O peaks. Concentration of oil in the samples was estimated by energy dispersion X-ray analysis. Initially the samples showed high concentration of carbon (about 38 at.%), while after plasma treatment the carbon concentration decreased below the detection limit. The cleaning efficiency was explained by diffusion of oil towards the surface where it was removed by oxidation with oxygen radicals.     

Chemiluminescence system for automatic determination of chemical oxygen demand using flow injection analysis

A novel chemiluminescence (CL) system for automatic determination of chemical oxygen demand (COD) combined with flow injection analysis is proposed in this paper. In this system, potassium permanganate is reduced to Mn²⁺ which is first adsorbed on a strongly acid cation-exchange resin mini-column to be concentrated during chemical oxidation of the organic compounds at room temperature, while the excessive MnO₄⁻ passes through the mini-column to be waste, then the concentrated Mn²⁺ is eluted reversely and measured by the luminol-H₂O₂ CL system. The calibration graph is linear in the range of 4-4000 mg l⁻¹ and the detection limit is 2 mg l⁻¹. A complete analysis could be performed in 1.5 min including washing and sampling, giving a throughout of about 40 h⁻¹. The relative standard deviation was 4.4% for 10 mg l⁻¹ COD (n=11), 4.8% for 100 mg l⁻¹ COD (n=11). This CL flow system for determination of COD is very simple, rapid and suitable for automatic and continuous analysis. The presented system has been applied successfully to the determination of COD of water samples.     

Study on photocatalytic oxidation for determination of the low chemical oxygen demand using a nano-TiO2-Ce(SO4)2 coexisted system

A new photocatalytic system, nano-TiO₂-Ce(SO₄)₂ coexisted system, which can be used to determine the low chemical oxygen demand (COD) is described. Nano-TiO₂ powders is used as photocatalyst in this system. The measuring method is based on direct determination of the concentration change of Ce(IV) resulting from photocatalytic oxidation of organic compounds. The mechanism of the photocatalytic oxidation for COD determination was discussed and the optimum experimental conditions were investigated. Under the optimum conditions, a good calibration graph for COD values between 1.0 and 12 mg l⁻¹ was obtained and the LOD value was achieved as low as 0.4 mg l⁻¹. When determining the real samples, the results were in good agreement with those from the conventional methods.     

H2O2-鲁米诺-荧光素钠-K2CO3高灵敏化学发光法测定二氧化碳

在碱性介质中, CO₃^2－对H₂O₂氧化鲁米诺化学发光反应具有重要作用, 荧光素钠对该反应具有很强的增敏作用. 据此, 建立了化学发光法测定二氧化碳的新方法. 方法的线性范围为1.0×10^－10～5.0×10^－6 mol•L^－1 CO₃^2－, 检出限为 1.2×10^－11 mol•L^－1 CO₃^2－ (相当于5.3×10^－10 g•L^－1 CO₂). 该方法用于室内外空气中二氧化碳含量的测定, 相对标准偏差1.8%～2.1% (n＝11), 加标实验回收率97.6%～101.4%. 论文还探讨了反应的发光机理, 发光反应很可能是由溶液中的CO₃^2－与H₂O₂作用而产生的活性自由基引发, 荧光素钠对发光的增敏作用为化学能量转移过程.