Concentrations Of Various Species Research Articles

UV-induced reactive species dynamics and product formation by chlorite

Chlorite (ClO2-) is a regulated byproduct of chlorine dioxide water treatment processes. The transformation of chlorite under UV irradiation into chloride (Cl-) and chlorate (ClO3-) involves reactive species chain reactions that could enhance chlorine dioxide water treatment efficiency while reducing residual chlorite levels. This study conducted a mechanistic investigation of chlorite phototransformation by analyzing reaction intermediates and stable end products, including chlorine dioxide (ClO2), free chlorine (HOCl/OCl-), hydroxyl‑radical (•OH), Cl-, and ClO3- through combined experimental and modeling approaches. Experiments were performed at UV254 irradiation in pure buffered water within the pH range of 6 to 8. Results indicated that the apparent quantum yields for chlorite phototransformation increased from 0.86 to 1.45, and steady-state •OH concentrations at 1 mM initial chlorite concentration rose from 8.16 × 10–14 M – 16.1 × 10–14 M with decreasing pH values. It was observed that under UV irradiation, chlorite acts as both a significant producer and consumer of reactive species through three distinct reaction pathways. The developed kinetic model, which incorporates optimized intrinsic chlorite quantum yields Φchloritein ranging from 0.33 to 0.39, effectively simulated the loss of oxidants and the formation of major products. It also accurately predicted steady-state concentrations of various species, including •OH, •ClO, Cl• and O3. For the first time, this study provides a comprehensive transformation pathway scheme for chlorite phototransformation. The findings offer important insights into the mechanistic aspects of product and oxidizing species formation during chlorite phototransformation.

Phenomenology of the Composition of PM2.5 at an Urban Site in Northern France

In this work, PM2.5 was sampled at Dunkerque, a medium-sized city located in northern France. The mean concentration of PM2.5 during the sampling period was 12.6 ± 9.5 μg·m−3. Samples were analyzed for elemental and organic carbon (EC/OC), water-soluble organic carbon (WSOC), humic-like substances (HULIS-C), water-soluble inorganic ions, and major and trace elements. The origin and the variations of species concentrations were examined using elemental enrichment factors, bivariate polar plot representations, and diagnostic concentration ratios. Secondary inorganic ions were the most abundant species (36% of PM2.5), followed by OC (12.5% of PM2.5). Secondary organic carbon (SOC) concentrations were estimated to account for 52% of OC. A good correlation between SOC and WSOC indicated that secondary formation processes significantly contribute to the WSOC concentrations. HULIS-C also represents almost 50% of WSOC. The determination of diagnostic ratios revealed the influence of anthropogenic emission sources such as integrated steelworks and fuel oil combustion. The clustering of 72 h air masses backward trajectories data evidenced that higher concentrations of PM2.5, OC, and secondary inorganic aerosols were recorded when air masses came from north-eastern Europe and the French continental sector, showing the considerable impact of long-range transport on the air quality in northern France.

Flow simulation in direct ethanol fuel cells using multifunctional anode catalysts

Fuel cells have been seen as a viable alternative to fossil fuel engines, mainly driven by environmental restrictions. In this work, a direct ethanol fuel cell is modeled using a dynamic model, which considers fuel and air flow, anode and cathode losses, membrane, multifunctional catalysts (Pt/C, Pt−Ru/C and Pt−Sn/C), temperature, and the variation of species concentration in relation to the current density, since the cell operation is influenced by them. The equations are discretized using the finite difference method and the integration is performed using the Rosenbrock method. The results obtained for the flow using the dynamic model developed reasonably agree with data found in the literature. The molar fractions of the species shown contribute to the understanding of the behavior of the reactive flow that occurs inside an ethanol fuel cell.

Sensitivity Analysis of Nanowire FET Biosensor

A nanowire junctionless FET biosensor has been modelled with COMSOL Multiphysics. The high sensitivity of the device in depletion regime was observed. The sensitivity dependence on variations of species concentration in analyte surrounding the nanowire has been studied. It has been demonstrated that the thinner is the nanowire, the higher is the sensitivity and even a single molecule affects the drain current. The model is useful for sensor optimization.

Determination of urea, phosphate, and potassium in agricultural runoff waters using electrochemical impedance spectroscopy.

Large-scale use of chemical fertilizers has resulted in the contamination of agricultural runoff waters by soil macronutrients NPK, whose detection is of significant interest. This work reports the determination of macronutrients in the form of urea (N), orthophosphate PO43- (P), and potassium K+ (K) in simulated agricultural runoff waters. Their solutions were prepared by extracting water-soluble constituents of soil. This'base' solution contains high concentrations of various species, including Cl-, SO42-, NO3-, PO43-, Na+, K+, and NH4+ along with natural organic matter. Predetermined amounts of urea (4 to 22.5 ppm), PO43- (7 to 50 ppm), and potassium K+ (25 to 250 ppm) were added to the base simulated runoff water to prepare standard stock solutions. Using stainless steel working and counter electrodes, a small AC perturbation (±10 mV vs. OCP, vs. Ag/AgCl) was applied and the frequency response of the working electrode-solution interface was measured from 1 Hz to 1 MHz. The interface itself was modeled as a suitable equivalent electrical circuit, and the magnitudes of its components were fitted from experimental data using nonlinear regression. It is observed that PO43- concentration is a linear function of charge transfer resistance arising from redox reaction, K+ concentration is a quadratic function of double-layer capacitance arising from its higher mobility, and urea concentration can be correlated as a linear function of constant phase element arising from its polarization in the presence of an applied electric field. The sensor exhibits good sensitivity, repeatability, and excellent performance against interfering species. These preliminary results show significant potential for development of a real-time or on-site sensing device.

VOC characteristics and their source apportionment in a coastal industrial area in the Yangtze River Delta, China

Volatile organic compounds (VOCs) are important precursors of secondary organic compounds and ozone, which raise major environmental concerns. To investigate the VOC emission characteristics, measurements of VOCs based on proton transfer reaction-mass spectrometry during 2017 were conducted in a coastal industrial area in Ningbo, Zhejiang Province, China. Based on seasonal variation in species concentration, the positive matrix factorization (PMF) receptor model was applied to apportion the sources of VOCs in each season. The PMF results revealed that unknown acetonitrile source, paint solvent, electronics industry, biomass burning, secondary formation and biogenic emission were mainly attributed to VOC pollution. Biomass burning and secondary formation were the major sources of VOCs and contributed more than 70% of VOC emissions in spring and autumn. Industry-related sources contributed 8.65%–31.2% of the VOCs throughout the year. The unknown acetonitrile source occurred in winter and spring, and contributed 7.6%–43.73% of the VOC emissions in the two seasons. Conditional probability function (CPF) analysis illustrated that the industry sources came from local emission, while biomass burning and biogenic emission mainly came from the northwest direction. The potential source contribution function (PSCF) model showed that secondary formation-related source was mainly from Jiangsu Province, northeastern China and the surrounding ocean. The potential source areas of unknown acetonitrile source were northern Zhejiang Province, southern Jiangsu Province and the northeastern coastal marine environments.

Combustion kinetic model optimization using the derived targets from MBMS experiments

Synchrotron-based molecular-beam mass spectrometry (MBMS) measurements can yield the concentrations of various species during combustion experiments. These quantitative data are helpful for combustion kinetic model development, validation, and optimization. The uncertainties of stable species can be limited within 30%, but for free radicals, the uncertainties can be large with a factor of 2–4 owing to the unknown photoionization cross sections. Therefore, measurements of free radicals are often used qualitatively for model validation, and how to utilize these measurements quantitatively for model optimization is still a challenge. In the present work, we propose to use derived targets, which are the ratios of the mole fractions of the same free radicals under two different experimental conditions, to optimize kinetic models. These derived targets have much smaller uncertainties compared to the original mole fractions because the unknown photoionization cross sections of the free radicals are canceled out, leading to more effective optimization results. To demonstrate this method, a dimethyl ether (DME) system and a methanol system are chosen as case studies. A global-sensitivity-based model analysis is first conducted to select informative targets for model optimization, i.e., derived targets of C2H5 in the DME system and the derived targets of CH3 in the methanol system. Model optimization is then performed using the ANN-MCMC method with these selected derived targets. The results of the global sensitivity analysis show that some important reactions can be highlighted when the derived targets are considered, while these reactions may not be important when considering only the original targets. The results of the comparison of two kinds of the optimized models show that better posterior models can be achieved by the model optimization based on derived targets than based on the original targets.

Numerical study of inhomogeneous deformation of gas diffusion layers on proton exchange membrane fuel cells performance

Gas diffusion layers play a critical role in the operation of proton exchange membrane fuel cells. As the most compressible component in proton exchange membrane fuel cells, the non-uniform deformation mainly occurs on the interface between bipolar plates and gas diffusion layers caused by the special channel-rib geometry of the flow field, which results in a non-uniform variation of physical properties of gas diffusion layers, such as porosity, effective electrical conductivity, and gas diffusivity, consequently affects the cell performance. In this paper, a two-dimensional, across-the-channel, multi-physics and two-phase flow model based on the spherical agglomerate assumption is developed to investigate the complicated relationships between the non-uniform deformation and variation of physical properties of the gas diffusion layers, as well as the cell performance. A modified diffusion coefficient is introduced to describe the effect of the variation of species concentration on the effective diffusion coefficient based on the Bruggeman formula. Simulation results show that an optimal cell performance can be achieved by balancing the variation of porosity, effective electrical conductivity, and effective gas diffusion coefficient with respect to different degrees of deformation of gas diffusion layers.

Determination of local defect density in diamond by double electron-electron resonance

Magnetic impurities in diamond influence the relaxation properties and thus limit the sensitivity of magnetic, electric, strain, and temperature sensors based on nitrogen-vacancy color centers. Diamond samples may exhibit significant spatial variations in the impurity concentrations hindering the quantitative analysis of relaxation pathways. Here, we present a local measurement technique which can be used to determine the concentration of various species of defects by utilizing double electron-electron resonance. This method will help to improve the understanding of the physics underlying spin relaxation and guide the development of diamond samples, as well as offering protocols for optimized sensing.

Impacts of Horizontal Resolution on Global Data Assimilation of Satellite Measurements for Tropospheric Chemistry Analysis

AbstractWe present the results from a global 0.56°‐resolution chemical data assimilation that integrates satellite observations of ozone, NO2, CO, HNO3, and SO2 from OMI, GOME‐2, SCIAMACHY, TES, MOPITT, and MLS. The assimilation is based on an ensemble Kalman filter technique and simultaneously optimizes ozone precursor emissions and concentrations of various species. The data assimilation at 0.56° resolution reduced model errors against independent surface, aircraft, and ozonesonde observations, which was larger than at coarser resolutions for many cases. By the data assimilation, surface model errors over major polluted regions were reduced by 33%–75% for NO2 and by 15%–18% for ozone. Agreements against assimilated observations for NO2 were improved using the data assimilation at 0.56° resolution by a factor of 1.5–3 compared to 2.8° resolution over major polluted regions. The estimated global total NOx emission over medium and strong source areas were smaller by 15% at 0.56° resolution than at 2.8° resolution associated with resolving small‐scale transport and chemistry processes, while 2%–26% smaller emissions were found for regional total emissions over Europe, the United States, China, India, and South Africa, with larger differences over megacities such as Los Angeles (−41%). The estimated ship emissions were 5%–7% smaller at 0.56° resolution over the Pacific and Atlantic. The 0.56°‐resolution data assimilation provides globally consistent analyses of the emissions and concentrations on a megacity scale, which benefit studies on air quality and its impact on human health at various spatial scales over different regions of the world.

Assessment of a flamelet approach to evaluating mean species mass fractions in moderately and highly turbulent premixed flames

Complex-chemistry direct numerical simulation (DNS) data obtained from lean methane-air turbulent flames are analyzed to perform a priori assessment of predictive capabilities of the flamelet approach to evaluating mean concentrations of various species in turbulent flames characterized by Karlovitz numbers Ka=6.0, 74.0, and 540. Six definitions of a combustion progress variable c are probed and two types of probability density functions (PDFs) are adapted: (i) actual PDFs extracted directly from the DNS data or (ii) presumed β-function PDFs obtained using the DNS data on the first two moments of the c-field. Results show that the mean density, the mean temperature, and the mean mass fractions of CH4, O2, H2O, CO2, CO, CH2O, CH3, and HCO are very well predicted using the temperature-based combustion progress variable cT and the actual PDF. For other considered species, the quantitative predictions are worse but still appear to be encouraging (with the exception of CH3O at Ka=540). The use of the flamelet library obtained from the equidiffusive laminar flame improves results for H2, HO2, and H2O2 at the highest Karlovitz number. Alternative definitions of the combustion progress variable perform worse and the reasons for this are explored. The use of the β-function PDF yields worse results for intermediate species such as OH, O, H, CH3, and HCO, with this PDF being significantly different from the actual PDF. Application of the flamelet approach to rates of production/consumption of various species is also addressed and implications of obtained results for modeling are discussed.

Prediction of mean radical concentrations in lean hydrogen-air turbulent flames at different Karlovitz numbers adopting a newly extended flamelet-based presumed PDF

A recent analysis (Lipatnikov et al., 2020) of complex-chemistry direct numerical simulation (DNS) data obtained from lean hydrogen-air flames associated with corrugated-flame (case A), thin-reaction-zone (case B), and broken-reaction-zone (case C) regimes of turbulent burning has shown that the flamelet concept (i) can predict mean concentrations of various species in those flames if the probability density function (PDF) for the fuel-based combustion progress variable c is extracted from the DNS data, but (ii) poorly performs for the mean rate W¯c of product creation. These results suggest applying the concept to evaluation of mean species concentration (but not the mean rate) in combination with another closure relation for W¯c whose predictive capabilities are better. This proposal is developed in the present paper whose focus is placed on studying a new flamelet-based presumed PDF P(c) for predictions of mean concentration of radicals in engineering computational fluid dynamics (CFD) applications. Analysis of the DNS data shows that (i) the flamelet PDF performs well at intermediate values of c in cases A and B, but should be truncated at small and large c, (ii) modeling P(c) in the radical recombination zone (i.e., at large c) is of importance for predicting mean concentrations of H,O, and OH. Accordingly, the flamelet PDF is truncated and combined with a uniform P(c) at large c. Moreover, the mean rate W¯c extracted from the DNS data is used to calibrate the PDF (the rate is considered to be given by another model). Assessment of the approach against the DNS data shows that it well predicts mean density, temperature, and concentrations of reactants, product, and the aforementioned radicals in cases A and B. In case C, the approach performs worse for OandOH at large c¯ and moderately underestimates the mean concentration of H in the entire flame brush.

The Aquifer-CO2Leak project: Numerical modeling for the design of a CO2 injection experiment in the saturated zone of the Saint-Emilion (France) site

The objective of the Aquifer-CO2Leak project is to get insights into carbon dioxide CO2 migration in aquifers within the context of Carbon Capture and Storage (CCS) and to test the different equipment necessary for CO2 monitoring. The underlying idea is to develop an experiment in the saturated zone (phreatic) of the underground limestone quarry located at Gironde department (France). It consists in injecting water, carrying dissolved gases (CO2 and krypton) and a fluorescent molecule, under controlled conditions. In this paper, we present the dimensioning study of the experiment by numerical simulations carried out using the simulator CooresFlow (IFPEN's in-house simulator for reactive transport in porous media). The important experiment parameters (injection flow rate, injected volume, the time to return in system equilibrium and wells location) were successfully estimated. In particular, the variation of species concentration in time and space was simulated and analyzed to define an experimental measurement schedule for the planned survey. Finally, a sensitivity analysis of the uncertain model parameters is presented. We found that the water table level and the dispersivity of the porous medium appear to be the most “sensitive” parameters.

Updated tropospheric chemistry reanalysis and emission estimates, TCR-2, for 2005–2018

Abstract. This study presents the results from the Tropospheric Chemistry Reanalysis version 2 (TCR-2) for the period 2005–2018 at 1.1∘ horizontal resolution obtained from the assimilation of multiple updated satellite measurements of ozone, CO, NO2, HNO3, and SO2 from the OMI, SCIAMACHY, GOME-2, TES, MLS, and MOPITT satellite instruments. The reanalysis calculation was conducted using a global chemical transport model MIROC-CHASER and an ensemble Kalman filter technique that optimizes both chemical concentrations of various species and emissions of several precursors, which was efficient for the correction of the entire tropospheric profile of various species and its year-to-year variations. Comparisons against independent aircraft, satellite, and ozonesonde observations demonstrate the quality of the reanalysis fields for numerous key species on regional and global scales, as well as for seasonal, yearly, and decadal scales, from the surface to the lower stratosphere. The multi-constituent data assimilation brought the model vertical profiles and interhemispheric gradient of OH closer to observational estimates, which was important in improving the description of the oxidation capacity of the atmosphere and thus vertical profiles of various species. The evaluation results demonstrate the capability of the chemical reanalysis to improve understanding of the processes controlling variations in atmospheric composition, including long-term changes in near-surface air quality and emissions. The estimated emissions can be employed for the elucidation of detailed distributions of the anthropogenic and biomass burning emissions of co-emitted species (NOx, CO, SO2) in all major regions, as well as their seasonal and decadal variabilities. The data sets are available at https://doi.org/10.25966/9qgv-fe81 (Miyazaki et al., 2019a).

An extended flamelet-based presumed probability density function for predicting mean concentrations of various species in premixed turbulent flames

Direct Numerical Simulation (DNS) data obtained by Dave and Chaudhuri (2020) from a lean, complex-chemistry, hydrogen-air flame associated with the thin-reaction-zone regime of premixed turbulent burning are analyzed to perform a priori assessment of predictive capabilities of the flamelet approach for evaluating mean species concentrations. For this purpose, dependencies of mole fractions and rates of production of various species on a combustion progress variable c, obtained from the laminar flame, are averaged adopting either the actual Probability Density Function (PDF) P(c) extracted from the DNS data or a common presumed β-function PDF. On the one hand, the results quantitatively validate the flamelet approach for the mean mole fractions of all species, including radicals, but only if the actual PDF P(c) is adopted. The use of the β-function PDF yields substantially worse results for the radicals’ concentrations. These findings put modeling the PDF P(c) on the forefront of the research agenda. On the other hand, the mean rate of product creation and turbulent burning velocity are poorly predicted even adopting the actual PDF. These results imply that, in order to evaluate the mean species concentrations, the flamelet approach could be coupled with another model that predicts the mean rate and turbulent burning velocity better. Accordingly, the flamelet approach could be implemented as post-processing of numerical data yielded by that model. Based on the aforementioned findings and implications, a new approach to building a presumed PDF is developed. The key features of the approach consist in (i) adopting a re-normalized flamelet PDF for intermediate values of c and (ii) directly using the mean rate of product creation to calibrate the presumed PDF. Capabilities of the newly developed PDF for predicting mean species concentrations are quantitively validated for all species, including radicals.

Evaluation of mean species mass fractions in premixed turbulent flames: A DNS study

Direct Numerical Simulation (DNS) data obtained by Dave and Chaudhuri (2020) from a lean, complex-chemistry, hydrogen-air flame associated with the thin-reaction-zone regime of premixed turbulent burning are analyzed (by adapting five alternative definitions of combustion progress variable c) in order to examine three different models that (i) are based on the flamelet paradigm and (ii) aim at evaluating mean concentrations of various species in applied CFD research into turbulent combustion. Mean mole fractions of all considered species and mean density are predicted if the laminar-flame profiles of species mole fractions and density, respectively, are directly averaged using a Probability Density Function (PDF) P(c). The best predictions are obtained by extracting P(c) from the DNS data and defining c based on hydrogen mass fraction. These predictions suggest that mean mole fractions of various species in a premixed turbulent flame can be evaluated at a post-processing stage of a CFD study by adopting P(c), obtained at the major stage of the simulations, to average a flamelet library. When applied in such a way, the flamelet paradigm is useful even for lean hydrogen-air flames and even at Karlovitz number as large as 13. If the same PDF is applied to average reaction rates from the same flamelet library, the mean rates of production/consumption of species n are poorly predicted, e.g. for radicals H, O, OH, HO2, and H2O2 if c is defined using hydrogen mass fraction. A hypothesis that conditioned rates 〈Wn|c〉 can be predicted using conditioned mole fractions 〈Xn|c〉, temperature 〈T|c〉, and density 〈ρ|c〉 is not supported either, e.g. for radicals O and OH. These differences between predictive capabilities of the first approach (directly averaging concentration profiles) and two other approaches (averaging reaction rates) are attributed to weakly (highly) non-linear dependencies of the concentrations (rates, respectively) on c.

Catalytic Synthesis of Oligosiloxanes Mediated by an Air Stable Catalyst, (C6F5)3B(OH2).

The utility of (C6F5)3B(OH2) as catalyst for the simple and environmentally benign synthesis of oligosiloxanes directly from hydrosilanes, is reported. This protocol offers several advantages compared to other methods of synthesizing siloxanes, such as mild reaction conditions, low catalyst loading, and a short reaction time with high yields and purity. The considerable H2O-tolerance of (C6F5)3B(OH2) promoted a catalytic route to disiloxanes which showed >99% conversion of three tertiary silanes, Et3SiH, PhMe2SiH, and Ph3SiH. Preliminary data on the synthesis of unsymmetrical disiloxanes (Si-O-Si') suggests that by modifying the reaction conditions and/or using a 1:1 combination of silane to silanol the cross-product can be favored. Intramolecular reactions of disilyl compounds with catalytic (C6F5)3B(OH2) led to the formation of novel bridged siloxanes, containing a Si-O-Si linkage within a cyclic structure, as the major product. Moreover, the reaction conditions enabled recovery and recycling of the catalyst. The catalyst was re-used 5 times and demonstrated excellent conversion for each substrate at 1.0 mol% catalyst loading. This seemingly simple reaction has a rather complicated mechanism. With the hydrosilane (R3SiH) as the sole starting material, the fate of the reaction largely depends on the creation of silanol (R3SiOH) from R3SiH as these two undergo dehydrocoupling to yield a disiloxane product. Generation of the silanol is based on a modified Piers-Rubinsztajn reaction. Once the silanol has been produced, the mechanism involves a series of competitive reactions with multiple catalytically relevant species involving water, silane, and silanol interacting with the Lewis acid and the favored reaction cycle depends on the concentration of various species in solution.

Influences of microtidal regime and eutrophication on estuarine zooplankton

This study describes the ecology of mesozooplankton in the shallows of the large central basin area of the Swan-Canning Estuary on the microtidal lower west coast of Australia during the mid-1980s when, as in most other south-western Australian estuaries, it was mesotrophic. As the vast majority of species reproduce within the estuary and there is a lack of a net upstream flow of bottom water during each tidal cycle to facilitate selective tidal transport, the populations of those species are considered autochthonous. Species restricted to the estuary accounted for 63% of the total number of species and 83% of abundance. Contributions by tychoplankton to total number of species (68%) and individuals (59%) exceeded the corresponding values of 18 and 39% for holoplankton and 14 and 2% for meroplankton. Low meroplankton values result from a paucity of benthic macroinvertebrate species with planktotrophic development. Comparisons with data for the shallow basin areas of the nearby highly eutrophic Peel-Harvey Estuary were used to indicate how mesozooplankton in the microtidal estuaries respond to excessive nutrient enrichment. The mean number of species in the Swan-Canning was essentially the same as in the Peel-Harvey, whereas concentrations were only half, reflecting the lower productivity of the former estuary. However, concentrations of the four most abundant species in the Swan-Canning, the amphipod Grandidierella propendatata, the calanoids Gladioferens imparipes and Acartia cf. clausi and a harpacticoid species, exceeded those of these species in the Peel-Harvey by between 1.6 and 11.7 times. Greater concentrations in the Swan-Canning were attributable to this mesotrophic system not undergoing the reduction in oxygen concentrations and/or environmental degradation, to which these species are susceptible. In contrast, concentrations of the amphipods Corophium minor and Tethygenia elanora and large nematodes, which are tolerant of degraded environmental conditions, were greater in the Peel-Harvey. Holoplankton made a far greater contribution in the Swan-Canning than Peel-Harvey, due to substantial numbers of copepods that benefit from good environmental conditions. Mesozooplankton composition in both estuaries underwent cyclical changes during the year due to time-staggered differences in seasonal concentrations of various species. Cyclical changes and variations in composition were more closely related to measured environmental variables in the Swan-Canning than Peel-Harvey estuaries. The concentrations of many species were greater at night than during the day presumably reflecting a nycthemeral response and/or low nocturnal oxygen concentrations at the bottom of the water column.

Electrochemical sensors as simple and cheap devices for rapid determination of various species in environmental samples

The electrochemical methods are very good tool for determination of trace concentrations of various species in water samples. The analysis carried out using these methods are usually simple, fast and also the cost of the required equipment is much lower comparing to other instrumental methods. Furthermore, the electroanalytical methods are easy to automate and computerize. Among five major groups of these methods (potentiometry, voltammetry, coulometry, conductometry and dielectrometry), potentiometry and voltammetry attract the greatest attention of researchers. In this paper, experimental results of research related to development of procedures (voltammetric and potentiometric) for the determination of elements in environmental water samples were presented. Due to their common occurrence in environment and possible toxic effects on living organisms, vanadium and nitrate ions were selected for investigation. Optimization of voltammetric procedure for V(V) determination were carried out in matrix containing different surfactants and humic acids, using lead film electrode as a working electrode. Results showed that only nonionic surfactant Brij-35 did not interfere with the voltammetric signal. Other surfactants as well as humic acids reduced the signal, and possibility of their elimination with suitable resins were also investigated. Potentiometric measurements were consisted of preparation and determination of analytical properties of nitrate ion-selective electrodes with solid contact. The results showed that among three different membrane composition, the best response was achieved by membrane containing: Ni(Phen)2, THTDPCl, PVC and NPOE in the ratio of 1:2:33:64 wt. %, respectively. With the detection limit of 2.8 × 10-6 mol L-1, the working concentration range from 5 × 10-5 to 1 × 10-1 mol L-1 and a slope of -55.1 mV per decade, this electrode showed good selectivity to sulfate, acetate, carbonate, dihydrogen phosphate, fluoride and chloride ions, and also good potential reversibility.

Simulation study on the microscopic characteristics of electrochemical Bunsen reaction in the sulfur–iodine cycle for renewable hydrogen production

The sulfur–iodine (SI) thermochemical water-splitting cycle is a promising hydrogen production process with high thermal efficiency and low pollution. The Bunsen reaction in the cycle using an electrochemical cell (EC) has been proposed and R&D on the cell has been carried out. To fill the knowledge gap in the microscopic characteristics of the electrochemical Bunsen reaction, a numerical study was conducted in this work. A two-dimensional, steady state, laminar and isothermal model of EC with detailed processes of flow, species transfer and electrode reactions was developed, and the simulated results showed good agreement with experimental data. The reaction rates, indicated in the form of species molar flux variation, increase with rising current density due to more electron transfer at a certain time, along with the increase of electric energy consumption from 9.1 W/m2 to 227.9 W/m2. Increasing the temperature inhibits the conversion and generation of species. Although higher flow rate reduces the flow residence time as well as the concentration variation of species, faster flow and higher bulk reactants concentration around the electrode surface lead to the increase of overall reaction rates. The consumption of pumping power also increases from 0.264 W/m2 to 6.661 W/m2 with rising flow rate. The optimal operating conditions of 4–5 A/dm2, 303–313 K and 0.01–0.02 m/s are obtained. The simulation favors a better understanding of the phenomena occurring in the EC and its further optimization.