Diffusion Coefficient Of Cd Research Articles

Evolution of Structure and Dynamic of Simulated CdTe Model According to the Melting Process

CdTe model containing 9955 atoms was built and simulated by the method of molecular dynamics (MD) with the Stillinger–Weber (SW) potential. The model was obtained by heating from 300K to 3000K at a rate of 1013 K/s. The structural properties of the model are investigated through the total energy per atom, the partial radial distribution functions (PRDFs), the coordination number distributions and the bond-angle distributions. Calculation results have shown that the model has a melting point of about 1370K and changes from tetrahedral to octahedral structure when the temperature of CdTe model is above the melting point. These results are consistent with the reported experimental and simulation results. In addition, the mobility of Cd and Te atoms is also researched through the mean squared displacement (MSD) and the diffusion coefficients of Cd and Te atoms.

Efficiency of a new allylagarose-assembled DGT in measuring Cd, Zn, and Pb bioavailability in sludge-treated soil

The purpose of this study was to assess and validate measures of cadmium (Cd), lead (Pb), and zinc (Zn) bioavailability in a contaminated calcareous soil treated with sewage sludge (0, 10, and 30 g kg −1 ) under peppermint ( Mentha pipertia L.) cultivation using new allylagarose-assembled diffusive gradients in thin-films technique (DGT). To achieve the best gel composition, various diffusive hydrogels were made from different amounts of acrylamide monomer (15, 20, and 25%) and allylagarose cross-linker (0.3, 0.4, and 0.6%). The DGT assembled with 15% acrylamide and 0.3% allylagarose was the best hydrogel based on the obtained swelling rate (3.2) and diffusion coefficients of Cd (5.81 ×10 cm 2 s −1 ), Pb (8.07 cm 2 s −1 ), and Zn (6.13 cm 2 s −1 ). Sewage sludge application increased resupply (R-value) and effective concentration (C E ) of Cd, Pb, and Zn. The highest amounts of C E -Zn (2202 μ g l −1 ), Cd (982.5 μ g l −1 ), and Pb (1847 μ g l −1 ) were observed in soil treated with 30 g kg −1 sewage sludge. Comparison of correlation revealed that 0.3% allylagarose-measured C E -Zn and Pb had a significant logarithmic correlation with the corresponding plant metals concentrations, while C E -Cd was linearly correlated with the plant Cd concentration. These results support the conclusion that the combination of 15% acrylamide and 0.3% allylagarose as a diffusive gel in DGT is a robust gel to predict metal bioavailability and can be reliably used to replace the patented gel cross-linked with agarose. • Increasing percentages of cross-linker led to a reduction in gel pore size. • The high swelling hydrogel facilitated the metals diffusion through the hydrogel. • Increasing sewage sludge level resulted in increasing the re-supply (R) of metals. • 15% acrylamide and 0.3% allylagarose gave the best estimate of bioavailability.

Uptake of cadmium by rice crop in sewage irrigated soil

The results of green house experiment indicated that the yield of root, shoot and total dry matter of rice increased from 0.18 to 0.23 g pot-1, from 1.49 to 1.87 g pot-1 and from 1.67 to 2.09 g pot-1, respectively with increasing levels of Cd-FA (fulvic acid). The dry matter yields, concentrations and uptake of Cd by rice were significantly and positively correlated with organic carbon and DTPA-extractable Cd in soil. Root density and root length of rice exhibited positive and significant correlation with organic carbon, CEC, EC and negative correlation with clay content of the soil. On the other hand, root radius and half distance between roots showed significant and negative correlation with these parameters. DTPA-extractable Cd increased with increasing levels of Cd-FA application in soils. A regression model developed was found to predict the uptake of Cd on the basis of root parameters (root radius, root length, root density, half distance between roots) and diffusion coefficient of Cd in soils with almost 95 % level of confidence.

Electrochemical Behavior of Cadmium in 1-Butyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)amide Room-temperature Ionic Liquid

Electrodeposition of cadmium (Cd) was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide (BMPTFSA) containing Cd(TFSA)2 as a Cd source with cyclic voltammetry and chronoamperometry on a glassy carbon electrode. The infrared spectroscopy showed Cd(II) in BMPTFSA is octahedrally coordinated with three TFSA–. Electrochemical reduction of Cd(II) to Cd(0) was suggested to be an electrochemically irreversible process involving 2 one-electron transfer steps. The diffusion coefficient of Cd(II) at 25°C was estimated to be 0.95×10−7cm2s−1. Electrodeposits obtained by galvanostatic and potentiostatic electrolysis were confirmed to be metallic Cd by X-ray diffraction and energy dispersive X-ray analysis. The nucleation process and the surface morphology of the electrodeposited Cd were found to depend on the applied potential, probably due to the change in the electric double layer structure by accumulation of BMP+ at the negatively polarized electrode surface. Furthermore, Cd nanoparticles were obtained in the ionic liquid by potentiostatic cathodic reduction at −2.6V vs. Ag/Ag(I).

First-principles multiple-barrier diffusion theory: The case study of interstitial diffusion in CdTe

The diffusion of particles in solid-state materials generally involves several sequential thermal-activation processes. However, presently, diffusion coefficient theory only deals with a single barrier, i.e., it lacks an accurate description to deal with multiple-barrier diffusion. Here, we develop a general diffusion coefficient theory for multiple-barrier diffusion. Using our diffusion theory and first-principles calculated hopping rates for each barrier, we calculate the diffusion coefficients of Cd, Cu, Te, and Cl interstitials in CdTe for their full multiple-barrier diffusion pathways. As a result, we found that the calculated diffusivity agrees well with the experimental measurement, thus justifying our theory, which is general for many other systems.

Effective concentration difference model to study the effect of various factors on the effective diffusion coefficient in the dialysis membrane

Cellulose acetate dialysis membrane (CDM) has been used in the diffusive gradients in thin films (DGT) technique, where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. Effective concentration difference model (ECDM), based on the assumption that the effective diffusion coefficient of metal ion in the dialysis membrane is determined by the effective concentration difference (Δ C e) across the dialysis membrane, is proposed and applied to study the effect of ionic strength, binding agent, ligands and Donnan potential on the effective diffusion coefficient. The effective diffusion coefficients of Cd 2+ through the dialysis membrane immersed in receptor solutions with binding agent were almost the same as those in receptor solutions without binding agent at higher ionic strengths (0.01–1 M) but much higher than those at lower ionic strengths (0.001–0.0001 M). The effective diffusion coefficients of Cd 2+ through the dialysis membrane immersed in deionized water receptor solutions with binding agent were not significantly different from those in synthetic receptor solutions (receptor solutions with various ionic strengths) with binding agent. The DGT-labile fractions were measured in synthetic solutions and natural waters, which indicated that the effective diffusion coefficients, through the dialysis membrane immersed in the deionized water solution with binding agent as receptor solution and in the spiked natural water as source solution, were more suitable for DGT application.

Square wave voltammetry of concentrated analytes in fully supported solutions – Cd(II)/Cd(Hg) couple in NaNO 3 medium

The influence of significant ohmic potential drop on diffusion-controlled peak currents in square wave voltammetry at macroelectrodes can be drastically reduced by appropriate choice of the square wave amplitude. This allows direct determinations of unusual high concentrations. The experimental verification of theoretical predictions and the analytical procedure validation are performed using a static mercury drop electrode and various concentrations of Cd(II) in 0.1 or 1 M NaNO 3. Diffusion coefficients of Cd(II) and apparent standard potentials of the Cd(II)/Cd(Hg) couple in these media are reported.

Cd 2+ transfer across water/1,2-dichloroethane microinterfaces facilitated by complex formation with 1,10-Phenanthroline

The transfer of Cd 2+ facilitated by 1,10-Phenanthroline (phen) was investigated at the microinterface of two immiscible electrolyte solutions, hosted by a 25 μm diameter orifice of a micropipette. Cyclic voltammetry (CV) was employed to examine the transfer in the conditions of the ligand (organic phase) in excess and Cd 2+ (aqueous phase) in excess. In these conditions, asymmetric (peak-shaped in the forward scan and steady state in the backward scan), and reversible steady state (for the two scan directions) voltammograms were observed. The dependence of half-wave potential on the ligand concentration suggested that the equilibrium was effectively displaced towards a 1:3 (Cd 2+:ligand) stoichiometry, with a formation constant, β 3 = 3.9 × 10 29. The diffusion coefficients of Cd 2+ in the aqueous solution and those of phen, Cd(phen) 3 2+ in organic phase were evaluated to be 6.5 × 10 −6, 5.8 × 10 −6, and 5.1 × 10 −6 cm 2 s −1 respectively, using CV.

Study of cadmium–humic interactions and determination of stability constants of cadmium–humate complexes from their diffusion coefficients obtained by scanned stripping voltammetry and dynamic light scattering techniques

Diffusion coefficients of Cd–humate complexes are dependent on pH and [Cd]/[Humic] Acid (HA)] ratio in a Cd–HA system. These two factors mainly control the mass transport and complexation kinetics of Cd that may influence bioavailability and toxicity of Cd species in environmental systems. Determination of diffusion coefficients of Cd–HA systems by Scanned stripping voltammetry and dynamic light scattering techniques can provide a better understanding of the systems and can be very useful for extracting other speciation parameters of the systems. This study revealed that Cd 2+ ion along with small dynamic Cd complexes was predominantly present in a Cd–HA system at pH 5 with high diffusion coefficients. HA molecules were in aggregated form at pH 5. However, HA molecules were in disaggregated form at pH 6 and concentrations of Cd 2+ ion and small Cd-dynamic complexes decreased with a decrease in diffusion coefficients of Cd complexes at this pH due to formation of Cd–humate complexes. No further decrease in the hydrodynamic radii of HA was observed with the increase of pH from 6 to 7. The Cd–humate system partially lost its lability at pH 7. Conditional stability constants were calculated for Cd–humate complexes by combining the diffusion coefficient data obtained by two techniques. The log K values calculated in this study are in good agreement with the data available from the literature.

Numerical design of a card and related physicochemical phenomena occurring inside agarose-immobilized bacteria: A valuable tool for increasing our knowledge of biosensors

The detection of heavy metals in the environment constitutes a very important challenge for European policies that focus on health and safety. Biosensors complement the physicochemical methods for the detection of heavy metals and toxic organic substances and yet are also a strong alternative. Several strains of bioluminescent bacteria were created in our laboratory to detect heavy metals, such as the Escherichia coli pBzntlux strain for cadmium detection. These bacteria were immobilized on agarose membrane of a 64-well card which was designed without specific knowledge of fluidic theory. The response of the E. coli pBzntlux strain immobilized in agarose was heterogeneous and necessitated a long induction time. We decided to use the multiphysics software COMSOL, which is capable of combining several differential equations (hydrodynamics, heat and mass transfer) in order to optimize hydrodynamics and transfer phenomena when bioluminescence occurs. As a result, the new card gave an excellent response with a shorter induction time and better homogeneity. To explain the signal of the new improved card, a diffusion study of Cd 2+ and oxygen for each card was carried out. The diffusion coefficients of Cd 2+ and oxygen in the agarose membrane were assessed to model the transfer kinetics within the immobilized matrix. Simulations showed that after 30 min (induction time) the inducer diffuses through the whole thickness of the well and does not restrict the bioluminescence. However, the oxygen concentration decreases from 100% at the top of the well to 10% at a depth of 3 mm; this result agrees with the experimental profile of bioluminescence (9 × 10 9 RLU at 1 mm falling to 4.2 × 10 3 RLU at 3 mm). We can suppose that the bioluminescence was restricted by the oxygen at the bottom of the wells. It justifies the improved signal of the new card (Card 2) as its low thickness resulted in the emitted light being less faded and diluted. This research provided a new insight into the behavior of chemicals within an immobilized matrix and the numerical design approach led to a better understanding of the hydrodynamics.

Adsorption of Cd(II) and Pb(II) from aqueous solutions on activated alumina

The ability of activated alumina as synthetic adsorbent was investigated for adsorptive removal of Cd(II) and Pb(II) ions from aqueous solutions. Various physico-chemical parameters such as pH, initial metal ion concentration, and adsorbent dosage level and equilibrium contact time were studied. The optimum solution pH for adsorption of Cd(II) and Pb(II) from aqueous solutions was found to be 5. Kinetics data were best described by pseudo-second order model. The effective particle diffusion coefficient of Cd(II) and Pb(II) are of the order of 10 − 10 m 2 / s . Values of mass transfer coefficient were estimated as 4.868 × 10 − 6 cm / s and 6.85 × 10 − 6 cm / s for Cd(II) and Pb(II) adsorption respectively. The equilibrium adsorption data for Cd(II) and Pb(II) were better fitted to Langmuir adsorption isotherm model. The thermodynamic studies indicated that the adsorption was spontaneous and exothermic for Cd(II) adsorption and endothermic for Pb(II). The sorption energy calculated from Dubinin–Radushkevich isotherm were 11.85 kJ/mol and 11.8 kJ/mol for the adsorption of Cd(II) and Pb(II) respectively which indicated that both the adsorption processes were chemical in nature. Desorption studies were carried out using dilute mineral acids. Application studies carried out using industrial waste water samples containing Cd(II) and Pb(II) showed the suitability of activated alumina in waste water treatment plant operation.

Removal of Cd(II) from aqueous solutions using clarified sludge

Clarified sludge is a major waste generating during steel making process. In India and in most industrial countries, the use of clarified sludge as a road ballast and land filter has had a very long history. In present study, clarified sludge has been characterized and used for the removal of Cd(II) from aqueous solutions. The effect of pH, adsorbent dosage, adsorbate concentration, contact time and temperature on adsorption process was studied in batch experiments. Kinetics data were best described by pseudo-second order model. The effective diffusion co-efficient of Cd(II) is of the order of 10 −11 m 2/s. The maximum uptake was 36.23 mg/g. The adsorption data can be well described by Langmuir isotherm. The result of the equilibrium studies showed that the solution pH was the governing factor affecting the adsorption. Mass transfer analysis was also carried out for the adsorption process. The thermodynamic studies indicated that the adsorption was spontaneous and exothermic in nature. The sorption energy calculated from Dubinin–Radushkevich isotherm indicated that the adsorption process is chemical in nature. Desorption as well as the application studies were carried out considering the economic viewpoint of wastewater treatment plant operations.

Use of Diffusive Gradients in Thin Films To Measure Cadmium Speciation in Solutions with Synthetic and Natural Ligands: Comparison with Model Predictions

The performance of the technique of diffusive gradients in thin films (DGT) was characterized in well-defined systems containing cadmium with chloride and nitrate ions, simple organic ligands (nitrilotriacetic acid and diglycolic acid), and Suwannee river fulvic acid for the pH range 5-8. Cd was fully labile in all Cd, Cl-, and NO3- solutions tested (I= 0.1 and 0.01 M), even atvery low Cd concentrations (10 nM), consistent with there being no binding of Cd to the diffusive gel. Diffusion coefficients of Cd-nitritotriacetic acid (NTA) and Cd-diglycolic acid (DGA) species were measured and found to be ca. 25-30% lower than the equivalent coefficient for free metal ions. These values were used to calculate concentrations of labile Cd from DGT measurements in solutions of Cd with NTA or DGA. Cd-NTA and Cd-DGA species were found to be fully DGT-labile. DGT devices that used a diffusive gel with a reduced pore size, which retarded the passage of fulvic acid species through the gel, were used to estimate the proportion of Cd complexed by fulvic acid. These results were compared with predictions of the solution speciation from models with default parameter values. ECOSAT, incorporating the NICA-Donnan model, correctly predicted the magnitude of the binding and its pH dependence, while predictions from WHAM V (with humic ion binding model V) and WHAM 6 (with humic ion binding model VI) were less satisfactory at predicting the pH dependence. Reasonable fits to the data could be obtained from WHAM 6 when the effective binding constant log K(MA) was changed from 1.6 to 1.5, the value of deltaLK1 from 2.8 to 1.0 to minimize the dependence on pH, and the value of deltaLK2 from 1.48 to 1.0 to decrease the strength of the strong bidentate and tridentate binding sites.

Electrophoretic method for the determination of diffusion coefficients of ions in aqueous solutions*

The electrophoretic method was recently developed for the determination of diffusion coefficients of ions in aqueous solution. By solving the Fick's second law in the presence of unlimited media and constant quantity of diffusing species we obtain a relationship between the diffusion coefficient and the standard deviation of the distribution profile. The diffusion coefficients of Cd(II), In(III), Zr(IV), Hf(IV), Pu(VI) and [InDTPA]2− in nitric acid solution were determined as well as the effective charge of In-DTPA complex at pH 4.50.

Diffusion at Au(100)/Cd 2+ interface during electrodeposition

The kinetics of thin alloy film formation and growth within the underpotential range of Cd electrodeposition on Au(100) have been studied at room temperature in 50 mM H 2SO 4+1 mM CdSO 4 solution. Calculations of the diffusion coefficients of Cd in the Au electrode surface, together with in situ atomic force microscopy (EC-AFM) observation and polarization experiments, have shown that the overall alloying process at the Au(100)/Cd 2+ interface consists of two processes: one very fast, which occurs within 2 ML and is characterized by D≈10 −16 cm 2 s −1; and another one, much slower, which is characterized by D≈10 −18 cm 2 s −1, suggesting a solid state diffusion process. The concentration distribution of Cd in the Au electrode surface was obtained. Based on this new kinetic approach to the alloying process at the metal/electrolyte interface, a mechanism was proposed for the surface alloying process that occurs in the underpotential region.

High resolution transmission electron microscopy determination of Cd diffusion in [formula omitted] single quantum well structures

The diffusion coefficient D( T) of Cd in CdSe ZnSe single quantum well (SQW) structures grown pseudomorphically on GaAs(001) is determined by high resolution transmission electron microscopy of annealed SQWs and subsequent digital analysis of lattice images. SQWs of 2 monolayer (ML) thickness were grown by molecular beam epitaxy. During growth the CdSe quantum wells (QWs) broaden to about 7 ML CdZnSe as measured by reflection high energy electron diffraction (RHEED). We find for the diffusion coefficient of Cd in ZnSe at temperatures between 340 and 400° C D( T) = 1.9 × 10 −4 [cm 2/s] · exp(− 1.8 [eV]/ kT).

Electrochemical Behavior of the Cd(II)/Cd(Hg) System in Aqueous Mixtures of Diols and Triols

The electrochemical behavior of the Cd(II)/Cd(Hg) couple (Cd(II) concentration ) in aqueous mixtures of 1,4‐butanediol (BD) and glycerol (GL) containing has been studied. The reversible half‐wave potentials, the diffusion coefficients, and the Walden products for Cd(II) have been determined by polarography, whereas the diffusion coefficient of Cd in mercury, the transfer coefficient for Cd(II) electroreduction, and the apparent standard rate constants have been obtained by cyclic voltammetry. The standard free energies of transfer of 1 mole of Cd(II) ions from water to BD‐water and to GL‐water mixtures are found to be always negative, indicating a higher stability of Cd(II) in organic‐aqueous mixtures than in pure water. The break‐up of these values into electrostatic and chemical contributions shows that all organic‐aqueous mixtures used here are more basic than pure water, and that Cd(II) solvation increases with the mole fraction of BD or GL. The structural properties of the liquid mixtures are analyzed using the Walden products at different BD or GL levels. The changes in the kinetics of the Cd(II)/Cd(Hg) system with solvent composition are discussed in terms of existing models. Results obtained are compared with those previously reported in aqueous mixtures of ethylene glycol and 1,2‐propanediol.

The influence of high pressure (up to 10 kbar) on the limiting currents of the Cd(II)/Cd(Hg) system

The electroreduction of cadmium(II) at a mercury electrode and the oxidation of cadmium amalgam in 4.0 M NaCl at pressures ranging from 0.001 to 10 kbar, using cyclic voltammetry and chronoamperometry, revealed a moderate decrease in the limiting currents and diffusion coefficients of Cd II in solution and Cd in mercury. The partial molar volume of the diffusion activation calculated from these dependences is equal to 1.1–1.2 and 0.93 cm 3 mol −1 for diffusion in 4.0 M NaCl and in mercury, respectively. The formal potentials of the Cd II/Cd(Hg) system expressed versus the ferrocene-ferricinium ion electrode as a function of pressure led to a value of 10.7 cm 3 mol −1 for the volume of the electroreduction reaction of Cd II.

Development and Laboratory Investigations of a Denuder Sampling System for the Determination of Heavy Metal Species in Flue Gases at Elevated Temperatures

Abstract A denuder sampling system was developed to measure volatile metals at elevated temperatures. By using the denuder technique it is possible to avoid condensation and adsorption losses in the sampling line. To investigate the behavior of heavy metal species under different physical and chemical conditions, a laboratory scale quartz stack was built. Metal aerosol generators based on evaporation, diffusion and condensation are described. The diameter of the generated particles varied between 0.05–0.3 μm. The day to day reproducibility of the generation varied between 0.6-5.0% for chromium and 2.8–4.0% for cadmium (95% stat. significance). Denuders coated by elemental silver seem to be an efficient means for sampling of elemental Cd at 200°C. The diffusion coefficient of Cd was calculated from experimental data, and the value of (0.42±0.04) cm2/s was obtained. A detection limit of 0.2 μg/m3 for Cd determination can be reached by using a Ag-denuder, when a sampling time of 30 min and a flow rate of 60l...

Rotating ring disk electrode in molten chloride

A rotating ring disk electrode rrde assembly for use in molten chloride at 723 K has been constructed. The electrode is made of nickel and high purity alumina. The rotating electrode sealing is made of glass cloth. By the use of this rotating ring disk electrode, cathodic reduction of CdCl 2 in molten LiCl-KCl eutectic melt at 723 K has been investigated in detail. The rotating ring disk system voltammograms have been obtained at rotation velocities of 500–3000 rpm and composition ranging from 0.002 to 0.1 M. As a result of rrde experiments, the existence of monovalent cadmium ion has been confirmed in LiCl-KCl. The standard potential of Cd(II)/Cd(0) is 1.98±0.07 V, and that of Cd(II)/Cd(I) is 2.3±0.1 V vs Li/Li +, respectively. From the dependence of the limiting current on the rotation velocity and concentration a diffusion coefficient of Cd(II) ion has been estimated to be D Cd (II)=2.1 (±0.3) x 10 −5 cm 2s −1 (2.1(±0.3) x 10 −9 m 2s −1).