Cadmium atomic layers on tellurium electrodes

The process of electrodeposition of atomic layers of cadmium Cd_ad at order of magnitude polycrystalline tellurium electrodes at potentials in excess of equilibrium potential E _Cd ²⁺/_Cd (underpotential deposition, UPD) is studied. In acid sulfate solutions (0.1 M H₂SO₄ + 0.05 M CdSO₄), the magnitude of underpotential (underpotential shift) ΔE ^UPD = 0.41 V. In cyclic voltammograms, the anodic oxidation of Cd_ad is recorded in the form of two peaks of anodic current that are displaced relative to one another in the potential scale (weakly and strongly bound adatoms). The cadmium UPD process on tellurium is accompanied by the diffusion of cadmium into the bulk of tellurium and a transition from a 2D structure Cd_ad/Te to 3D CdTe nanostructures, which are distributed in the tellurium matrix. In contrast with tellurium, the Te/CdTe_nano heterostructure exhibits photoelectrochemical activity, i.e. it generates a cathodic photocurrent.     

Acid-base properties of the surfaces of CdxHg1–xTe solid solutions

The acid-base properties of actual CdTe and CdHgTe surfaces were investigated by means of non-aqueous conductometric titration for pHpzc determination, mechanochemistry, and UV spectroscopy. It was shown that the alkaline nature of their surface was due to the dissociative adsorption of atmospheric water flowing on the coordination-saturated surface atoms of cadmium with vacancy defects. The adsorbed water was involved in the formation of tellurium oxide TeO₂ and H₂TeO₃ tellurous acid in the dispersion of CdTe and CdHgTe.     

Electrodeposition of cadmium telluride from electrolytes based on ethylene glycol

Electrochemical behavior of cadmium and tellurium ions in their joint reduction on a glassy carbon electrode in a nonaqueous electrolyte based on ethylene glycol was studied. An X-ray phase analysis and transmission electron microscopy were used to determine the phase composition and particle size of the electrodeposited CdTe films.     

The Isoelectric Point of an Exotic Oxide: Tellurium (IV) Oxide

The pH-dependent surface charging of tellurium (IV) oxide has been studied. The isoelectric point (IEP) of tellurium (IV) oxide was determined by microelectrophoresis in various 1-1 electrolytes over a concentration range of 0.001–0.1 M. In all electrolytes studied and irrespective of their concentration the zeta potential of TeO₂ was negative over the pH range 3–12. In other words the IEP of TeO₂ is at pH below 3 (if any). TeO₂ specifically adsorbs ionic surfactants, and their presence strongly affects the zeta potential. In contrast the effect of multivalent inorganic ions on the zeta potential of TeO₂ is rather insignificant (no shift in the IEP). In this respect TeO₂ is very different from metal oxides.     

Conductometric studies and application of new Schiff base ligand as carbon paste electrode modifier for mercury and cadmium determination

A new chemically modified carbon paste electrode by 2,2?-((pyridine-2,6-diylbis(azanylylidene))bis(methanylylidene))diphenol (L) ligand has been made and used as a sensor for determination of trace mercury and cadmium ions with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. Complexation studies of the ligand with Cu²⁺, Zn²⁺, Hg²⁺, Ni²⁺ and Cd²⁺ ions by conductometric method in acetonitrile–ethanol mixture at 25°C show that the ML complexes have formed. The formation constants of complexes were calculated from the computer fitting of the molar conductance–mole ratio data, and the stability of the resulting complexes varied in order of Cd²⁺ > Hg²⁺ > Cu²⁺ > Zn²⁺ > Ni²⁺. Then a simple and effective chemically modified carbon paste electrode with L was prepared, and the electrochemical properties and applications of the modified electrode were investigated. Under the optimal conditions, the detection limit was 0.0494 μg L^?1 and 0.0782 μg L^?1 for cadmium and mercury ions, respectively, and the linear range for both metal ions were from 1 to 100 μg L^?1. The electrode shows high sensitivity, reproducibility and low cost, and was successfully applied to determination of Cd²⁺ and Hg²⁺ ions in water samples with recovery in the range of 97–101%.     

Ligand displacement-induced fluorescence switch of quantum dots for ultrasensitive detection of cadmium ions

This paper reports the construction of a simple CdTe quantum dots (QDs)-based sensor with 1,10-phenanthroline (Phen) as ligand, and the demonstration of a novel ligand displacement-induced fluorescence switch strategy for sensitive and selective detection of Cd²⁺ in aqueous phase. The complexation of Phen at the surface quenches the green photoluminescence (PL) of QDs dominated by a photoinduced hole transfer (PHT) mechanism. In the presence of Cd²⁺, the Phen ligands are readily detached from the surface of CdTe QDs, forming [Cd(Phen)₂(H₂O)₂]²⁺ in solution, and as a consequence the PL of CdTe QDs switches on. The detection limit for Cd²⁺ is defined as ∼0.01 nM, which is far below the maximum Cd²⁺ residue limit of drinking water allowed by the U.S. Environmental Protection Agency (EPA). Two consecutive linear ranges allow a wide determination of Cd²⁺ from 0.02 nM to 0.6 μM. Importantly, this CdTe QDs-based sensor features to distinctly discriminate between Cd²⁺ and Zn²⁺, and succeeds in real water samples. This extremely simple strategy reported here represents an attempt for the development of fluorescent sensors for ultrasensitive chemo/biodetection.     

Electrosynthesis of cadmium selenide films on a selenium-modified gold surface

A two-step method for the growth of CdSe films is described that is based on the initial chemical modification of a polycrystalline gold surface with a selenium overlayer. In the second step, this overlayer is cathodically stripped as Se²⁻ in a Se(IV)-free electrolyte medium (0.1 M Na₂SO₄) that is dosed with the requisite amount of Cd²⁺ ions. Unlike the classical cathodic route, this new approach does not suffer from problems with excess Se admixed with CdSe. The two-step approach is validated using a combination of voltammetry, microgravimetry, and photoelectrochemical experiments.     

Sorption mechanisms of cadmium onto nano-hydroxyapatite: Comparative uptake studies and correlative solubility analysis

Hydroxyapatite (HAP) nanorod was synthesized by using ordered bicontinuous microemulsion, and was characterized by X-ray diffraction spectrum, scanning electron microscopy and high-resolution transmission electron microscopy. The solubility was investigated using ion chromatogram measurement, and was sensitively dependent on the value of pH. The capabilities to capture cadmium ions of HAP nanorods and micro-particles from aqueous salt solution were studied, and besides, X-ray diffractometry was used in order to characterize the mechanisms of cadmium uptake. As Cd²⁺ adsorption occurred, it has undergone the coprecipitation of Cd₂P₂O₇ crystal to give multiple solids composed of HAP and Cd₂P₂O₇ crystallites, which affected the dissolution of hydroxyapatite. During Cd²⁺ sorption process, solubility variations of the sediments showed a more complex pattern than previously reported. Contribution of surface mechanisms, in association with precipitation of cadmium phosphate phases, could explain this behavior.     

Photoinduced cathodic deposition of CdTe nanoparticles on polycrystalline gold substrate

A combination of photocathodic stripping and precipitation was used to prepare CdTe nanoparticles (size range: 30–60 nm) that were immobilized on a polycrystalline Au substrate. Thus visible light irradiation of a Te modified Au surface generated Te²⁻ species in situ followed by interfacial reaction with added Cd²⁺ ions in 0.1 M Na₂SO₄ electrolyte. The resultant CdTe compound semiconductor deposited as nanosized particles uniformly dispersed on the Au substrate surface. This approach to CdTe nanoparticle deposition was monitored by a combination of electrochemical methods (voltammetry, chronoamperometry) and quartz crystal microgravimetry in the “dark” and under illumination. The synthesized CdTe nanoparticles were characterized by scanning electron microscopy and energy dispersive X-ray analyses and laser Raman spectroscopy.     

Sonoelectroanalysis: Anodic Stripping Voltammetric Determination of Cadmium in Whole Human Blood

The quantitative detection of cadmium in human blood is shown to be possible by anodic stripping voltammetry under conditions of insonation. An immersion horn probe is introduced into a thermostatted conventional three‐electrode cell opposite a Nafion‐coated mercury plated glassy carbon electrode. The enhanced mass transport associated with power ultrasound yields efficient preconcentration of the cadmium before it is detected using anodic differential‐pulse stripping voltammetry. Insonation further offers the crucial benefits of first surface activation and cleaning, helping to prevent electrode fouling by the organic components in blood and second fully equilibrating “free” and “bound” Cd²⁺ ions in the complex matrix. Acoustic streaming and cavitation promote the mass transport of cadmium to the surface of electrode, facilitating measurements in solutions of low cadmium concentration, where “silent” measurements fail to yield an analytical signal. The system is calibrated using standard micro additions of cadmium to give the total amount of cadmium in blood. The calibration plot, showing the dependence of the cadmium stripping peak height on cadmium concentration in 1 : 50 diluted blood samples, was linear in the range 1×10^?10 M to 4×10^?9 M Cd²⁺. The values of cadmium concentration obtained using sonoelectroanalytical methodology were compared with the results obtained by independent atomic absorption spectroscopy (AAS) measurements and good agreement was found.     

Complexation in Binary Cd2[Fe(CN)6]–M(II) Systems (M = Mn,Co, Ni,Cu, Zn) in Gelatin-Immobilized Cadmium(II) Hexacyanoferrates(II)

Complexation processes that occur between cadmium(II) hexacyanoferrate(II) (Cd₂[Fe(CN)₆]) and 3d-metal ions M(II) (M = Mn, Co, Ni, Cu, Zn) in thin gelatin layers with the immobilized cadmium(II) hexacyanoferrates when brought in contact with aqueous solutions of d-metal chlorides are studied. Cd²⁺ ions were found to be replaced to some extent by M²⁺ ions of the indicated d metals (except for Mn(II)) and form binuclear (dd)-metal hexacyanoferrates(II). A complete replacement of Cd(II) and formation of M₂[Fe(CN)₆] was observed in none of the cases.     

Novel potentiometric sensor for the determination of Cd2+ based on a new nano-composite

A novel ion selective carbon paste electrode for Cd²⁺ ions based on 2,2′-thio-bis[4-methyl(2-amino phenoxy) phenyl ether] (TBMAPPE) as an ionophore was prepared. The carbon paste was made based on a new nano-composite including multi-walled carbon nanotubes (MWCNTs), nanosilica and room-temperature ionic liquid, 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆). The constructed nano-composite electrode showed better sensitivity, selectivity, response time, response stability and lifetime in comparison with typical Cd²⁺ carbon paste sensor for the successful determination of Cd²⁺ ions in water and in waste water samples. The best performance for nano-composite sensor was obtained with an electrode composition of 18% TBMAPPE, 20% BMIM-PF₆, 48% graphite powder, 10% MWCNT and 4% nanosilica. The new electrode exhibited a Nernstian response (29.95?±?0.10?mV?decade^?1) toward Cd²⁺ ions in the range of 3.0?×?10^?8 to 1.0?×?10^?1?mol?L^?1 with a detection limit of 7.5?×?10^?9?mol?L^?1. The potentiometric response of prepared sensor was independent of the pH of test solution in the pH range 3.0 to 5.5. It had a quick response with a response time of about 6?s. The proposed electrode showed fairly good selectivity over some alkali, alkaline earth, transition and heavy metal ions.     

A dispersive liquid–liquid microextraction based on a task-specific ionic liquid for enrichment of trace quantity of cadmium in water and food samples

In this work, a hydrophilic task-specific ionic liquid (TSIL) of 1-chloroethyl-3-methylimidazolium chloride functionalized with 8-hydroxyquinoline was used in a dispersive liquid–liquid microextraction method followed by flame atomic absorption spectrometry for the enrichment and determination of trace amounts of cadmium (Cd²⁺) ions. The simultaneous chelation and extraction of Cd²⁺ ions was carried out by the TSIL. Fine droplets of the water-immiscible TSIL containing target analyte were generated in situ by addition of an anion exchanger potassium hexafluorophosphate (KPF₆) salt to the sample tube. After phase separation by centrifugation for 4 min, the sedimented TSIL was diluted with acidified ethanol for measurement of Cd²⁺ content. Some significant parameters influence the preconcentration of Cd²⁺ ions such as sample pH, TSIL volume, amount of KPF₆, non-ionic surfactant and salt concentration were investigated. Under the optimal conditions, calibration curve was linear in the range of 5–250 µg L^?1 Cd²⁺ with correlation coefficient of 0.9975 and a detection limit of 0.55 µg L^?1. The relative standard deviation for six replicate measurements of 50 µg L^?1 Cd²⁺ was 1.5%. The method was successfully applied for the extraction and determination of Cd²⁺ ions in water and food samples.     

Fabrication of Fe(CN)63− Functionalized PDDA/CdTe Layer‐by‐layer Film with Good Electron Transfer Ability

(PDDA/CdTe)_n layer‐by‐layer (LBL) film immobilized with Fe(CN)₆^3? was fabricated on the gold electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to investigate the electrochemical properties of this film. The peak current of the immobilized Fe(CN)₆^3? increased as the number of the bilayers increased and was proportional to the scan rate. Compared with pure (PDDA/CdTe)_n and (PDDA/PSS)_n LBL film, Fe(CN)₆^3? immobilized (PDDA/CdTe)_n LBL film had good electron transfer ability. The immobility of Fe(CN)₆^3? into the film was attributed to its interaction with Cd²⁺ on the surface of CdTe QDs. Fe(CN)₆^3? also can interact with other metal ions, which would make Fe(CN)₆^3? release from the film. The concentrations of metal ions will affect the CV response of Fe(CN)₆^3? immobilized LBL film. It has provided a novel prototype of device or sensor for quantitative detection of metal ions.     

Quantum dot-based "turn-on" fluorescent probe for detection of zinc and cadmium ions in aqueous media

Health or environmental issue caused by abnormal level of metal ions like Zn²⁺ or Cd²⁺ is a worldwide concern. Developing an inexpensive and facile detection method for Zn²⁺ and Cd²⁺ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn²⁺ and Cd²⁺ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S²⁻). The presence of Zn²⁺ (or Cd²⁺) can “turn-on” the weak fluorescence of QDs quenched by S²⁻ due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn²⁺ (or Cd²⁺) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd²⁺). The limit of detection (LOD) for Zn²⁺ and Cd²⁺ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn²⁺ and Cd²⁺ over other metal ions and was successfully used in the detection of Zn²⁺ or Cd²⁺ in real water samples.     

CdTe/CdS共敏化TiO2电极材料的制备与光电性能

将电沉积法和化学浴沉积法结合,分别将CdTe和CdS量子点纳米晶材料引入到TiO_2纳米管阵列上制备CdTe/CdS量子点共敏化TiO_2光电极。利用扫描电镜、X射线衍射和X射线能量色散光谱等测试手段对所得样品的形貌、晶型和组分进行表征。在模拟太阳光照射条件下,通过电化学工作站测试其光电化学性能。研究结果表明,相对于单一量子点敏化CdS/TiO_2和CdTe/TiO_2光电极而言,共敏化CdTe/CdS/TiO_2光电极表现出更好的光电转化性能,短路电流密度和光电转换效率分别可以达到3.1 m A·cm~(-2)和1.85%。此外,采用电化学阻抗测试技术对材料性能提升的原因进行深入的探究。     

CdTe/CdS共敏化TiO2电极材料的制备与光电性能

将电沉积法和化学浴沉积法结合,分别将CdTe和CdS量子点纳米晶材料引入到TiO₂纳米管阵列上制备CdTe/CdS量子点共敏化TiO₂光电极。利用扫描电镜、X射线衍射和X射线能量色散光谱等测试手段对所得样品的形貌、晶型和组分进行表征。在模拟太阳光照射条件下,通过电化学工作站测试其光电化学性能。研究结果表明,相对于单一量子点敏化CdS/TiO₂和CdTe/TiO₂光电极而言,共敏化CdTe/CdS/TiO₂光电极表现出更好的光电转化性能,短路电流密度和光电转换效率分别可以达到3.1 mA·cm^-2和1.85%。此外,采用电化学阻抗测试技术对材料性能提升的原因进行深入的探究。     

Photochemical synthesis of cadmium sulfide nanoparticles

The formation of cadmium sulfide nanoparticles upon UV irradiation of aqueous solutions of cadmium thiosulfates was established on the basis of spectroscopic and macroscopic data. The yield and size of the cadmium sulfide nanoparticles depend on the ratio of cadmium to thiosulfate ions in solution, the concentration of the solution, and the irradiation duration. The cadmium sulfide nanoparticles with a diameter of 4 nm were obtained by the photolysis of solutions with a concentration of 10⁻³ mol L⁻¹ at the ratio S₂O₃ ²⁻: Cd²⁺ = 2: 1.     

Electrochemical Sensing of Mercury over Cadmium and Lead Cations by the Redox-Active Polyazacycloalkane Ligand 1,1″: 1′,1′′′-Bis[ethane-1,2-diylbis(iminomethylene)]bis[ferrocene]

The coordination behaviour of the redox-active polyazacycloalkane L¹ against the toxic heavy-metal ions Cd²⁺, Pb²⁺, and Hg²⁺ was studied in THF/H₂O 70 : 30 (containing 0.1 mol⋅dm⁻³ of (Bu₄N)ClO₄). The crystal and molecular structure of the cadmium complex [Cd(L¹)(NO₃)₂] ( 1 ) was determined by X-ray single-crystal analysis. The cadmium ion is in a 4+2 surrounding with the ligand L¹ acting as tetradentate and the apical positions occupied by the O-atoms of the nitrate anions. An electrochemical study reveals that L¹ shows a selective electrochemical response against Hg²⁺ over Cd²⁺ and Pb²⁺.     

Constant Current Stripping Chronopotentiometry for the Study of Adsorbing Inert and Electrochemically Nonreversible Metal Complexes at Low Concentrations: Application to Cd and Zn Metallothioneins

Constant current chronopotentiometric stripping analysis using adsorptive accumulation and negative stripping current (AdSCP) was applied for the study of behavior of rabbit liver Cd‐Zn and Zn metallothionein (Cd‐Zn‐MT, ZnMT) on hanging mercury drop electrode. Electrochemically inert or labile behavior of complexes can be distinguished with the application of high (1000 nA) or low (100 to 20 nA) current. Using high current, no influence of added Cd²⁺ or Zn²⁺ ions on the reduction of Cd(II) or Zn(II) complexed within MT molecule was observed, except of additions of Cd²⁺ to ZnMT, where bound Zn(II) was substituted by cadmium ions. With lowering of stripping current and increasing concentration of added Cd²⁺ or Zn²⁺ ions in solution progressive formation of reorganized complex with labile behavior is observed. Parallel measurement using DC voltammetry with different rates of polarization or differential pulse voltammetry were in agreement with AdSCP measurement. However, only chronopotentiometric method combines good sensitivity and signal separation at μM concentrations, inevitable in MT studies.