Thiourea Concentration Research Articles

Numerical simulation and experiment in the systems of labile complexes of metals. Silver reduction from the thiourea electrolyte

Voltammograms of silver reduction from complex thiourea electrolytes with the ligand to metal concentration ratio varied from 1 to 50 were measured on the freshly prepared surface of silver electrode. The results were analyzed using the numerical model of this electrode process which takes into account homogeneous chemical reactions proceeding in solution, diffusion–migration transfer of the species present in solution, and electrode reactions participated by electroactive components of the electrolyte. We estimated the values of standard exchange current density for partial electrode reactions in which silver complexes with different number of ligands can take part. The highest electrochemical activity is exhibited in solutions with the low concentration of complex-forming agent – by silver aqua complexes, while in solutions with high thiourea concentration – by silver complexes with one ligand. It was found that kinetic hindrances to discharge of the thiourea silver complexes unlikely to be due to the adsorption of thiourea molecules blocking the growth sites or to the adsorption of complex silver ions. The results admit interpretation of the mechanism of electrode process either from the viewpoint of simultaneous discharge of all the complex silver ions present or from the viewpoint of discharge of silver complex with one ligand in combination with rapid chemical reactions of dissociation of other, non-discharging silver complexes.

Selective oxidation of thiourea with H2O2 catalyzed by [RuIII(edta)(H2O)]−: kinetic and mechanistic studies

Reported here is the first example of a ruthenium complex, [Ru(III)(edta)(H(2)O)](-) (edta(4-) = ethylenediaminetetraacetate), that catalyzes the oxidation of thiourea (TU) in the presence of H(2)O(2). The kinetics and mechanism of this reaction were investigated in detail by using rapid-scan spectrophotometry as a function of both the hydrogen peroxide and thiourea concentrations at pH 4.9 and 25 °C. Spectral analyses and kinetic data clearly support a catalytic process in which hydrogen peroxide reacts directly with thiourea coordinated to the Ru(III)(edta) complex. HPLC product analyses revealed the formation of formamidine disulfide (TU(2)) as a major product at the end of the catalytic process, however, formation of other products like thiourea dioxide (TUO(2)), thiourea dioxide (TUO(3)) and sulfate was also observed after longer reaction times. Catalytic intermediates such as [Ru(III)(edta)(OOH)](2-) and [Ru(V)(edta)(O)](-) were evidently found to be non-reactive in catalyzing the oxidation of thiourea by H(2)O(2) under the specified conditions.

Synthesis of pyramidal and prismatic hexagonal MoO3 nanorods using thiourea

The hexagonal phase of MoO3 is attractive for electrochemical applications owing to its arrangement of atoms, which offers a large number of intercalation sites. The number of intercalation sites also depends on the orientation of the specific crystallographic plane. In this report we present a facile and low cost method to synthesize the metastable hexagonal phase of MoO3 containing NH4+ and H2O in the form of nanorods (pyramidal and prismatic) using a thiourea synthesis. The unique hexagonal phase of MoO3 was realized using a single step solvothermal process. In this work, thiourea provides the ammonium ions which alter the growth rate and stabilize the hexagonal framework. The morphology of the resulting samples changes from pyramidal to prismatic when the thiourea concentration is increased. The phase compositions and the morphologies of the as prepared samples were investigated by X-ray diffractometry, thermogravimetric analysis, X-ray dispersive spectroscopy and Field emission scanning electron microscopy, respectively. On the basis of our findings, we propose a growth model with plausible growth mechanisms to account for their formation process.

Sustained Immersion Tin Deposition on Copper from Choline Chloride Based Aqueous Solution without Reducing Agent

Sustained immersion tin (Sn) deposition onto a copper (Cu) surface was achieved from choline chloride aqueous (ChCl-H2O) solution free of reducing agents. The electrode potentials of Cu and Sn were investigated by open-circuit potential (OCP) to reveal the driving force of Sn deposition process in ChCl-H2O solution. Thiourea reversed the electrode potentials of Cu and Sn, causing the replacement reaction between Sn2+ and Cu occurring. The replacement reaction is significantly influenced by the concentration of ChCl, SnCl2, and thiourea. The phenomenon of sustained Sn deposition was mainly facilitated by diffusing of Cu into the Sn coating and the reaction between Sn2+ and Cu+. Furthermore, Sn coating got in ChCl-H2O solution had fairly good performance such as solderability.

Shape-controlled synthesis of three-dimensional branched CdS nanostructure arrays: structural characteristics and formation mechanism

Through a combination of electrodeposition and subsequent solvothermal reaction, three-dimensional (3D) branched CdS nanostructure arrays were fabricated by nanowires self-assembly in ethanediamine solution containing thiourea and hexamethylenetetramine (HMTA) for the first time, where HMTA acted as a capping agent. In the absence of HMTA, only disordered CdS nanowires were obtained. The reaction conditions influencing the synthesis of 3D branched CdS nanostructure arrays, such as the concentration of HMTA and thiourea, reaction temperature and reaction time, were studied and optimized. The 3D branched CdS nanostructure arrays were characterized by X-ray diffraction, field emitting scanning electron microscopy and transmission electron microscopy. The results show that HMTA played an important role in the formation of 3D branched CdS nanostructure arrays. A growth process of HMTA-assisted gradual crystallization and subsequent oriented attachment was proposed as a plausible mechanistic interpretation for the formation of the 3D branched nanostructure arrays. In addition, the photoluminescence property of the novel 3D branched CdS nanostructure arrays was investigated.

Recovery of gold and silver from spent mobile phones by means of acidothiourea leaching followed by adsorption using biosorbent prepared from persimmon tannin

A new approach of recovering precious metals from printed circuit boards (PCBs) of mobile waste by acidothiourea leaching followed by selective adsorption on low-cost and environmentally benign biomass sorbent prepared from easily available agricultural waste is suggested. The influence of various parameters like thiourea (TU) concentration, acid concentration, pulp density, temperature, and contact time were studied for gold and silver leaching using a batchwise method. It was found that the PCB sample with smaller particle size distribution (53 to 75μm) yielded higher amounts of gold and silver being leached into the solution. The optimum conditions for the leaching of gold were found to be 0.5M TU in 0.05M H2SO4 at 45°C, while that of silver were 0.5M TU in 0.01M H2SO4 at 60°C. Under the optimum leaching conditions, an average of 3.2mg/g of gold and 6.8mg/g of silver were extracted from incinerated sample of PCBs of mobile waste. Kinetic studies revealed that the complete leaching of silver was achieved in less than 2h, while it took approximately 6h at ambient temperature in the case of gold. Presence of 0.01M ferric ions facilitated the gold dissolution rate and complete leaching was achieved within 2h. Conventional copper cementation for recovery of gold and silver from pregnant leached liquor was not so effective. Adsorptive recovery of dissolved gold and silver using activated carbon as well as crosslinked persimmon tannin gel was also examined. Low-cost persimmon tannin extract crosslinked with sulfuric acid was found to be a promising material for the complete recovery of gold and silver from the leached liquor. This adsorbent not only adsorbed the dissolved precious metals selectively but also reduced the adsorbed cationic species of gold to the elemental gold.

Preparation and formation mechanism of smooth and uniform Cu2O thin films by electrodeposition method

Smooth and uniform Cu2O thin films were prepared by electrodeposition on Sn-doped indium oxide substrates (ITO) in Cu(Ac)2 electrolytes with thiourea addition. The influence of deposition potential and thiourea concentration on the formation of these thin films was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results show that smooth and uniform Cu2O thin films were achieved by electrodeposition under the potential of −0.1V (vs. SCE) with 0.5mM thiourea, which exhibited obvious absorbance and photocurrent response in visible light range. In addition, as the concentration of thiourea increased, the density of Cu2O thin films decreased. Based on this, the thiourea assisted growth process was proposed as a plausible mechanism for the formation of smooth and uniform Cu2O thin films.

One-step bleaching process for cotton fabrics using activated hydrogen peroxide

Cotton fabric was bleached in a simple and economic process using a bleaching system composed of hydrogen peroxide activated with thiourea. Different bleaching trials were carried out with varying hydrogen peroxide and thiourea concentrations, as well as the bleaching medium temperature. The obtained results reveal that bleached cotton fabric with satisfactory whiteness index and reasonable tensile strength can be obtained by treating the fabric at 90°C in a bleaching bath containing 6g/l hydrogen peroxide, 1.5g/l thiourea and 1g/l non-ionic wetting agent using a material to liquor ratio of 1:20. These optimum conditions lead to completion of the bleaching process in a reasonable duration of 1h. Lower concentrations of the activator thiourea were found to prolong the bleaching duration without getting satisfactory whiteness index. Higher concentrations of the activator were found to cause early termination of the oxidizing species leading to bad whiteness index.

Determination of mercury in phosphate fertilizers by cold vapor atomic absorption spectrometry

In this paper, a method for the determination of mercury in phosphate fertilizers using slurry sampling and cold vapor atomic absorption spectrometry (CV QT AAS) is proposed. Because mercury (II) ions form strong complexes with phosphor compounds, the formation of metallic mercury vapor requires the presence of lanthanum chloride as a release agent. Thiourea increases the amount of mercury that is extracted from the solid sample to the liquid phase of the slurry. The method is established using two steps. First, the slurry is prepared using the sample, lanthanum chloride, hydrochloric acid solution and thiourea solution and is sonicated for 20min. Afterward, mercury vapor is generated using an aliquot of the slurry in the presence of the hydrochloric acid solution and isoamylic alcohol with sodium tetrahydroborate solution as the reducing agent. The experimental conditions for slurry preparation were optimized using two-level full factorial design involving the factors: thiourea and lanthanum chloride concentrations and the duration of sonication.The method allows the determination of mercury by external calibration using aqueous standards with limits of detection and quantification of 2.4 and 8.2μgkg−1, respectively, and precision, expressed as relative standard deviation, of 6.36 and 5.81% for two phosphate fertilizer samples with mercury concentrations of 0.24 and 0.57mgkg−1, respectively. The accuracy was confirmed by the analysis of a certified reference material of phosphate fertilizer that was provided by the National Institute of Standards & Technology (NIST). The method was applied to determine mercury in six commercial samples of phosphate fertilizers. The mercury content varied from 33.97 to 209.28μgkg−1. These samples were also analyzed employing inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS results were consistent with the results from our proposed method.

Interface characteristics of CdS/Cu(In,Ga)Se2 thin-film solar cells by using photoreflectance spectroscopy

We investigated the CdS/Cu(In,Ga)Se2 interface characteristics of Cu(In,Ga)Se2 (CIGS) thin-film solar cells by using photoreflectance spectroscopy and their influence on the photovoltaic performance. We prepared CIGS solar cells with CdS and CIGS layers fabricated by using different methods of chemical bath deposition (CBD). The thiourea concentration in the CBD-CdS process was varied from 0.025 M to 0.1 M. The final In-Ga-Se deposition time for the CIGS film’s deposition was varied from 300 s to 490 s. We fabricated solar cells with thin films fabricated by using a combination of these conditions. The transition energies changed from 2.277 eV to 2.387 eV and the conversion efficiencies changed from 14.13% to 15.81% depending on the fabrication process. The formation of different states in CdS/CIGS resulted in different conversion efficiencies, as well as different band alignments at the CdS/CIGS interface.

Investigation of the ZnSxSe1-x thin films prepared by chemical bath deposition

The ZnSxSe1−x thin films were prepared by chemical bath deposition technique on glass substrates. The composition ‘x’ was varied from 0 to 1 by changing the concentration of thiourea and sodium selenosulphate in the precursors. The morphology, structural and optical properties of the ZnSxSe1−x thin films were characterized by energy dispersive spectrometer, scanning electron microscopy, X-ray diffraction and UV-Vis spectrophotometer. The results reveal that the ZnSxSe1−x films are cubic zinc blende structure for x = 0, 0.19, 0.25, and amorphous for x = 0.75, 1. The optical band gap of the ZnSxSe1−x films increase from 2.88 to 3.76 eV when the value of ‘x’ increases from 0 to 1. The growth mechanism of the ZnSxSe1–x films was discussed.

Photoreflectance characteristics of chemical-bath-deposited-CdS layer in Cu(In,Ga)Se2 thin-film solar cells

The authors have characterized the CdS layer in Cu(In,Ga)Se2 thin-film solar cells using photoreflectance (PR) spectroscopy and investigated its influence on the photovoltaic performance. The CdS layer was fabricated by chemical bath deposition with various concentrations of ammonia (1.0–3.0 M), thiourea (0.025–0.1 M), and Cd-salt (0.0004–0.003 M) as well as various thicknesses (30–90 nm). The PR transition energy in CdS increased from 2.282 to 2.366 eV as the thiourea concentration increased from 1.0 to 3.0 M, whereas it decreased as the thickness of CdS increased. The conversion efficiency depended on neither the ammonia and the Cd-salt concentrations nor the thickness of CdS, whereas it changed from 14.72% to 15.81% as the thiourea concentration decreases from 3.0 to 1.0 M.

In vitro inhibition of pigmentation and fiber development in colored cotton

Colored cotton has naturally pigmented fibers. The mechanism of pigmentation in cotton fiber is not well documented. This experiment was conducted to study the effects of respiratory chain inhibitors, i.e., rotenone and thiourea, on pigmentation and fiber development in colored cotton. After 1 d post-anthesis, ovaries were harvested and developing ovules were cultured on the liquid medium containing different concentrations of rotenone and thiourea for 30 d. The results demonstrate that both respiratory inhibitors reduced fiber length and ovule development under ovule culture conditions, and the inhibition efficiency of rotenone was much higher than that of thiourea. Rotenone and thiourea also showed significant effects on fiber pigment (color) development in colored cotton. In green cotton fiber, rotenone advanced fiber pigment development by 7 d at 200 μmol/L, while thiourea inhibited fiber pigmentation at all treatment levels (400, 600, 800, 1000, and 2000 μmol/L). Both respiratory inhibitors, however, had no significant effects on pigmentation of brown cotton fibers. The activities of cytochrome c oxidase (COX) and polyphenol oxidase (PPO) decreased significantly with increasing levels of both respiratory inhibitors. It is suggested that both respiratory inhibitors have important roles in deciphering the mechanism of pigmentation and fiber development in colored cotton.

Determinación experimental de los parámetros óptimos de operación en el proceso de electrolixiviación y electrodeposición secuencial de oro en soluciones ácidas de tiourea a partir de sulfuros concentrados

Se investigó a nivel de laboratorio las variables de operación (concentración de reactivos, pH y potencial de oxidación) del proceso de lixiviación de piritas auríferas procedentes de río Tablachaca (Ancash Perú) con Tiourea (TU) seguido de electro-deposición de oro. El estudio experimental, se desarrolló en tres etapas: Oxidación de Tiourea, Lixiviación de oro y Electro-deposición de oro. Como una alternativa a los agentes químicos, la oxidación de TU se realizó vía electrólisis para producir Disulfuro Formamidina (FDS), el cual, sirve como oxidante en la disolución de oro. El grado de conversión óptima de tiourea a disulfuro formamidina se obtiene en 2,5 h aplicando una FEM de 4,5 V con un pH igual 1,5. Los compartimientos anódico y catódico del reactor electroquímico fueron separados por una membrana aniónica con la finalidad de eliminar reacciones indeseables en el cátodo. Previo a la etapa de lixiviación, el mineral fue lavado con ácido sulfúrico para eliminar los agentes consumidores de ácido y mantener de este modo un pH constante durante el tiempo que dure la lixiviación. Durante la lixiviación de oro, se estudió las velocidades de disolución en función de las concentraciones de TU, FDS y pH. Finalmente, se efectuó una prueba de lixiviación en tiempos prolongados usando los parámetros óptimos de operación obtenidos en las pruebas anteriores. La prueba de electro-deposición se llevó a cabo usando la técnica de electrodiálisis en una celda de tres compartimentos El bajo consumo de Tiourea (1,76 kg/TM mineral) demuestra que es una alternativa viable desde el punto de vista económico.

Characterization of the ZnS thin film buffer layer for Cu(In, Ga)Se2 solar cells deposited by chemical bath deposition process with different solution concentrations

ZnS buffer layer thin films for Cu(In, Ga)Se2 (CIGS) have been prepared by chemical bath deposition (CBD) technique onto the ITO coated glasses at 80°C bath temperature, using zinc sulfate hepta-hydrate (ZnSO4·7H2O), thiourea (SC(NH2)2) and ammonia (NH4OH) as reacting chemicals. The concentrations of thiourea and ammonia were varied while the concentration of ZnSO4 was immobilized at 0.03M. The thickness, transmittance, morphology of ZnS films were measured and the band gap was calculated according to the equation related with the absorption coefficient. Through the analysis of the parameters, we could conclude that the physical and optical properties of different ZnS thin films were influenced severely by the concentration of the two reacting chemicals and then the optimal concentration group of SC(NH2)2 and NH4OH solutions can come to 0.3M and 1.5M, respectively.

Preparation, characterization, and electrochemical studies of sulfur-bearing nickel in an ammoniacal electrolyte: the influence of thiourea

Sulfur-bearing nickel was prepared by a direct electrodeposition in an ammoniacal Ni(II) electrolyte containing thiourea. This sulfur-bearing nickel showed an excellent dissolving activity when used as anodic materials in the traditional Watt bath. The influence of thiourea on the surface microstructure, crystallization texture, and electrocrystallization process of sulfur-bearing nickel were investigated by scanning electron microscopy, X-ray diffraction, and electrochemical techniques. The results show that the S element is uniformly distributed in the electrodeposited nickel. The prepared nickel samples present a blade shape microstructure, and the blade size decreases by the addition of thiourea. Sulfur-bearing nickel exhibits face-centered cubic structure and (111) preferred orientation, and the orientation distribution is strengthened with increased thiourea concentration. The nucleation parameters, such as N0, A, and J0, are obtained from the initial parts of the transients making use of Sharifker–Mostany theoretical model. Both the nucleation rate and the vertical growth rate are increased by the addition of thiourea, leading to finer grains and better dissolving activity.

Synthesis, structure, and optical properties of CdS thin films nanoparticles prepared by chemical bath technique

CdS nanocrystalline thin films were deposited onto glass substrates by chemical bath deposition (CBD). The films deposited at 80°C for 6h with two different concentrations of thiourea. The deposition parameters were optimized. The obtained films were characterized for structural and optical properties, X-ray diffraction patterns revealed that the films were nanocrystalline in nature with cubic structures. A blue shift in the band gap was observed in the UV–visible absorption spectra indicating the formation of nano particles of sizes between 3.826 and 8nm.

The Influence of Impurities on Electroplated FeCoZr High Frequency Properties through Thiourea Containing Electrolyte

FeCoZr magnetic alloy films were electrodeposited on ITO conductive glass from sulfate baths with different thiourea concentration. The composite, structure and magnetic properties of FeCoZr films were investigated as a function of thiourea concentration. The sulfur content of the films increases almost linearly with increasing thiourea concentration. All thin films have crystalline texture with (110) plane parallel to the film plane. As thiourea concentration increases from 0.5 to 4.0 g/L, films coercivity increases from 19 to 56 Oe, the squareness ratio decreases from 0.74 to 0.15. The natural resonant frequency (fr) of films linearly increase from 0.35 to 2.00 GHz with the increasing of thiourea concentration in the bath. It has been proved to be a new way to adjust the resonant frequency of soft magnetic material for high frequency application.

Investigation of CuInS2 Thin Film Formation by a Low-Temperature Chemical Deposition Method

Copper indium disulfide (CuInS(2), CIS) thin films were prepared by an alternative solution-based coating process adapted from the well-established aqueous metal salt/thiourea precursor system. The temperature for the decomposition of the precursors and the formation of CIS was lowered significantly to 130 °C by using the strongly coordinating solvent pyridine instead of the commonly used water. In addition, the influence of different annealing temperatures and concentrations of thiourea (TU) in the precursor solution on the obtained CIS samples was investigated. The films possess highly beneficial properties for photovoltaic applications, showing a chalcopyrite crystal structure, a high optical absorption (>10(4) cm(-1)) and an optical band gap between 1.45 and 1.51 eV. Chemical and morphological changes during the thin film formation were detected and explained by time-resolved simultaneous grazing incident small- and wide-angle X-ray scattering (GISAXS, GIWAXS) measurements, scanning electron microsccopy (SEM) and simultaneous thermogravimetry/mass spectroscopy (TG/MS).

Microstructure, magnetic and magnetoimpedance properties in electrodeposited NiFe/Cu and CoNiFe/Cu wire with thiourea additive in plating bath

Magnetic thin films of NiFe and CoNiFe alloys were electrodeposited from three different deposition baths onto copper wires of 100-μm diameter. The magnetic and magnetoimpedance (MI) properties of the samples along with their microstructure were investigated as a function of thiourea additive concentrations (CT) in the plating bath. For all intermediate frequencies, the MI ratio increased with thiourea concentration in plating bath up to a critical concentration of 80mg/l and then decreased considerably. The change in MI with thiourea concentration in electrodeposition bath was attributed to the grain size reducing action of thiourea, which in turn enhances the soft magnetic properties of the films. At higher concentration of thiourea, the sulfur inclusion increased the magnetic softness and MI value enhanced considerably. The origin of MI lies in the combined effect of domain wall motion and spin rotation, which contributes to permeability. Inductance spectroscopy (IS) was used to evaluate the magnetic characteristic of the samples by modeling coated wires in terms of equivalent electrical circuit; namely parallel LR (inductance and resistance) circuit in series with series LR circuit. The domain wall motion was found to be greatly affected by thiourea addition in the bath, which was revealed through the study of variation of these circuit parameters. The domain wall motion thereby affects the magnetic softness of samples, which is reflected in the MI enhancement.