Thiourea Concentration Research Articles

Investigations on thiourea content in ternary Sn–Ag–Cu bath using electrochemical studies

We have developed a methane sulfonic acid (MSA) based ternary electrolytic bath for co-deposition of the eutectic Sn–Ag–Cu films. The bath contains thiourea (TU), which functioned as an effective chelating agent in controlling the bath stability as well as the elemental and microstructural properties of the deposited film. A study of the bath behaviour at TU concentrations in the range 0.06–0.2 M is undertaken with the help of elemental and microstructure analysis, cyclic voltammetry (CV) and impedance analysis. The deposited films have close to eutectic composition with slightly higher Cu content for all the TU concentrations. On the other hand, the microstructure is found to be increasingly refined with increasing TU content. The CV and impedance analysis confirm chelation of Ag and Cu with TU and absence of such chelation with Sn ions. It also indicates close deposition potentials for each metal ion. Impedance analysis specifically reveals presence of an adsorbed insulating film on cathode surface, contributed by MSA or water. It also reveals competitive deposition between the insulating film and metal ions.

Response Surface Modelling and Optimization of Mercury Extraction through Emulsion Liquid Membrane

Mercury(II) is a very harmful metal, highly toxic, and carcinogenic in nature. Experiments were carried out using the emulsion liquid membrane (ELM) technique in order to evaluate the maximum extraction of mercury(II) from aqueous solutions of mercuric chloride using 33 factorial design. The ELM consisted of di-2-ethylhexylphosphoric acid as a carrier, toluene as an organic solvent, span 80 as a surfactant, and sulphuric acid with thiourea solution as stripping phase. The three factors for the factorial design were mercury(II) concentration in the aqueous solution, that is, feed phase concentration, carrier concentration in the membrane phase, and sulphuric acid concentration in the stripping phase. The study has also highlighted the effects of various other parameters, such as pH of the feed phase and thiourea concentration on mercury(II) extraction. The optimization of the factors to obtain maximum extraction were carried out by incorporating main effect plots, interaction plots, analysis of variance (ANOVA), normal probability plots, residual plots, surface plots, and contour plots. A reduced model developed by regression analysis was suggested in which the experimental data were fitted very well. The results showed that it is possible to extract mercury(II) up to 98% from aqueous solutions at the optimum conditions.

Ultra Sensitive Quantification of Thiourea at Nanomolar Level by Catalytic‐Kinetic Differential Pulse Voltammetry

AbstractA new simple and highly selective and sensitive catalytic differential pulse voltammetry procedure for the determination of thiourea at nanomolar level is reported. Thiourea has a catalytic effect on the oxidation of Janus green by iodate in the hydrochloric acid medium. The potential was scanned in the negative direction and the differential pulse voltammograms were recorded. The variations of the peak current with hydrochloric acid concentration, oxidant, Janus green, pulse amplitude, pulse time and scan rate were optimized. Under the optimized conditions, the relationship between the peak current and concentration of thiourea was obtained. It is shown that the calibration curve is linear in the range of 0.01–6.00 µg/mL. The detection limit of the method was 0.005 µg/mL. The relative standard deviation for 6 replicate determinations of 0.01, 0.50 and 2.00 µg/mL is equal to 2.25%, 1.52% and 1.03%, respectively. The method was applied to the determination of thiourea in fruit juices with satisfactory results.

Methods to Break Seed Dormancy of Rhynchosia capitata, a Summer Annual Weed

Dormancy of weed seeds is a significant feature contributing to their survival rate since it helps the weeds to avoid herbicides and other weeding practices along with unfavorable environmental conditions. We investigated the effects of different dormancy breaking treatments on the germination of Rhynchosia capitata, a common summer annual weed, which is emerging as a weed threat in Pakistan. Seeds were soaked in thiourea, KNO3, HCl, HNO3, and H2SO4, and they were also mechanically scarified (sandpaper). Results indicated that R. capitata seeds show signs of physical dormancy that is mainly due to the impermeability of their coat. Mechanical scarification and acid scarification (soaking of seeds in H2SO4 for 60 and 80 min and in HCl for 12 and 15 h) were very efficient in breaking dormancy and promoting germination. Seed soaking in HNO3 for 1 to 5 d showed little effect whereas various concentrations of thiourea and KNO3 were ineffective in breaking R. capitata seed dormancy.

Iron removal from kaolin using thiourea assisted by ultrasonic wave

In the present study a bleaching process of a kaolinite was carried out using thiourea as the leachant agent in the iron removal process, in the absence and presence of ultrasound. The effect of thiourea was investigated together with other factors, such as thiourea concentration, temperature, treatment time, and ultrasonic parameters. The optimum conditions for the maximum whiteness of 89% with ultrasound were determined as follows: reaction temperature, 20 °C; ultrasound frequency, 80 kHz; ultrasound power, 500 W; thiourea concentration, 0.4 wt.%; pH, 3.0; reaction time, 20 min. The assistance of ultrasound led to a remarkable acceleration for the iron leaching process, and dramatic reduction in the concentration of leach reagent, irradiation time, and reaction temperature, when compared with the conventional bleaching method using thiourea in the absence of ultrasound.

A mathematical model to predict the grain size of nanocrystalline CdS thin films based on the deposition condition used in the sol–gel spin coating method

Design of experiment (DOE) based on central composite design (CCD) has been employed for the development of a mathematical model correlating the important process parameters like thiourea concentration (U), annealing temperature (A), rotational speed (S), and annealing time (T) of the spin coating process for the preparation of CdS thin films. The experiments were conducted as per the design matrix. Nanocrystalline CdS thin films have been prepared using cadmium nitrate and thiourea as precursors by sol gel spin coating method using the results of the mathematical model. The prepared CdS films have been characterized and the crystal structure and grain size of the samples were analyzed using X-ray diffraction technique. The adequacy of the developed models was checked by analysis of variance (ANOVA) technique. The accuracy of prediction has been carried out by conducting confirmation test. Using this model, the main effect of process parameters on grain size of CdS films have been studied. These parameters were optimized to obtain minimum grain size using the Microsoft excel solver. The results have been verified by depositing CdS films using the optimized conditions. These films have been characterized using X-ray diffraction technique and the grain size is found to be 8.8 nm. The high resolution transmission electron microscopy (HRTEM) analysis showed the grain size of the prepared CdS film to be ∼7 nm. UV–vis spectroscopy analysis revealed that CdS films exhibited quantum confinement effect.

Thionine sensitized areobic photooxidation of thiourea in acidic medium

An investigation of the thionine sensitized aerobic photooxidation of thiourea was observed spectrophotometrically at a wavelength of 598 nm. Articles reported two types of reactions which generally occur in the presence of oxygen: 1) Singlet oxygen, produced by dye sensitization due to the hydrolysis that reacts with thiourea to form oxidative products like urea and other sulfur-containing fragments and 2) bleaching of dye, which leads to the reduction. The rate of reaction in all studied parameters followed first order kinetics with respect to maximum absorption of the dye in the visible band region. Reaction kinetics was significantly dependent upon the medium and the reaction accelerated more rapidly at low pH. A direct relation was exhibited between the thiourea concentration and dye sensitizer, which was not pragmatic with the concentration of dye. The reaction was effected by the temperature, and the values of energy parameters suggested that the energy of activation was low while the entropy of activation increases with the rise in temperature, which indicated a highly solvated state of intermediate complex. Lower value of ΔH* and ΔG* at elevated temperature showed that free energy is the driving force for the completion of reaction. A mechanism based on the above findings has been suggested.

Ultrasensitive and selective colorimetric detection of thiourea using silver nanoprobes

A novel colorimetric thiourea (TU) sensor was developed utilizing citrate modified silver nanoparticles (AgNPs). The introduction of TU reduced the overall surface charges of the AgNPs, resulting in aggregation of AgNPs and a colorimetric response correlating with the concentration of TU. The detection of TU could be realized within 2 min, with an ultralow detection limit of 0.8 nM by the absorption method. In addition, the AgNPs sensor also showed good selectivity in the presence of potential interfering compounds. Since common steps such as modification and separation could be successfully avoided, the sensor developed here could provide a simple, cost-effective yet rapid and sensitive measurement tool for TU detection, and may provide new opportunities in the development of sensors for food safety and environmental monitoring in the future.

Mesoporous Electrodeposited-CoS Film as a Counter Electrode Catalyst in Dye-Sensitized Solar Cells

In this study, a mesoporous CoS film was deposited onto a fluorine-doped tin oxide glass substrate to form a counter electrode (CE) in dye-sensitized solar cell (DSSC) using a potentiodynamic deposition in the presence of thiourea (TU). The function of potentiodynamic deposition used to prepare the mesoporous CoS CE was firstly investigated. It can be found that the reverse sweep (0.2 V to −1.2 V vs. Ag/AgCl) can facilitate the formation of CoS with excellent electrocatalytic activity for I−/I3− redox reaction, and the forward sweep (−1.2 V to 0.2 V vs. Ag/AgCl) can profit the deposit with crude morphology to increase its active surface area. Moreover, TU was found to act as an accelerator to enhance the deposition rate, thus the concentration of TU did result in the change in the surface morphology and electrocatalytic behaviors of CoS deposit. After the optimization of TU concentration, a DSSC assembled with a CoS CE prepared in 0.75 M TU showed a superior cell efficiency of 6.22% in comparison to a DSSC with a sputtered-Pt CE (5.80%). This enhanced efficiency was attributed to the increased active surface area and the lower charge transfer resistance for I3− reduction.

Simultaneous determination of trace lead, tin and cadmium in biological samples by a chemical vapor generation-four-channel atomic fluorescence spectrometry dual gas–liquid separator system

A novel, accurate, and precise method is described for simultaneous determination of trace lead (Pb), tin (Sn) and cadmium (Cd) in biological samples by chemical vapor generation (CVG) coupled with non-dispersive atomic fluorescence spectrometry. A chemical vapor generation dual gas–liquid separator system for Pb, Sn and Cd determination assembled with atomic fluorescence spectrometry was proposed. The system consists of two peristaltic pumps as the liquid driver, two gas–liquid separators and an atomic fluorescence detector. In the first gas–liquid separator system, the main Cd vapor and some SnH4 were carried out with reductant solution I, and in the second gas–liquid separator system, the main PbH4 and some SnH4 were carried out with reductant solution II. Cadmium vapor generation was based on hydrochloric acid, cobalt chloride, thiourea and KBH4 concentrations of the first system, SnH4 generation was based on hydrochloric acid and KBH4 concentrations, and PbH4 was based on hydrochloric acid, potassium ferricyanide and KBH4 concentrations of the second system. The operating conditions of the instrumentation were optimized, including the flow rates of carrier and shield gas. The conditions of chemical vapor generation for Pb, Sn and Cd were studied in detail. Under optimized experimental conditions, the blank signal was satisfactorily minimized, giving limits of detection of 0.071, 0.058 and 0.002 ng ml−1 for Pb, Sn and Cd respectively. The relative standard deviation (R.S.D.) was respectively 1.3%, 3.4% and 2.9% for 10 ng ml−1 of Pb, Sn and 2 ng ml−1 of Cd (n = 7). Finally, the proposed method was successfully applied to the simultaneous determination of Pb, Sn and Cd in a series of Chinese certified biological reference materials using simple aqueous standard calibration techniques, with analytical results in good agreement with the certified values.

Thiourea–thiocyanate leaching system for gold

The leaching of gold in thiourea –thiocyanate solutions has been studied by the rotating-disc technique using ferric sulfate as oxidant. The effects of initial concentrations of ferric, thiourea (Tu) and thiocyanate as well as temperature and pH on gold leaching rates were studied. An initial gold leaching rate in the order of 10 − 9 mol cm − 2 s − 1 was obtained at 25 °C, which was higher than rates obtained when either ferric–thiocyanate or ferric–thiourea solutions were used separately. The synergistic effect was attributed to the formation of a mixed ligand complex Au(Tu) 2SCN. Determinations of apparent activation energy indicate that the process was controlled by a combination of chemical reaction and diffusion in the mixed lixiviant system. Open circuit potentials show that thiocyanate stability is increased in the mixture.

Simultaneous speciation of inorganic arsenic and antimony in water samples by hydride generation-double channel atomic fluorescence spectrometry with on-line solid-phase extraction using single-walled carbon nanotubes micro-column

A new method was developed for the simultaneous speciation of inorganic arsenic and antimony in water by on-line solid-phase extraction coupled with hydride generation-double channel atomic fluorescence spectrometry (HG-DC-AFS). The speciation scheme involved the on-line formation and retention of the ammonium pyrrolidine dithiocarbamate complexes of As(III) and Sb(III) on a single-walled carbon nanotubes packed micro-column, followed by on-line elution and simultaneous detection of As(III) and Sb(III) by HG-DC-AFS; the total As and total Sb were determined by the same protocol after As(V) and Sb(V) were reduced by thiourea, with As(V) and Sb(V) concentrations obtained by subtraction. Various experimental parameters affecting the on-line solid-phase extraction and determination of the analytes species have been investigated in detail. With 180 s preconcentration time, the enrichment factors were found to be 25.4 for As(III) and 24.6 for Sb(III), with the limits of detection (LODs) of 3.8 ng L − 1 for As(III) and 2.1 ng L − 1 for Sb(III). The precisions (RSD) for five replicate measurements of 0.5 μg L −1 of As(III) and 0.2 μg L −1 of Sb(III) were 4.2 and 4.8%, respectively. The developed method was validated by the analysis of standard reference materials (NIST SRM 1640a), and was applied to the speciation of inorganic As and Sb in natural water samples.

One-step template-free electrosynthesis of 300 μm long copper sulfide nanowires

We report a one-step template-free electrosynthesis method for high-aspect-ratio copper sulfide nanowires from dilute copper solution containing thiourea on platinum and stainless steel surfaces. Fast pulse electrodeposition produced a deposit composed of copper sulfide nanowires with Cu to S at% ratios of ca. 1, lengths up to 300 μm, and diameters between 40 and 600 nm, depending on the deposition conditions. The main part of the deposit was found to be amorphous. Crucial parameters that decide the dimensions are thiourea and copper ion concentrations, potential, and the on–off cycle time of the pulse electrodeposition process. A nanowire growth mechanism which accounts for these parameters is also proposed.

Effect of Sulfur Incorporation on Coercivity in CoFe Nanowires

In this study we report for the first time the effect of sulfur incorporation on coercivity in CoFe nanowires. The CoFe alloys were deposited from a sulfate bath with varying concentrations of thiourea in polycarbonate membranes. The physical incorporation of sulfate anions from the electrolyte was also taken into account as a source of sulfur which was not considered earlier. The deposition was done potentiostatically to control the composition of the CoFe nanowires. A low coercivity (soft nanowire) in the range of 120-130 oersteds was obtained for samples containing low S at%. Also the amount of sulfur seemed to have an effect on the microstructure of the deposits. A low thiourea concentration was determined to be ideal to achieve low coercivities. Composition and surface morphology was studied using EDAX and SEM respectively. Coercivity was studied using an Alternating Gradient Magnetometer (AGM) with fields applied upto 1Tesla.

Development of Mathematical Model for Prediction and Optimization of Particle Size in Nanocrystalline CdS Thin Films Prepared by Sol-Gel Spin-Coating Method

Nanocrystalline CdS thin films have been prepared by the sol-gel spin-coating method. The influence of spin-coating process parameters such as, thiourea concentration (U), annealing temperature (A), rotational speed (S), and annealing time (T), and so on, on the properties of the prepared films have been studied. The experiments have been carried out based on four factor-five-level central composite designs with the full replication technique, and mathematical models have been developed using regression technique. The central composite rotatable design has been used to minimize the number of experimental parameters. The analysis of variance technique is applied to check the validity of the developed models. The developed mathematical model can be used effectively to predict the particle size in CdS nanocrystalline thin films at 95 pct confidence level. The results have been verified by depositing the films using the same condition. An ultraviolet-visible optical spectroscopy study was carried out to determine the band gap of the CdS nanocrystalline thin films. The band gap has been observed to depend strongly on particle size, and it indicated a blue shift caused by quantum confinement effects. The high-resolution transmission electron microscopy analysis showed the grain size of the prepared CdS film to be 6 nm. The main and interaction effects of deposition parameters on the properties of CdS nanocrystalline thin films also have been studied.

Growth and Optical Properties of Cd1-xZnxS Thin Films

Highly transparent cadmium zinc sulfide (Cd1-xZnxS) thin films were deposited by chemical bath deposition (CBD) under various ammonia and thiourea concentrations, which strongly affected the optical properties of Cd1-xZnxS films at different deposition stages: homogeneous reaction, atom-by-atom process and cluster-by-cluster deposition. Ammonia bound metal ions and, according to complex ion dissociation and equilibrium constants, released small concentration of ions. The hydrolysis of thiourea in the alkaline medium, provided by ammonia hydrolysis, released sulfide ion S2- resulting in the formation of Cd1-xZnxS thin films. In the CBD deposition process, it was important to control the ions concentration released by these two agents. Otherwise, there would be immediate precipitation or existed a large amount colloids in the reactive bath preventing the deposition of thin films. The influences of various ammonia and thiourea concentrations on the growth mechanism and the optical properties of thin films were investigated. The transmission spectra (TS) and spectra-ellipsometry (SE) were measured and the data were modeled and fitted, giving the parameters which were further to estimate the quality of thin films. The optical properties and the parameters indicated that the ammonia concentration played an important role for obtaining high quality Cd1-xZnxS films. All parameters showed that it was more essential to control ammonia concentration in CBD deposition of high quality thin films, compared with thiourea.

Synthesis and characterization of alginate‐g‐vinyl sulfonic acid with a potassium peroxydiphosphate/thiourea system

AbstractAlginate‐g‐vinyl sulfonic acid graft copolymer was synthesized through the graft copolymerization of vinyl sulfonic acid (VSA) onto alginate with an efficient system, i.e., potassium peroxydiphosphate (PDP)/thiourea in an aqueous medium. The effects of the concentration of thiourea, PDP, hydrogen ion, alginate, and VSA along with the time and temperature on the graft copolymerization were studied by the determination of the grafting parameters (grafting ratio, add‐on, conversion, grafting efficiency, and homopolymer). The synthesized graft copolymer was characterized by FTIR analysis. Thermogravimetric analysis showed that the alginate‐g‐vinyl sulfonic acid is thermally more stable than alginate. Water swelling capacity, metal ion sorption, flocculation, and resistance to biodegradability studies of synthesized graft copolymer have been performed with respect to the parent polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Influence of Thiourea Dimers in the Chemical Bath Deposition Process of Metal Sulfides

The chemical bath deposition of metal sulfide, especially CdS, is the most common way of growing buffer layers in the chalcopyrite photovoltaic solar cells. From the kinetic point of view, the reactions should always be reproducible with the same initial reactant concentration of thiourea, ammonia, and cadmium salt, the same temperature, and the same deposition time. But different reaction kinetics of CdS molecule formation and deposition is observed. Different thiourea lots with nominally the same purity show different kinetics of the reaction and resulting CdS layer thicknesses after the reaction.

Effect of [Zn]/[S] ratios on the properties of chemical bath deposited zinc sulfide thin films

ZnS thin films have been prepared by chemical bath deposition (CBD) technique onto glass substrates deposited at about 80 °C using aqueous solution of zinc sulfate hepta-hydrate, ammonium sulfate, thiourea, ammonia and hydrazine hydrate. Ammonia and hydrazine hydrate were used as complexing agents. The influence of the ratio of [Zn]/[S] on formation and properties of ZnS thin films has been investigated. The ratio of [Zn]/[S] was changed from 3:1 to 1:9 by varying volumes and/or concentrations of zinc sulfate hepta-hydrate and thiourea in the deposition solution. The structural and morphological characteristics of films have been investigated by X-ray diffraction (XRD), scanning electron microscope and UV–vis spectroscopic analysis. ZnS films were obtained with the [Zn]/[S] ratio ranged from1:1 to 1:6. In the cases of [Zn]/[S] ratio ≥ 3:1 or ≤1:9, no deposition was found. Transparent and polycrystalline ZnS film was obtained with pure-wurtzite structure at the [S]/[Zn] ratio of 1:6. The related formation mechanisms of CBD ZnS are discussed. The deposited ZnS films show good optical transmission (80–90%) in the visible region and the band gap is found to be in the range of 3.65–3.74 eV. The result is useful to further develop the CBD ZnS technology.

A study toward the physicochemical properties of graft copolymer (partially carboxymethylated guar gum‐g‐N,N′‐dimethylacrylamide): Synthesis and characterization

AbstractUnreported graft copolymer of N,N′‐dimethylacrylamide (DMA) with partially carboxymethylated guar gum (CmgOH) has been synthesized and the reaction conditions have been optimized for affording maximum grafting using a potassium peroxymonosulphate (PMS)/thiourea (TU) redox initiators under nitrogen atmosphere. The study of graft copolymerization has been performed to observe maximum value of grafting parameters except percentage of homopolymer by varying the concentrations of DMA, PMS, and TU. The grafting parameters increase continuously on increasing the concentration of DMA from 8 × 10−2 to 24 × 10−2 mol dm−3, PMS from 5 × 10−3 to 21 × 10−3 mol dm−3, and TU from 1.6 × 10−3 to 4.8 × 10−3 mol dm−3. The optimum temperature and time for grafting of DMA onto CmgOH were found to be 35°C and 120 min, respectively. The water‐swelling capacity of graft copolymer is investigated. Flocculation property for both coking and noncoking coals is studied for the treatment of coal mine waste water. The graft copolymer is characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010