Thiocyanate Solutions Research Articles

Flame atomic absorption spectrometric determination of silver after preconcentration on Amberlite XAD-16 resin from thiocyanate solution

A method of silver preconcentration by using a column containing Amberlite XAD-16 resin and this future determination by a flame AAS after elution is proposed. The effect of the factors such as pH, the nature of complexing agent, sample volume, flow rate, the type and concentration of elution solution on the preconcentration efficiency have been investigated. The influence of some matrix elements on the recovery of silver were also examined. It was found, that the quantitative recovery of thiocyanate complex of silver was obtained from nitric acid solution (pH 2) as 99.20±0.07% at the 95% confidence level. A preconcentration factor up to 75 could be obtained. The detection limit of silver was 0.047 mg l −1. The adsorption of silver onto Amberlite XAD-16 can be formally described by a Langmuir equation with maximum adsorption capacity 4.66 mg g −1 (0.043 mmol g −1). The proposed method was applied to determination of silver in standard alloy with relative error 6.25%.

A separation method to overcome the interference of aluminium on zinc determination by inductively coupled plasma atomic emission spectroscopy

The use of polyurethane foam (PUF) to separate zinc from large amounts of aluminium and its determination by inductively coupled plasma atomic emission spectroscopy technique (ICP-AES) in aluminium matrices is described. The proposed method is based on the solid-phase extraction of the zinc(II) cation as a thiocyanate complex. Parameters such as effect of pH on zinc sorption, zinc desorption from the foam and analytical features of the procedure were studied. Results showed that the zinc(II) cation within the range from 0.02 to 65.0 μg in 0.2 mol l −1 thiocyanate solution and pH range from 1.0 to 4.0, could be quantitatively extracted by 0.1 g of PUF. The precision of the method was calculated as the relative standard deviation from a series of seven measurements. It was 3.9% for 1.0 μg of zinc in a volume solution of 50 ml. The proposed procedure was used for zinc determination in both aluminium alloys and salts with zinc concentration in the range from 50 to 300 μg g −1. A standard addition technique was used and achieved results showing that this procedure has good accuracy and precision.

A macromolecular N, N-dichlorosulfonamide as oxidant for thiocyanates

Macroporous S/DVB copolymer containing N, N-dichlorosulfonamide groups was used for removal of thiocyanate ions from aqueous solutions. This copolymer contains active chlorine in functional groups (8.2 meq Cl ∗/g) and oxidises thiocyanates to considerably less toxic products (such as sulphate, cyanate, carbonate and ammonium ions). The resin was employed in static and dynamic conditions and thiocyanate solutions containing 116 or 560 ppm SCN − were treated. The effects of various parameters on the rates of reaction have been studied. The proposed method is particularly advantageous for treating highly diluted solutions. Using this redox copolymer, it was possible to reduce thiocyanate concentration in solutions below 0.5 mg SCN −/dm 3. The oxidation capacity of the resin was found to be nearly 60 mg SCN −/g. The resin was especially efficient for removal of SCN − ions from neutral and weakly acidic solutions, whereas in alkaline media it lost a part of its oxidising properties as a result of escape of active chlorine. Reactivation of the stripped resin was performed in a one-step treatment by an acidified solution of sodium chlorate(I). The regenerated copolymer can be reused in the next cycle.

Extraction of Ag(I) from aqueous thiocyanate solution with Primene JMT or TOA

Using Primene JMT or TOA, the extraction of thiocyanic acid and of Ag(I) thiocyanato-complex from aqueous thiocyanate solution was studied. On extraction of thiocyanic acid using aqueous phase containing 1.0 M NH 4SCN and an organic phase containing 100–300 kg m −3 Primene JMT or TOA, (RNH 3 +·SCN −) o and (R 3NH +·SCN −) o were formed with apparent equilibrium constants, log K ex,a, of 8.7 and 6.5, respectively. The extraction of 1×10 −3 M Ag(I) from aqueous ammonium thiocyanate solutions by the thiocyanate salts of Primene JMT or TOA at concentrations ranging from 100 to 300 kg·m −3, and in the presence of ammonium thiocyanate at concentrations of 0.5–3.0 M can be summarized as follows: 2( RNH 3 +· SCN −) o + Ag( SCN) 3 2− = K ex,3 (( RNH 3 +) 2· Ag( SCN) 3 2−) o +2 SCN −, logK ex,3 =1.6 2( R 3 NH +· SCN −) o + Ag( SCN) 3 2− = K ex,3 (( R 3 NH +) 2· Ag( SCN) 3 2−) o +2 SCN −, logK ex,3 =2.5.

Spectrochemistry of Solutions: A Vibrational Spectroscopic Study of Ion Pairing and Upper Stage Transition of Magnesium (II) and Calcium (II) by Thiocyanates in Liquid Ammonia

Ion pairing and upper stage transition of magnesium (II) and calcium (II) with thiocyanate ion has been studied by Infrared and Raman spectroscopy. A complete picture of species present in thiocyanate solutions has been established. The spectral profile consists of five thiocyanate species namely; a triple-ion, [SCN - M - NCS]1:1 contact ion pair (M - NCS] solvent-shared ion pair (NH) M - NH - NCS] “free” thiocyanate ion (SCN) and an upper stage transition arising from the excitation of a linear species already in a vibrational level above the ground state i.e. v2 bending vibration. This was a feature observed on the lower wavelength. UNISWA Research Journal of Agriculture, Science and Technology Vol. 4 (1) 2000: pp 10-15

Cerium(IV) ammonium nitrate mediated thiocyanation of dienes: Some interesting observations

Various 1,3-dienes when treated with a solution of cerium(IV) ammonium nitrate and ammonium thiocyanate in acetonitrile afforded the isothiocyanatothiocyanates via a [3,3] sigmatropic rearrangement. Electron rich dienes afforded the γ-thiocyanato-α,β-unsaturated carbonyl compounds under similar experimental conditions.

Structure and optical properties of molybdenum disulphide (MoS2) thin film deposited by the dip technique

Molybdenum dichalcogenides appear to be very promising semiconductor materials for various applications such as solar cells [1, 2], rechargeable batteries [3] and solid lubricants for metallic and ceramic surfaces in environments where hydrocarbon or other fluid-based lubricants are unsuitable, such as in high vacuum or high temperature applications [4, 5]. They have also been widely used in space-technology where their low co-efficient of friction in vacuum is of particular value [6]. These applications arise from the optical, electrochemical and mechanical properties of these compounds. They exhibit a layer-type structure in which monolayers of Mo are sandwiched between monolayers of sulphur, which are held together by relatively weak van der Waals forces. These materials have band gaps (1.78 eV) well-matched to the solar spectrum [7]. A number of methods exist for the production of MoS2 thin films, including sputtering [8–10], electrochemical deposition [7, 11], and pulsed laser deposition [12–15]. In this communication, preliminary results on structural and optical properties of MoS2 thin films produced by a dip-coating [16, 17] technique are reported. In the film deposition process the substrate was first immersed and then withdrawn vertically from the freshly prepared methanolic solution of ammonium molybdate and ammonium thiocyanate at a controlled speed of about 1.33 mm/s with the help of a pulley and geared motor. The substrate with the liquid layer adhering to it was then transferred to a high temperature furnace under atmospheric conditions for heat treatment. The chemicals reacted on the substrate and form the desired solid film according to the following reaction.

Chemical modification oftussah silk with acid anhydrides

Tussah silk fibroin was chemically modified by acylation with aliphatic, aromatic, and hydrophobic acid anhydrides. The tussah silk fibers were pretreated by immersing them in a lithium thiocyanate (LiSCN) solution and then acylated in dimethylformamide (DMF) at elevated temperatures. Using this method, acylated tussah silk fibers with weight gains of 8–22% could be obtained. The pretreatment with LiSCN was necessary to promote the acylation. Without it, the reaction did not proceed. The optimum temperature and reaction time of the pretreatment was 55°C and 60 min, respectively. When examining the physical properties and the thermal behavior of both pretreated and acylated tussah silk, it was found that the mechanical properties and the position of the major DSC endothermic peak remained unchanged, regardless of pretreatment and acylation. The moisture regain of the pretreated tussah silk increased slightly while the moisture regain of the acylated silk decreased linearly with increasing weight gain. The chemical modification allows for a wide control of the tussah silk fiber's properties, making it possible to use tussah silk for the development and production of novel textile and biomaterials. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 382–391, 2000

Speeds of Sound and Viscosities of Potassium Thiocyanate in Water, Methanol, and Propylene Carbonate

Measured speeds of sound, structural relaxation times, and the viscosities of aqueous, methanolic, and propylene carbonate solutions of potassium thiocyanate are reported as functions of concentration (0.0049 ≤ m/mol kg–1 ≤ 22.924) and temperature (273.15 ≤ T/K ≤ 343.15). The primary solvation number of the SCN– ion has been estimated to be 11.6 in a water medium. The total solvation numbers corresponding to the concentration at which the isentropic compressibility isotherms converge for potassium thiocyanate in methanol and propylene carbonate media were estimated to be 5.2 and 1.9, respectively. Structural transition in aqueous potassium thiocyanate solution has been observed in the concentration range of c. 4.0–5.5 mol kg–1 which was assigned due to the counterbalance between the structural-breaking effect of the K+ ion and the ion-association of K+ and SCN– ions.

Adsorption and thermodynamic characteristics of Hg(II)-SCN complex onto polyurethane foam

The sorption of Hg(II) in the presence of sodium thiocyanate solution onto polyurethane (PUR) foam, an excellent sorbent, has been investigated in detail. Maximum sorption of Hg(II) is achieved from 0.1 M hydrochloric acid solution containing 7.5×10 −2 M sodium thiocyanate in 5 min. The sorption data followed both Freundlich and Langmuir adsorption isotherms. The Freundlich constants 1/ n and sorption capacity, C m, are evaluated to be 0.44±0.02 and (3.86±0.89)×10 −3 mol g −1. The saturation capacity and adsorption constant derived from Langmuir isotherm are (6.88±0.28)×10 −5 mol g −1 and (5.6±0.37)×10 4 dm 3 mol −1 respectively. The mean free energy ( E) of Hg(II)-SCN sorption onto PUR foam computed from D–R isotherm is 12.4±0.3 kJ mol −1 indicating ion-exchange type mechanism of chemisorption. The variation of sorption with temperature yields thermodynamic parameters of Δ H=−30.7±1.2 kJ mol −1, Δ S=−70.1±4.1 J mol −1 K −1 and Δ G=−9.86±0.77 kJ mol −1 at 298 K. The negative value of enthalpy and free energy reflects the exothermic and spontaneous nature of sorption. On the basis of the sorption data, sorption mechanism has been proposed.

Coordination of Thiocyanate Ions to Rare Earth Ions in Concentrated Aqueous Rare Earth Thiocyanate Solutions

Coordination of Thiocyanate Ions to Rare Earth Ions in Concentrated Aqueous Rare Earth Thiocyanate Solutions

Isentropic Compressibility of Aqueous and Methanolic Sodium Thiocyanate Solutions

The speed of sound in aqueous and methanolic sodium thiocyanate solutions was measured as a function of temperature (∼293.15 ≤ T/K ≤ 323.15) and concentration (∼0.0146 ≤ m/(mol kg-1) ≤ 17.328). The isentropic compressibility isotherms for aqueous sodium thiocyanate systems converge at a particular concentration characteristic of the primary hydration shell of the solute. For the methanolic sodium thiocyanate system isentropic compressibility isotherms vary smoothly with concentration. The primary solvation number of the thiocyanate ion has been estimated to be 12.8 in aqueous medium. The total primary solvation number of sodium thiocyanate in methanol medium was found to be 3.7.

Recovery of palladium(II) and gold(III) from diluted liquors using the resin duolite GT-73

The adsorption of Pd(II) and Au(III) on the Duolite GT-73 has been investigated. The results obtained in chloride media showed a higher adsorption for Au(III) (0.58±0.03 mmol/g resin) than for Pd(II) (0.262±0.015 mmol/g resin); however, the adsorption for Pd(II) is faster. The influence of several variables such as the hydrochloric acid concentration in both metals adsorption and the addition of thiocyanate and dioxan in the study of Pd(II) has also been considered. None of the variables tested result in an improvement of the resin capacity of the metal considered, only a slightly higher adsorption for Pd(II) is observed for a HCl concentration of 0.01 M. The adsorption of Pd(II) has also been carried out in the nitrate medium, in this case the experiments were limited by the low solubility of Pd(II) in this medium (HNO 3=1.0 M). The metal adsorption found was 0.35 mmol/g resin. Acidified thiourea or sodium thiocyanate solutions as well as a hydrochloric acid solution were used for the elution of the metals, the concentrated thiourea at high acidity being the most effective one for Pd(II) as well as for Au(III). In general, the greater both the concentration of thiourea and the acidity of the solution, the easier the elution of the two metals. On the other hand, Cu(II) was readily eluted by hydrochloric acid, in contrast elutions of Au(III) and Pd(II) are less easy. Separation of Pd(II) and Au(III) from Ni(II) and Cu(II) aqueous solutions by using Duolite GT-73 is discussed. Separation of metal mixtures was carried out at different pH to improve the selective adsorption.

The decameric structure of bovine pancreatic trypsin inhibitor (BPTI) crystallized from thiocyanate at 2.7 A resolution.

The structure of a monoclinic form of bovine pancreatic trypsin inhibitor (BPTI) crystallized from a thiocyanate solution has been determined and refined at 2.7 A resolution. The space group is P21 with a = 71.56, b = 73.83, c = 64.47 A, beta = 93.9 degrees and Z = 20. The ten independent molecules were located by a multi-body molecular-replacement search as developed in the AMoRe program, starting from a single monomer model (PDB code: 6PTI). The molecular arrangement of the subunits is a decamer resulting from the combination of two orthogonal fivefold and twofold non-crystallographic axes. This builds a globular micelle-like particle which minimizes hydrophobic interactions with the solvent. The refinement was conducted with non-crystallographic symmetry constraints up to a final residual of R = 0.20 (Rfree= 0.26). The root-mean-square deviations from ideal geometry were 0.015 A and 1.6 degrees on bond distances and bond angles, respectively. Several sites for thiocyanate ions were analyzed.

Gel Spinning from Cellulose/Aqueous Calcium Thiocyanate System and the Fiber Properties.

For the purpose to develop regenerated cellulose fiber with high dry and wet tenacity, we tried gel spinning from cellulose/aqueous calcium thiocyanate solution system. The system at 125°C was extruded into air at 10°C under various spinning draft, followed by extraction of the solvent using acetone or ethanol. The fiber served to the measurements of dry and wet tensile properties, birefringence, and fibrillation resistance grade. The degree of the orientation and strength under wet and dry states monotonically increased with an increase of spinning draft. The filament spun at the draft of 6 showed the highest wet/dry tenacity ratio (=0.96) among those of other commercially available regenerated cellulose fibers. The fibrillation resistance grade as well as dry/wet tenacity were also greater than those of cupra and lyocel for textile use.

Formation of Irreversible Gels of Cellulose/Aqueous Calcium Thiocyanate Solution and Its Application to Wet Spinning.

We attempted to develop a high wet strength cellulose fiber using cellulose/aqueous calcium thiocyanate solution (aq.Ca(SCN)2) gel, as a precursor. The aq.Ca(SCN)2 showed a high dissolving power against several cellulose resources. The cellulose/aq.Ca(SCN)2 gel generated using various organic and inorganic gelling agents were examined in terms of tenacity, elongation, and the morphology. From the results, it was found that rigid and homogeneous cellulose gels with low crystallinity were formed in a short time when ketones, such as acetone and methyl ethyl ketone, and alcohols, such as methanol and ethanol, were used as a gelling agent since aq.Ca(SCN)2 is extracted from the cellulose solution. The wet spinning of the cellulose/aq.Ca(SCN)2 system was carried out using acetone or ethanol as a gelling agent. In both cases, we successfully obtained cellulose filaments with much higher tensile strength in conditioned and wet states than that of commercially available viscose and cuprammonium rayons for cloth uses.

Gelation and Gel Structure of Cellulose/aqueous Calcium Thiocyanate Solution System.

The gelation conditions of cellulose/aqueous calcium thiocyanate solution system were determined by temperature jump method and the structure of the gel was analyzed by DSC and R-ray measurements. The time necessary to occurring gelation was shorter for the higher molecular weight sample, the solution with higher concentration, and at lower temperature. For the all solutions, cloud point was observed before occurring gelation, suggesting that the gelation was induced by Liquid-liquid two phase separation. The heat to formation of l mol of network junctions in the gel and the mean molecular weight of the chain adjoining adjacent crosslinks were estimated from melting point determined by ball drop method and the heat of fusion by DSC. The X-ray diffraction curve indicated that the gel is almost amorphous.

Solid‐liquid extraction behavior of trivalent rare earths by tributyl phosphate at high temperatures

Solid–liquid extraction behaviors of trivalent rare earths (La–Lu, Y) from ammonium thiocyanate solution by tributyl phosphate using molten paraffin wax as diluent were studied and optimum extraction conditions were determined. In 10 mL of aqueous RE3+ solution where CRE(III) = 4.0 × 10−3 mol·L−1, when additions of tributyl phosphate and ammonium thiocyanate are 5.00 mL and 2.80 g, respectively, extraction distribution ratios are over 10. The procedure can be used for rapid extraction separation of rare earths. An extraction mechanism was also investigated, and the complex species extracted into organic phase is RE(TBP)(SCN)(NO3)2. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 229–233, 1999

Preferential solvent interactions and the dissolution of the B-type crystalline polymorph of starch in aqueous solutions

The preferential interactions of starch in aqueous solutions of low-molecular-weight solutes were probed using densimetric techniques which have previously been applied to proteins and nucleic acids. In d-glucitol solutions, the starch was preferentially hydrated, whereas in solutions of urea and guanidinium thiocyanate there was a preferred interaction of the solute with the starch chain. In solutions of d-glucose and glycerol no preferential interactions were observed. The effect of the same solutes on the dissolution temperature, T m, of the crystalline B-type polymorph of starch was examined by calorimetry. The addition of the hydroxy compounds glycerol, d-glucose and d-glucitol elevated T m, while the addition of urea and guanidinium thiocyanate caused a depression. For starch–urea–water mixtures, Flory theory predictions of the melting temperature were in good agreement with experiment, but were poor for starch– d-glucitol–water and starch–glucose–water mixtures. The neglect of non-configurational contributions to the entropy of mixing were identified as the principal reason for this lack of agreement.

Large Enhancement in Photocurrent Efficiency Caused by UV Illumination of the Dye-Sensitized Heterojunction TiO2/RuLL‘NCS/CuSCN: Initiation and Potential Mechanisms

Wide-band-gap, dye-sensitized, heterojunctions of the composition n-TiO2/Ru-dye/p-CuSCN undergo large increases in efficiency when subjected to low-power UV illumination (<40 mW/cm2) for periods between 10 and 30 min. Ru-dye refers to any of several ruthenium polypyridyl dyes. The UV illumination increases the incident-photon-to-current-efficiency for light absorbed by the dye by a factor of 5−10 and increases the open circuit voltage by 100−300 mV. This beneficial effect is stable for months after the UV illumination is terminated. Investigation of the effects of varying the UV wavelength and the applied bias show that the reaction(s) responsible for the increase in efficiency begin with the oxidation of some interface species by a photoexcited hole in the TiO2 valence band. Treatment of the TiO2/dye/CuSCN cells with oxidized thiocyanate in solution causes a similar increase in the efficiency of dye sensitization. Results from TiO2 and CuSCN photoelectrochemical cells are also presented. The combined res...