Dünnschichtchromatographie als Hilfsmittel in der radiochemie. 6. Mitteilung. 1. Trennung von Sn, 125Sb und 125mTe. - 2. Trennung von As,Sb und Sn

1. Thin-layer chromatography is applied to the separation of the nuclids of the decay-chain: ¹²⁵Sn → ^125mTe. Different factors influencing the separation are investigated. The method can be used for the carrier-free separation of ^125mTe. 2. As, Sb and Sn have been separated by thin-layer chromatography.     

Preparation of a118Te/118Sb radionuclide generator

The development of a new radionuclide generator, based on¹¹⁸Te/¹¹⁸Sb, has been studied. The 3.5 minute¹¹⁸Sb daughter activity decays principally by positron emission and has potential use as a flow tracer. The¹¹⁸Te parent is conveniently produced by proton bombardment of antimony targets. A simple and efficient scheme for the separation of radiotellurium from proton-irradiated antimony targets has been developed, and thin-target cross sections for¹²¹Sb(p, 4n)¹¹⁸Te and competing reactions have been determined. For antimony targets irradiated with 46 MeV protons, the yields (mCi/g Ah) of¹¹⁸Te,^119mTe and¹¹⁹Te were measured to be 0.71, 0.33 and 1.9, respectively. The adsorption and elution characteristics of activated carbon for tellurium have been evaluated for use as a column chromatography adsorbent in a¹¹⁸Te/¹¹⁸Sb generator. The conditions for optimal¹¹⁸Sb elution and minimal¹¹⁸Te breakthrough for promising systems are presented.     

Separation of trace elements,In(III), Sn(IV), Sb(V) and Te(IV) by adsorption on activated carbon and graphite

Adsorption behaviour of trace elements, In(III), Sn(IV), Sb(V) and Te(IV) on activated carbon and graphite powder was studied. Adsorption characteristics of the ions enabled the separation of In(III)–Sn(IV), Sn(IV)–Sb(V) and Sb(V)–Te(IV) pairs. Applications to practical separation, milking of^113mIn from¹¹³Sn, removal of tin impurity from¹¹⁹Sb, and milking of¹¹⁹Sb from^119mTe, are presented.     

Adsorption and colloidal behavior of traces of hexavalent tellurium in aqueous solutions

The solutions of carrier-free^125mTe(VI) have been prepared by oxidizing^125mTe(IV) with bromine. Using carrier-free^125mTe(VI) as a tracer, the effects of pH, NaCl concentration, and tellurium(VI) concentration on the adsorption and colloidal properties of tellurium(VI) in NaCl solution have been studied. It has been found that traces of tellurium(VI) are adsorbed on filter paper and show colloidal behavior in the basic region. A method has been devised for the separation of carrier-free^125mTe from its parent nuclide¹²⁵Sb, based on the adsorption properties of^125mTe(VI) in basic solutions.     

Preparation of99Mo,132Te isotopes and99mTc,132I generators

Adsorption and desorption of⁹⁵Zr−⁹⁵Nb,⁹⁹Mo,¹⁰³Ru,¹³²Te and²³⁹Np in a HCl-alumina system were studied in order to purify⁹⁹Mo and¹³²Te obtained by the cation-exchange separation of fission products and to prepare highly pure^99mTc and¹³²I generators.⁹⁹Mo and¹³²Te, of which radionuclidic purity was over 99.99% and 99.999%, respectively, could be obtained by passing the cation-exchange separated Mo and Te fractions through alumina columns, by washing with HCl and finally by eluting⁹⁹Mo with 1M NH₄OH and¹³²Te with 3M NaOH. In order to raise the recovery of⁹⁹Mo and¹³²Te from the alumina columns, they should be eluted as quickly as possible after the adsorption. The direct use of the alumina column containing⁹⁹Mo or¹³²Te as the generator allowed milking of^99mTc or¹³²I, of which radionuclidic purity was over 99.999%. Milking yields of^99mTc with 0.1M HCl and¹³²I with 0.01M NH₄OH were 77% and 90%, respectively. The latter value was much higher than that in usual performance of the generator.     

Synthesis and Crystal Structure of Manganese‐tris(1,2‐ethanediamine)tetratelluride [Mn(en)3]Te4 Exhibiting Intermolecular Interactions between the Tetratelluride Anions

Air‐sensitive black crystals of the new compound [Mn(en)₃]Te₄ were synthesized by reacting MnCl₂ · 4 H₂O, K₂Te₃ and elemental Te in 1,2‐ethanediamine (en) under solvothermal conditions at 433 K. The compound crystallizes in the monoclinic space group P2₁/n with lattice parameters a = 839.51(7) pm, b = 1551.3(1) pm, c = 1432.6(1) pm, and β = 90.28(2)°. Isolated [Mn(en)₃]²⁺ cations and Te₄^2– anions are arranged in an alternating fashion parallel to the crystallographic b‐axis. One terminal Te atom of the Te₄^2– anions exhibits a short intermolecular contact to a neighboured anion thus forming Te₈^4– anions. A slightly longer interionic Te…Te separation is observed between two of the inner Te atoms of neighboured Te₈^4– anions. Taking these longer separations into account infinite Te‐chains are formed running parallel to [001]. The intermolecular Te…Te interactions affect the Te–Te bond lengths within the Te₄^2– anion leading to a lengthening of the average Te–Te distance. Short N–H…Te distances indicate hydrogen bonding between the cations and anions. DTA‐TG measurements show that at 441 K the material decomposes in one step. The resulting crystalline material consists of MnTe₂ and Te.     

Sorption and separation of some elements of nuclear importance using Chelex-100

Chelex-100, in the anionic form has been studied for its ability to perform selective separation and concentration of some metal ions of nuclear importance from mineral acid solutions. The sorption behavior of Zr(IV)–Nb(V), Mo(VI), Tc(VII), Te(IV) and U(VI) from solutions of hydrochloric and sulphuric acids on Chelex-100 has been studied under static and dynamic conditions. Mo(VI) and Tc(VII) have been concentrated on the resin from hydrochloric or sulphuric acid solutions at low acidities probably, as the anions MoO ₄ ^2– and TcO ₄ ^– , respectively. Te(IV) has been isolated from hydrochloric acid solutions of normalities 6 in the form of the anionic chloro complex TeCl ₆ ^2– . Optimum conditions for elution and separation of Mo(VI), Tc(VII), Te(IV) and U(VI) were recommended.     

Preparation of Photocatalytic Au–Ag2Te Nanomaterials

A facile approach has been developed for the preparation of various morphologies of Au–Ag₂Te nanomaterials (NMs) that exhibit strong photocatalytic activity. Te NMs (nanowires, nanopencils, and nanorice) were prepared from TeO₂ in the presence of various concentrations (16, 8, and 4 M ) of a reducing agent (N₂H₄) at different temperatures (25 and 60 °C). These three Te NMs were then used to prepare Au–Ag₂Te NMs by spontaneous redox reactions with Au³⁺ and Ag⁺ ions sequentially. The Au–Ag₂Te nanopencils exhibit the highest activity toward degradation of methylene blue and formation of active hydroxyl radicals on solar irradiation, mainly because they absorb light in the visible region most strongly. All three differently shaped Au–Ag₂Te NMs (10 μg mL^?1) provide a death rate of Escherichia coli greater than 80 % within 60 min, which is higher than that of 51 % for commercial TiO₂ nanoparticles (100 μg mL^?1). Under light irradiation, the Au NPs in Au–Ag₂Te NMs enhance the overall photo‐oxidation ability of Ag₂Te NMs through faster charge separation because of good contact between Ag₂Te and Au segments. With high antibacterial activity and low toxicity toward normal cells, the Au–Ag₂Te NMs hold great potential for use as efficient antibacterial agents.     

Anion-exchange and solvent extraction studies on the separation of radioiodine with particular reference to the production of 123I via proton irradiation of 123Te metal target

The separation of radioiodine was investigated using two wet chemical procedures, namely anion-exchange and solvent extraction. Some factors affecting the separation, such as HCl, NaOH and tetrabutyl ammonium bromide (TBAB) concentrations, used solvents ethyl acetate, benzene and carbon tetrachloride and different quaternary ammonium salts were studied. For each procedure the optimum conditions were deduced. The separation of ¹²³I was effected from proton-irradiated ¹²³Te target under the optimized conditions of the two procedures. The yield of ¹²³I obtained using the Dowex 21k anion-exchanger and tetrabutyl ammonium bromide solution as eluting agent was 88±3%; the radionuclidic purity was high and the time needed was 60 minutes. In solvent extraction process using TBAB in ethyl acetate as the extracting agent, the yield of ¹²³I was low (47±3%), the radionuclidic purity was not as good as in the anion-exchange method, and the time needed was 150 minutes. Therefore, the anionexchange method is preferable. A comparison of this wet chemical method of separation of ¹²³I with the commonly used dry distillation method is given. The wet method appears to be more suitable when a ¹²³Te metal target is used.     

Enriched stable isotopes for 123I production: Pathways and prospects

Large-scale production of radioisotopes for medical application was impeded by limited capabilities of the electromagnetic separation. Nowadays the centrifuge separation process involves more than two dozens of chemical elements. The cost of isotopes is incomparably lower than of those produced by electromagnetic separation, which has made enriched isotopes more practicable and has extended their application scope. The development of new isotope targets has ensured the realization of more effective schemes of ¹²³I production. The processes of ¹²⁴Xe and ¹²³Te production are reviewed.     

Development of an ion-exchange method for separation of radioiodine from tellurium and antimony and its application to the production of 124I via the 121Sb(α,n)-process

A novel anion-exchange chromatographic method for separation of radioiodine from an antimony target irradiated with ³He- or α-particles was developed, with separation yield of radioiodine amounting to 90 ± 5 % and its decontamination factor from the Te and Sb radionuclides to ~10⁴. The optimized separation method developed was then applied to the production of ¹²⁴I via the ¹²¹Sb(α,n)¹²⁴I process using a highly enriched ¹²¹Sb target. Quality control tests showed that the separated ¹²⁴I occurred >99 % as iodide and the longer lived impurities ¹²⁶I and ¹²⁵I amounted to 0.16 % and <0.05 %, respectively. The trace level of inactive Sb impurity was determined by ICP–OES.     

Neutron activation analysis of PbxSn1-xTe using extraction chromatography

A simple procedure of neutron activation analysis for the determination of 16 impurities in Pb_xSn_1–xTe with detection limits from 1×10^–4% for Ni and Zr to 2×10^–9% for Sc has been developed. The procedure is based on extraction chromatographic separation of impurities from the irradiated sample.     

Flotation method for separation of elemental Te with Se as collector

Summary A method combining co-precipitation of traces of elemental Te on Se as carrier with organic solvent flotation is described. The best reduction and flotation conditions (hydrochloric and phosphinic acid concentrations, amount of Se, solvent used) were chosen. The recoveries for 100g of Te(IV) (AAS measurement in MIBK) and 2g of Te (radiochemical measurement with¹²⁷Te) were 98% and 84–88%. The method was applied for separation of Te(IV) from copper metallurgy dust and slag.

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Flotationsverfahren zur Abtrennung von elementarem Tellur mit Selen als Kollektor

Zusammenfassung Die Kombination der Mitfällung von Spuren elementaren Tellurs auf Selen als Trägersubstanz mit der Flotation mit Hilfe eines organischen Lösungsmittels wurde beschrieben. Die besten Bedingungen zur Reduktion und Flotation (Salzsäure-und Phosphinsäurekonzentration, Selenmenge, Lösungsmittel) wurden ausgewählt. Die Wiederfindungsraten für 100g Te(IV) (AAS-Bestimmung in MIBK) und 2g Te (radiochemische Messung mit¹²⁷Te) waren 98% bzw. 84–88%. Das Verfahren wurde zur Trennung von Te(IV) aus dem Staub und der Schlacke der Kupfermetallurgie verwendet.

     

Separation of carrier-free 111In, 116,117Te and 116,116m,117Sb from a 11B-induced silver target

Heavy-ion activation with ~55 MeV ¹¹B beam on silver target leads to the production of carrier-free ¹¹¹In, ^116,117Te and ^116,116m,117Sb radioisotopes in the target matrix. Liquid-liquid extraction, using Aliquat-336 and trioctylamine (TOA) as liquid anion exchangers in HNO₃ and HCl medium, respectively, and di-(2-ethylhexyl)phosphoric acid (HDEHP) as liquid cation exchanger in ammoniacal medium was used to investigate the separation of the produced radioisotopes from the bulk target matrix.     

Sorption characteristics and separation of tellurium ions from aqueous solutions using nano-TiO2

Titanium dioxide nanoparticles (nano-TiO₂) were employed for the sorption of Te(IV) ions from aqueous solution. A detailed study of the process was performed by varying the sorption time, pH, and temperature. The sorption was found to be fast, equilibrium was reached within 8 min. When the concentration of Te(IV) was below 40 mg L⁻¹, at least 97% of tellurium was adsorbed by nano-TiO₂ in the pH range of 1-2 and 8-9. The sorbed Te(IV) ions were desorbed with 2.0 mL of 0.5 mol L⁻¹ NaOH. The sorption data could be well interpreted by the Langmuir model with the maximum adsorption capacity of 32.75 mg g⁻¹ (20 ± 0.1 °C) of Te(IV) on nano-TiO₂. The kinetics and thermodynamics of the sorption of Te(IV) onto nano-TiO₂ were also studied. The kinetic experimental data properly correlated with the second-order kinetic model (k₂ = 0.0368 g mg⁻¹ min⁻¹, 293 K). The overall rate process appeared to be influenced by both boundary layer diffusion and intra-particle diffusion. The mean energy of adsorption was calculated to be 17.41 kJ mol⁻¹ from the Dubinin-Radushkevich (D-R) adsorption isotherm at room temperature. Moreover, the thermodynamic parameters for the sorption were estimated, and the ΔH⁰ and ΔG⁰ values indicated the exothermic and spontaneous nature of the sorption process, respectively. Finally, Nano-TiO₂ as sorbent was successfully applied to the separation of Te(IV) from the environmental samples with satisfactory results (recoveries >95%, relative standard deviations was 2.0%).     

Chalcogen Bonding with Diaryl Ditellurides: Evidence from Solid State and Solution Studies.

The chalcogen bonding (ChB) ability of Te is studied in symmetrical diaryl ditellurides ArTeTeAr. Among the two Te σ-holes, the one along the less polarized Te−Te bond was calculated as the more electropositive. This counter-intuitive situation is due to the hyperconjugation contribution from Te lone pair to the σ* of the adjacent Te which coincides with σ-hole along the more polarized Te−Ar bond. ArTeTeAr showed notable structural features in the solid state as a result of intermolecular Te⋅⋅⋅Te ChB, such as a Te₄ rectangle through dimer aggregation or a triangular Te₃ motif, where one Te interacts with both Te atoms of a neighboring molecule through both its σ-hole and lone pair, in a slightly frustrated geometry. Lewis acidity of ArTeTeAr was also evaluated by NMR with R₃PO as σ-hole acceptors in different solvents. Thus, ¹²⁵Te NMR allowed monitoring Te⋅⋅⋅O interaction and delivering association constants (K_a) for 1 : 1 adducts. The highest value of K_a=90 M⁻¹ was measured for the adduct between ArTeTeAr bearing CF₃ groups and Et₃PO in cyclohexane. Notably, by using nBu₃PO, Te⋅⋅⋅O interaction was revealed by ¹⁹F-¹H HOESY showing spatial proximity between CF₃ and CH₃ of nBu₃PO.     

Trennung von Spurenelementaktivitäten aus Neutronenbestrahltem Selen mit Hilfe der Gegenstrom-Ionenwanderung

For the determination of trace elements in neutron irradiated, selenium by gamma-ray spectrometry the separation of the matrix activity is often necessary. In model experiments the decontamination of cation and anion impurities from the matrix solution was investigated by the counter current ion migration. After a processing of 3 hrs the trace activities of Co, Cr, Ga, Na and Zn were decontaminated from Se with a factor of >10³. For the trace elements As and Te representing the anionic constituents, a decontamination factor of 3·10² was obtained.     

Electrochemistry of tellurium(IV) in KCl−AlCl3 melts

The reduction of Te(IV) at tungsten electrodes in basic and neutral KCl?AlCl₃ melts has been studied in the temperature range from 300 to 400°C using cyclic voltammetry and differential pulse polarography. In basic melts Te(IV), present as TeCl₆^2? and TeCl₅^?, is reduced to soluble Te(II) species, which can be further reduced to elementary tellurium insoluble in tungsten. The divalent species are stabilized by increasing the temperature. From the pCl^? dependence of the reduction process, Te(II) in basic melts is suggested to be present as TeCl₃^? and TeCl₂. In neutral melts a third oxidation state (possibly monovalent tellurium) is formed when Te(II) is reduced.     

A Study of Competitive Coordination of Benzochalcogenazole Ligands by Heteronuclear NMR Spectroscopy

Complexes of 2-methyl(phenyl)benzo-1,3-tellurazole and 2-methyl(phenyl)benzo-1,3-selenazole with tungsten pentacarbonyl and boron trifluoride were studied by heteronuclear NMR spectroscopy (¹H, ¹³C, ⁷⁷Se, and ¹²⁵Te). The coordination mode of the ambident ligand can be determined from the coordination shifts of the ¹²⁵Te and ⁷⁷Se NMR signals: upfield at coordination via Te and Se atoms and downfield at N coordination.     

Antibacterial Activities of Tellurium Nanomaterials

We prepared four differently shaped Te nanomaterials (NMs) as antibacterial reagents against Escherichia coli. By controlling the concentrations of hydrazine (N₂H₄) as reducing agent, NaCl, and temperature, we prepared Te nanowires, nanopencils, nanorices, and nanocubes. These four Te NMs resulted in a live/dead ratio of E. coli cells of less than 0.1, which is smaller than that of Ag nanoparticles. The order of antibacterial activity against E. coli is nanocubes ≈ nanorices > nanopencils ≈ nanowires. This is in good agreement with the concentration order of tellurite (TeO₃²⁻) ions released from Te NMs in E. coli cells, revealing that TeO₃²⁻ ions account for the antibacterial activity of the four Te NMs. We found that spherical Te nanoparticles (32 nm in diameter) with TeO₃²⁻ ions were formed in the E. coli cells. Compared to Ag nanoparticles that are commonly used as antibacterial reagents, Te NMs have higher antibacterial activity and lower toxicity. Thus, Te NMs hold great practical potential as a new and efficient antibacterial agent.