The relativistic contribution to the singlet-triplet excitation energy in methylene

The relativistic correction to the s²p²-sp³ energy separation in the carbon atom is shown to be 120 cm^?1 which is too small to resolve the discrepancies between theory and experiment for the ¹A₁-³B₁ energy separation in methylene.     

Identification and Separation of Some Anions on Plain and Mixed Adsorbent Layers Using Water as Eluent

The analytical potential of water as an eluent in thin layer chromatographic separation of various anions on plain adsorbent layers (silica gel "G" alumina, and cellulose) as well as on beds containing different combinations of silica gel, alumina, or cellulose has been investigated. In addition to some important separation of anions, microgram separation of IO⁻₄ from milligram quantities of IO⁻₃, Bro⁻₃, MoO²⁻₄, and Fe (CN)³⁻₆ has been realized. The effect on pH of the sample in the separation of IO⁻₄ from accompanying ions has also been studied. The limits of detection and dilution limits of anions on alumina thin layers have been determined. NO⁻₂ in artificial seawater has been detected. The effect of CaCl₂, MgCl₂, and NaHCO₃ on some ternary separations of analytical importance has been examined.     

Charge exchange and charge separation processes of [C3Hn]2+ and [C3Dn]2+ (n = 1–6) dications

The charge exchange and charge separation processes of a series of [C₃H_n]²⁺ and [C₃D_n]²⁺ (n = 1–6) dications have been investigated experimentally in a mass spectrometer of reversed geometry. The relative reaction cross-sections for charge exchange with nitrogen exhibited a 20-fold variation which has implications for the interpretation of 2E spectra with respect to dication relative intensities. Charge separation resulting in deprotonation was observed for all [C₃D_n]²⁺ species investigated, while de-deuteronation was observed for [C₃D_n]²⁺ (n = 1–4) only. Intercharge separations calculated from the observed ion kinetic energies released upon charge separation suggest linear structures for [C₃D_n]²⁺ and [C₃D_n]²⁺ (n = 1–2) and cyclic structures for [C₃D_n]²⁺ (n = 3–6) and [C₃D_n]²⁺ (n = 3–4).     

Sulfur speciation by capillary zone electrophoresis: conditions for sulfite stabilization and determination in the presence of sulfate, thiosulfate and peroxodisulfate

Capillary zone electrophoresis (CZE) was used for the separation of the sulfur species SO₃ ^2–, SO₄ ^2–, S₂O₃ ^2– and S₂O₈ ^2–. Using an electrolyte system with 9.5 mmol L^–1 potassium chromate as UV-absorbing probe and 1 mmol L^–1 diethylenetriamine (DETA) as electroosmotic flow modifier, various possibilities for the stabilization of sulfite and electrophoretic separation of the sulfur anions were investigated. By adding 5% propanol as a stabilizer to both the working electrolyte and the sample solution, a good stabilization for sulfite and a separation of the sulfur anions in a short analysis time (4 min) was achieved. The advantages by using propanol instead of other stabilizers often used in analytical techniques are discussed. The electrophoretic separation of the sulfur anions was optimized with respect to the pH of the working electrolyte and concentration of the electroosmotic flow modifier (DETA). The detection limits achieved for SO₃ ^2–, SO₄ ^2–, S₂O₃ ^2– and S₂O₈ ^2– were 0.35, 0.25, 0.78 and 0.80 mg L^–1, respectively. Received: 16 December 1999 / Revised: 7 March 2000 / Accepted: 14 March 2000     

Production of no-carrier-added 177Lu via the 176Yb(n, &;#947;)177Yb &;#8594; 177Lu process

No-carrier-added ¹⁷⁷Lu was produced by the ¹⁷⁶Yb(n,)¹⁷⁷Yb¹⁷⁷Lu process using enriched ¹⁷⁶Yb₂O₃. The radiochemical separation of the nca ¹⁷⁷Lu from the macroscopic ytterbium target was investigated by reversed-phase ion-pair HPLC. Effects of the concentrations of 2-hydroxyisobutyric acid and 1-octanesulfonate in the eluent, the amount of Yb₂O₃, the type and length of the C₁₈ column on the separation efficiency were examined. Under optimum conditions, the nca ¹⁷⁷Lu was obtained in radiochemically pure form from 5 mg of Yb₂O₃ with a separation yield of 84%.     

Effect of alkali metals and metal-ammonia complexes on electroosmosis,effective field strength,and resolution in the separation of diuretics by CZE

The counter ion in CZE separation systems affects resolution, effective field strength and electroosmosis. Alkali metals (lithium, sodium, potassium, and cesium), the ammonium ion, and several complexes of metals with ammonia ([Ag(NH₃)₂]⁺, [Cu(NH₃)₄]²⁺, [Zn(NH₃)₄]²⁺, [Cd(NH₃)₄]²⁺, [Ni(NH₃)₆]²⁺, and [Co(NH₃)₆]²⁺) have been studied for their effect on the separation of diuretics. With the alkali metals the electroosmotic flow velocity decreased and the effective field strength and resolution increased as the hydrated radius of the alkali metal decreased. All the metal-ammonia complexes except that with silver greatly reduced the electroosmotic flow velocity (V_eo) and had only a slight effect on the effective field strength (E_eff). Because these complexes had a negligible effect on the ionic strength of the buffer, they enabled high separating power to be maintained during the separation, and hence the use of more energy in the separation system. This yielded better resolution of the compounds, but the analysis time was then compromised. A simultaneous reduction in capillary length and V_eo while maintaining the high voltage enabled increased resolution without an increase in analysis time. The ability to control V_eo by adding small concentrations (< 100 μM ) of metal complexes to the buffer solution makes it possible to adjust the analysis time and capillary length independently while employing high separation power.     

Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation

The separation of C₂H₂/CO₂ is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)₄] ( FeNi‐M′MOF , pyz=pyrazine), with multiple functional sites and compact one‐dimensional channels of about 4.0 Å for C₂H₂/CO₂ separation. This MOF shows not only a remarkable volumetric C₂H₂ uptake of 133 cm³ cm^?3, but also an excellent C₂H₂/CO₂ selectivity of 24 under ambient conditions, resulting in the second highest C₂H₂‐capture amount of 4.54 mol L^?1, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C₂H₂ molecules and the binding sites of FeNi‐M′MOF . This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi‐M′MOF as a promising material for C₂H₂/CO₂ separation.     

Variations in the gross alpha and beta activity in surface waters at the Atomic Weapons Establishment Aldermaston (UK)

N,N,N′,N′-tetra-2-ethylhexyldiglycolamide (T2EHDGA) has been used for the preferential extraction of ⁹⁰Y from its mixture with ⁹⁰Sr from HNO₃ as well as HCl medium. The separation efficiencies have been found out under varying experimental conditions. The extracted species were determined from T2EHDGA concentration variation experiments carried out at 3 M nitric acid as well as HCl and were found out to be Y(X₃)₃·3(TEHDGA)_(o) for both the extraction systems, where X = NO₃ ⁻ and Cl⁻, respectively. Comparison of the T2EHDGA and TODGA based separation methods is also made. In order to avoid third phase formation, iso-decanol has been used as the modifier in all the studies. The modifier content was optimized to 30% for 4 M HCl and 20% for 6 M HNO₃ as the feed aqueous phases. Separation schemes were developed for the separation of carrier free ⁹⁰Y and the purity was checked by the half-life measurement method.     

Intramolekularer Antiferromagnetismus in [Cr2(μ-NH2)3(NH3)6]I3

Intramolecular Antiferromagnetism in [Cr₂(μ-NH₂)₃(NH₃)₆]I₃ The magnetism of [Cr₂(μ-NH₂)₃(NH₃)₆]I₃ which consists of binuclear cations with NH₂^?-bridged face-sharing octahedral coordination polyhedra and a metal-metal separation of 264.9 pm can be explained by antiferromagnetically exchange-coupled Cr^III-3d³ pairs. The magnetochemical analysis in the temperature range 5 K – 295 K on the basis of the isotropic Heisenberg model (spin Hamiltonian ? = ?2 J?₁ · ?₂) leads to the parameter value J = ?98(3) cm^?1. Compared to the exchange coupling in corresponding binuclear chromium compounds with OH^? bridges and identical metal-metal separation the strength of the coupling is significantly enhanced (J_NH2/J_OH ≈? 1.6).     

Coprecipitation of 15-crown-5 ether complexes of lead and strontium with tungstosilicic acid

Lead as well as strontium form low solubility compounds of composition (ML₂)₂A·nH₂O, (M=Pb²⁺, Sr²⁺), in the presence of 15-crown-5 (L) and tungstosilicic acid (H₄A) in acid media as found by radiometric precipitation titration. “Sandwich” structure of crown-ether complexes of lead and strontium could be expected due to the small size of cavity of 15-crown-5. Coprecipitation of PbL_2/su2+ with crown complexes of strontium cation after adding tungstosilicic acid was studied in 0.01 mol·dm⁻³ HNO₃. A significant influence of H⁺ cation in 1 mol·dm⁻³ HNO₃ on coprecipitation of lead was observed. Formation of HL⁺ complexes by protonisation of 15-crown-5 competes to the formation of ML₂ ²⁺ complexes (approximately twenty percent of 15-crown-5 are used for creation of HL⁺ complexes). Formation of low solubility salts was utilised for separation of lead from strontium in 0.01 mol·dm⁻³ HNO₃. The ratio of constant stability of lead and strontium β‘ with 15-crown-5 in 0.01 mol·dm⁻³ HNO₃ was calculated. The separation factor S(Pb/Sr) depends on the ratio of stability constants β_PbL2/β_SrL2 The precipitation method can be used for separation of metals with high constant stability with crown ethers from solutions containing other metals in the case of gradual addition of crown.     

Mixed Metal–Organic Framework with Multiple Binding Sites for Efficient C2H2/CO2 Separation

The separation of C₂H₂/CO₂ is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal–organic framework (M′MOF), [Fe(pyz)Ni(CN)₄] ( FeNi-M′MOF , pyz=pyrazine), with multiple functional sites and compact one-dimensional channels of about 4.0 Å for C₂H₂/CO₂ separation. This MOF shows not only a remarkable volumetric C₂H₂ uptake of 133 cm³ cm⁻³, but also an excellent C₂H₂/CO₂ selectivity of 24 under ambient conditions, resulting in the second highest C₂H₂-capture amount of 4.54 mol L⁻¹, thus outperforming most previous benchmark materials. The separation performance of this material is driven by π–π stacking and multiple intermolecular interactions between C₂H₂ molecules and the binding sites of FeNi-M′MOF . This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi-M′MOF as a promising material for C₂H₂/CO₂ separation.     

Overcoming the Trade-Off between C2H2 Sorption and Separation Performance by Regulating Metal-Alkyne Chemical Interaction in Metal-Organic Frameworks

Designing porous materials for C₂H₂ purification and safe storage is essential research for industrial utilization. We emphatically regulate the metal-alkyne interaction of Pd^II and Pt^II on C₂H₂ sorption and C₂H₂/CO₂ separation in two isostructural NbO metal–organic frameworks (MOFs), Pd/Cu-PDA and Pt/Cu-PDA . The experimental investigations and systematic theoretical calculations reveal that Pd^II in Pd/Cu-PDA undergoes spontaneous chemical reaction with C₂H₂, leading to irreversible structural collapse and loss of C₂H₂/CO₂ sorption and separation. Contrarily, Pt^II in Pt/Cu-PDA shows strong di-σ bond interaction with C₂H₂ to form specific π-complexation, contributing to high C₂H₂ capture (28.7 cm³ g⁻¹ at 0.01 bar and 153 cm³ g⁻¹ at 1 bar). The reusable Pt/Cu-PDA efficiently separates C₂H₂ from C₂H₂/CO₂ mixtures with satisfying selectivity and C₂H₂ capacity (37 min g⁻¹). This research provides valuable insight into designing high-performance MOFs for gas sorption and separation.     

Ge‐Mediated Modification in Ta3N5 Photoelectrodes with Enhanced Charge Transport for Solar Water Splitting

Ta₃N₅ is a promising photoanode candidate for photoelectrochemical water splitting, with a band gap of about 2.1 eV and a theoretical solar‐to‐hydrogen efficiency as high as 15.9 % under AM 1.5 G 100 mW cm^?2 irradiation. However, the presently achieved highest photocurrent (ca. 7.5 mA cm^?2) on Ta₃N₅ photoelectrodes under AM 1.5 G 100 mW cm^?2 is far from the theoretical maximum (ca. 12.9 mA cm^?2), which is possibly due to serious bulk recombination (poor bulk charge transport and charge separation) in Ta₃N₅ photoelectrodes. In this study, we show that volatilization of intentionally added Ge (5 %) during the synthesis of Ta₃N₅ promotes the electron transport and thereby improves the charge‐separation efficiency in bulk Ta₃N₅ photoanode, which affords a 320 % increase of the highest photocurrent comparing with that of pure Ta₃N₅ photoanode under AM 1.5 G 100 mW cm^?2 simulated sunlight.     

The boron trifluoride nitromethane adduct

The separation of the boron isotopes using boron trifluoride·organic-donor, Lewis acid·base adducts is an essential first step in preparing ¹⁰B enriched and depleted crystalline solids so vital to nuclear studies and reactor applications such as enriched MgB₂, boron carbide, ZrB₂, HfB₂, aluminum boron alloys, and depleted silicon circuits for radiation hardening and neutron diffraction crystal structure studies. The appearance of this new adduct with such superior properties demands attention in the continuing search for more effective and efficient means of separation. An evaluation of the boron trifluoride nitromethane adduct, its thermodynamic and physical properties related to large-scale isotopic separation is presented. Its remarkably high separation factor was confirmed to be higher than the expected theoretical value. However, the reportedly high acid/donor ratio was proven to be an order of magnitude lower. On-going research is determining the crystal structure of deuterated and ¹¹B enriched ¹¹BF₃·CD₃NO₂ by X-ray and neutron diffraction.     

Cadmium Preconcentration from Aqueous Environmental Samples Using Microcrystalline Phenolphthalein Modified by Crystal Violet

Abstract

The present work describes a novel method for cadmium preconcentration and separation with microcrystalline phenolphthalein. Phenolphthalein as an extractant modified by crystal violet was originally applied to cadmium extraction from aqueous solution. Cadmium(II) as CdI₃ ^? and CdI₄ ^2? can associate with the cationic crystal violet (CV⁺) forming water‐insoluble ion‐association complexes (CdI₃ ^?) · (CV⁺) and (CdI₄ ^2?) · (CV⁺)₂, which are quantitatively adsorbed on microcrystalline phenolphthalein over the pH range from 1.0 to 6.0. All experimental parameters necessary for successful preconcentration and separation have been investigated and optimized. The study shows that common metal ions, such as Zn(II), Fe(II), Co(II), Ni(II), Mn(II), Cr(III) and Al(III), cannot interfere with cadmium extraction in this microcrystalline system by controlling acidity. The extraction can be accomplished in 15 min. The interaction between CdI₃ ^?and CdI₄ ^2? and CV⁺ plays an important role in the extraction process. The reported method was successfully applied to the preconcentration and separation of cadmium in synthetic samples and real samples with satisfactory results. The results proved that it is an efficient and attractive technique for cadmium preconcentration and separation at trace level.     

Extraction of tungsten and rhenium by basic or neutral extractants in xylene from mineral acidic media

Extraction of WO ₄ ^2– and ReO ₄ ^– by Adogen-381, tricaprylmethylammonium chloride, Hyamine 10-X, trioctylphosphine oxide or dibenzylsulphoxide in xylene from HNO₃, HCl or H₂SO₄ acid medium was investigated. Based on the separation factors obtained, the separation of ReO ₄ ^– from WO ₄ ^2– was elucidated. ReO ₄ ^– was separated from WO ₄ ^2– in high radiochemical purity: >99.9% by three successive extractions and strippings using Adogen-381 from HCl or HNO₃ acid medium.     

Enrichment of Magnesium Isotopes by N3O2 Azacrown Ion Exchange Resin

The elution chromatographic separation of magnesium isotopes was investigated by chemical ion exchange with the synthesized 1,7-dioxa-4,10,13-triazacyclopentadecane-4,10,13-trimerrifield peptide resin [N₃O₂·3M]. The capacity of novel N₃O₂ azacrown ion exchanger was 0.21 meq/g dry resin. The heavier isotopes of magnesium concentrated in the resin phase, while the lighter isotopes are enriched in the solution phase. The glass ion exchange column used in our experiment was 30 cm long with inner diameter of 0.2 cm, and the 2.0M NH₄Cl solution was used as an eluent. The separation factors of ²⁴Mg-²⁵Mg, ²⁵Mg-²⁶Mg, and ²⁴Mg-²⁶Mg were 1.030, 1.009, and 1.027, respectively.     

Sequential distillation of fission-produced radioiodine and radioruthenium from sulfuric acid solutions

Fission-produced ¹³¹I and ¹⁰³Ru radionuclides have been separated sequentially by distillation from H₂SO₄ of controlled chemical composition. The thermal-neutron irradiated uranium trioxide targets were digested in 2M NaOH solution and then, the supernatant solution was acidified to 20% H₂SO₄ with addition of a few drops of H₂O₂ solution. On boiling for 3.5 hours, ≥99.99%¹³¹I was volatilized, passed through 3M H₂SO₄ traps, and then collected in 0.1M NaOH + 0.01% Na₂S₂O₃ solution with a recovery yield of 73.6%. The product radionuclide had high radiochemical and radionuclidic purities. After separation of ¹³¹I, the fission-product solution was acidified to 40% H₂SO₄ acid containing KMnO₄ as an oxidant and boiled for 40 minutes. Ruthenium nuclides were volatilized and collected in 0.1M NaOH solution. Gamma-ray spectrometry showed that the separation and the recovery yields of ¹⁰³Ru were ≥99.99 and 65%, respectively, with ~92% radionuclidic purity, measured immediately after separation. The radionuclides of ¹³²I and ¹⁰⁶Rh were the main contaminants detected in the obtained ¹⁰³Ru product solution. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of Er3+ and Sm3+ on phase separation and crystallization in Na2O/K2O/BaF2/BaO/Al2O3/SiO2 glasses

Thermal annealing of Sm⁺³ or Er⁺³ doped Na₂O/K₂O/BaF₂/BaO/Al₂O₃/SiO₂ glasses led to the precipitation of nanocrystalline BaF₂. The mean crystallite sizes were in the range from 9 to 15 nm as shown by XRD line broadening. Whereas glasses without rare earth oxides showed crystallites homogenously dispersed in the amorphous matrix, those doped with 0.05 mol% ErF₃ or SmF₃ showed highly agglomerated crystals. The latter was due to droplet phase separation in the rare earth doped glasses as proved by transmission electron microscopy while in the undoped glasses phase separation did not occur. Furthermore, the size of the droplets depended on the BaO-concentration. Fluorescence emission spectra of a samarium doped sample showed higher intensities than in the glasses they were prepared from.     

Stepwise Engineering the Pore Aperture of a Cage-like MOF for the Efficient Separation of Isomeric C4 Paraffins under Humid Conditions

The separation of isomeric C4 paraffins is an important task in the petrochemical industry, while current adsorbents undergo a trade-off relationship between selectivity and adsorption capacity. In this work, the pore aperture of a cage-like Zn-bzc (bzc=pyrazole-4-carboxylic acid) is tuned by the stepwise installation methyl groups on its narrow aperture to achieve both molecular-sieving separation and high n-C₄H₁₀ uptake. Notably, the resulting Zn-bzc-2CH₃ (bzc-2CH₃=3,5-dimethylpyrazole-4-carboxylic acid) can sensitively capture n-C₄H₁₀ and exclude iso-C₄H₁₀, affording molecular-sieving for n-C₄H₁₀/iso-C₄H₁₀ separation and high n-C₄H₁₀ adsorption capacity (54.3 cm³ g⁻¹). Breakthrough tests prove n-C₄H₁₀/iso-C₄H₁₀ can be efficiently separated and high-purity iso-C₄H₁₀ (99.99 %) can be collected. Importantly, the hydrophobic microenvironment created by the introduced methyl groups greatly improves the stability of Zn-bzc and significantly eliminates the negative effect of water vapor on gas separation under humid conditions, indicating Zn-bzc-2CH₃ is a new benchmark adsorbent for n-C₄H₁₀/iso-C₄H₁₀ separation.