High performance of phosphonate-functionalized mesoporous silica for U(VI) sorption from aqueous solution

The renaissance of nuclear energy promotes increasing basic research on the separation and enrichment of nuclear fuel associated radionuclides. Herein, we report the first study for developing mesoporous silica functionalized with phosphonate (NP10) as a sorbent for U(VI) sorption from aqueous solution. The mesoporous silica was synthesized by co-condensation of diethylphosphatoethyltriethoxysilane (DPTS) and tetraethoxysilane (TEOS), using cationic surfactant cetyltrimethylammonium bromide (CTAB) as the template. The synthesized silica nanoparticles were observed to possess a mesoporous structure with a uniform pore diameter of 2.7 nm, and to have good stability and high efficiency for U(VI) sorption from aqueous solution. A maximum sorption capacity of 303 mg g(-1) and fast equilibrium time of 30 min were achieved under near neutral conditions at room temperature. The adsorbed U(VI) can be easily desorbed by using 0.1 mol L(-1) HNO(3), and the reclaimed mesoporous silica can be reused with no decrease of sorption capacity. In addition, the preconcentration of U(VI) from a 100 mL aqueous solution using the functionalized mesoporous silica was also studied. The preconcentration factor was found to be as high as 100, suggesting the vast opportunities of this kind of mesoporous silica for the solid-phase extraction and enrichment of U(VI).     

Preparation, characterization and application of thorium oxalate for sorption of plutonium and americium from aqueous solution

Synthetic inorganic exchangers exhibit good thermal and radiation stability. Thorium oxalate precipitate shows potential for co-precipitation of plutonium and americium from oxalate supernatant generated during plutonium oxalate precipitation. In the present study, efforts were made to prepare thorium oxalate precipitate to be used for column operation. Distribution ratios were determined to optimize conditions for sorption of plutonium and americium on thorium oxalate from nitric acid + oxalic acid solutions with composition similar to that of oxalate supernatant. Column experiments were also performed to evaluate the sorption capacity of thorium oxalate for plutonium and americium from the same medium. The result showed that, thorium oxalate prepared in 1.75M HNO₃ at 70 °C is suitable for column operations. These studies showed that plutonium and americium could be simultaneously removed from aqueous solutions with composition similar to plutonium oxalate waste using glass column packed with thorium oxalate and these nuclides could be recovered by eluting with 3M HNO₃.     

A high efficient sorption of U(VI) from aqueous solution using amino-functionalized SBA-15

Uranium is one of the most hazardous heavy metal due to its long half-life radioactivity, high toxicity and mobility as aqueous uranyl ion (UO₂ ²⁺) under ordinary environmental conditions. Herein, amino functionalized SBA-15 (APSS) was developed as a rapid and efficient sorbent for removal of U(VI) from the environment. The APSS sample was synthesized by grafting method and was characterized by SEM, NMR, SAXS, and N₂ sorption/desorption isothermal experiments. The sorption of U(VI) by APSS was investigated under different conditions of pH, contact time, initial U(VI) concentration, ionic strength and solid–liquid ratio. The results show that the sorption of U(VI) by APSS is strongly dependent on pH but independent of ionic strength and solid–liquid ratios (m/V). The sorption is ultrafast with an equilibrium time of less than 30 min, and the sorption capacity is as large as 409 mg/g at pH 5.3 ± 0.1. Besides, the U(VI) sorption by APSS from extremely diluted solution and the desorption of U(VI) from APSS were also studied. It is found that 100 mg of APSS can almost completely remove the U(VI) ions from 4 L aqueous solution with the U(VI) concentration as low as 4.2 ppb and the sorbed U(VI) can be completely desorbed by 0.1 mol/L nitric acid. The results strongly reveal the high performance of the APSS material in the removal and preconcentration of U(VI) from the aqueous solution.     

The surface tension of poly(acrylic acid) in aqueous solution

Summary Surface tension has been measured of polyacrylic acidwater solutions with pH 3–11. Until approximately pH 4.6 corresponding to 10% neutralization, PAA-solutions are surface active and inactive at higher pH, time dependence of equlibrium surface tension is analysed. Non-ionized neutral chain segments are surface active, their diffusion to surface is rate determining.

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Zusammenfassung Es wurde die Oberflächenspannung von wäßrigen Polyacrylsäure-Lösungen der pH-Werte von 3–11 gemessen. Bis zu einem pH-Wert von etwa 4.6, d. h. 10% Neutralisation, sind die Lösungen oberflächenaktiv, bei höheren pH-Werten inaktiv. Es wird die Zeitabhängigkeit der Einstellung der Gleichgewichtsoberflächenspannung analysiert. Nicht ionisierte, neutrale Kettensegmente sind oberflächenaktiv. Diffusion zur Oberfläche ist der zeitbestimmende Faktor.

     

Equilibrium sorption of hexavalent chromium from aqueous solution using synthetic hematite

Hematite sample prepared by transformation of ferrihydrite was used to remove Cr(VI) from aqueous solution. Effects of initial concentration, contact time, pH, ionic strength, and temperature were investigated. The data were fitted to Langmuir, Freundlich, Dubinin-Kaganer-Radushkevich and Temkin models of adsorption. The results showed the best fit to the Langmuir isotherm. The increase of pH as well as that of increasing ionic strength resulted in the decrease of adsoiption of Cr(VI). Two kinetic models namely pseudo-first order and pseudo-second order were used to fit the experimental data. The thermodynamic parameters were found, and the results indicated spontaneous and exothermic nature of the process.     

Selective sorption of uranium from aqueous solution by graphene oxide-modified materials

Journal of Radioanalytical and Nuclear Chemistry - The effect of competing ions on the sorption behaviour of uranium onto carboxyl-functionalised graphene oxide (COOH-GO) were studied in batch...     

The structure and transport properties of poly(methacrylic acid) in aqueous solution

Diffusion and anisotropic electrical conductivity measurements have been used to investigate the structure of poly(methacrylic acid) in aqueous solution at various degrees of neutralization. Both kinds of measurement indicate that the polyion chain opens from a coiled to an extended configuration as the chain is neutralized. In addition it was found that, at low concentrations, the opening of the chain is a two-step process, whereas at higher concentrations the mechanism involves a single step.     

Calorimetric investigation of poly(methacrylic acid) and poly(acrylic acid) in aqueous solution

The enthalpy of dissociation of poly(acrylic acid) and of poly(methacrylic acid) in water and in 0.5N NaCl at 25°C has been measured over a wide range of degrees of neutralization of the polyelectrolytes. In the case of poly(methacrylic acid) the calorimetric data permit the direct evaluation of the enthalpy of conformational transition of the polymer. For this transition, with the aid of standard free energy data derived from potentiometric titrations, the change in entropy was also estimated. The relative accuracy of the thermodynamic data, and the possibility of deriving therefrom information on the mechanism of transitions of the type, globular coils → expanded coils for partially hydrophobic synthetic polyelectrolytes in aqueous solution are discussed.     

Direct methylation at the surface of Carbopack B Part II: Determination of phenoxyalkanoic acid herbicides

The determination of phenoxyalkanoic acids in different types of water within the limits of the European drinking water guideline is described. Most of these acids are used world-wide as herbicides and growth regulators. Compounds having an acidic hydrogen in their structure are very strongly adsorbed on Carbopack B, a special graphitized carbon black. This effect was used for the transformation of analytes to methyl esters directly on the surface of the adsorbent, using trimethylsulfonium hydroxide (TMSH) as derivatization reagent. After elution with ethyl acetate the derivatives were identified and quantified by gas chromatography/mass spectrometry (GC/MS). The interaction between analyte and adsorbent and the yields of the derivatization step are influenced by the length of the alkanoic chain. Received: 21 June 1999 / Revised: 23 August 1999 / Accepted: 24 August 1999     

Highly efficient sorption of U(VI) from aqueous solution using amino/amine-functionalized magnetic mesoporous silica nanospheres

The amino/amine-functionalized magnetic mesoporous silica nanospheres (MSN-DETA) exhibited relatively high sorption capacity (q_m?=?153.68 mg/g) as well as excellent selectivity for U(VI). The U4f_7/2 X-ray photoelectron spectrometry revealed two binding energies at 380.8?±?0.3 eV (with the proportion of 75.2%) and 382.3?±?0.3 eV, which indicated the inner-surface complexation mechanism. The sorption isotherms fitted well with the Langmuir model, whereas the sorption kinetics could be fitted by pseudo-second-order model. The U(VI)-loaded MSN-DETA could be efficiently regenerated by acidified EDTA (0.4 M). These findings indicated that MSN-DETA could be used as a potential material for the efficient sorption/separation of U(VI) from wastewater.

     

The structure and synthesis of plutonium(III) chlorides from aqueous solution

The preparation and structure of three trivalent plutonium chloride compounds from aqueous solution is reported. Two of the three are plutonium tetraaquatetrachloro complexes exhibiting a cis and a trans arrangement of Cl about the Pu. The identification of the coordination number of 4 with respect to Cl and the isomerism are both unprecedented in actinide solution chemistry. The third complex is a hexaaquadichloro complex of Pu(III), predicted by available thermodynamic data.     

2-chlorophenol sorption from aqueous solution using granular activated carbon and polymeric adsorbents

Adsorption equilibrium and kinetics of 2-chlorophenol (2-CP) one of the chlorophenols (CPs) onto bituminous coal based Filtrasorb-400 grade granular activated carbon and three different types of polymeric adsorbents were studied in aqueous solution in a batch system. Langmuir isotherm models were applied to experimental equilibrium data of 2-CP adsorption. Equilibrium data fitted very well to the Langmuir equilibrium models of 2-CP. Adsorbent monolayer capacity Q Langmuir constant b and adsorption rate constants k _a were evaluated. 2-CP adsorption using GAC is very rapid in the first hour of contact where 70–80% of the adsorbate is removed by GAC followed by a slow approach to equilibrium. Whereas in case of polymeric adsorbents 60–65% of the adsorbate is removed in the first 30 min which is then followed by a slow approach to equilibrium. The order of adsorption of 2-CP on different adsorbents used in the study is found to be in following order: F-400 > XAD-1180 > XAD-4 > XAD-7HP.     

Adsorption of Cu(II) from aqueous solution by anatase mesoporous TiO2 nanofibers prepared via electrospinning

Anatase mesoporous titanium nanofibers (m-TiO(2) NFs) have been synthesized from calcination of the as-spun TiO(2)/polyvinyl pyrrolidone (PVP)/pluronic123 (P123) composite nanofibers at 450 °C in air for 3h. The structures and the physicochemical properties of m-TiO(2) NFs are characterized by scanning electron microscopy, X-ray diffraction, nitrogen adsorption-desorption isotherm analysis, and determination point of zero charge, respectively. An investigation of Cu(II) adsorption onto m-TiO(2) NFs has been studied in this research. The pH effect, adsorption kinetics, and adsorption isotherms are examined in batch experiments. Experimental data were analyzed using pseudo-first order and pseudo-second order kinetic models. It was found that adsorption kinetics were the best fitting by a pseudo-second order kinetic model. The optimum pH for Cu(II) adsorption was found to be 6.0. The equilibrium data were analyzed by the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, which revealed that the Freundlich isotherm is the best-fit isotherm for the adsorption of Cu(II). Compared to the TiO(2) NFs (regular anatase titanium nanofibers) in the same experimental conditions to elucidate the role of the mesoporous structure of m-TiO(2) NFs, experimental results showed that the m-TiO(2) NFs had a better adsorption capacity for Cu(II) due to its higher surface area.     

固相萃取-衍生化-气相色谱法测定血液中的3种苯氧羧酸类除草剂

建立了一种血液中2,4-二氯苯氧乙酸(2,4-D)、2-(2,4-二氯苯氧)-丙酸(2,4-DP)和4-氯-2-甲基-苯氧乙酸(MCPA)3种苯氧羧酸类除草剂的分析方法.血样用0.1 mol/L盐酸稀释后用GDX401大孔树脂吸附、用乙醚洗脱,萃取物用二氯丙醇在硫酸催化下进行酯化衍生,衍生物经气相色谱-电子捕获检测.2,4-D、2,4-DP和MCPA的检测限分别为20,8和40 ng/mL.定量分析用2,4-二氯苯乙酸作内标,线性关系和回收率结果均令人满意.     

Preparation and characterization of manganese(IV) in aqueous acetic acid

Mn(IV) acetate was generated in acetic acid solutions and characterized by UV-vis spectroscopy, magnetic susceptibility, and chemical reactivity. All of the data are consistent with a mononuclear manganese(IV) species. Oxidation of several substrates was studied in glacial acetic acid (HOAc) and in 95:5 HOAc-H(2)O. The reaction with excess Mn(OAc)(2) produces Mn(OAc)(3) quantitatively with mixed second-order kinetics, k (25.0 °C) = 110 ± 4 M(-1) s(-1) in glacial acetic acid, and 149 ± 3 M(-1) s(-1) in 95% AcOH, ΔH(?) = 55.0 ± 1.2 kJ mol(-1), ΔS(?) = -18.9 ± 4.1 J mol(-1) K(-1). Sodium bromide is oxidized to bromine with mixed second order kinetics in glacial acetic acid, k = 220 ± 3 M(-1) s(-1) at 25 °C. In 95% HOAc, saturation kinetics were observed.     

Extraction of thorium from aqueous nitric acid solution by bis-2-(butoxyethyl ether) (DBC)

The solvent extraction of thorium(IV) (4.3·10^–4M) from nitric acid solution by bis-2-(butoxyethyl ether) (butex or DBC) has been studied. It has been investigated as a function of nitric acid, extractant and metal ion concentration. The effect of equilibration time, diverse ions and salting-out agent on the extraction has also been examined. Among anions, fluoride, phosphate, oxalate and perchlorate have reduced the extraction. Cations such as Na(I), K(I), Ca(II), Zn(II), Al(III), Ti(IV), Zr(IV) except Sr(II) and Pb(II) do not interfere in the extraction. The extraction is enhanced upto 97% in three stages at 6M HNO₃ having 2.94M NaNO₃ as salting-out agent. The extraction is found to be independent of thorium concentration in the range studied (4.3·10^–4–4.3·10^–2M). The temperature (18–45°C) has an adverse effect on the extraction. A 1% solution of ammonium bifluoride is found to be a good stripping solution and recovery of thorium is >98%.     

Time-dependent Cu-induced gelation of poly(ethylene-alt-maleic acid) in aqueous solution

The complexation of Cu²⁺ ions with an alternating copolymer of maleic acid (MAc) and ethylene in aqueous solution was followed through turbidimetry and absorption spectrophotometry as a function of the polymer concentration and the metal ion-to-polymer molar ratio, r. The introduction of Cu²⁺ ions was performed in aqueous solution through neutralization of the polyacid with Cu(OH)₂ powder. A gelation window between homogeneous and phase-separated solutions was observed in the phase diagram of the polymer/Cu²⁺ mixture and the viscoelastic properties of the hydrogels were evaluated through rheology measurements. It is found that the stiffness of the hydrogels can be tuned by the polymer concentration and the mixing ratio r. Moreover, the stiffness of the hydrogels increases substantially with time. In fact, this time evolution may be as long as one month or longer if the composition of the aqueous solution is close to the gelation threshold. The gelation properties can be qualitatively explained from the possible formation of binuclear polymer/Cu²⁺ complexes in aqueous solutions, as indicated from the absorption spectroscopy results.     

Ion-exchange sorption of silver(I) chloride complexes from aqueous HCl solutions

The ion-exchange sorption of silver(I) chloride complexes from 1–4 M aqueous solutions of HCl on a series of Purolite anionites with various functional groups was studied. The ion-exchange equilibria in the systems were found to be anomalous according to Raman spectroscopy, which does not significantly affect the sorption properties of the ionites.