Valency stabilization of polyvalent ions during gamma irradiation of their aqueous solutions by sacrifical protection

Polyvalent ions are very sensitive to gamma irradiation in aqueous solutions. The present work is a part of a more comprehensive study dealing with the stabilization of certain oxidation states of some polyvalent ions during their gamma irradiation in aqueous systems. Sulphite ions, being well known reducing agents has been used for stabilizing Fe(II) ions in aqueous solutions during gamma radiolysis. Fe(II) ions in solution are known to be readily oxidized by gamma radiations in such a way that a 10^–3N solution decays completely in about 2 hours at a dose rate 310 Gy/hr. In presence of an excess of sulphite ions it was found that Fe(II) ions were stabilized for extended time periods depending on the amount of sulphite ions used. The conditions of stabilization and its limits in the studied case has been identified.     

Valence stabilization of polyvalent ions during gamma irradiation of their aqueous solutions by sacrificial protection. III-Valence stabilization of Fe(II) ions by organic additives

Valence stabilization of polyvalent ions in gamma irradiated aqueous solutions is sometimes necessary in some chemical operations. In previous publications, valence stabilization of some polyvalent ions in solution upon gamma irradiation was achieved by using inorganic additives capable of interacting with the oxidizing or reducing species formed during water radiolysis. The results showed that the nature and duration of valence stabilization of Fe(II) depend on the concentration of the inorganic additives used. In the present work, a series of some organic additives has been used to investigate their capability in inducing valence stabilization of polyvalent iron ions, taken as an indicator, in aqueous acidic solutions when subjected to extended gamma irradiation. The results showed that the efficiency of valence stabilization depends on the amount and chemical structure of the organic additive used.     

Decomposition of pesticide chlorfenvinphos in aqueous solutions by gamma-irradiation

The effectiveness of radiolytic decomposition of widely used organophosphorus pesticide chlorfenvinphos using γ-irradiation from ⁶⁰Co source was investigated using HPLC and ion-chromatography for monitoring of decomposition products. In terms of irradiation dose the Microtox toxicity of irradiated solutions was examined, and also effect of irradiation on ability of irradiated chlorfenvinphos solutions to inhibit activity of enzyme acetylcholi-nesterase was investigated.     

Tunable stabilization of gold nanoparticles in aqueous solutions by mononucleotides

Gold nanoparticles are one of the popular nanomaterials, widely used in biosensor applications as well as nanostructure construction. An essential attribute of these gold nanoparticles (Au-nps) is their stabilization against salt-induced aggregation. In this work, utilization of deoxyribonucleotides (dNTPs) as a tunable surface-stabilization agent for Au-nps was investigated. It was found that surfaces of Au-nps are covered by a layer of dNTPs after an adequate incubation with dNTPs solutions. Electrostatic repulsion among dNTP-coated Au-nps could prevent aggregation of Au-nps at a high salt concentration. The strength of dNTP-based protection can be manipulated by changing preparation protocols (e.g., incubation temperature, ionic strength, and ratio of Au-nps to dNTPs). Four different types of dNTPs exhibit different binding affinity to Au-nps and thus various stabilization efficiency in the order of dATP > dCTP > dGTP approximately dTTP. Moreover, this salt-induced aggregation can be reinitiated by the increase of solution temperature, which leads to a partial removal of the protective dNTP layer on Au-nps. The advantage of thermally tunable aggregation/dispersion of Au-nps mediated by dNTP adsorption offers a useful approach for the preparation of biomolecule (oligonucleotides and oligopeptides) modified nanoparticles in applications of bioassay and nanobiotechnology.     

Effect of 60Co gamma-irradiation on dilute aqueous solutions of surfactants

Present work deals with the effects of gamma irradiation from 60Co gamma-ray source upon aqueous solutions of three kinds of surfactants. When dilute aqueous solutions of sodium dodecyl sulfate (SDS, anionic), cethyl trimethyl ammonium chloride (CTAC, cationic), and polyoxyethylene lauryl ether (POE, non-ionic) were irradiated with gamma-rays at a room remperature, the residual concentration, products, surface tension, and forming power were examined by colorimetric method, IR spectrophotometric method, gaschromatography, Ross-Miles method, and Traube's stalagnometer etc.. These surfactants were decomposed by the irradiation and thus the surface tension increased and the forming power, on the contrary, decreased with dose. Radiation chemical yields (G-value) of the degradation were about 1 for the solutions of SDS and CTAC, and about 0.3 for the POE solution. From the experimental results, it was found that following chemical reactions seem to occur followed by the radiolysis of water; a) bond cleavage of ester for SDS, of CN for CTAC, and of oxyethylene for POE, b) hydrogen abstraction from the surfactants, c) production of CO bond in the presence of dissolved oxygen.     

Electrosorption of ions from aqueous solutions by nanostructured carbon aerogel

Electrosorption is generally defined as potential-induced adsorption on the surface of charged electrodes. After polarization of the electrodes, ions are removed from the electrolyte solution by the imposed electric field and adsorbed onto the surface of the electrodes. Experimental and modeling studies were conducted using two types of carbon aerogel composites of different surface areas to provide a better understanding on the mechanisms of electrosorption. The experimental results revealed that no significant specific adsorption of F- ions occurred, while strong specific adsorption was observed for NO3- and Cu2+ ions. In addition, although the two types of carbon aerogel electrodes had different surface areas, their capacities were found to be very similar because of the electrical double-layer overlapping effect in micropores. An electrical double-layer model developed in our previous work (16), in which the electrical double-layer overlapping correction is included, is expanded in the present work by considering the effect of the specific adsorption on the electrosorption process. Modeling results were compared with experimental data obtained under various conditions. When the overlapping effect and specific adsorption were considered, the model provided results that were in good agreement with experimental data.     

Solubilization of lanthanide ions by cyclodextrins in basic aqueous solutions

Cyclodextrins form complexes with lanthanide ions in basic aqueous solutions. This complex formation in basic solution dramatically enhances the solubility of lanthanide ions, which are otherwise insoluble due to the formation of hydroxide gels. Solutions of the -cyclodextrin-Ce³⁺ complex effectively hydrolyze 2-deoxyadenosine-5-monophosphate to 2-deoxyadenosine.     

The stabilization of managese(III) by azide ions in aqueous solution

The evidences of spontaneous oxidation of Mn(II) by the dissolved oxygen in azide buffer medium, which is dependent on the N (-)(3)HN (3) concentration, suggested a formation of stable Mn(III) complexes due to marked colour changes. Spectrophotometric studies combined with coulometric generation of Mn(III), in presence of large excess of Mn(II), showed a maximum absorbance peak at 432 nm. The molar absorptivity increases with azide concentration (0.44-3.9 mol 1(-1)) from 3100 to 6300 mol(-1) 1 cm(-1), showing a stepwise complex formation. Potential measurements of the Mn(III) Mn(II) system in several azide aqueous buffers solutions: 1.0 x 10(-2) mol 1(-1) HN(3), (0.50-2.0 mol 1(-1)) N(-)(3) and 5.0 x 10(-2) mol 1(-1) Mn(II) and constant ionic strength 2.0 mol 1(-1), kept with sodium perchlorate, leads to the conditional potential, E(0')x, in several azide concentrations at 25.0 +/- 0.1 degrees C. Considering the overall formation constants of Mn(II) N (-)(3), from former studies, and the potential, E(0')s = 1.063 V versus SCE, for Mn(III) Mn(II) system in non-complexing media, it was possible to calculate the Fronaeus function, F(0)(L), and the following overall formation constants: beta(1) = 1.2 x 10(5) M(-1), beta(2) = 6.0 x 10(8) M(-2), beta(3) = (2.4 +/- 0.7) x 10(11) M(-3), beta(4) = (1.5 +/- 0.5) x 10(11) M(-4) and beta(5) = (9.6 +/- 0.8) x 10(11) M(-5) for the Mn(III) N (-)(3) complexes. These data give important support to understand the importance of Mn(II) and Mn(III) synergistic effect on the analytical method of S(IV) determination based on the Co(II) autoxidation.     

Removal of radiocobalt ions from aqueous solutions by natural halloysite nanotubes

In this study, natural halloysite nanotubes (HNTs) were applied to remove radiocobalt from wastewaters under various environmental parameters such as contact time, pH, ionic strength, foreign ions and temperature by using batch technique. The results indicated that the sorption of Co(II) on HNTs was dependent on ionic strength at pH < 8.5 and independent of ionic strength at pH > 8.5. Langmuir and Freundlich models were applied to simulate the sorption isotherms of Co(II) at three different temperatures of 293, 313 and 333 K. Langmuir model fitted the sorption isotherms of Co(II) on HNTs better than Freundlich model. The thermodynamic parameters (ΔG ⁰, ΔS ⁰ and ΔH ⁰) calculated from the temperature-dependent sorption isotherms manifested that the sorption of Co(II) on HNTs was an endothermic and spontaneous process. The sorption of Co(II) was dominated by outer-sphere surface complexation or ion exchange at low pH, whereas inner-sphere surface complexation or precipitation was the main sorption mechanism at high pH. The experimental results show that HNTs have good potentialities for cost-effective disposal of cobalt-bearing wastewaters.     

Biosorption of copper ions from aqueous solutions by Spirulina platensis biomass

In this study, the economically important micro-alga (cyanobacterium) Spirulina platensis was used as biosorbent for the removal of copper from aqueous solutions. The cyanobacterium was exposed to various concentrations of copper and adsorption of copper by the biomass was evaluated under different conditions that included pH, contact time, temperature, concentration of adsorbate and the concentration of dry biomass. Increased adsorption of copper by the non-living biomass was recorded with gradually increasing pH, and a maximal uptake by the biomass was observed at pH 7. The adsorption of copper was found to increase gradually along with decrease in biomass concentration. Biosorption was found to be at a maximum (90.6%), in a solution containing 100 mg copper/L, at pH 7, with 0.050 g dry biomass and at 37 °C with 90 min of contact time. Analysis of the spectrum obtained with atomic absorption spectrophotometer (AAS), indicated that the adsorbent has a great potential to remove copper from aqueous media contributing to an eco-friendly technology for efficient bioremediation in the natural environment.     

Pulse radiolysis of aqueous solutions of tetraphenylphosphonium ions

The reactions of tetraphenylphosphonium ion (Ar₄P⁺) with e_aq⁻, H atoms and OH radicals have been investigated. The absorption spectra of three transient species were obtained. Ar₄P· radicals formed by the reaction: Ar₄P⁺ + e_aq⁻ → Ar₄P· have a maximum absorption at 305 nm [ε₃₀₅ = (9400 ± 300) dm³ mol⁻¹ cm⁻¹] and decays by second-order kinetics with the rate constant 2k = (2·7 ±0·4) × 10⁹ dm³ mol⁻¹ s⁻¹. H atoms and OH radicals form transient adducts to the phenyl groups of the Ar₄P⁺ ion with the rate constants of (1·5 ± 0·3) × 10⁹ dm³ mol⁻¹ s⁻¹ and (3·0±0·3) × 10⁹ dm³ mol⁻¹ s⁻¹, respectively. Both adducts have broad absorption spectra at 300≈380 nm (λ_max = 340 nm) with the molar extinction coefficients ε₃₄₀ = 5400±300 dm³ mol⁻¹ cm⁻¹ for the H adduct and ε₃₄₀ = 3500±200 dm³ mol⁻¹ cm⁻¹ for the OH adduct.     

Structural parameters of the nearest surrounding of lanthanide ions in aqueous solutions of their salts

Published data on the structural characteristics of the local surrounding of lanthanide ions in aqueous solutions of respective salts obtained by different research methods under standard conditions are reviewed. Structural parameters like the coordination number, interparticle distance, parameters of the second coordination sphere, and types of ionic association are discussed.     

Thermochemical transformations of hydrocarbonate ions in aqueous solutions

The influence of heat treatment on the reactivity index k ₁, pH value, and content of hydrocarbonate ions HCO₃⁻ in an aqueous solution was examined. The factors responsible for enhanced reactivity of thermally activated water were discussed.     

Removal of Th4+ ions from aqueous solutions by graphene oxide

The removal of Th⁴⁺ ions from aqueous solutions was investigated using single-layer graphene oxide (GO) as a sorbent which was prepared by the modified Hummers’ method through batch adsorption experiments at room temperature. Structural characterizations of the sorbent were also investigated. The influences of the pH value of solution, contact time, sorbent dose, ionic strength, the initial metal ion concentration and temperature on the adsorption of Th⁴⁺ were also investigated. These results indicated that the adsorption of Th⁴⁺ was dependent on the pH and independent on the ionic strength. The sorbent provided significant Th⁴⁺ removal (>98.7 %) at pH 3.0 and the adsorption equilibrium was achieved after only 10 min. The Langmuir adsorption isotherm fit the absorption profile very closely, and indicated that a maximum adsorption capacity of 1.77 mmol g^?1 of GO (411 mg g^?1) after 2 h. The thermodynamic parameters showed that this adsorption process was endothermic and spontaneous. Moreover, the desorption level of Th⁴⁺ from GO, by using 0.1 mol L^?1 H₂SO₄ as a stripping agent, was 84.2 ± 1.2 %, and that of 0.5 mol L^?1 HNO₃ as a stripping agent, was 79.8 ± 3.0 %.     

Sorption of strontium ions from aqueous solutions by oxidized multiwall carbon nanotubes

Multiwall carbon nanotubes (MWCNTs) oxidized by nitric acid solution were used to investigate the adsorption behavior of strontium from aqueous solutions similar to the nuclear waste media. The physical properties of both as produced and oxidized MWCNTs were studied by Boehm’s titration method and nitrogen adsorption/desorption. The results showed that the surface properties of MWCNTs such as specific surface area, functional groups and the total number of acid sites were improved after oxidation. Furthermore, the effect of solution conditions such as initial concentration of strontium(II), pH, ionic strength, MWCNT concentration and contact time were studied at room temperature. The results of this study showed that the adsorption of strontium(II) was significantly influenced by the pH value and the solution ionic strength. According to the Langmuir model, the maximum adsorption capacities of strontium(II) onto the as produced and oxidized MWCNTs were obtained as 1.62 and 6.62 mg g^?1, respectively. The contact time to reach equilibrium was 100 min. The good adsorption of strontium(II) on oxidized MWCNTs at the lower ionic strength, the relatively high pH and the short equilibrium time indicate that the oxidized MWCNTs have great potential applications in the field of the environmental protection.     

Removal of heavy metal ions from aqueous solutions by alkaline-earth metal phosphates

The possibility of utilization of calcium or magnesium phosphates of various composition for heavy and non-ferrous metal extraction from aqueous solutions has been studied. The efficiency of the phosphates in removal of Pb(II), Cr(III) and Fe(III) ions has been shown to decrease in the following sequence: Mg₃(PO₄)₂>MgNH₄PO₄>Ca₃(PO₄)₂>CaHPO₄>Ca₁₀(PO₄)₆(OH)₂ which is inverse to their hydrolytic stability series. It has been established that phosphates of non-apatite structure are capable of binding up to 12 mmol g⁻¹ of the named heavy metals by a chemical interaction. Hydroxyapatite interacts with the polyvalent metal ions via either the above mentioned or ion-exchange mechanism, depending on preparation method used for the apatite and the nature of metal.