Search results for "aqueous solution"
showing 10 items of 1610 documents
Cobalt Metal-Organic Framework Based on Layered Double Nanosheets for Enhanced Electrocatalytic Water Oxidation in Neutral Media
2020
A new cobalt metal-organic framework (2D-Co-MOF) based on well-defined layered double cores that are strongly connected by intermolecular bonds has been developed. Its 3D structure is held together by π-π stacking interactions between the labile pyridine ligands of the nanosheets. In aqueous solution, the axial pyridine ligands are exchanged by water molecules, producing a delamination of the material, where the individual double nanosheets preserve their structure. The original 3D layered structure can be restored by a solvothermal process with pyridine, so that the material shows a "memory effect"during the delamination-pillarization process. Electrochemical activation of a 2D-Co-MOF@Nafi…
Oxidation of oxalate ion in aqueous suspensions of TiO2 by photocatalysis and ozonation
2005
Abstract Oxalate anion has been oxidized in aqueous alkaline solution by using ozonation and photocatalysis in the presence of TiO 2 . A batch annular reactor has been used for carrying out reactivity runs in the presence of air/ozone, air/ozone/near UV irradiation, air/ozone/TiO 2 , air/near UV-irradiated TiO 2 and air/ozone/near UV-irradiated TiO 2 . The Langmuir–Hinshelwood kinetic model adequately describes the photocatalytic results obtained at different reaction conditions and allows determining the values of the kinetic and equilibrium adsorption constants. The contemporary presence of photocatalysis and ozonation shows a significant improvement of the process performance as the oxid…
Degradation of passive layers of iron studied by conversion electron Mössbauer spectroscopy
1995
Integral electron Mossbauer spectroscopy (ICEMS) and additionally some electrochemical methods were used to characterize the passivation process of iron (low carbon steel) in sulfate, sulfate+sulfite (a possible model solution of acid rain) solutions and in phosphate buffer. The phase compositions and thicknesses of the passive layers formed due to the electrochemical polarizations were analyzed in dependence on the duration of the anodic passivations and on the pH of the used electrolytes. The passive layer, as determined from the Mossbauer spectra, consists mainly of γ-FeOOH, however in sulfite confining sulfate aqueous solution at pH 3.5 Fe 3 C and despite ex-situ circumstances FeSO 4 .H…
Effect of Anions and Oxygen on the Kinetics of the Anodic Dissolution of Nickel
2006
An electrochemical impedance spectroscopy study on electrochemical dissolution and active/passive transition of polycrystalline nickel in acid media has been performed in sulfate and nitrate aqueous solutions. Oxygen favors the nickel electrodissolution in a nitrate aqueous acid medium, but the dissolution decreases in the sulfate medium due to nickel passivation. The anion and oxygen effect is analyzed from a model where Ni(I) species are stabilized on the Ni metal surface and all anions present in the solution compete in the neutralization of Ni(I) and Ni(II) and in the solubilization of Ni(II).
Mixed aggregates based on tetronic-fluorinated surfactants for selective oils capture
2015
Abstract An aqueous star-like copolymer solution was titrated with perfluoro carboxylic acids at various compositions to prepare a polymeric surfactant composed of fluorinated nano-domains. The copolymer is X-shaped where each arm contains ethylene oxide and propylene oxide repetitive units linked to a central ethylenediamine group. The aggregation behavior of the hybrid macromolecule was studied from the physico-chemical point of view by changing parameters like temperature and composition. The solubilization of perfluorinated and hydrogenated alcohols in mixed self-assembled structure revealed that a selectivity toward the fluorinated moiety can be done. The self-assembled structures are …
Conductimetric study of struvite crystallization in water as a function of pH
2017
Abstract The main objective of this work was to investigate the best pH for phosphorus removal from synthetic aqueous solutions using chemical precipitation of struvite, at constant temperature. The experimental approach, developed in the present study, consisted to precipitate struvite in synthetic wastewater containing PO 4 3− , NH 4 + and Mg 2+ ions in an equal molar ratio, using a stirred tank with continuous monitoring by conductimetry, at 25 °C. Different laboratory experiments were used to evaluate the effects of pH in the range of 8.5 till 11.8, on size, shape, and purity of the precipitated crystals. Struvite crystals were characterized by Infrared spectroscopy (FTIR), scanning ele…
Aminosäureester als chirale Hilfsgruppen bei Barbier-Reaktionen in wäßriger Lösung
1991
Amino Acid Esters as Chiral Auxiliaries in Barbier-Type Reactions in Aqueous Solution Valine and proline benzyl ester are converted into the aliphatic and aromatic α-oxo amides 5 by activation of the respective α-oxo acid by means of N,N′-diisopropylcarbodiimide. The α-oxo amides 5 undergo Barbier-type reactions with differently substituted allyl halides in the presence of zinc and pyridinium toluenesulfonate in water/THF (2:1, v/v) at 4°C. Thereby, the α-hydroxy amides 8/9 are formed in high yields and, in the case of the proline ester amides, with diastereomer ratios of 4–6:1. In the absence of any allyl halide, or if the addition of the allyl moiety to the carbonyl groups is only slow, t…
Micelles of Polysoaps: The Role of Bridging Interactions
1996
Polysoaps, hydrophilic polymers incorporating amphiphilic monomers, form intrachain micelles in aqueous media. The micelles are similar to those formed by monomeric amphiphiles but are also endowed with a swollen, starlike corona formed by the spacer chains joining the amphiphiles. Long polysoaps form strings comprising many intrachain micelles. Exchange of amphiphiles between such micelles may give rise to bridging attraction, resulting in the adoption of a collapsed configuration in which the swollen micelles are close packed into a spherical globule. Upon addition of free amphiphiles, this structure unravels in a highly nonlinear fashion. Titration by surfactants, and the resulting swell…
New Self-Assembling Polyaspartamide-Based Brush Copolymers Obtained by Atom Transfer Radical Polymerization
2009
A simple and efficient method for the synthesis of polyaspartamide-based brush copolymers using Atom Transfer Radical Polymerization (ATRP) is here presented. The syntheses were performed by using two subsequent steps. In the first step the macroinitiator was obtained by the conjugation of a proper number of 2-bromoisobutyryl bromide (BIB) residues to the R, -poly(N-2-hydroxyethyl)-D,L-aspartamide (PHEA) side chains, obtaining the PHEA-BIB copolymer. PHEA-BIB copolymer was used as “multi-functional macroinitiator” for the polymerization via ATRP of hydrophilic methacrylic monomers, such as methacrylic acid (MA), obtaining PHEA-IB-poly(MA) copolymer, sodium methacrylate (MANa+), obtaining PH…
Polyacrylates in aqueous solution. The dependence of protonation on molecular weight, ionic medium and ionic strength
2003
Abstract The protonation constants of polyacrylates with different molecular weights ( W =2000–750 000 Da) were determined in different ionic media (alkali metal chlorides and nitrates, tetraalkylammonium chlorides), at 25 °C, by potentiometric measurements (H + –glass electrode). Literature data were also considered. Different models used to analyse protonation data were compared: the first was the modified Henderson–Hasselbalch two-parameter equation, and the second was the three-parameter equation proposed by Hogfeldt. The dependence on the ionic strength of the different supporting electrolytes and all the protonation parameters involved in the two models showed the trend Et 4 N + ≫Li +…