Search results for "aqueous solution"
showing 10 items of 1610 documents
Comparison of adsorption equilibrium models and error functions for the study of sulfate removal by calcium hydroxyapatite microfibrillated cellulose…
2017
In the present study, the adsorption of sulfates of sodium sulfate (Na2SO4) and sodium lauryl sulfate (SLS) by calcium hydroxyapatite-modified microfibrillated cellulose was studied in the aqueous solution. The adsorbent was characterized using elemental analysis, Fourier transform infrared, scanning electron microscope and elemental analysis in order to gain the information on its structure and physico-chemical properties. The adsorption studies were conducted in batch mode. The effects of solution pH, contact time, the initial concentration of sulfate and the effect of competing anions were studied on the performance of synthesized adsorbent for sulfate removal. Adsorption kinetics indica…
Modeling the acid-base properties of molybdate(VI) in different ionic media, ionic strengths and temperatures, by EDH, SIT and Pitzer equations
2017
This paper reports the results of a study on the determination of the protonation constants of MoO42 −, in NaClaq, NaNO3aq, KClaq, at different ionic strengths (0 < I/mol dm− 3 ≤ 5.0 in NaClaq, 0 < I/mol dm− 3 ≤ 3.0 in NaNO3aq and KClaq) and temperatures (278.15 ≤ T/K ≤ 318.15 in NaClaq, only 298.15 K in NaNO3aq and KClaq), by potentiometric (ISE-H+ glass electrode) and spectrophotometric (UV/Vis) titrations. After a critical analysis of results and literature findings, the proposed speciation model takes into account the formation of two monomeric and four heptameric species, namely: MoO4H−, MoO4H2, (MoO4)7H86 −, (MoO4)7H95 −, (MoO4)7H104 − and (MoO4)7H113 −. Due to the complexity of…
A highly stable and hierarchical tetrathiafulvalene-based metal organic framework with improved performance as a solid catalyst
2018
[EN] Herein we report the synthesis of a tetrathiafulvalene (TTF)-based MOF, namely MUV-2, which shows a non-interpenetrated hierarchical crystal structure with mesoporous one-dimensional channels of ca. 3 nm and orthogonal microporous channels of ca. 1 nm. This highly stable MOF (aqueous solution with pH values ranging from 2 to 11 and different organic solvents), which possesses the well-known [Fe3(¿3-O)(COO)6] secondary building unit, has proven to be an efficient catalyst for the aerobic oxidation of dibenzothiophenes.
Microscopic aspects of solute-solute interactions induced by the solvent
1996
Nous presentons les plus importants resultats que nous ayons obtenus par des simulations etendues de dynamique moleculaire de solutions aqueuses contenant des modeles de solute hydrophiles et hydrophobes. Ces simulations determinent les forces induites par le solvant sur les solutes (SIFs) en fonction du type de solute, de la separation solute-solute et de leur orientation mutuelle. Les proprietes structurales et dynamiques du solvant autour des solutes ont ete analysees pour comprendre leur relation avec les SIFs. les presents resultats sont compares a des observations experimentales et precedentes stimulations sur des solutions aqueuses de biomolecules.
Dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry for the determination of nitro musks in surface water and w…
2011
A new, simple, fast and high sensitive analytical method based on dispersive liquid-liquid microextraction (DLLME) followed by gas chromatography-mass spectrometry (GC-MS) for the simultaneous determination of nitro musks in surface water and wastewater samples is presented. Different parameters, such as the nature and volume of both the extraction and disperser solvents and the ionic strength and pH of the aqueous donor phase, were optimized. Under the selected conditions (injection of a mixture of 1 mL of acetone as disperser solvent and 50 μL of chloroform as extraction solvent, no salt addition and no pH adjustment) the figures of merit of the proposed DLLME-GC-MS method were evaluated.…
Intramolecular proton transfer of serine in aqueous solution. Mechanism and energetics
2000
Serine amino acid in aqueous solution is theoretically studied at the B3PW91/6-31+G** level using a dielectric continuum solvent model. Neutral and zwitterionic structures in the gas phase and in solution are described and the proton-transfer mechanism is discussed. A neutral conformation in which the carboxyl hydrogen atom is already oriented toward the amino group seems to be the absolute energy minimum in the gas phase and the most stable neutral form in solution. The absolute energy minimum in solution is a zwitterionic form. The energy barrier for proton transfer is predicted to be very small, in particular when zero-point-energy contributions are added. Our calculations allow the dyna…
Phosphatidylcholine-Gramicidin a Interaction Study in Non-Aqueous Solvent with a new HPLC-SEC Column
1985
Abstract A new HPLC-SEC column, Ultrastyragel 500 A, has been assayed in order to check the separation between gramicidin A and phosphatidylcholine in tetrahydrofuran. The good resolution of both compounds has allowed the quantitation of lipid-polypeptide interaction in terms of the binding ratio parameter, BR. A BR value of 3.6 moles of phosphatidylcholine per mole of gramicidin A has been obtained for a 0.1 % (w/v) phosphatidylcholine solution as eluent. The suitability of this support for studies on lipid-polypeptide interactions in non-aqueous solvents is demonstrated.
On the ionizing properties of supercritical carbon dioxide: uncatalyzed electrophilic bromination of aromatics
2014
Supercritical carbon dioxide (scCO2), a solvent with a zero dipole moment, low dielectric constant, and no hydrogen bonding behavior, is a suitable medium to perform the uncatalyzed electrophilic bromination of weakly activated aromatics with no interference of radical pathways. The ability of scCO2 to promote these reactions matches those of strongly ionizing solvents such as aqueous acetic and trifluoroacetic acids. Conversely, carbon tetrachloride, with similar polarity parameters to scCO2, leads exclusively to side chain functionalization. The strong quadrupole moment, and the acidic, but non basic, Lewis character of carbon dioxide, are proposed as key factors for the singular performa…
Zur polymerisation und copolymerisation des natriumvinylsulfonats
1959
Natriumvinylsulfonat (VS-Na) zeigt in konzentrierten wasrigen Losungen eine ausgepragte Polymerisationsneigung. Die Polymerisationsgeschwindigkeit und der erreichte Umsatz hangen stark von der Aciditat der Losungen ab. Es wurde gefunden, das mit der Polymerisationsdauer und mit wachsendem Umsatz auch die Molekulargewichte der Polymerisate ansteigen. Wasserunlosliche oder nur begrenzt losliche ungesattigte Verbindungen wie Styrol, Vinylacetat und andere konnen in Dimethylsulfoxyd in homogener Losung mit VS-Na copolymerisiert werden. Sodiumvinylsulphonate (VS-Na) shows a strong tendency for polymerization in concentrated aqueous solutions. The rate of polymerization and the conversion depend …
Design, characterization and evaluation of hydroxyethylcellulose based novel regenerable supersorbent for heavy metal ions uptake and competitive ads…
2017
Abstract Hydroxyethylcellulose succinate-Na (HEC-Suc-Na) was designed and evaluated for removal of some heavy metal ions from aqueous solution. Pristine sorbent HEC-Suc-Na was thoroughly characterized by FTIR and solid-state CP/MAS 13C NMR spectroscopy, SEM-EDS and zero point charge analyses. Langmuir isotherm, pseudo second order kinetic and ion exchange models provided best fit to the experimental data of sorption of metal ions. Maximum sorption capacities of supersorbent HEC-Suc-Na for sorption of heavy metal ions from aqueous solution as calculated by Langmuir isotherm model were found to be 1000, 909.09, 666.6, 588 and 500 mg g−1 for Pb(II), Cr(VI), Co(II), Cu(II) and Ni(II), respectiv…