Weak Acidic Aqueous Solutions Research Articles

Modification of Poly(hydroethyl acrylate)-Grafted Cross-linked Poly(vinyl chloride) Particles via Surface-Initiated Atom-Transfer Radical Polymerization (SI-ATRP). Competitive Adsorption of Some Heavy Metal Ions on Modified Polymers

Poly(hydroethyl acrylate) (PHEA) has been grafted from the surfaces of cross-linked poly(vinyl chloride) (PVC) beads with their surface labile chlorines as initiation sites, using a copper-mediated surface-initiated atom-transfer radical polymerization (SI-ATRP) methodology. The graft reaction exhibits first-order kinetics with respect to the polymerization time in the low-monomer-conversion stage, as is typical for ATRP. A percentage of grafting (PG%) of 190.4% was achieved in 10 h. The ester groups of the poly(hydroethyl acrylate)-grafted cross-linked poly(vinyl chloride) beads (PHEA−PVC) were then hydrolyzed to yield carboxyl groups. Then, the bare PVC beads; the PHEA−PVC beads; and the hydrolyzed product, poly(acrylic acid)-grafted cross-linked poly(vinyl chloride) beads (PAA−PVC), were used for the extraction of heavy metal ions such as Cu(II), Hg(II), Zn(II), and Cd(II) in weak acidic aqueous solution. It was found that the former two had better loading capacities toward Hg(II) ion. The adsorbed ions were eluted by repeated treatment with acetic acid. The chelating resins did not lose their activity even after the 10th regeneration. The material described herein is regenerable and has the advantage of mobility of the graft chains in the removal of heavy metal ions from aqueous mixtures.

The characterization and bioelectrocatalytic properties of hemoglobin by direct electrochemistry of DDAB film modified electrodes

Direct electrochemistry of hemoglobin can be performed in acidic and basic aqueous solutions in the pH range 1–13, using stable, electrochemically active films deposited on a didodecyldimethylammonium bromide (DDAB) modified glassy carbon electrode. Films can also be produced on gold, platinum, and transparent semiconductor tin oxide electrodes. Hemoglobin/DDAB films exhibit one, two, and three redox couples when transferred to strong acidic, weak acidic and weak basic, and strong basic aqueous solutions, respectively. These redox couples, and their formal potentials, were found to be pH dependent. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ deposition of DDAB on gold disc electrodes and hemoglobin deposition on DDAB film modified electrodes. A hemoglobin/DDAB/GC modified electrode is electrocatalytically reduction active for oxygen and H 2O 2, and electrocatalytically oxidation active for S 2O 4 2− through the Fe(III)/Fe(II) redox couple. In the electrocatalytic reduction of S 4O 6 2−, S 2O 4 2−, and SO 3 2−, and the dithio compounds of 2,2′-dithiosalicylic acid and 1,2-dithiolane-3-pentanoic acid, the electrocatalytic current develops from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in neutral and weakly basic aqueous solutions. Hemoglobin/DDAB/GC modified electrodes are electrocatalytically reduction active for trichloroacetic acid in strong acidic buffered aqueous solutions through the Fe(III)/Fe(II) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in weak acidic and basic aqueous solutions. The electrocatalytic properties were investigated using the rotating ring-disk electrode method.

Kinetics and mechanism of the reaction between chromium(III) and 3,4-dihydroxyphenylpropionic (dihydrocaffeic) acid in weak acidic aqueous solutions

The reaction of 3,4-dihydroxyphenylpropionic acid (dihydrocaffeic acid, hydcafH3) with chromium(III) in weak acidic aqueous solutions has been shown to take place through various oxygen-bonded intermediates. The formation of the oxygen-bonded complexes upon substitution of water molecules of the chromium(III) coordination sphere takes place in at least three stages, the first of which has an observed rate constant k1(obs)=k1K0′[hydcafH3][H+] where K0′ corresponds to the Cr(H2O)63+ complex dissociation equilibrium. The second and third stages are ligand concentration independent and are thus attributed to isomerisation and chelation processes. The corresponding activation parameters are ΔH2≠=78±3 kJmol−1, ΔS2≠=−49±9 JK−1mol−1, ΔH3≠=60±9 kJmol−1 and ΔS3≠=−112±39 JK−1mol−1. The kinetic results support associative mechanisms and the nature of the electronic spectra a catecholic-type of coordination at the pH and concentration range studied and reported in this paper. The associatively activated substitution processes are accompanied by proton release causing a pH decrease. At lower acid concentration oxidation of the ligand takes place with concomitant high increase in the UV and VIS absorbance.

The electropolymerization and electrocatalytic properties of polymerized new fuchsin film modified electrodes

Electropolymerization of new fuchsin produces two types of stable and electrochemically active films in strong and weak acidic aqueous solutions. These films can be produced on glassy carbon, platinum, gold, and transparent semiconductor tin oxide electrodes. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of poly (new fuchsin) films. New fuchsin is a molecule that has three branched monomers, and its polymerization forms a dendrimer. The polymer films showed redox couples, and when transferred to various acidic to weak basic aqueous solutions, the formal potential versus pH plot had a slope of −60 mV pH −1. The electrocatalytic reduction of HNO 2 by poly (neutral red) in a strong acidic aqueous solution showed obvious electrocatalytic reduction activity. A modified electrode containing a hybrid of two organic films was also prepared from poly (new fuchsin) and poly (neutral red) films. The two films, with a formal potential difference of about 0.6 V, were both electrocatalytically active for IO 3 − oxidation, but produced different products in strongly acidic aqueous solution. The electrocatalytic reduction of BrO 3 − was achieved only by poly (neutral red) in a strongly acidic aqueous solution. The polymer films also reduced SO 5 2−, IO 4 − and Cr 2O 7 2− electrocatalytically, and oxidized ascorbic acid electrocatalytically in aqueous solution.

The bioelectrocatalytic properties of cytochrome C by direct electrochemistry on DNA film modified electrode

The direct electrochemistry of cytochrome C can be performed in weak acidic and basic aqueous solutions. Cytochrome C can be deposited as a stable and electrochemically active film on a deoxyribonucleic acid (DNA) modified glassy carbon electrode. These films can also be produced on gold, platinum, and transparent semiconducting tin oxide electrodes. Two-layer modified electrodes containing cytochrome C and a DNA film were prepared by the deposition of cytochrome C on a DNA film modified electrode. The cytochrome C/DNA film was electrocatalytically oxidation active for l-cysteine in a pH 8.3 tris(hydroxymethyl)aminomethane (TRIS)-buffered aqueous solution through both Fe III and Fe IV species. The electrocatalytic oxidation current developed from the anodic peak of the redox couple. The electrocatalytic oxidation properties of ascorbic acid, NH 2OH, N 2H 4, and SO 3 2− by a cytochrome C/DNA film were also determined, and shown to be electrocatalytically active. An electrochemical quartz crystal microbalance, cyclic voltammetry, and direct spectroelectrochemistry were used to study in situ DNA deposition on a gold disc electrode and cytochrome C deposition on DNA/Au and DNA/GC films. The direct electrochemistry of cytochrome C can also be performed, and it can be deposited as a stable and electrochemically active film on polyvinyl sulfonate, polystyrene sulfonate, TiO 2, and polyethylene glycol modified glassy carbon electrodes. The results show that cytochrome C interacts with, and deposits on, a DNA film modified electrode, and that the cytochrome C (Fe III) oxidized form is more easily deposited on a DNA film than the cytochrome C (Fe II) reduced form.

Crystal Structure and Absorption Spectra of Triguanidinium Bis(N-methyliminodiacetato)dioxoneptunate(V) {C(NH2)3}3[NpO2(mida)2

This paper is a continuation of our on-going program for studying the structure and properties of pentavalent neptunium compounds with organic ligands containing several electron-donating atoms. Previously, we studied the neptunium(V) complexes with anions of pyridinecarboxylic acids, polypyridines, and found that the Np ion coordinates the oxygen and nitrogen atoms of heterocyclic ligands to form stable chelate rings [1‐3]. As is known, neptunium(V) in weak acid and basic aqueous solutions forms stable complexes with aliphatic polyaminoacetic acids (complexones). The compositions and stability constants were determined for the Np complexes with the anions of the following acids: iminodiacetic (H 2 ida), N -methyliminodiacetic (H 2 mida), ethylenediaminetetraacetic (H 4 edta), diethylenetetraminepentaacetic, and N -hydroxyethyliminodiacetic. It was noted that the complexes of pentavalent actinides in solutions are less stable than the complexes of hexavalent actinides with the same ligands [4‐6]. However, only neptunium(V) ethylenediaminetet

A multi-state empirical valence bond model for acid–base chemistry in aqueous solution

Classical molecular dynamics simulations in conjunction with a multi-state empirical valence bond (MS-EVB) model are used to study proton transport in strong and weak acid aqueous solutions. The strong acid, HCl, is modeled in its ionized state by inserting a chloride counter ion into the protonated water solution. Both equilibrium and dynamical properties differ only slightly from the previously studied isolated excess proton in water. The free-energy profile as a function of the separation between the excess charge and chlorine atom reveal minimal barrier for the anion-excess charge separation. To model the weak acid, protonated imidazole, the MS-EVB model was extended to include the protonated form of the acid in the EVB description, so that the dissociation step can be studied. Free energy profiles for the weak acid deprotonation show that several solvation shells around the weak acid molecule need to be included in the EVB model to correctly describe the stabilization of the solvated species. Structurally, one water molecule is coordinated to the proton donor in the protonated acid case, while two water molecules coordination is likely when the acid is deprotonated.

酸性雨中和剤としてのカキ殻の溶解特性

Acidification of forest soils by acid rain is one of the most crucial topics today. On the other hand, the disposal method of waste oyster shell as industrial waste have not been detected. Here, we tried to reuse the oyster shell as neutralizer for acid rain. Dominant component of oyster shell is calcite (CaCO3, wt%>98) which is able to be dissolved easily in neutral or weak acidic aqueous solutions. Acid rain was collected and analyzed the components in order to investigate the neutralization effects by waste oyster shell.

Electropolymerization of iron phenanthrolines and voltammetric response for pH and application on electrocatalytic sulfite oxidation

Polymerization from the complexes of iron(II) tris(1,10-phenanthroline) can be initiated by electrochemical reduction between pH 2 and 7 in aqueous solution to produce stable and electrochemically active films on both glassy carbon electrodes and transparent semiconductor indium oxide electrodes. Some of the other complexes of iron(II) tris(5-chloro-1,10-phenanthroline) and iron(II) tris(5-methyl-1,10-phenanthroline) can also produce polymer films in aqueous solution. Iron(II) tris(5-NH 2-1,10-phenanthroline) in a non-aqueous solution can produce a polymer film which is stable in acidic and basic aqueous solution when transfered to a weak acidic aqueous solution and electrochemically oxidized and shows similar properties to the former films. Electroreduction and then electrooxidation of the monomer of iron(II) phenanthrolines in aqueous solution leads to the adherence of a polymeric film on a glassy carbon electrode or an indium oxide electrode. There are higher electrode surface coverage and polymerization rates at pH 4.0 and 3.0 than at the more acidic or basic buffer solutions of pH 1.7 and 6.0. The density of the surface coverage on the glassy carbon electrode surface is approximately 1 × 10 −9 to 3 × 10 −9 mol cm −2. The electrode surface coverage Γ increases quickly over the first 10 scans, then the coverage rate slows and becomes a constant after about 50 scans. The polymeric films were obtained with a formal potential and responded between pH 1 and 14 with a slope of −60 mV (pH) −1. The polymer film from iron(II) tris(5-NH 2-1,10-phenanthroline) can perform the electrocatalytic oxidation of sulfite to sulfate in pH 2.0 aqueous solution.

Rapid determination of kinetic parameters for the electrocatalytic reduction of dioxygen by vitamin B 12 adsorbed on glassy carbon electrode

In this paper, the electrochemical behavior of vitamin B 12, ie cyanocobalamin (abbr. VB 12) in a weak acidic aqueous solution and adsorbed on glassy carbon (GC) surface (abbr. VB 12(ad)/GC) in different pH buffer solutions have been described by using cyclic voltammetry ( cv). It is found that VB 12 and VB 12(ad)/GC exhibit catalytic activity for the electroreduction of O 2 according to two reduction peaks at −0.50 and −1.00 V vs. sce; but their electrocatalytic activity is very unstable. Based on the method of hydrodynamic amperometry [B. Miller and S. Bruckenstein, J. electrochem. Soc. 117, 1033 (1970)], some kinetic parameters for the electrocatalytic reduction of O 2 by VB 12(ad)/GC have been determined rapidly by using a linear rotation-scan method [Rongzhong Jiang and Shaojun Dong, Electrochim. Acta 35, 1451 (1990)]. These kinetic parameters indicate that the reduction of O 2 on VB 12(ad)/GC gives water predominantly in both potential ranges which correspond to those two reduction peaks. Possible reaction mechanisms have been suggested.

Spectrophotometric determination of boron by solvent extraction with 2-hydroxy-2-methylbutyric acid and malachite green.

A very simple and sensitive method for the spectrophotometric determination of boron was developed. Boron was found to react with 2-hydroxy-2-methylbutyric acid in weak acidic aqueous solution at room temperature to form a complex anion which can be extracted into chlorobenzene with malachite green in a single extraction; boron is determined indirectly by measuring the absorbance of malachite green in the extract at 629 nm. The calibration graph is linear over the range (7.50 × 10-7 - 2.00 × 10-5) mol dm-3 boron; the apparent molar absorptivity is 6.50 × 104 dm3 mol-1 cm-1. The method is applied to the determination of micro amounts of boron in natural waters with satisfactory results.

Extraction of molybdenum(VI) from weak acid aqueous solutions by quaternary ammonium salts

Extraction of molybdenum(VI) from weak acid aqueous solutions by quaternary ammonium salts

Coa/Coß-Isom erie der Corrinoide. Partialsynthese und Escherichia coli -Aktivität weiterer Isomerenpaare der (Co-M ethyl)-corrinoide Coa/Co/Msomerism of Corrinoids. Partial Synthesis and Escherichia coli Activity of Further Isomer Pairs o f the (Co-methyl)-Corrinoids

In 2-methyladenyl-(Cobeta-methyl)-cobamide and in adenyl-(cobeta-methyl)-cobamide the nucleotide base is coordinated to the cobalt atom in neutral and weak acidic aqueous solutions (in the corresponding adenosylcorrinoids the nucleotide base is not coordinated). 2-Methylthioadenyl-(Cobeta-methyl)-cobamide resembles, with regard to the coordination of the nucleotide base, the benzimidazole-corrinoids. The partial synthesis via cobalt (I) corrinoids results in a variable proportion: (Coalpha-methyl) isomer/(Cobeta-methyl) isomer, e. g. 7/93 (cobalamin) and 50/50 (p-cresylcobamide). This proportion is generally low, if in the corresponding cyanocorrinoid the nucleotide base is firmly coordinated; it is high, if the coordination in the corresponding cyanocorrinoid is weak or absent. These results are compatible with the assumption that in the cobalt (I) corrinoids the nucleotide base is to a certain extent coordinated. In Escherichia coli 113-3 the examined (Coalpha-methyl)-corrinoids show a weaker bioactivity than the corresponding (Cobeta-methyl)-corrinoids.

ChemInform Abstract: A THEORETICAL TREATMENT OF THE KINETICS OF IRON DISSOLUTION AND PASSIVATION

AbstractDas anodische Verhalten von hoch reinem Fe in schwach wäßrigsaurer Lösung, die frei von Sauerstoff und oberflächenaktiven Verbindungen ist, wird in verschiedenen Bereichen (aktive Auflösung, Übergangs‐ und präpassiver Bereich, Passivitätszustand) beobachtet.

A theoretical treatment of the kinetics of iron dissolution and passivation

The anodic behaviour of highly pure iron in weak acid aqueous solutions which are free of oxygen and surface active compounds takes place in different ranges: active dissolution, transition range, prepassive range and passive state. This is indicated by the experimentally observed current-density potential curves which show a maximum I and a minimum in the transition range, a further increase in the prepassive range and a maximum II before reaching the passive state. Different mechanisms including consecutive and parallel steps are discussed in order to find the kinetic equation describing the complete anodic behaviour. The derived kinetic equations are examined by computer simulations. The simulated cd potential curves were compared with the experimental ones. A dissolution mechanism is postulated which satisfies the experimental results. The active dissolution range is characterized by the consecutive (Bockris-) mechanism including the adsorbed species (FeOH) ads. In the transition range a second intermediate [Fe(OH) 2] ads is formed, which acts as a membrane inhibitor on the active dissolution. The prepassive range can be described by further electrochemical parallel steps starting from this second intermediate. The passivation is due to the formation of nonporous oxide layers which arise from [Fe(OH) 3]-oxide phase and [Fe(OH) 2] ads including Fe 2O 3 and Fe 3O 4.