Systematic studies on adsorption of lead on sea nodule residues

Lead adsorption from aqueous solutions was studied with the aim of detoxifying industrial effluents before their safe disposal onto land or into river waters. Sea nodule residue (SNR), a waste material containing oxides and oxyhydroxides of manganese, iron, silicon, etc., was used as an effective adsorbent for lead in this study. The effect of various parameters such as contact time, initial lead concentration, pulp density, particle size of the adsorbent, pH, and temperature was studied to optimize the conditions for maximum adsorption. Adsorption followed first-order kinetics and 99% of lead adsorption was achieved at a solid:liquid ratio of 1:330, in the pH range 5.5-6.0 at a particle size of -150 microm in 8 h for solution containing 200 ppm lead. The adsorption capacity was found to be 99.0 mg of lead per gram of SNR and the adsorption isotherms followed the Langmuir and Freundlich adsorption models. The mechanism of adsorption of lead onto the sea nodule residue was also investigated. It was possible to reduce the lead level from 25-200 ppm to acceptable levels (0.1 ppm) by adsorption over this solid waste.     

Flow Injection Manifold for Simultaneous Spectrophotometric Determination of Bi (III), Pb (II)

Abstract

A FIA assembly producing a carrier with pH which can be adjusted to the desired pH value is propposed. It is based on the merging of two different solutions, one of them at constant flow-rate and the other at variable flow-rate. This manifold has been used for the simultaneous determination of Bi(III) and Pb(II) with Arsenazo III. Calibration curves are linear in the 1.0-11.0 ppm Bi (III) range at pH 0.25 and 1.0-12.1 ppm Pb (II) at pH 2.15. The effect of foreign ions is also reported.     

95Mo and 17O NMR studies of aqueous molybdate solutions

Aqueous molybdate solutions with molybdenum concentrations of [Mo]=1, 0.4, and 0.2 M have been studied by NMR at pH 7-1 and in 0.3-6 M HClO4. The 95Mo NMR spectrum of isopolyanion (IPA) Mo7O24(6-) (I) at pH=5 consists of a signal at 210 ppm and two overlapping peaks at 32 and approximately 15 ppm with the intensity ratio approximately 1:4:2, and that of beta-Mo8O26(4-) (II) consists of two signals at approximately 100 and 10 ppm with the intensity ratio approximately 1:3. A broad 95Mo NMR line at around 0 ppm was observed in the pH range of IPA Mo36O112(8-) (III), and a signal of cationic oxospecies including MoO2(2+) (IV) was observed from -62 to -69 ppm. Two protonation sites of IPA I have been identified from 17O NMR spectra, which suggests binding of up to two protons. The distribution diagram, derived from the 95Mo NMR spectra, is given for [Mo]=0.4 M. The 95Mo NMR signals shift to lower frequencies with increasing number and strength of the Mo-O terminal bonds.     

Effect of gold oxide in measurements of colloidal force

Atomic force microscopy, contact-angle, and spectroscopic ellipsometry measurements were employed to investigate the presence and properties of gold oxide on the surface of gold metal. It was found that, in agreement with available literature, unoxidized gold surfaces were hydrophobic, whereas oxidation rendered the surface highly hydrophilic. The oxide could be removed with ethanol or base but appeared to be stable over long periods in water or salt solutions between pH 3 and 7. After oxidation, the oxide layer thickness, determined using ellipsometry, was consistent with an approximate monolayer of Au-O bonds at the gold surface. The presence of gold oxide was found to alter significantly the electrical double-layer characteristics of the gold surface below pH 6 and may explain the apparent inconsistencies in observed force behavior where gold is employed as well as aiding in design of future microfluidic systems which incorporate gold as a coating.     

Complexometric determination of copper and iron in silicon with a cupric ion-selective electrode

A method is described for the complexometric determination of copper(II) and iron(III) in silicon with the cupric ion-selective electrode as endpoint detector. The sample is dissolved with hydrogen fluoride, hydrogen peroxide, and gold(III) as catalyst. The silicon matrix is then removed distilling off the azeotropic mixture containing hydrofluorosilicic acid. The residue is dissolved with 0.5 M sulfuric acid and the resulting solution divided into two parts. Copper is determined over the first by TETREN at pH 5.0–6.0. The copper-iron sum is determined over the second part, by EDTA at pH 1.0–1.5. The effect of Al(III), Mn(II), and Zn(II) ions is investigated. Applications of the method of the determination of copper and iron in silicon samples from different manufacturers, is illustrated. Copper at level of 10 ppm was analyzed with a relative standard deviation of 6%. Iron at level of 5000 ppm was analyzed with a relative standard deviation of about 2.5%.     

Effects of solution pH on sulfite oxidation at a gold electrode

Journal of Solid State Electrochemistry - The oxidation of sulfite at a renewable gold electrode in solutions with pH values ranging from 2 to 14 was studied using voltammetry. The voltammogram...     

Electrogenerated chemiluminescence of luminol on a gold-nanorod-modified gold electrode

Electrogenerated chemiluminescence (ECL) of luminol on a gold-nanorod-modified gold electrode was studied, and five ECL peaks were obtained under conventional cyclic voltammetry in both neutral and alkaline solutions. Among them, four ECL peaks (ECL-1-4) were also observed on a gold-nanosphere-modified gold electrode, but the intensities of these ECL peaks were enhanced about 2-10-fold on a gold-nanorod-modified gold electrode in neutral solution. One new strong ECL peak (ECL-5) was obtained at -0.28 V (vs SCE) on a gold-nanorod-modified gold electrode in both neutral and alkaline solutions and enhanced with an increase in pH. In strong alkaline solutions, ECL-1 and ECL-2 on a gold-nanosphere-modified electrode were much stronger than those on a gold-nanorod-modified gold electrode, while ECL-3-5 appeared to only happen on a gold-nanorod-modified gold electrode. The emitter of all the ECL peaks was identified as 3-aminophthalate. The ECL peaks were found to depend on the scan direction, the electrolytes, the pH, and the presence of O(2) and N(2). The reaction pathways for ECL-4 have been further elucidated, and the mechanism of the new ECL peak (ECL-5) has been proposed. The results indicate that a gold-nanorod-modified gold electrode has a catalytic effect on luminol ECL different from that of a gold-nanosphere-modified gold electrode, revealing that the shape of the metal nanoparticles has an important effect on the luminol ECL behavior. The strong ECL of luminol in neutral solution obtained on a gold-nanorod-modified electrode may be used for the sensitive detection of biologically important compounds in physiological conditions.     

Photoinitiated gold sol generation in aqueous Triton X-100 and its analytical application for spectrophotometric determination of gold

Gold complex, HAuCl(4) has been transformed into pink-coloured stable gold sol having lambda(max) at 523 nm (in=3.06x10(3)1.mol(-1)cm(-1)) at room temperature in aqueous Triton X-100 (TX-100) upon photoirradiation. It is a very rapid and simple process and the absorbance at 523 nm is a direct measure of gold concentration. Beer's law is obeyed in the range of 0-150 ppm of gold. The relative standard deviation for 22.7 and 90.9 ppm of gold are 2.8 and 2.5% respectively. The 95% confidence limit (ten determinations) for 22.7 ppm of gold is 23.6+/-0.5 ppm. Sandell sensitivity is 6.44x10(-2) mug cm(-2). TX-100 acts both as a reducing agent and a stabilizer here. Statistical parameters, effects of TX-100 concentration, irradiation time and interferents are studied. The method is applicable for ore and synthetic mixture analysis.     

13C-labeled N-acetyl-neuraminic acid in aqueous solution: detection and quantification of acyclic keto, keto hydrate, and enol forms by 13C NMR spectroscopy

Aqueous solutions of N-acetyl-neuraminic acid (Neu5Ac, 1) labeled with (13)C at C1, C2, and/or C3 were analyzed by (13)C NMR spectroscopy to detect and quantify the acyclic forms (keto, keto hydrate, enol) present at varying pHs. In addition to pyranoses, solutions contained the keto form, based on the detection of C2 signals at approximately 198 ppm (approximately 0.7% at pH 2). Spectra of [2-(13)C] and [3-(13)C] isotopomers contained signals arising from labeled carbons at approximately 143 and approximately 120 ppm, respectively, which were attributed to enol forms. Solution studies of [1,2,3-(13)C3] 1 substantiated the presence of enol (approximately 0.5% at pH 2). Enol was not detected at pH > 6.0. A C2 signal observed at approximately 94 ppm was identified as C2 of the keto hydrate (approximately 1.9% at pH 2), based partly on its abundance as a function of solution pH. Density functional theory (DFT) calculations were used to study the effect of enol and hydrate structure on J(CH) and J(CC) values involving C2 and C3 of these forms. Solvated DFT calculations showed that (2)J(C2,H3) in cis and trans enols have similar magnitudes but opposite signs, making this J-coupling potentially useful to distinguish enol configurations. Solvent deuterium exchange studies of 1 showed rapid incorporation of (2)H from (2)H2O at H3 axial in the pyranoses at p(2)H 8.0, followed by slower exchange at H3 equatorial. The acyclic keto form, which presumably participates in this reaction, must assume a pseudo-cyclic conformation in solution in order to account for the exchange selectivity. Weak (13)C signals arising from labeled species were also observed consistently and reproducibly in aqueous solutions of (13)C-labeled 1, possibly arising from products of lactonization or intermolecular esterification.     

Fluorescence determination of the pesticide asulam by flow injection analysis.

This paper presents the analytical determination of the pesticide Asulam based on its native fluorescence. The method was optimized in either a flow injection analysis (FIA) assembly or in batch. The maximum fluorescence intensity was observed for basic pH solutions and at a lamda(ex) of 258 nm and a lamda(em) of 342 nm. The influence of different empirical parameters, such as the pH, the presence of surfactants, solvent polarity or solved oxygen amount, was studied. The calibration range was fitted with a linear equation from 0.01-3 mg l(-1) Asulam and 0.005-15 mg l(-1) Asulam for batch and continuous-flow, respectively. The RSD for both procedures was 1.0%. After testing the influence of a large series of potential interferents, the method was applied to water samples from different locations.     

Gold nanoparticles as a colorimetric sensor for protein conformational changes

Spherical gold nanoparticles and flat gold films are prepared in which yeast iso-1-cytochrome c (Cyt c) is covalently bound to the gold surface by a thiol group in the cystein 102 residue. Upon exposure to solutions of different pH, bound Cyt c unfolds at low pH and refolds at high pH. This conformational change causes measurable shifts in the color of the coated nanoparticle solutions detected by UV-VIS absorption spectroscopy and in the refractive index (RI) of the flat gold films detected by surface plasmon resonance (SPR) spectroscopy. Both experiments demonstrate the same trend with pH, suggesting the use of protein-covered gold nanoparticles as a simple colorimetric sensor for conformational change.     

Spectrophotometr1c determination of cadmium with 2-(5-chloro-2-pyridylazo)-5-dimethylaminophenol

The reaction between cadmium and 2-(5-chloro-2-pyridylazo)-5-dimethylaminophenol (5-Cl DMPAP) in aqueous alcohol media at pH 8.8-10.7 results in an intense violet colour which is stable for at least 8 hr. The composition is 2:1 reagent:metal and the formation constant (5.29 +/- 0.01) x 10(18). Beer's law is obeyed up to 1.34 ppm of cadmium at 550 nm. The optimal concentration range (Ringbom) is between 0.16 and 0.72 ppm. The apparent molar absorptivity at 550 nm is (1.20 +/- 0.01) x 10(5) l.mole(-1). cm(-1), making the sensitivity one of the highest known. The interference due to copper(III), iron(III), cobalt(II), nickel(II), gold(III), zinc(II) and manganese(II) can be suppressed.     

Inorganic polarography in organic solvents-III Analytical applications of metal-acetylacetonate complexes in toluene

Indium and palladium are determined polarographically with a dropping mercury electrode in a toluene phase, following extraction as the acetylacetonates from aqueous solutions containing 2-10 ppm of the metals (or 0.1-0.5 ppm with a greater ratio of sample volume to solvent volume). Of 31 elements examined, only Co(III), Cr(III), Cu(II), Fe(III), In, Mo(VI), Pd and Ti(IV) gave extractable complexes with reduction waves in the available potential range. Specificity for palladium is obtained by extraction at pH 0.5, and for indium at pH 9 m the presence of cyanide and ascorbic acid as masking agents.     

Preconcentration of 198Au in a green alga, Rhizoclonium</p> </p>

Summary The bioaccumulation of ¹⁹⁸Au radionuclide, by Rhizoclonium riparium a member of Chlorophyceae has been studied. It has been observed that accumulation of gold on Rhizoclonium is almost pH independent and slightly higher at basic pH. Accumulation of gold was studied with ¹⁹⁸Au radiotracer, 0.1, 1 and 5 ppm concentrations of gold. It has been concluded from the biochemical analysis that the gold accumulation is due to adsorption in the cellulose and not in protein, fat and carbohydrate. Accumulated gold was recovered when washed with conc. HNO₃.</p> </p>     

Atomic-fluorescence characteristics and analytical determination of manganese in an air-acetylene flame

The atomic-fluorescence characteristics of manganese atoms in a premixed nitrogen-shielded air-acetylene flame are described. Excitation is obtained at 280 nm from a microwave-excited electrodeless discharge tube. A detection limit of 0-001 ppm for the determination of manganese by atomic-fluorescence spectroscopy is obtained by measurement of the resonance fluorescence observed at this wavelength. In addition to several other weaker atomic-fluorescence signals observed from manganese atoms in the flame, weak resonance fluorescence at 258 and 260 nm from manganese ions stimulated by ion line-emission from the source has been recorded. Linear calibration graphs for atomic-fluorescence measurement at 280 nm are obtained over the range 0.0025-10 ppm of manganese in aqueous solution. Of 26 foreign anions and cations examined for interference at the 1000-fold weight excess level only four produced interference. Large amounts of Si, Th and V interfere by scattering of the incident radiation, while Mg causes depression of the atomic fluorescence by a chemical effect.     

Electrochemical characteristics of thin nickel hexacyanoferrate films formed on gold and thiol self-assembled monolayers modified gold electrodes.

Nickel hexacyanoferrate (NiHCF) film was prepared and characterized on gold and thiol self-assembled monolayers (SAMs)-modified gold electrodes. It was found that the film exhibited some different electrochemical characteristics compared with that found on a carbon electrode. In the presence of K+, the film exhibited a redox peak at about 0.5 V. The peak potential shifted linearly with the K+ concentration over the range of about 0.1 mM - 0.1 M with slopes of 54 - 60 mV per log[K+]. However, in solutions containing Na+, Li+ or NH4+ ion the film did not generate well-defined peaks, or even a visible redox peak. Therefore, the film showed a selective potential response to K+. The voltammetric behavior of NiHCF film varied with thiols, the preparation procedure and the solution pH. Under certain conditions, the characteristics of the film could be improved to some extent.     

Colloid stability of thymine-functionalized gold nanoparticles

Gold nanoparticles surface-coated with thyminethiol derivatives containing long hydrocarbon chains have been prepared. The diameter of the particles is 2.2 and 7.0 nm, respectively, with a relatively narrow size distribution. Thyminethiol derivatives are attached to the gold particle surfaces with thymine moieties as the end groups. The colloid stability of the gold nanoparticles as a function of the type and concentration of monovalent salt, pH, and particle size was investigated in alkaline, aqueous solutions. The gold particles are stable in concentrated NaCl and KCl solutions, but are unstable in concentrated LiCl and CsCl solutions. The larger gold particles are more sensitive to salt concentration and aggregate at lower salt concentrations. The reversible aggregation and dispersion of the gold particles can be controlled by changing the solution pH. The larger gold particles can be dispersed at higher pH and aggregate faster than the smaller particles, due to stronger van der Waals forces between the larger particles. Hydration forces play an important role in stabilizing the particles under conditions where electrostatic forces are negligible. The coagulation of the gold nanoparticles is attributed to van der Waals attraction and reduced hydration repulsion in the presence of LiCl and CsCl.     

Spectrophotometric determination of platinum with o-phenylenediamine

Platinum(IV or II) reacts with o-phenylenediamine, at pH 6.5, to form light blue solutions having maximum absorption at 703 nm. The reaction, slow at room temperature, is complete in 3-4 min at temperatures near 100 degrees . Use of dimethylformamide in the solution prevents precipitation of the reaction product. The colour is stable for at least 24 hr. Effects of heating temperature and time, pH, reagent concentration, and other variables have been studied. The system conforms to Beer's law over the concentration range investigated. Optimum concentration range for measurement in 10-mm cells is 0.4-1.4 ppm of platinum; the molar absorptivity is 9.83 x 10(3) l. mole(-1). mm(-1). Interference from foreign ions has been evaluated, and methods for removal or masking of interferences have been tested. In the colour-forming reaction, platinum(IV) is reduced by the organic reagent to platinum(II), which is then complexed with the reagent. The metal : ligand ratio of 1 : 2 was indicated by solution spectrophotometric measurements, and was confirmed on the solid reaction product by elemental analysis and by mass spectrometric examination.     

Rise in the pH of an unfrozen solution in ice due to the presence of NaCl and promotion of decomposition of gallic acids owing to a change in the pH

Oxidative decomposition of gallic acid occurs in alkaline solutions but hardly arises in acidic solutions. We have found that the addition of sodium chloride promotes the decomposition of gallic acid caused by freezing even under neutral and acidic conditions. Even at pH 4.5, gallic acid was decomposed by freezing in the presence of NaCl; however, in the absence of NaCl, it was hardly decomposed by freezing at pH lower than 7. Chloride ions are more easily incorporated in ice than sodium ions when the NaCl solution is frozen. The unfrozen solution in ice becomes positively charged, and as a result, protons transfer from the unfrozen solution to the ice. We measured the pH in the unfrozen solution which coexists with single-crystal ice formed from a 5 mmol dm(-3) NaCl solution and determined the pH to be 8.6 at equilibrium with CO(2) of 380 ppm or 11.3 in the absence of CO(2) compared to pH 5.6 in the original solution. From the model calculation performed for gallic acid solution in the presence of 5 mmol dm(-3) NaCl, it can be estimated that the amount of OH(-) transferred from the ice to the solution corresponds to 1.26 x 10(-5) mol dm(-3). The amount of OH(-) transferred is concentrated into the unfrozen solution and affects the pH of the unfrozen solution. Therefore, the pH in an unfrozen gallic acid solution in ice becomes alkaline, and the decomposition of gallic acid proceeds. It is expected that other base-catalyzed reactions in weakly acidic solutions also proceed by freezing in the presence of NaCl without the need for any alkaline reagents.