Mmol Dm Research Articles

Adsorption thermodynamic and kinetic studies of Pb(II) removal from water onto a versatile Al 2O 3-supported iron oxide

The use of versatile sorbents has been investigated for wastewater treatment. An investigation into the use of activated alumina-supported iron oxide (denoted as FeAA), which is a by-product of the wastewater treatment plant. In our previous study, the FeAA has successfully been as heterogeneous photoassisted Fenton catalyst for degradation azo dye at neutral pH 7.0. In this work, the test and use of FeAA as adsorbent for the removal of lead (Pb 2+) from water are carried out. The highest Pb 2+ adsorption capacity was determined as 0.14 mmol g −1 for 0.8 mmol dm −3 initial Pb 2+ concentration at pH 5.0 and 318 K. Adsorption data were well described by the Langmuir model and the thermodynamic constants of the adsorption process: Δ G°, Δ H° and Δ S° were evaluated as −19.4 kJ mol −1 (at 318 K), 25.73 kJ mol −1 and 0.113 J mmol −1 K −1, respectively. The pseudo-first-order and pseudo-second-order kinetic models were applied to test the experimental data. The pseudo-second-order kinetic model provided the best correlation of the experimental data compared to the pseudo-first-order model.

Thermodynamics and kinetics of adsorption of Cu(II) onto waste iron oxide

This study investigates low-cost sorbents as replacements for current costly methods of removing heavy metals from solution. This investigation explores the waste iron oxide material (F1), which is a by-product of the fluidized-bed reactor (FBR)–Fenton reaction, for use in the treatment of the wastewater in Taiwan. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the F1. In this investigation, F1 are tested as adsorbents for removing copper (Cu 2+) from aqueous solutions. The highest Cu 2+ adsorption capacity of F1 adsorbent was determined as 0.21 mmol g −1 for 0.8 mmol dm −3 initial Cu 2+ concentration at pH 6.0 and 300 K. Adsorption data were well described by the Freundlich model and the thermodynamic constants of the adsorption process, Δ G°, Δ H° and Δ S° were evaluated as −6.12 kJ mol −1 (at 318 K), 9.2 kJ mol −1 and 48.19 J mol −1 K −1 (at 318 K), respectively. Additionally, a pseudo-second-order rate model was adopted to describe the kinetics of adsorption.

The effect of solution level on calorific and dosimetric results in a 70 kHz tower type sonochemical reactor

In order to design and optimise sonochemical reactors it is important to study the impact of liquid level, or path length, on the standing wave phenomena and the influence this has on temperature increase and OH radical rate of production. In this work, an ultrasonic tower type reactor operating at 70 kHz is investigated with results from variations to liquid levels reported. Calorimetry data was obtained using a modified reactor set up with temperature change monitored at selected points within the chamber. OH radical rate of formation was shown via chemical dosimetry, following the conversion of terephthalic acid (TA) to 2-hydroxyterephthalic acid (HTA). The results obtained have shown that changes in solution depth of a few millimetres significantly impacts on the interaction of the propagated and reflected waveforms with the results of calorific measurements and HTA rates of formation varying by 90% (750 J) and 88% (80 mmol dm −3 min −1) between the operational extremes over the studied depth range.

Effect of sodium cation on the electrochemical reduction of CO2 at a copper electrode in methanol

The electrochemical reduction of CO2 with a Cu electrode in methanol was investigated with sodium hydroxide supporting salt. A divided H-type cell was employed; the supporting electrolytes were 80 mmol dm−3 sodium hydroxide in methanol (catholyte) and 300 mmol dm−3 potassium hydroxide in methanol (anolyte). The main products from CO2 were methane, ethylene, carbon monoxide, and formic acid. The maximum current efficiency for hydrocarbons (methane and ethylene) was 80.6%, at −4.0 V vs Ag/AgCl, saturated KCl. The ratio of current efficiency for methane/ethylene, rf(CH4)/rf(C2H4), was similar to those obtained in LiOH/methanol-based electrolyte and larger relative to those in methanol using KOH, RbOH, and CsOH supporting salts. In NaOH/methanol-based electrolyte, the efficiency of hydrogen formation, a competing reaction of CO2 reduction, was suppressed to below 4%. The electrochemical CO2 reduction to methane may be able to proceed efficiently in a hydrophilic environment near the electrode surface provided by sodium cation.

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.

Pore water phosphate and ammonia below the permanent halocline in the south-eastern Baltic Sea and their benthic fluxes under anoxic conditions

In this paper the results of a study on the distribution of pore water phosphates and ammonia, and their fluxes under anoxic condition in a deep (> 70 m) accumulation-type bottom of the south-eastern Baltic Sea, namely in the Gdańsk Deep and the adjacent areas, are presented. All measurements were taken during the growth period, i.e. in September 2000, April 2001 and June 2002. Benthic phosphate and ammonia fluxes were estimated using Fick's First Law. Phosphate and ammonia concentrations ranged from 7.5 to 266.3 μmol dm − 3 and from 53.6 to 1248.3 μmol dm − 3 , respectively. The values recorded in the central part of the Gdańsk Deep were lower than those found both on its slopes and on the SW slope of the Gotland Deep. The lowest phosphate contents were typical of the Oblique Sill which separates the Gdańsk and Gotland Deeps. In 1993–2002, as a result of anoxia the sediments in the Gdańsk Deep released about 5.1 × 10 3 t P and 22.8 × 10 3 t N. These loads supplied on average 1.5% and 0.9% of phytoplankton's demand for P and N, respectively. In comparison to the total external load of nutrients discharged to the Gulf of Gdańsk (i.e. 8.79 × 10 3 t year − 1 P tot and 130.79 × 10 3 t year − 1 N tot; [Witek, Z., Humborg, Ch., Savchuk, O., Grelowski, A. and Łysiak-Pastuszak, E., 2003. Nitrogen and phosphorus budgets of the Gulf of Gdańsk (Baltic Sea). Est. Coast. Shelf Sci., 57:239–248.]), the return flux of P and N from the anoxic sediments to the water column in the Gdańsk Deep was a minor source of these elements.

Removal of 4-chlorophenol by soybean peroxidase and hydrogen peroxide in a discontinuous tank reactor

A discontinuous tank reactor was used to eliminate 4-chlorophenol using soybean peroxidase (SBP) and hydrogen peroxide in an attempt to reduce the concentrations of buffer solutions used and to avoid adding polyethylene glycol. The stirred-tank reactor was operated in different operating conditions, and the influence of enzyme and substrate concentrations on the elimination of 4-chlorophenol was determined. Most of the assays provided good elimination percentages, which reached almost 90% for an enzyme concentration of 7.5·10 –3 mg cm –3 and a stoichiometric ratio of 1:1 for both substrates, when concentrations of 1.5 mmol dm –3 or less were used. This work is a first step in the study of the SBP/4-chlorophenol system in order to observe the influence of the reagents concentrations when no polyethylene glycol is added.

Lipase‐catalyzed dynamic hydrolytic resolution of (R,S)‐2,2,2‐trifluoroethyl α‐chlorophenyl acetate in water‐saturated isooctane

AbstractThe hydrolytic resolution of (R,S)‐2,2,2‐trifluoroethyl α‐chlorophenylacetate in water‐saturated isooctane containing Lipase MY(I) at 35 °C is selected as the best reaction condition for producing (R)‐α‐chlorophenyl acetic acid. The kinetic constants, and hence an enantiomeric ratio of 33.6, are estimated and employed for the modeling of time‐course conversions of both substrates by considering product inhibition and enzyme deactivation effects. A successful dynamic kinetic resolution is also achieved, giving the desired (R)‐α‐chlorophenylacetic acid of 93.0% yield and eeP = 89.5% when 80 mmol dm−3 trioctylamine acting as the racemization catalyst and enzyme activator is initially added. Copyright © 2006 Society of Chemical Industry

Partitioning of a Model Corrosion Inhibitor in Emulsions

As the majority of corrosion inhibitors used in oil production are surfactants, they are are not only adsorbing to metal surfaces, but also at the oil/water (o/w) interface and onto dispersed solid particles. In the present work, the partitioning of cetyltrimethylammonium bromide (CTAB) between the aqueous bulk and the o/w interface is investigated. Zeta potential measurement of oil droplets at different CTAB concentrations has been utilized to study the adsorption process at the o/w interface. The CTAB reached an adsorption maximum at the critical micelle concentration. Upon dilution, the CTAB desorbed to equilibrium values within minutes. A new method has been utilized for determining the concentration of CTAB in the continuous phase of an o/w emulsion. The effects of some selected parameters were investigated in a fractional factorial experimental design, and the main effects were determined by blocking the experiments for each effect. The average loss of CTAB due to emulsification of 5% oil was found to be 0.34 and 0.24 mmol dm−3, 15 minutes and 315 minutes after emulsification, respectively. The loss of CTAB was higher for samples with an initial concentration of 3 mmol dm−3 than for those with an initial concentration of 1 mmol dm−3. Of the parameters investigated, the presence of 3% NaCl had the highest impact on the CTAB loss for the samples taken 15 minutes after emulsification, while the presence of 100 ppm MEG had the highest impact 315 minutes after emulsification. The presence of NaCl and MEG increased the aqueous concentration of CTAB.

Integrated Bienzyme Chip for Ethanol Monitoring

AbstractAn ethanol chip biosensors based on bienzymatic system has been developed. Horse radish peroxidase and alcohol oxidase have been co‐immobilized into a polypyrrole matrix, as well as the mediator, onto the integrated working electrode. Variables that affect to the chronoamperometric response of ethanol have been optimized through the experimental design methodology. Under these conditions, the slopes of several calibrations curves show a reproducibility, repeatability and limit of detection of 6.09% (n=5), 9.03% (n=5) and 2.98±0.38 mmol dm−3 (α=β=0.05, n=3), respectively. Finally, the biosensors based on platinum chips were applied to the determination of ethanol in white wine samples, obtaining successful results.

Two-Dimensional Photoluminescence Behavior of Langmuir-Blodgett Monolayers and Multilayers Composed of Decatungstoeuropate

Decatungstoeuropate/dimethyldioctadecylammonium (EuW10/DODA) Langmuir-Blodgett (LB) monolayers and multilayers (7 layers) were fabricated by using aqueous solution of EuW10 with different concentration (1.0–3.0 μmol dm−3). The results of specular X-ray reflectivity (SXR) and grazing incidence X-ray diffraction (GIXD) measurements for the EuW10/DODA LB films indicated an increase in the interlayer distance and in-plane molecular ordering for the film fabricated with the concentrated EuW10 solution, reflecting the dense packing of DODA and EuW10 molecules. Their photoluminescence property also depended on the concentration of the EuW10 solution. With an increase in the EuW10 concentration in the subphase, both the relative intensity of the 5D0→7F1 transition and the emission lifetime increased. The lifetime of emission of the EuW10 LB monolayers changed from 0.8±0.1 ms (1.0 μmol dm−3) to 1.0±0.1 ms (2.1 μmol dm−3) and 1.3±0.1 ms (3.0 μmol dm−3), which became closer to that (2.6 ms) of the solid, and EuW10/DODA LB multilayers had the same tendency. The elongation of the emission lifetime was due to a decrease in the number of aqua molecules within the Eu3+-coordination sphere, which will be caused by the dense and regular packing of EuW10 molecules.

Spectrophotometric Determination of Trace Amount of Copper(II) Ion Based on Complexation with an Anthraquinone Derivative

The spectrophotometric determination of Cu(II) with an anthraquinone derivative (Alizarin Red S) has been investigated. The experimental conditions, such as the pH of the sample and concentration of ligand, were optimized. This method is simple and sensitive for determination of Cu(II) ion. The interfering effects of diverse ions were investigated. Copper ion was determined by measuring the absorbance of the Cu(II)-ARS complex at 510 nm. Beer's law was obeyed over the concentration range of 0.011 - 0.320 mmol dm(-3) and the detection limit (S/N = 3) was 0.038 microg cm(-3). The relative standard deviation at 20 microg cm(-3) was 1.02% (n = 5). The method was applied for real samples.

Removal of Cr(VI) and Cr(III) from Aqueous Solutions and Industrial Wastewaters by Natural Clino-pyrrhotite

This paper introduced a simple method of treating Cr(Vl)-bearing toxic wastewaters using a natural mineral: clino-pyrrhotite. Laboratory bench-scale mixing experiments were carried out in both Cr(VI)-bearing artificial solutions and industrial wastewaters under controlled conditions. The effects of solution pH, Cr(VI) concentration, mineral grain size, mineral/solution ratio, and reaction time on the Cr(VI) removal were studied. Chromium was effectively removed from the solutions and wastewaters. After the treatment, the liquid was clean enough to be discharged directly into the natural environment. The Cr(VI) removal process involved sequentially the adsorption of Cr(VI), in the form of Cr2O7(2-) or CrO4(2-), onto the mineral surface, the reduction of the adsorbed Cr(VI) to Cr(lll), catalyzed at the vacant Fe sites of the mineral, and finally the precipitation of Cr(lll) as Cr2S3, Cr2O3, and Cr(OH)3 solid phases. Conditions such as a fine mineral grain size, an excessive quantity of clino-pyrrhotite and a weak acidic media, favored the removal process. For clino-pyrrhotite with a restricted grain size, the minimum required quantity of the mineral was proportional to the total quantity of Cr(VI) to be removed. Quantitatively, one cubic meter of industrial wastewater that contained approximately 1 mmol dm(-3) of Cr(VI) and had a pH value between 1 and 10 would be effectively treated after it was in contact with 220 kg of 145 +/- 28 microm clino-pyrrhotite for an hour. Furthermore, the quantity of the final solid waste byproduct was small, and the solid residue of clino-pyrrhotite could be reused after a simple rinse with water. Compared to the previous Cr(VI)-bearing wastewater treatment schemes, this method was simple, effective, economical, and environmentally sound. It has great potential for use in industrial-scale applications.

A noninterference polypyrrole glucose biosensor

In order to eliminate the interference of impurities, such as ascorbic acid, a noninterference polypyrrole glucose biosensor was constructed with a four-electrode cell consisting of a polypyrrole film electrode, a polypyrrole-glucose oxidase electrode, a counter electrode and a reference electrode. The pure catalytic current of glucose oxidase (GOD) can be obtained from the difference between response currents of two working electrodes with and without GOD. The effects of potential, pH and temperature on analytical performance of the glucose biosensor were discussed. The optimum pH and apparent activation energy of enzyme-catalyzed reaction are 5.5 and 25 kJ mol(-1), respectively. The response current of the biosensor increases linearly with the increasing glucose concentration from 0.005 to 20.0 mmol dm(-3). The results show the glucose biosensor with under 2% of relative deviation has good ability of anti-interference. The glucose biosensor was also characterized with FT-IR and UV-vis spectra.

Mn‐peroxidase production by Panus tigrinus CBS 577.79: response surface optimisation and bioreactor comparison

AbstractThis study reports the statistical optimisation through response surface methodology of the growth medium for Panus tigrinus manganese‐dependent peroxidase (MnP) production in shaken culture. Three crucial variables, including carbon source, malonic acid and Mn2+, were optimised in a nitrogen‐limited medium. Sucrose was the best carbon source for MnP production. Mn2+ ions and malonic acid significantly stimulated MnP production at an optimal concentration of 53 mg dm−3 and 8.2 mmol dm−3, respectively, resulting in 0.83 U cm−3. Further experiments were performed in lab‐scale stirred tank (STR) and bubble‐column (BCR) reactors using the previously optimised liquid medium. BCR proved to be more adequate than STR in supporting MnP production, leading to 3700 U dm−3 after 144 h with a productivity of 25.7 U dm−3 h−1. On a comparative basis with other production data in lab‐scale reactors, these results appear to be compatible with scale transfer. Copyright © 2006 Society of Chemical Industry

Fabrication of Pd–Ni alloy nanowire arrays on HOPG surface by electrodeposition

Pd–Ni alloy nanowires with diameters 50–300 nm and lengths of over 250 μm have been obtained by electrochemical step edge decoration (ESED). The fabrication by ESED is accomplished on highly oriented pyrolytic graphite by applying three potential pulses in succession: an oxidizing “activation” pulse, a reducing “nucleation” pulse, and a reducing “growth” pulse. The alloy composition is controlled by adjusting the ion concentration ratio of palladium and nickel, and the deposition processes. The scanning electron microscopy (SEM) images reveal that the alloy nanowires fabricated by this procedure are separate, parallel, and continuous. The composition of alloy nanowires can be controlled in the range of 8–15 wt.% Ni when the ion concentration ratio of palladium and nickel is 7:3 in the solution containing 70 mmol dm −3 Pd(NH 3) 4Cl 2. The reaction mechanism involves nucleation at potential of −1.1 V SCE to −2.0 V SCE and growth at potential of −0.3 V SCE to −0.5 V SCE.

Influence of medium on the kinetics of oxidation of iron(II) ion with t-butyl hydroperoxide

AbstractThe oxidation of iron(II) with tert-butyl hydroperoxide was investigated in the absence of oxygen in water, methanol, and the dichloromethane—methanol solvent mixture (φr = 2:1). The oxidation rate depends on solvent polarity; measured in the presence of SCN− at constant 0.8 mmol dm−3 HCl, the rate constant increases with the polarity decrease passing from water and methanol to the dichloromethane—methanol solvent mixture. Further, in non-aqueous solutions at this acid concentration the rate constant was higher than the rate constant in the presence of Cl− only. The oxidation rate measured in the [FeCl]2+ complex in dichloromethane—methanol was slow in acidic medium and increased by decreasing the acid concentration. Approaching the physiological pH conditions the rate constant attained the value of an order of magnitude of 103 dm3 mol−1 s−1, while very little alteration of stoichiometry of the oxidation reaction was observed. The rate constant measured in the presence of Cl− strongly depends on electrolyte concentration at concentrations less than 0.5 mmol dm−3 HCl, both in MeOH and the solvent mixture. Based on these results, a possible mechanism of the influence of solvent, acidity, and ligand type on the rate constant is discussed. We assume that the oxidation proceeds by an inner-sphere mechanism considering that the breakdown of the successor inner-sphere complex forming reactive alkoxyl radicals is probably the rate-limiting step.

Equilibrium and structure of the Al(iii)-ethylenediamine-N,N′-bis(3-hydroxy-2-propionate) (EDBHP) complex. A multi-method study by potentiometry, NMR, ESI MS and X-ray diffraction

The equilibrium and structure of the complex formed by Al(III) and ethylenediamine-N,N'-bis(3-hydroxy-2-propionate) (EDBHP2-) have been studied using pH-potentiometry, 1H and 27Al NMR, ESI MS and single crystal X-ray diffraction methods. The EDBHP ligand is a strong Al-binder in aqueous solution for pH between 4 and 8 and for c(Al) = c(EDBHP)> or = 0.1 mmol dm(-3). The dominating complex identified by ESI MS and potentiometry is a neutral dimer, Al2L2(OH)2, with logbeta(22-2) = 14.16 +/- 0.03. In the solid Al2(EDBHP)2(OH)2.2H2O the Al(III) ions are connected through a double hydroxo bridge. Both four-dentate organic ligands are coordinated terminally through two carboxylate groups and two N-donors forming three five-membered chelate rings. The hydroxyl groups of the ligand EDBHP remain protonated and are not coordinated to the aluminium ions. The structure and composition of the dimer are very likely the same in solution and the solid state.

Ionic Liquid|Water Interface: A New Electrified System for Electrochemistry

A room-temperature ionic liquid (RTIL) consisting of hydrophobic cations and anions forms a two-phase system with water (W). The interface between the RTIL and W is inevitably electrified because of the dissolution of cations and anions constituting the RTIL into the W phase and the two-phase system should, hence, be considered as a new electrochemical system where the phase-boundary potential across the RTIL|W interface plays a key role in determining physicochemical properties of the two-phase system, notably the interfacial charge transfer and the structure of the electrical double layers at the interface. When the solubility of the RTIL in W is on the order of a few mmol dm−3 or higher, the RTIL|W interface behaves as an electrochemically nonpolarized interface; the phase-boundary potential is determined by the composition of the two phases. At the opposite extreme where the solubility is a few tens µmol dm−3 or lower, the interface can be taken as an electrochemically polarized interface, since the phase-boundary potential can be controlled by externally applying a voltage across the two terminals of the cell that comprises the RTIL|W interface. This electrochemical polarizability allows us to employ a variety of electrochemical techniques for studying the RTIL|W interface. Electrochemical view points as well as electrochemical techniques are powerful in clarifying the unique properties of this new electrified interface. Conversely, this two-phase system poses us intriguing problems, which can in turn widen the scope of electrochemistry.

Extraction ofCandida rugosa lipase from aqueous solutions into organic solvents by forming an ion-paired complex with AOT

Candida rugosa lipase was extracted from aqueous solutions into organic solvents by forming an ion-paired complex with sodium bis(2-ethylhexyl)sulfosuccinate (AOT). The optimal aqueous pH for lipase recovery was 4.5 and the optimal CaCl2 concentration was 10 mmol dm−3. The lipase recovery decreased with increasing aqueous enzyme concentration but increased with increasing AOT concentration in the organic phase. The presence of polar co-solvents in the aqueous phase did not obviously improve the lipase recovery, which was also little influenced by the type of hydrophobic organic solvent used for solubilising AOT. Surprisingly, no detectable activity of the ion-paired C. rugosa lipase was observed for both the esterification of lauric acid with 1-propanol in isooctane and the hydrolysis of olive oil in isooctane containing an appropriate amount of water. The ion-paired C. rugosa lipase mediated the enantioselective crystallisation of racemic ketoprofen in isooctane, indicating the feasibility of using it as a chiral mediator for the enantioseparation of hydrophobic racemic compounds in organic systems. Copyright © 2006 Society of Chemical Industry