Mmol Dm Research Articles

An annual survey of bacterial production, respiration and ectoenzyme activity in coastal NW Mediterranean waters: temperature and resource controls.

We simultaneously measured bacterial production (BP), bacterial respiration (BR), alkaline phosphatase activity (phos) and ectoaminopeptidase activity (prot) in relation to biogeochemical parameters, nutritive resources and in situ temperature over a 1-year survey at the long-term observatory the SOLEMIO station (Marseille bay, NW Mediterranean Sea). Despite its proximity to the coast, oligotrophic conditions prevailed at this station (yearly mean of Chl a = 0.43 μg dm(-3), NO3 = 0.55 μmol dm(-3) and PO4 = 0.04 μmol dm(-3)). Episodic meteorological events (dominant winds, inputs from the Rhone River) induced rapid oscillations (within 15 days) in temperature and sometimes salinity that resulted in rapid changes in phytoplankton succession and a high variability in C/P ratios within the particulate and dissolved organic matter. Throughout the year, BP ranged from 0.01 to 0.82 μg C dm-(3) h-(1) and bacterial growth efficiency varied from 1 to 39%, with higher values in summer. Enrichment experiments showed that BP was limited most of the year by phosphorus availability (except in winter). A significant positive correlation was found between in situ temperature, BP, BR and phos. Finally, we found that temperature and phosphate availability were the main factors driving heterotrophic bacterial activity and thus play a fundamental role in carbon fluxes within the marine ecosystem.

Chemical repair activity of free radical scavenger edaravone: reduction reactions with dGMP hydroxyl radical adducts and suppression of base lesions and AP sites on irradiated plasmid DNA.

Reactions of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) with deoxyguanosine monophosphate (dGMP) hydroxyl radical adducts were investigated by pulse radiolysis technique. Edaravone was found to reduce the dGMP hydroxyl radical adducts through electron transfer reactions. The rate constants of the reactions were greater than 4 × 108 dm3 mol−1 s−1 and similar to those of the reactions of ascorbic acid, which is a representative antioxidant. Yields of single-strand breaks, base lesions, and abasic sites produced in pUC18 plasmid DNA by gamma ray irradiation in the presence of low concentrations (10–1000 μmol dm−3) of edaravone were also quantified, and the chemical repair activity of edaravone was estimated by a method recently developed by the authors. By comparing suppression efficiencies to the induction of each DNA lesion, it was found that base lesions and abasic sites were suppressed by the chemical repair activity of edaravone, although the suppression of single-strand breaks was not very effective. This phenomenon was attributed to the chemical repair activity of edaravone toward base lesions and abasic sites. However, the chemical repair activity of edaravone for base lesions was lower than that of ascorbic acid.

Development of Biosensor for Catechol Using Electrosynthesized Poly(3‐methylthiophene) and Incorporation of LAC Simultaneously

AbstractSimultaneous electropolymerization of 3‐methylthiophene and incorporation of Laccase (LAC) was carried out in the presence of propylene carbonate as a medium by amperometric method. This enzyme modified electrode was used for the sensing of polyphenol. Catechol is taken as a model compound for the study. UV‐Vis spectral studies suggest no denaturation of LAC in presence of propylene carbonate. The SEM studies reveal the surface morphology and incorporation of LAC in P3MT with agglomerated flaky masses are observed in with and without enzyme micrographs. The cyclic voltammograms were recorded for 0.01 mM catechol on plain glassy carbon, polymer and enzyme incorporated electrodes at pH 6.0 and scan rate 50 mV s−1. The fabricated electrochemical biosensor was used for the determination of catechol in aqueous solution by Differential Pulse Voltammetry (DPV) technique. The concentration linear range of 8×10−8 to 1.4×10−5 M a value of MichealisMenten constant Km=7.67 µmol dm−3 and activation energy is 32.75 kJ mol−1. It retains 83 % of the original activity after 60 days which is much higher than that of other biosensors. The developed biosensor was used to quantify catechol in the determination in real samples.

Degradation of the azo dye Acid Red 1 by anodic oxidation and indirect electrochemical processes based on Fenton's reaction chemistry. Relationship between decolorization, mineralization and products

Solutions of 236mg dm−3 Acid Red 1 (AR1), an azo dye widely used in textile dying industries, at pH 3.0 have been comparatively treated by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) at constant current density (j). Assays were performed with a stirred tank reactor equipped with a Pt or boron-doped diamond (BDD) anode and an air-diffusion cathode for H2O2 generation from O2 reduction. The main oxidizing agents were hydroxyl radicals produced at the anode from water oxidation in all methods and in the bulk from Fenton's reaction between generated H2O2 and 0.5mmol dm−3 Fe2+ in EF and PEF. For each anode, higher oxidation power was found in the sequence AO-H2O2<EF<PEF. The oxidation ability of the BDD anode was always superior to that of Pt. Faster and similar decolorization efficiency was achieved in EF and PEF owing to the quicker destruction of aromatics with hydroxyl radicals produced in the bulk. The PEF process with BDD was the most potent method yielding almost total mineralization due to the additional rapid photolysis of recalcitrant intermediates like Fe(III)-carboxylate complexes under UVA irradiation. The increase in j always enhanced the decolorization and mineralization processes because of the greater production of hydroxyl radicals, but decreases the mineralization current efficiency. A total of 11 aromatic intermediates, 15 hydroxylated compounds, 13 desulfonated derivatives and 7 short-linear carboxylic acids were identified. NH4+, NO3− and SO42− ions were released during azo dye degradation. From the products detected, a comprehensive reaction sequence for AR1 mineralization is proposed. The relationship between decolorization, mineralization and products formed is finally discussed.

Quest for Ether-Coordinated Superoxide Ionic Liquids

Superoxide anion O2 – is obtained by one electron reduction reaction of the oxygen molecule (O2 + e → O2 –)[1]. Since O2 – has one unpaired electron it is also used for the radical polymerization initiator for organic synthesis[1]. Generally O2 – is dissolved in aprotic solvents because it decomposes in the presence of H2O or protic solvents (e.g. 2O2 − + H2O → O2 + HO2 − + OH− and 2HO2 − → O2 + 2OH−). It is known that potassium superoxide (KO2) has little solubility even in dimethylsulfoxide, a highly polar aprotic organic solvent. Researcher has demonstrated that the solubility of KO2 in aprotic solvents increases dramatically by adding 18-crown-6-ether[1]. Nevertheless, the maximum solubility of superoxide is only about 20 mmol dm–3 in aprotic solvents. Spectacularly improving the concentration of superoxide anion, it could be one method that we synthesize novel superoxide compounds in the liquid state at room temperature while the reported quaternary alkylammonium superoxides are all solid at room temperature[4]. In this work, we tried to synthesize superoxide ionic liquids by complexation of K+ cation to decrease charge density of cations substantially. KO2, a yellow solid at room temperature, was chosen as an O2 − source and mixed with two kinds of chain ethers i.e. diethylene glycol dimethyl ether (G2) and tetraethylene glycol dimethyl ether (G4), and a macrocyclic ether i.e. 18-crown-6-ether. Mixture of KO2 and each ether was stirred at 500 rpm and heated under several situations in a glove box of Ar atmosphere (H2O, O2 < 1 ppm). Molar ratio of KO2 : ether was 2 : 1 for G2, 1 : 1 for G4, and 1 : 1 for 18-crown-6-ether. It was visually judged from the absence of discoloration and precipitation of the mixture if these two substances chemically reacted without substantial decomposition of O2 –. The coordination of 18-crown-6-ether to K+cation was checked with Raman spectrometry. Figure 1 schematically illustrates possible states of K+ cation complxed with three kinds of ethers : (a) G2, (b) G4, and (c) 18-crown-6-ether (K+ : G2 = 1 : 2, K+ : G4 = 1 : 1, K+ : 18-crown-6-ether = 1 : 1 in molar). KO2 and G2 or G4 did not result in a liquid state even at 60 °C. By contrast, the mixture of KO2 and 18-crown-6-ether became clear yellow liquid at 50 °C (see Figure 2 (b)). The melting point was 41 ~ 42 °C. We speculate that the strong coordination ability of 18-crown-6-ether to K+cation contributed to the sizable decrease in charge density of cations and thereby the melting point of the superoxide became near room temperature. Figure 3 demonstrates the Raman spectra for (a) uncomplexed liquid 18-crown-6-ether and (b) liquid [(18-crown-6)K]O2 measured at 50 °C. For the latter case we observed evolution of sharp peaks between 860 and 900 cm–1 in comparison of the former case. It is attributed to the conformation change of 18-crown-6-ether from Ci conformation to D3d conformation[5]. This strongly suggersts that 18-crown-6-ether coordinates K+to form much weaker Lewis acidic cation.[1] D. T. Sawyer et al., Acc. Chem. Res., 14, 393 (1981).[2] K. Yamaguchi et al., Inorg. Chem., 25, 1289 (1986).[3] K. Fukuhara et al., J. Mol. Struct., 224, 203 (1990).

Electrochemical Quartz Crystal Microbalance Analysis of Nitrogen Oxide-Promoted Platinum Dissolution in HClO4

To elucidate the mechanism of NaNO2-promoted Pt dissolution, the weight loss of Pt black-deposited Au quartz resonators was measured in 0.1 mol dm–3 HClO4 containing NaNO2 under potential cycling and constant potential conditions. A continuous weight loss of ca. 50–60 ng cm–2 cycle–1 was detected in the presence of 10 mmol dm–3 NaNO2 during potential cycling above a high potential limit of 1.2 V vs RHE (VRHE) and below a low potential limit (EL) of 0.9 VRHE. A weight loss was observed at constant potentials (0.6–0.8 VRHE) when oxides were initially present; the net weight loss (Δw) magnitude increased as the amount of the initially formed Pt oxide increased. These results indicate that Pt dissolution occurred when Pt oxides were reduced in the presence of NaNO2. The good agreement between the Δw per potential cycle and the Δw at a constant potential (EL of the potential cycling = constant potential) revealed that the formation of Pt oxides in the positive sweep was required for the continuous weight loss under potential cycling. The Δw value increased for higher concentrations of NaNO2 under both conditions. The products of NaNO2 reduction were thought to participate in Pt dissolution.

Effects of metal ions on Pt electrode dissolution in H2SO4 solution enhanced by the presence of H2O2

Successive potential cycling of a Pt plate electrode was conducted in H2O2-containing 0.5 mol dm−3 H2SO4 in the presence of metal ions such as Fe (Fe2+, Fe3+), Ce (Ce3+, Ce4+), and Mn (Mn2+) ions. First, the potential cycling in 294 mmol dm−3 H2O2 + 0.5 mol dm−3 H2SO4 without any metal ions confirmed the weight loss of the Pt electrode, which implies Pt dissolution. When the metal ions were added to the solution, the Pt electrode dissolution during the potential cycling was very significant; the Pt weight sharply decreased in the presence of both Fe2+ and H2O2. In addition, this enhanced Pt dissolution depended on both the Fe2+ and H2O2 concentrations, and the maximum Pt weight loss (257 μg) was obtained at the Fe2+ and H2O2 concentrations of 10 and 294 mmol dm−3, respectively. The Fe2+ and H2O2 concentration dependences of the Pt dissolution also correlated with the consumption rate of H2O2. These results revealed that the Fe2+ and H2O2 synergically enhanced the Pt dissolution rate.

Combining the Photocatalyst Pt/TiO2 and the Nonphotocatalyst SnPd/Al2O3 for Effective Photocatalytic Purification of Groundwater Polluted with Nitrate

We investigated photocatalytic reduction of NO3– in real groundwater in the presence of the photocatalyst Pt/TiO2 and the nonphotocatalyst SnPd/Al2O3, which were dispersed in the groundwater, under irradiation at λ > 300 nm, with glucose as a hole scavenger. In this system, photocatalytic H2 evolution (2H+ + 2e– → H2) proceeded over Pt/TiO2, and nonphotocatalytic, that is, conventional catalytic, reduction of NO3– with H2 (NO3– + 5/2H2 → 1/2N2 + 2H2O + OH–) occurred over SnPd/Al2O3. NO3– (1.0 mmol dm–3) in the groundwater completely and selectively decomposed to N2 (yield 83%) after 120 h with a 300 W Xe lamp (λ > 300 nm) over the Pt/TiO2–SnPd/Al2O3 system in combination with photooxidative pretreatment of the groundwater over Pt/TiO2 to decompose organic compounds. The decomposition rate of NO3– in the groundwater was still slower than that in an aqueous NO3– solution even after the pretreatment of the groundwater. The lower photocatalytic performance was due to poisoning of Pt/TiO2 with sulfate and silicate ions and poisoning of SnPd/Al2O3 with polymerized silicate ions. On the other hand, cations, including Na+, K+, Mg2+, and Ca2+, in the groundwater did not affect the photocatalytic and catalytic performances of the system. Sulfate ions adsorbed on the Pt sites on Pt/TiO2, where H2 evolution occurs, and silicate ions deactivated the oxidation sites on TiO2 by reacting with the surface hydroxyl groups, leading to a decline in the photocatalytic performance of Pt/TiO2.

N2H4 electrooxidation at negative potential on novel wearable nano-Ni-MWNTs-textile electrode

Abstract A new composite Ni electrode is simply prepared by electrodeposition of nano-scaled Ni particles onto multi-walled carbon nanotubes (MWNTs)-enabled conductive textile fiber (cosmetic cotton) which owns an especial three-dimensional (3D) network structure. The morphology and phase structure of the Ni-MWNTs-textile electrode are characterized by scanning electron microscope, transmission electron microscope and X-ray diffraction spectrometer, and the catalytic performance for the N 2 H 4 electrooxidation is tested by linear sweep voltammetry and chronoamperometry. The results show that the Ni-MWNTs-textile electrode exhibits a remarkably high catalytic activity and good stability for N 2 H 4 electrooxidation. The onset potential stays at around −0.9 V and the oxidation current density reaches as high as 12 mA cm −2 in the solution containing 1 mol dm −3 NaOH and 20 mmol dm −3 N 2 H 4 at around −0.80 V, both of which outstrip the previous reports.

Antiproliferative effects of prenylflavonoids from hops on human colon cancer cell lines

In recent years, interest in hop-derived constituents, especially for prenylflavonoids has grown, as they have a wide range of biological properties including antioxidant, anticarcinogenic and antimicrobial activities. Two main hop prenylflavonoids, xanthohumol and isoxanthohumol, and hop extract enriched in prenylflavonoids, were tested for their antiproliferative activities on colon cancer cell lines, HT-29 and SW620, and a noncancerous cell line, IEC-6. It was confirmed that both xanthohumol and isoxanthohumol inhibited cell proliferation, even at micromolar concentrations. For cell line HT-29, the IC50 was 1.2 ± 0.9 and 16.9 ± 0.9 µmol dm−3 for xanthohumol and isoxanthohumol, respectively. Similar values were obtained for SW620 cells (2.5 ± 0.2 and 37.3 ± 3.2 µmol dm–3). None of the pure prenylflavonoids that were tested affected the proliferation of the noncancerous cell line, IEC-6. The effect of the hop extract containing xanthohumol was also tested for antiproliferative activities on the cancer cell lines, HT-29 (IC50 = 3.1 ± 0.2 µmol dm–3) and SW620 (IC50 = 1 ± 0.2 µmol dm−3), and on the cell line, IEC-6 (IC50 = 65.5 ± 11.3 µmol dm−3). The results showed a similar trend to that for pure compounds, suggesting a possible future application of hop extracts in the pharmaceutical industry. Copyright © 2014 The Institute of Brewing & Distilling

Analysis of selected compounds in the surface water of lake Oleckie Wielkie

Abstract The paper presents the results of research on the content of 16 PAH, selected anions and heavy metals in samples collected from Lake Oleckie Wielkie. The samples were collected at seven locations around the lake within about 15 m from the shore in November 2012. The highest total concentration of 16 PAH (68.58 μmol dm−3) was found in water sample no. 7, and the lowest in water samples no. 1, 4 and 5. The obtained results do not exceed the levels of standards accepted in Poland for the surface water. The analysis of collected water samples, performed with the isotachophoresis method, showed a low content (less than 4 mg dm−3) of the analyzed anions: nitrates(V), nitrates(III), chlorides, sulphates(VI), sulphates(IV), phosphates(V) and hydrocarbonates(IV), as well as a low content of the analyzed heavy metals.

Influence of cationic structures on oxygen reduction reaction at Pt electrode in fluorohydrogenate ionic liquids

Various parameters related to the oxygen reduction reaction (ORR) on a Pt electrode such as kinetically limited current density (jk), yield of H2O2 (XH2O2), and solubility (C) and diffusion coefficient (D) of oxygen were evaluated at 298 K in fluorohydrogenate ionic liquids (FHILs) using the rotating ring-disk electrode (RRDE) method. The FHILs investigated in this study were 1-ethyl-3-methylimidazolium fluorohydrogenates (EMIm(FH)1.3F and EMIm(FH)2.3F), N-ethyl-N-methyl pyrrolidinium fluorohydrogenates (EMPyr(FH)1.7F and EMPyr(FH)2.3F), trimethylsulfonium fluorohydrogenate (S111(FH)1.9F), triethyl-n-pentylphosphonium fluorohydrogenate (P2225(FH)2.1F), and 5-azoniaspiro[4.4]nonane fluorohydrogenate (AS[4.4](FH)2.0F). Among them, EMPyr(FH)1.7F showed the largest jk value (−1.5 mA cm−2) at 0.7 V vs. RHE. EMPyr(FH)1.7F, EMPyr(FH)2.3F, and P2225(FH)2.1F showed small XH2O2 values around 1.5% at a disk electrode potential of 0.2 V vs. RHE. The C and D values obtained for the FHILs were in the ranges of 0.23–1.3 mmol dm−3 and (1.1–3.2) × 10−5 cm2 s−1, respectively. The crossover currents of oxygen in the FHILs were estimated using the obtained C and D values, which were of the same order of magnitude as that for a 0.5 M H2SO4 aqueous solution.

Synthesis of CdS quantum dots decorated graphene nanosheets and non-enzymatic photoelectrochemical detection of glucose

ABSTRACT Graphene-CdS quantum dots (QDs) hybrid materials were successfully prepared via one-step hydrothermal method. CdS QDs with average size of ∼6 nm were dispersed on graphene sheets with high coverage through non-covalent bonding. Photocurrent and electrochemical impedance spectroscopy (EIS) results suggested that the best dosage of graphene oxide for graphene-CdS hybrid materials is 0.5% (G0.5-CdS). When G0.5-CdS QDs was used as photoanode materials in non-enzymatic sensor, and the sensor was used to detect glucose and displayed satisfactory analytical performance with good linear range from 0.1∼4 mmol dm−3 with a detection limit of 7 μmol dm−3 at a signal-to-noise ratio of 3. The sensor also possessed high selectivity and durability in trace detection of glucose.

Oxidative and reductive degradation of sulfamethoxazole in aqueous solutions: decomposition efficiency and toxicity assessment

Under radiolytic conditions at a concentration of 0.1 mmol dm−3 the reactions of sulfamethoxazole, a worldwide used anti-infective sulfonamide antibiotic, were mainly induced by hydroxyl radicals. With a dose of 5 kGy complete degradation of aromatic system was observed. The sulfur of the molecule was entirely transformed to SO4 2–, while NO3 – and NH4 + were formed from the nitrogen content. The chemical oxygen demand and total organic carbon values indicated complete mineralization during irradiation. In pursuance of toxicity tests, the observed increase in mortality of Vibrio fischeri bacteria was mainly due to H2O2 formed during the radiolytic procedure. The results showed that the degradation was effective; therefore, the irradiation technology can be recommended for treatment of wastewater containing sulfamethoxazole.

Solubility and Diffusion Coefficient of Oxygen in Protic Ionic Liquids with Different Fluoroalkyl Chain Lengths

A series of protic ionic liquids (PILs) were synthesized from N,N-diethylmethylamine (dema) and three kinds of fluoroalkylsulfonic acids having different chain lengths (H-SO3(CF2)nF, n=1∼3) as electrolytes for fuel cells. Solubility and diffusion coefficient of oxygen in those PILs were determined from 30°C to 120°C by the combination measurement of linear-sweep voltammetry and hydrodynamic chronocoulometry with a rotating disk electrode (RDE). The solubility and diffusion coefficient of oxygen in N,N-diethylmethylammonium heptafluoropropanesulfonate ([dema][HfO]) was 10.5mmol dm−3 and 1.48×10−6 cm2 s−1 at 120°C, respectively. With increasing the fluoroalkyl chain length of anion, the solubility increased. In contrast, the diffusion coefficient decreased. The activation energies of oxygen diffusion in N,N-diethylmethylammonium pentafluoroethanesulfonate ([dema][PfO]) and [dema][HfO] were estimated to be 35.5kJmol−1 and 38.4kJmol−1 from the Arrhenius plots, respectively. The permeabilities of oxygen in the synthesized PILs were also estimated and compared with Nafion® in water to discuss oxygen cross-over in fuel cell application.

A first pre‐pilot system for the combined treatment of dye pollutants by electrocoagulation/EAOPs

AbstractBACKGROUNDBased on promising results obtained at laboratory scale with a two‐step electrochemical treatment of Tartrazine solutions by electrocoagulation (EC) coupled with electrochemical advanced oxidation processes (EAOPs), this work addresses its scale‐up to degrade 1.85 dm3 of solutions of this dye. Monopolar and bipolar configurations have been compared in EC. The effect of supporting electrolyte, pH, applied current, dye concentration and electrolysis time has been assessed.RESULTSElectrocoagulation with four Fe electrodes was first optimized for the treatment of 278 mg dm−3 Tartrazine solutions. The bipolar series configuration led to enhanced coagulation due to the larger electrode consumption. Solutions with 0.05 mol dm−3 NaCl at pH 6.3 were quickly decolorized with 60% total organic carbon removal, being more convenient than Na2SO4 and NaNO3 electrolytes due to the synergistic action of coagulation and oxidation by active chlorine. Among the EAOPs, carried out with a Ti/IrO2‐RuO2 anode and an air‐diffusion cathode to electrogenerate H2O2, electro‐Fenton (EF) with 0.5 mmol dm−3 Fe2+ was much better than electro‐oxidation owing to the oxidative action of active chlorine and •OH formed in the bulk from Fenton's reaction. Photoelectro‐Fenton (PEF) was even better by the additional photolysis of by‐products under incident UVA photons.CONCLUSIONSThe use of an EC reactor in bipolar configuration for 12.5 min at 1.50 A followed by PEF treatment for 360 min at 1.50–2.00 A ensured mineralization &gt;90%, which encourages further optimization at larger scale for the treatment of a variety of organic pollutants in real wastewaters. © 2014 Society of Chemical Industry

Decolorization and mineralization of Orange G azo dye solutions by anodic oxidation with a boron-doped diamond anode in divided and undivided tank reactors

The decolorization and mineralization of 100 cm3 of 0.52-6.34mmol dm−3 Orange G azo dye solutions at pH 3.0 and current density between 33.3 and 150mAcm−2 have been studied by anodic oxidation (AO) using a divided or undivided tank reactor with a boron-doped diamond (BDD) anode and a stainless steel cathode. In both systems, organics were destroyed by hydroxyl radicals generated at the BDD anode from water oxidation. Solutions with 0.52mmol dm−3 of the dye were completely decolorized in both cells, more rapidly at greater current density. The divided cell always gave faster decolorization than the undivided one. Overall mineralization in the divided tank reactor was attained in less than 330min operating at current densities≥66.7mAcm−2, whereas in the undivided cell, this was feasible at times as long as 420min for 150mAcm−2. For Orange G contents up to 6.34mmol dm−3, total mineralization at 100mAcm−2 was also more easily reached in the divided cell. The mineralization current efficiency always rose at lower current density and higher dye content. The dye decayed obeying a pseudo-first-order kinetics and its apparent rate constant increased at higher current density. A similar electrolysis time was required for total decolorization and disappearance of Orange G, indicating that aromatic by-products were rapidly destroyed and did not accumulate in the medium. Final carboxylic acids like maleic, tartronic, acetic, formic, oxalic and oxamic were generated, whereas ammonium and sulfate were the main inorganic ions released during Orange G mineralization.

Cesium Adsorption by Synthetic Todorokite-Type Manganese Oxides

Abstract Synthetic todorokite-type manganese oxides containing magnesium (todorokite(Mg)), calcium (todorokite(Ca)), and iron-doped todorokite containing magnesium (Fe-todorokite(Mg)) were treated with acid solutions to obtain protonated todorokite(Mg-H), todorokite(Ca-H), and Fe-todorokite(Mg-H), respectively, and studied for cesium adsorption from the aqueous solutions. The cesium adsorption rate was slow to attain equilibrium in 24 h at pH 4.4–5.5 (uncontrolled); the adsorptive capacities were 0.50 mmol g−1 for todorokite(Mg-H), 0.49 mmol g−1 for todorokite(Ca-H), and 0.27 mmol g−1 for Fe-todorokite(Mg-H). The cesium adsorptive capacity was significantly dependent on pH, increasing with increase in pH. A partial substitution of Mn by Fe (7.2 wt %) in the framework of todorokite greatly decreased the cesium adsorptive capacity compared to metal-undoped todorokite. The distribution coefficient Kd values of the protonated materials for Na+, K+, Cs+, Mg2+, and Ca2+ at 1.0 mmol dm−3 in acidic pH showed that the materials preferred Cs+ over other cations. Both todorokite(Mg-H) and todorokite(Ca-H) were effective for cesium adsorption completely (ca. 100%) from drinking water intentionally contaminated with 0.1 mmol dm−3 CsCl at solution-to-solid ratio of 0.1–1.0 dm3 g−1.

A new non-enzymatic glucose sensor based on copper/porous silicon nanocomposite

Cu/PSi (copper/porous silicon) nanocomposite powder was prepared by chemical etching of silicon (Si) powder in a HF/HNO3 solution, followed by electrodless plating of copper nanoparticles on the etched PSi powder in a solution containing CuSO4 as a metal precursor. The resulting nanocomposite was characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and FT–IR spectroscopy. The copper nanoparticles in PSi support show the good chemical and electrochemical stability as well as electrocatalytic effect on Glc oxidation, hence the Cu/PSi nanocomposite was used to modify carbon paste electrode (CPE) to fabricate non-enzymatic Glc sensor. The electrocatalytic activity of Cu/PSi nanocomposite was investigated for Glc oxidation in alkaline and neutral solutions using cyclic voltammetry and chronoamperometry. The novel developed sensor displayed a fast amperometric response time of less than 4 s, long time stability, good signal reproducibility and two linear ranges from 1.0 to 190.0μmol dm−3 and 190μmol dm−3 to 2.3mmol dm−3 of Glc with a detection limit of 0.2μmol dm−3. The sensor exhibited no interference from common interferences such as ascorbic acid, dopamine, uric acid, fructose and citric acid. The good analytical performance, low cost and easy preparation method made this novel electrode material promising for the development of effective Glc sensor.

Cobalt oxide nanoparticles anchored to multiwalled carbon nanotubes: Synthesis and application for enhanced electrocatalytic reaction and highly sensitive nonenzymatic detection of hydrogen peroxide

Cobalt (II) dicobalt (III) oxide nanoparticles anchored to multiwalled carbon nanotubes were synthesized for the first time by a microwave decomposition method using cobalt nitrate as a precursor and multiwalled carbon nanotubes as a scaffold. The nanostructure was then employed as the modifier of a carbon paste electrode. The kinetics of the charge transfer process across the modified electrode/solution interface was studied. The modified electrode was then applied to fabricate an enzyme-less hydrogen peroxide biosensor. The mechanism and kinetics of the electrocatalytic reduction and oxidation reactions of hydrogen peroxide on the modified electrode surface were studied by cyclic voltammetry and chronoamperometry. The catalytic rate constants of the hydrogen peroxide electroreduction and electrooxidation processes by an active cobalt species, and the diffusion coefficient of hydrogen peroxide were reported. An amperometric method was developed for determination of hydrogen peroxide based on its electrocatalytic reduction with a sensitivity of 1002.8mAmol−1 dm3cm−2 and a limit of detection of 2.46μmol dm−3. The sensor had the advantages of high electrocatalytic activity and sensitivity, with a simple fabrication method without complications of immobilization steps and using any enzyme or reagent.