Mmol Dm Research Articles

Limiting diffusion coefficients of glufosinate ammonium, cymoxanil and imidacloprid in aqueous solutions

We have measured the limiting diffusion coefficients of three different pesticides in aqueous solutions: glufosinate ammonium, cymoxanil and imidacloprid, highly used for tomato production. The experiments were carried in aqueous solutions, at 25 °C, at concentrations below 3 mmol dm−3 (depending on the solubility of pesticides). Mutual diffusion coefficients (D) obtained by using the Taylor dispersion technique, and by using pure water and different solutions of concentration c, as carrier stream and injection solutions, respectively, show that the systems can be analyzed as binary ones. The hydrodynamic radii and the respective limiting diffusion coefficients of the glufosinate anion, cymoxanil and imidacloprid have also been estimated. For the electrolyte glufosinate ammonium, by using the Nernst equation, it is also possible to estimate the limiting molar conductivity of the glufosinate anion.In order to mimic field conditions, we have measured the tracer diffusion coefficients of glufosinate ammonium in aqueous solutions of ammonium nitrate at different concentrations, permitting us to analysis the salting-in effects on the diffusion of this pesticide.From these measurements useful information on the thermodynamic, transport and structural parameters can be obtained, allowing a better understanding of the behaviour of these compounds in aqueous solution.These studies have been complemented with 1H and 31P NMR spectroscopy in order to obtain more additional structural information on the interaction of ammonium nitrate with glufosinate-ammonium in aqueous solution. The results obtained support the hypothesis of salting-in effects on the diffusion of this pesticide in aqueous solution.

Bifunctional wood for electrocatalytic CO2 reduction to formate and electroanalytical detection of myricetin and cadmium (II)

In this work, we first discover the new bifunctional abilities of wood for highly selective electrocatalytic CO2 reduction to formate and highly sensitive electroanalytical detection of myricetin and cadmium (II). The highly developed microchannels in wood ensure most effective reactant and electrolyte transport, great facilitating the electrode reaction. The activated wood electrode displays excellent electrocatalytic CO2 reduction activity, attained the highest formate Faradaic Efficiency (FE) of 70.8% at −1.8 V with high current density of 53.8 mA cm−2 in aqueous solution, and displayed at least 24 h CO2 electrolysis durability. Furthermore, the wood is also first utilized as new electrode matrix for electroanalytical detection of drug (myricetin is as an example) and heavy metal ion (cadmium (II) is as an example). Compared with traditional glassy carbon electrode (GCE) and its derived modified electrodes, the wood electrode exhibits a wide linear detection range (0.01–50 μmol dm−3) and a low detection limit (0.002 μmol dm−3, S/N = 3) for myricetin, and displays a wide linear detection range (0.1–20 μg l−1) and a low detection limit (0.05 μg L−1, S/N = 3) for cadmium (II). These remarkable bifunctional performances of low cost wood electrode show great potential for large-scale using in CO2 electroreduction and electroanalytical detection.

Quantitative characterization of oligomeric state of G-quadruplex antithrombin aptamers by size exclusion HPLC

A quantitative technique for estimation of the oligomeric state of G-quadruplexes has been developed for the first time. The simplest 15-mer G-quadruplex antithrombin aptamer HD1 and its analogues, namely RA36 as a covalent dimer of HD1 as well as GL2–HD1 as a non-covalent dimer with G-quadruplex lock, were used as model objects. HD1 and RA36 have been shown to be single-stranded G-quadruplexes, whereas GL2–HD1 forms non-covalent dimers (GL2–HD1)2 in a concentration-dependent manner, affording ∼50% of the dimers at 1 mmol dm−3 concentration.

Effects of primary C1–C6 linear alcohol addition and sonochemically decomposed products on multi-bubble sonoluminescence

Multi-bubble sonoluminescence (MBSL) was measured in Ar-saturated water containing 2 mmol dm−3 of a series of alcohols under sonication at a frequency of 410 kHz. The sonoluminescence intensity was weakened in the presence of the alcohols. The effect was emphasized further when an alcohol with a longer alkyl chain was added. The spectral and temporal changes are presumed to be attributable to gaseous products generated by sonochemical decomposition of alcohols. Gas generation, originating from alcohol decomposition, was observed even in the short 2 min sonication. When compared with the case of ethanol addition, larger amounts of gaseous products were generated when long chain 1-hexanol was added. The increase in gaseous product yield indicates that the alcohol decomposition proceeds with the progress of the sonication. The present study evaluated the dependency of MBSL on the hydrophobicity of added alcohol and characteristics of the decomposed gas products, such as solubility to water and specific heat ratio.

Conformational change of L-phenylalanine in fluorinated alcohol-water mixed solvents studied by IR, NMR, and MD simulations

To clarify the unique solvation properties of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) on a biomolecule of L-phenylalanine (Phe), the solvation structure of Phe in HFIP-water mixed solvents at 70 mmol dm−3 has been observed over the entire range of HFIP mole fraction xHFIP using infrared (IR), 1H and 13C NMR techniques with a help of molecular dynamics (MD) simulation. The solvation structure of Phe in the HFIP solvents has been compared with that in 2-propanol (2-PrOH)-water mixed solvents and the structure of L-leucine (Leu) in both alcohol-water mixed solvents previously reported. The results from IR, NMR, and MD simulations showed that water molecules hydrogen-bonded with the Phe carboxylate group are gradually replaced by HFIP with increasing xHFIP. In contrast, the replacement of water molecules by HFIP on the Phe aminium group does not easily take place. These findings arise from the high electron acceptability and the very low electron donicity of the HFIP hydroxyl group due to the electron drawing of the six fluorine atoms. In the 2-PrOH solutions, the replacement of water on the carboxylate group by 2-PrOH less easily occurs with increasing x2-PrOH compared to HFIP because of the lower electron acceptability of 2-PrOH. The solvation for the Phe hydrophilic parts is similar to that of Leu. The most significant difference between HFIP and 2-PrOH was observed for the solvation of the Phe phenyl group. The hydrophobic hydration shell around the phenyl group is collapsed with increasing alcohol content in both alcohol solutions. Instead of water, the HFIP fluorine atoms significantly interact with the phenyl hydrogen atoms, whereas 2-PrOH molecules do not markedly approach the hydrogen atoms. The conformational change of Phe molecule against the dihedral angle of Cγ-Cβ–Cα-COO− takes place with increasing HFIP content, but does not with the increase in 2-PrOH. This is attributed to the steric hindrance between the large phenyl group and the carboxylate group remarkably solvated by HFIP molecules.

Electrochemical detection of 8-hydroxyguanine using screen-printed carbon electrodes modified with carboxy-functionalized multi-walled carbon nanotubes

The paper presents the findings of an optimization and validation results of electrochemical detection of 8-hydroxyguanine, a major marker of oxidative stress, using disposable screen-printed carbon electrode (SPCE) modified with carboxy-functionalized multi-walled carbon nanotubes (MWCNTs-COOH). Several types of bare and modified SPCEs were tested and modification with MWCNTs-COOH was found superior in terms of measured current response, level of background currents, and sensitivity in oxidation of 8-hydroxyguanine. The effect of pH and composition of supporting electrolyte on current response and peak potential were also evaluated. Validation parameters were calculated for optimum pH 7 of 0.01 mol dm−3 phosphate buffer. The sensor showed the highest sensitivity of 0.0625 µA dm3 μmol−1 within the linear range 0.3–12 μmol dm−3 with a limit of detection as low as 0.57 μmol dm−3. Extended linear range 0.3–240 μmol dm−3 is feasible with a sensitivity of 0.0523 µA dm3 μmol−1. Intra-day and inter-day assays within 3 days were performed to verify the repeatability of modified screen-printed carbon sensors. Finally, the sensor was utilized for electrochemical monitoring of stability of 8-hydroxyguanine when stored in room temperature, in the refrigerator, or frozen and thawed.

A novel characteristic of salicylate UV absorbers: suppression of diethylhexyl 2,6-naphthalate (Corapan TQ)-photosensitized singlet oxygen generation.

2-Ethylhexyl salicylate (EHS, octyl salicylate) and homomenthyl salicylate (HMS, homosalate) are UV-B absorbers used in cosmetic sunscreens. Diethylhexyl 2,6-naphthalate (DEHN, tradename Corapan TQ) used as a mildly effective photostabilizer for labile butylmethoxydibenzoylmethane, the most widely used UV-A absorber, is an efficient singlet oxygen photosensitizer with a high quantum yield of singlet oxygen generation ΦΔ = 0.44 in ethanol. The effects of EHS, HMS, l-ascorbic acid (AA, vitamin C), 3-O-ethyl-l-ascorbic acid (3-EtAA) and Trolox (TX, a water-soluble analogue of vitamin E) on DEHN-photosensitized singlet oxygen generation have been studied through measurements of time-resolved near-infrared phosphorescence in ethanol. These compounds suppress DEHN-photosensitized singlet oxygen generation. 40% of ΦΔ is decreased by adding 32 mmol dm-3 EHS or HMS. ΦΔ is decreased to a half by adding 3.0 mmol dm-3 TX. Fluorescence and transient absorption measurements suggest that the observed suppression is due to the quenching of the excited singlet state of DEHN by EHS, HMS, AA and 3-EtAA. These compounds do not quench the excited triplet state of DEHN. On the other hand, TX quenches both the excited singlet and triplet states of DEHN. It was shown that these UV-B absorbers have a novel characteristic as a suppressor of photosensitized singlet oxygen generation. Suppressing singlet oxygen generation is an important method for the prevention of skin damage. To the best of our knowledge, this is the first report on the suppression of photosensitized singlet oxygen generation by UV absorbing molecules.

Graphite sheet as a novel material for the collection and electrochemical sensing of explosive residues

This work presents the use of a graphite sheet (graphite papers) as a new platform for the collection and sensing of explosive residues. This material offers a lightweight, highly conductive, flexible platform that can be cut in several ways, enabling for the collection of explosive residues at the place of interest, without any further sample preparation steps. As a proof-of-concept, the device was utilised for the collection and electrochemical sensing of 2,4,6-trinitrotoluene (TNT) residues. The GS has a remarkable performance for the sensing of TNT within the supporting electrolyte (0.1 mol dm−3 HCl) resulting in a linear range between 1 and 1300 μmol dm−3 and detection limit of 0.06 μmol dm−3 using square-wave voltammetry (SWV). Five surfaces (granite, gloved and bare hands, metal and cash banknotes) were contaminated with traces of TNT and the collection was performed using the graphite sheet (1 cm2 square pieces were swiped over the different surfaces). The results obtained using SWV enabled the identification of TNT residues, at quantities of 0.01–0.23 ng (quantification by the measured coulometric charge of the SWV scan), demonstrating that this novel material can be used as a promising device at crime scene investigations.

Calcium Oxalate Precipitation in Model Systems Mimicking the Conditions of Hyperoxaluria

AbstractThis work focuses on systematic research of spontaneous precipitation of calcium oxalate in model systems mimicking the chemical conditions typical for hyperoxaluria. For this purpose, model systems of three different complexities (simple, NaCl, and artificial urine system) and two initial pH (pHi = 5.0 and pHi = 9.0) at 37 °C are studied. In all investigated systems, dominant precipitation of calcium oxalate monohydrate (COM) is observed, except in artificial urine system at pHi = 9.0, ci(C2O42−) ≥ 6.0 mmol dm−3 and ci(Ca2+) ≥ 7.5 mmol dm−3, where precipitation of a mixture of calcium oxalate monohydrate and calcium oxalate dihydrate occurs. The significant difference is mainly observed in COM crystal morphology. In a simple system, COM precipitates in a dendritic form; in NaCl system, dendritic form and irregular shapes are found, while in the artificial urine, prismatic hexagonal and aggregated COM crystals precipitate.

Phosphoric Acid Diethylmethylammonium Trifluoromethanesulfonate-Based Electrolytes for Nonhumidified Intermediate Temperature Fuel Cells.

The present study reports a new series of electrolytes for nonhumidified intermediate temperature fuel cells (IT-FCs). This series of new mixed electrolytes, composed of phosphoric acid (PA) and diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), was designed as nonhumidified IT-FC electrolytes. The mixed electrolytes show a higher thermal stability than pure PA, which is dehydrated at ITs. The thermal stability of the mixed electrolytes could be explained by the interaction between the triflate group in [dema][TfO] and PA, as indicated by Fourier transform infrared and proton nuclear magnetic resonance (1H NMR) spectroscopies. On the other hand, the ionic conductivity and proton transference number of the mixed electrolytes were similar to those of the pure PA. However, the oxygen reduction reaction (ORR) activity of a platinum catalyst is significantly enhanced in the mixed electrolytes, which was due to the several orders of magnitude increase in oxygen solubility by the addition of [dema][TfO] to PA. Specifically, for the equimolar fraction mixed electrolyte, the diffusion coefficient and the solubility of oxygen were ca. 1.47 × 10-5 cm2 s-1 and ca. 1.28 mmol dm-3 at 150 °C, respectively. The addition of [dema][TfO] to PA could significantly enhance the ORR activity. Therefore, the PA_[dema][TfO] mixed electrolyte can be one of the solutions to develop nonhumidified intermediate FC electrolytes.

LC–MS/MS determination of N-acetylaspartic acid in dried blood spot for selective screening of Canavan disease

Canavan disease is a serious rare neurometabolic disorder characteristic of an accumulation of N-acetylaspartic acid (NAA) in biological fluids. Its determination mainly in urine is the key part of the diagnostic procedure. Despite the several advantages of using dried blood spot (DBS) samples for clinical analysis, it has not been reported for this purpose so far. Therefore, this work was focused on the development of a HPLC–MS/MS method for the determination of NAA in a dried blood spot. The method using a stable isotope-labeled internal standard was elaborated and partially validated, with an estimated limit of quantification of 0.06 μmol dm−3, and with intra-day and inter-day precisions up to 4.1 and 8.0%, respectively. The elaborated method was applied for the NAA determination in healthy controls and in two siblings with Canavan disease. There were three quantification approaches evaluated using one-point calibration as well as calibration curves with and without matrix. The results correlated very well and exhibited parallelism of one-point calibration and calibration curve approaches. The mean NAA concentrations determined in DBS of control newborns and older children (10 months–7 years) were 0.9 and 0.5 μmol dm−3, respectively. Patients were clearly distinguished from controls, considering the NAA concentrations were more than 10 times higher than in an aged-matched control group.

Selective voltammetric determination of α-lipoic acid on the electrode modified with SnO2 nanoparticles and cetyltriphenylphosphonium bromide

Sensitive voltammetric method for α-lipoic acid determination based on glassy carbon electrode (GCE) modified with SnO2 nanoparticles (SnO2 NP) dispersion in cetyltriphenylphosphonium bromide (CTPPB) (SnO2 NP-CTPPB/GCE) has been developed. The comparison to other surface active compounds as dispersive agents has been performed. The electrodes surface has been characterized by scanning electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and chronoamperometry. Statistically significant decrease of charge transfer resistance (10.8 ± 0.4 kΩ vs. 181 ± 7 kΩ for GCE and 71 ± 3 kΩ for SnO2 NP-H2O/GCE) and higher effective surface area (13.7 ± 0.2 mm2 vs. 8.2 ± 0.3 mm2 for GCE and 12.1 ± 0.2 mm2 for SnO2 NP-H2O/GCE) has been obtained for SnO2 NP-CTPPB/GCE. α-Lipoic acid oxidation on SnO2 NP-CTPPB/GCE is a two-electron diffusion-controlled pH independent process leading to β-lipoic acid formation. Under conditions of differential pulse voltammetry in Britton–Robinson buffer pH 4.5, the linear dynamic ranges are 0.50–50 and 50–400 μmol dm−3 of α-lipoic acid with the limits of detection and quantification of 0.13 and 0.43 μmol dm−3, respectively. The method developed has been successfully applied for the pharmaceutical dosage form analysis.

Electrochemical determination of indole-3-acetic acid and indole-3-butyric acid using HPLC with carbon felt detector

Method for the determination of two auxins, indole-3-acetic acid and indole-3-butyric acid, is developed using HPLC with electrochemical detection. As the working electrode, recently developed carbon felt detector with high conversion degree was employed. Optimum conditions, i.e. separation on 125-4 Lichrospher 100, RP-18 column with mobile phase consisting of buffer pH 4.0 and methanol (40:60, v/v) and detection at potential + 1.5 V, allow to obtain linear concentration dependences in the concentration range from 1 to 100 µmol dm−3, with determination limits of 1.1 µmol dm−3 and 1.8 µmol dm−3 for indole-3-acetic and -butyric acid, respectively. Applicability of the method was verified by the determination of both analytes in rooting preparation; the results were in agreement with the reference method, although not with the values declared by the manufacturer.

Radiation induced degradation of ciprofloxacin and norfloxacin: Kinetics and product analysis

Ionizing radiation induced degradation of two fluoroquinolone antibiotics, ciprofloxacin and norfloxacin was investigated in 0.1 mmol dm–3 aqueous solutions. The rate constants, directly determined by pulse radiolysis, were 7.2 × 109 mol–1 dm3 s–1 and 5.4 × 109 mol–1 dm3 s–1 for •OH reaction and 8.2 × 109 mol–1 dm3 s–1 and 7.3 × 109 mol–1 dm3 s–1 for hydrated electron reaction with ciprofloxacin and norfloxacin, respectively. Absorption bands of several transient intermediates were observed on the pulse radiolysis spectra. For end product characterization samples were irradiated in a 60Co–γ irradiation chamber, they were analyzed by taking the UV–Vis spectra and by LC separation with MS detection. Based on their structures, most of the products presumably had lost their antibacterial activity. For both compounds products reflecting reaction on the quinolone part (hydroxylated molecules) or on the piperazinyl moiety (desethylene derivatives) were observed.

Cationic Poly([R]-3-hydroxybutyrate) Copolymers as Antimicrobial Agents.

Poly([R]-3-hydroxybutyrate) (PHB), a natural biodegradable polyester, has attracted much attention as a new biomaterial because of its sustainability and good biocompatibility. In this study, it is discovered that PHB can be conveniently functionalized to obtain a number of platform chain architectures that may provide a wide range of functional copolymers. In a transesterification reaction, linear (di-hydroxylated) and star shaped (tri- and tetra-hydroxylated) PHB oligomers are synthesized, followed by copolymerization with 2-(dimethylamino)ethyl methacrylate and quaternization with benzyl bromide to afford antimicrobial properties. The antimicrobial activities of the quaternary salts against clinically relevant pathogens on the interactions with outer and cytoplasmic membranes, lethal mechanisms, multipassage resistance, and synergy effect with antibiotics are investigated. Cationic PHB copolymers show effectiveness as antimicrobial agents, with minimum inhibitory concentration values 0.24-0.65µm (or µmol dm-3 ) (or 32-128µg mL-1 ) against Gram-positive and Gram-negative bacteria. Modifying the copolymer architectures into star shapes results in enhanced effectiveness to disrupt the membrane integrity. Synergistic effects are attained for all the quaternized PHB derivatives when they are used together with tobramycin. Multipassage resistance does not occur in both the linear and star derivatives against Gram-negative bacteria after 20 passages.

Cyanide-Free Displacement Silver Plating Using Highly Concentrated Aqueous Solutions of Metal Chloride Salts

We report a novel, cyanide-free, and low-cost displacement silver (Ag) plating bath, i.e., AgCl-dissolved highly concentrated CaCl2/LiCl aqueous solution. Compared to dilute CaCl2/LiCl solutions, this aqueous solution exhibited much higher AgCl solubility because of the high activity of Cl–; the maximum AgCl solubility was achieved at 44.4 mmol dm–3 (i.e., [Ag(I)] = 8.07 g kg−1 H2O). Smooth Ag deposits with a lusterless gray-colored appearance were successfully obtained by displacement plating on a Cu substrate. The mechanism of smooth Ag plating is discussed in terms of its electrochemical and diffusive properties.

Suppression of riboflavin-sensitized singlet oxygen generation by l-ascorbic acid, 3-O-ethyl-l-ascorbic acid and Trolox

Riboflavin (RF), a water-soluble vitamin B2, is an endogenous singlet oxygen photosensitizer in human skin and eye. Time profiles of the near-infrared phosphorescence of singlet oxygen generated by RF have been measured in the absence and presence of l-ascorbic acid (AA, vitamin C), 3-O-ethyl-l-ascorbic acid (3-EtAA) and Trolox (TX, a water-soluble analogue of vitamin E) in phosphate buffer (pH 6.8). These substances suppress the RF-photosensitized singlet oxygen generation. For example, the quantum yield of singlet oxygen generation is decreased to a third by adding 0.4 mmol dm-3 AA or TX (the concentration of dissolved oxygen in air-saturated water is 0.27 mmol dm-3). AA and TX are more efficient suppressors of RF-photosensitized singlet oxygen generation than 3-EtAA. The bimolecular rate constants for quenching of the excited singlet and triplet states of RF by AA, 3-EtAA and TX have been determined through measurements of fluorescence and transient absorption. These measurements suggest that the observed suppression is due to the quenching of the excited singlet and triplet states of RF by AA, 3-EtAA and TX. The bimolecular rate constants for quenching of singlet oxygen by AA, 3-EtAA and TX were determined to be 1.8 × 108, 0.27 × 108, and 4.4 × 108 mol-1 dm3 s-1, respectively.

An electrochemical sensor for the detection of pesticides based on the hybrid of manganese phthalocyanine and polyaniline

A mimic enzymeless electrochemical sensor (M-Eless-ES) based on the terminal alkynyl substituted manganese phthalocyanine (MnPc-TA) and 4-azido polyaniline (N3-PANI) hybrid was constructed and tested as a selective and sensitive pesticide sensor. A new electrode modification technique, solid state electropolymerization of a film, was developed for the preparation of ITO/MnPc-TA/N3-PANI electrode as M-Eless-ES for the first time in this study. During construction of ITO/MnPc-TA/N3-PANI electrode, MnPc-TA was firstly deposited on indium tin oxide coated glass substrate (ITO) with Langmuir Blodgett (LB) technique. Then 4-azidoaniline (N3-ANI) was bonded to the terminal alkynyl substituents of MnPc-TA (ITO/MnPc-TA/N3-ANI) with click chemistry (CC) and finally ANI groups of the solid MnPc-TA/N3-ANI hybrid film was electropolymerized on ITO surface to form ITO/MnPc-TA/N3-PANI electrode. The modified electrode was characterized with square wave voltammetry (SWV), X-ray diffraction (XRD), scanning electron microscope (SEM), and fourier transform infrared (FT-IR). Finally, ITO/MnPc-TA/N3-PANI electrode was tested as potential M-Eless-ES for the fenitrothion, eserine, and diazinon via SWV technique. Different voltammetric responses were observed for each pesticide. Observation of a new redox peak due to the interaction of the electrode with the fenitrothion indicated its distinct selectivity for this pesticide. The limit of detection (LOD) (0.049 μmol dm−3 for fenitrothion, 0.088 μmol dm−3 for eserine and 0.062 μmol dm−3 for diazinon), wide linear ranges, and especially higher selectivity were observed with ITO/MnPc-TA/N3-PANI which are the basic requirements for the practical applications for the pesticide sensing. Reproducibility, easy of construction, and stability of the electrode are other superior advantages. As a real sample application, ITO/MnPc-TA/N3-PANI sensor was successfully employed for determining the fenitrothion residue in rosehip sample.

Boosting CH3OH Production in Electrocatalytic CO2 Reduction over Partially Oxidized 5 nm Cobalt Nanoparticles Dispersed on Single-Layer Nitrogen-Doped Graphene.

Herein, we successfully synthesized partially oxidized 5 nm cobalt nanoparticles dispersed on a single-layer nitrogen-doped graphene (SL-NG) (denoted as PO-5 nm Co/SL-NG) catalyst by a unique and simple one-pot synthesis strategy, which was efficiently applied for highly selective electrocatalytic reduction of carbon dioxide to methanol in 0.1 mol dm-3 aqueous NaHCO3 medium under mild conditions, reaching the maximum faradaic efficiency (FE) of 71.4% for methanol at -0.90 V versus saturated calomel electrode (SCE), possessing a strong electrocatalytic current density of 4 mA cm-2 and a high yield of 1.10 mmol dm-3 h-1, and the corresponding overpotential is as low as 280 mV. Moreover, at -1.0 V versus SCE, a high current density of 10 mA cm-2 can be obtained, and the FE for methanol still remains 23.2%. Notably, the proposed catalyst exhibits prominent stability after 10 h electroreduction of CO2, and the morphology, particle size, structure, and element contents of the catalyst almost remain stable. This work first provides an advanced PO-5 nm Co/SL-NG for selective electroreduction of carbon dioxide into methanol, which simultaneously possesses the merits of high current density, low overpotential, high selectivity, superior FE, and good stability, outperforming most reported electrocatalysts.

Adsorption of Pluronic Surfactants in Alkylene Carbonates on Silica.

Adsorption of triblock Pluronic surfactants bearing poly(ethylene oxide) (PEO) chains of different lengths, L-62 (5 EO groups on each end), L-64 (13 EO groups on each end), and F-68 (79 EO groups on each end), on silica has been characterized using atomic force microscopy (AFM). The solvent used herein was a mixture of ethylene carbonate (EC) and propylene carbonate (PC). The three Pluronic surfactants were dissolved in the mixed solvent, with the PEO chain acting as a solvophilic group and the poly(propylene oxide) (PPO) chain acting as a solvophobic group. The approaching force curve measurements for the three Pluronics (at 10 mmol dm-3) revealed repulsive forces from an apparent separation of 20-30 nm. The most solvophilic Pluronic surfactant with the longest PEO chain (F-68) showed continuously increasing repulsive interaction with decreasing separation. The Milner-Witten-Cates (MWC) theory described the repulsive force curve data of F-68, suggesting that F-68 forms a polymer brush on the silica surface. The retracting force curve measurements detected stretching forces for the three Pluronic systems. These stretching forces were observed more frequently for the L-62 system than for the F-68 system, but the pull-off distance was shorter for L-62 than for F-68.