二甲醚在Pt电极上吸附和氧化的循环伏安和原位FTIR光谱研究

运用电化学循环伏安法(CV)和原位傅立叶变换红外(FTIR)反射光谱, 研究了不同pH值溶液中二甲醚(DME)在Pt电极上的解离吸附和氧化过程. 稳态CV结果给出, 在0.1 mol·L-1 H2SO4溶液中, 当电位处于0.05-0.35 V (vs RHE)区间, 约70%的Pt表面位被DME的解离吸附产物占据. DME电氧化反应的活性随pH值增加而下降, 在0.1 mol·L-1 NaOH溶液中, 氢的吸脱附几乎不受抑制且观察不到明显的氧化电流, 表明DME醚键上氧原子的质子化是其发生解离吸附和氧化的必要条件. 原位FTIR光谱研究给出DME解离吸附和氧化过程的分子水平信息, 指出DME在低电位区间解离生成线型吸附态CO(COL)毒性中间体. 当电位高于0.55 V(vs RHE)时, COL开始氧化为CO2; 在0.75-1.00 V(vs RHE)的电位区间则可同时发生经活性中间体(HCOOH)的氧化过程.     

Electrodeposition of the Charge-Transfer Complex Generated during Electrooxidation of o-Tolidine and the Effects of Coexisting Chondroitin Sulfate

The electrochemical quartz crystal microbalance (EQCM) technique was used to investigate the electrodeposition of the charge-transfer complex (CTC) generated during electrooxidation of o-tolidine (o-TD) in Britton-Robinson buffers and the effects of coexisting chondroitin sulfate (CS). A V-shaped frequency response to the cyclic voltammetric switching of o-TD indicated the precipitation and dissolution of the poorly soluble CTC, an oxidation intermediate, formed at the Au electrode during the redox switching of o-TD in a neutral or a weakly acidic medium (pH=4.07-6.50). The effects of potential scan rate, solution pH, and several supporting electrolytes were examined. The depth of the V-shaped frequency curves (-Δf_0V) was related to the supporting electrolyte used, with a decreasing sequence for −Δf_0V as 0.20 mol·L⁻¹ NaNO₃ > 0.20 mol·L⁻¹ NaClO₄ > 0.10 mol·L⁻¹ Na₂SO₄. The −Δf_0V response to the redox switching of the CTC/o-TD “couple” was enhanced by the introduction of CS because of the formation of the CTC-CS adduct, as also characterized and supported by UV-Vis and FTIR spectrophotometry. The molar ratio (x) of the CTC to CS in the adduct and the electrode-collection efficiency of the CTC (η) were estimated using EQCM. The values of −Δf_0V increased with the increase in CS concentration, with a linear range from 0.75 to 15.2 μmol·L⁻¹, and a detection limit down to 50 nmol·L⁻¹. The new method proposed for CS assay was characterized by a dynamically renewed surface of the detection electrode.     

Role of Bridge-bonded Formate in Formic Acid Dehydration to CO at Pt Electrode: Electrochemial in-situ Infrared Spectroscopic Study

Formic acid (HCOOH) decomposition at Pt film electrode has been studied by electrochem- ical in situ FTIR spectroscopy under attenuated-total-reflection configuration, in order to clarify whether bridge-bonded formate (HCOOb) is the reactive intermediate for CO_ad for-mation from HCOOH molecules. When switching from HCOOH-free solution to HCOOH-containing solution at constant potential (E=0.4 V vs. RHE), we found that immediately upon solution switch CO_ad formation rate is the highest, while surface coverage of formate is zero, then after CO_ad formation rate decreases, while formate coverage reaches a steady state coverage quickly within ca. 1 s. Potential step experiment from E=0.75 V to 0.35 V, reveals that formate band intensity drops immediately right after the potential step, while the CO_ad signal develops slowly with time. Both facts indicate that formate is not the reactive intermediate for formic acid dehydration to CO.     

Hierarchical Unfolding of Mj HSP16.5

Mj HSP16.5 is a small heat shock protein (sHSP) from the hyperthermophilic methanoarchaeon, Methanococcus jannaschii (Mj), which lives at the environment of high temperature up to 94 °C. The structural data showed that Mj HSP16.5 was a 24-mer that formed a hollow sphere with octahedral symmetry. Mj HSP16.5 was very stable at pH 7 that it maintained the 24-mer structure even at 85 °C. In the present study, we investigated the unfolding process of Mj HSP16.5 in the presence of denaturants using several techniques, including circular dichroism (CD), dynamic light scattering (DLS), fluorescence spectroscopy, and size exclusive chromatography (SEC). We found that 8 mol·L⁻¹ urea had no obvious effect on the structure of Mj HSP16.5 at pH 7. The unfolding of Mj HSP16.5 at pH 7 in the presence of guanidine hydrochloride (GdHCl) showed hierarchical behavior. Three significant transitions were observed around 2.0, 3.0, and 6.0 mol·L⁻¹ GdHCl at pH 7. ANS (8-anilino-1- naphthalenesulfonic acid) titration results showed that the binding ability of Mj HSP16.5 to ANS decreased gradually as the concentration of GdHCl increased until around 2.0 mol·L⁻¹ GdHCl, indicating surface hydrophobic area change, and this first transition was companioned with precipitation of Mj HSP16.5. Acrylamide quenching of fluorescence showed that the Stern-Volmer constant changed at about 3.0 mol·L⁻¹ GdHCl, indicating changes of the dimeric interface, and this phase transition was companioned with oligomeric state change from 24-mer to small oligomers (4-mer to 8-mer). The last unfolding phase started around 5.0 mol·L⁻¹ GdHCl, with a midpoint of 6.1 mol·L⁻¹ GdHCl, and Mj HSP16.5 was completely unfolded at 7.0 mol·L⁻¹ GdHCl. We also found that Mj HSP16.5 could be quite easily unfolded at pH 3, where it could be completely unfolded in 4.0 mol·L⁻¹ GdHCl.     

The formation of carbon dioxide during glycerol electrooxidation in alkaline media: First spectroscopic evidences

In this work we investigate the glycerol electrooxidation reaction on polycrystalline gold in alkaline media. By using in situ FTIR we demonstrate for the first time the unambiguous presence of CO₂ as electrooxidation product of glycerol in alkaline media. The estimation of OH^? consumption during the electrooxidation of glycerol allows us to explain the formation of CO₂ as a consequence of a sudden decrease of pH inside the thin layer, which forces glycerol (or their fragments) to react with water, thus forming CO₂.     

Adsorption and electrooxidation of dimethyl ether on platinized platinum electrode in sulfuric acid solution

Adsorption and oxidation of dimethyl ether (DME) on the Pt/Pt electrode from 0.5 M H₂SO₄ is studied by measuring transients of current and potential, charging curves, and curves of electrooxidation in the adsorbed layer and also by cyclic voltammetry and steady-state polarization measurements. The DME adsorption is accompanied by dehydrogenation and destruction of its molecules to form a chemisorbed adsorbate that mainly consists of C1 species (HCO_ads and/or CO_ads) with (under certain conditions) a small amount of species that desorb at cathodic polarization. The adsorption and electrooxidation of DME are inhibited by adsorbed oxygen. The possible schemes of DME oxidation, where the reaction of DME chemisorption products with adsorbed oxygen-containing species is the limiting stage, are discussed.     

In situ emulsification microextraction using a dicationic ionic liquid followed by magnetic assisted physisorption for determination of lead prior to micro-sampling flame atomic absorption spectrometry

For the first time, a simple and efficient in situ emulsification microextraction method using a dicationic ionic liquid followed by magnetic assisted physisorption was presented to determine trace amounts of lead. In this method, 400 μL of 1.0 mol L⁻¹ lithium bis (trifluoromethylsulfonyl) imide aqueous solution, Li[NTf₂], was added into the sample solution containing 100 μL of 1.0 mol L⁻¹ 1,3-(propyl-1,3-diyl) bis (3-methylimidazolium) chloride, [pbmim]Cl₂, to form a water immiscible ionic liquid, [pbmim][NTf₂]₂. This new in situ formed dicationic ionic liquid was applied as the acceptor phase to extract the lead-ammonium pyrrolidinedithiocarbamate (Pb-APDC) complexes from the sample solution. Subsequently, 30 mg of Fe₃O₄ magnetic nanoparticles (MNPs) were added into the sample solution to collect the fine droplets of [pbmim][NTf₂]₂, physisorptively. Finally, MNPs were eluted by acetonitrile, separated by an external magnetic field and the obtained eluent was subjected to micro-sampling flame atomic absorption spectrometry (FAAS) for further analysis. Comparing with other microextraction methods, no special devices and centrifugation step are required. Parameters influencing the extraction efficiency such as extraction time, pH, concentration of chelating agent, amount of MNPs and coexisting interferences were studied. Under the optimized conditions, this method showed high extraction recovery of 93% with low LOD of 0.7 μg L⁻¹. Good linearity was obtained in the range of 2.5–150 μg L⁻¹ with determination coefficient (r²) of 0.9921. Relative standard deviation (RSD%) for seven repeated measurements at the concentration of 10 μg L⁻¹ was 4.1%. Finally, this method was successfully applied for determination of lead in some water and plant samples.     

Molecular Modification of Single Cobalt Sites Boosts the Catalytic Activity of CO2 Electroreduction into CO

Electroreduction of CO₂ into carbonaceous fuels or industrial chemicals using renewable energy sources is an ideal way to promote global carbon recycling. Thus, it is of great importance to develop highly selective, efficient, and stable catalysts. Herein, we prepared cobalt single atoms (Co SAs) coordinated with phthalocyanine (Co SAs-Pc). The anchoring of phthalocyanine with Co sites enabled electron transfer from Co sites to CO₂ effectively via the π-conjugated system, resulting in high catalytic performance of CO₂ electroreduction into CO. During the process of CO₂ electroreduction, the Faradaic efficiency (FE) of Co SAs-Pc for CO was as high as 94.8 %. Meanwhile, the partial current density of Co SAs-Pc for CO was −11.3 mA cm⁻² at −0.8 V versus the reversible hydrogen electrode (vs RHE), 18.83 and 2.86 times greater than those of Co SAs (−0.60 mA cm⁻²) and commercial Co phthalocyanine (−3.95 mA cm⁻²), respectively. In an H-cell system operating at −0.8 V vs RHE over 10 h, the current density and FE for CO of Co SAs-Pc dropped by 3.2 % and 2.5 %. A mechanistic study revealed that the promoted catalytic performance of Co SAs-Pc could be attributed to the accelerated reaction kinetics and facilitated CO₂ activation.     

Determination of Psoralen and Isopsoralen in Traditional Chinese Medicines by Capillary Zone Electrophoresis with Amperometric Detection

A simple, reliable and reproducible method was developed for determination of psoralen and isopsoralen in several traditional Chinese medicines, such as Shouwu Pian, Gubenkechuan Pian, was described in this paper. It was based on capillary zone electrophoresis with amperometric detection (CZE-AD). A carbon-disc electrode was used as working electrode. The optimal conditions of separation and detection were pH7.6 phosphate buffer (20 mM), 20 kV for the separation voltage and 1.00V (vs. Ag/AgCl) for the detection potential. The linear ranges were 6.90 × 10^-5~1.30 × 10^-7 mol L^-1for psoralen and 5.0 × 10^-5~1.80 × 10^-7 mol·L^-1 for isopsoralen with the correlation coefficient of 0.9984 and 0.9994, respectively. The detection limits for psoralen and isopsoralen were 4.2 × 10^-8 mol·L^-1 and 6.0 × 10^-8 mol·L^-1 based on the signal to noise ratio of 3. The method built in this paper was directly applied to the determination of several traditional Chinese medicines with some simple pretreatment. The assay result was satisfactory.     

Electrosyntheses of free-standing poly(dibenzo-18-crown-6) films in boron trifluoride diethyl etherate on stainless steel electrode

High-quality free-standing poly(dibenzo-18-crown-6) (PDBC) films with a conductivity of 4.1 × 10⁻² S cm⁻¹ and good thermal stability were synthesized electrochemically on stainless steel electrode by direct anodic oxidation of dibenzo-18-crown-6 (DBC) in pure boron trifluoride diethyl etherate (BFEE). In this medium, the oxidation potential onset of DBC was measured to be only 0.98 V vs. SCE, which was much lower than that in acetonitrile + 0.1 mol L⁻¹ Bu₄NBF₄ (1.45 V vs. SCE). PDBC films obtained from this medium showed good redox activity and stability in BFEE. The structural characterization of PDBC was performed using UV-vis, FTIR spectroscopy. The results of quantum chemistry calculations of DBC monomer and FTIR spectroscopy of PDBC films indicated that the polymerization mainly occurred at C₍₄₎ and C₍₅₎ positions). Fluorescent spectral studies indicated that PDBC was a blue light emitter. To the best of our knowledge, this is the first report on the electrodeposition of free-standing PDBC films.     

SDS‐modified Nanoporous Silver as an Efficient Electrocatalyst for Selectively Converting CO2 to CO in Aqueous Solution

Selectively electrochemical conversion of CO₂ into organic fuel using renewable electricity is one of the most sought‐after processes. In this paper, we report the electrochemical reduction of CO₂ (CO₂RR) on the nanoporous Ag electrodes made of compacted Ag nanoparticles (AgNPs), which were prepared by one‐step reduction in the water phase with or without the surfactant sodium dodecyl sulfate (SDS). The scanning electron microscope (SEM) characterizations show that the compacted Ag electrodes have the nanoporous morphology formed by stacking AgNPs. Compared with the nanoporous Ag electrode without SDS modification (C‐AgNPs), the SDS‐modified AgNPs electrode (C‐AgNPs‐SDS) is highly effective in improving selective CO production in a wide range of potentials (–0.69 V — –1.19 V, vs. RHE), with a Faradaic efficiency of 92.2% and a current density of –8.23 mA·cm^–2 for CO production at –0.79 V (vs. RHE). C‐AgNPs‐SDS is also catalytically stable with only less than 7% deactivation after 8 h of continuous electrolysis.     

Tuning the Composition of PdCuNi Hollow Nanospheres for Low Cost and Efficient Catalyst Towards Glycol Electrooxidation

In this research, we reported an effective approach to prepare low cost and efficient electrocatalyst for the glycol electrooxidation. The synthetic process involves the replacement reactions between CuCl₂/H₂PdCl₄ and Ni nanospheres template. Through controlling the precursor ratio, the Pd/Cu/Ni ratio of the final trimetallic products can be tuned. The prepared electrocatalysts present a monodispersed nanospheres structure with a hollow cavity. The prepared Pd₄₁Cu₂₇Ni₉ shows the best catalytic activity (0.021 A cm⁻² at 0.9 V vs. RHE) for glycol electrooxidation, which is much higher than that of the commercial Pd/C (0.0014 A cm⁻² at 0.9 V vs. RHE).     

Biosensor based on laccase and an ionic liquid for determination of rosmarinic acid in plant extracts

Novel biosensors based on laccase from Aspergillus oryzae and the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆) and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄) were constructed for determination of rosmarinic acid by square-wave voltammetry. The laccase catalyzes the oxidation of rosmarinic acid to the corresponding o-quinone, which is electrochemically reduced back to rosmarinic acid at +0.2 V vs. Ag/AgCl. The biosensor based on BMIPF₆ showed a better performance than that based on BMIBF₄. The best performance was obtained with 50:20:15:15% (w/w/w/w) of the graphite powder:laccase:Nujol:BMIPF₆ composition in 0.1 mol L⁻¹ acetate buffer solution (pH 5.0). The rosmarinic acid concentration was linear in the range of 9.99 × 10⁻⁷ to 6.54 × 10⁻⁵ mol L⁻¹ (r = 0.9996) with a detection limit of 1.88 × 10⁻⁷ mol L⁻¹. The recovery study for rosmarinic acid in plant extract samples gave values from 96.1 to 105.0% and the concentrations determined were in agreement with those obtained using capillary electrophoresis at the 95% confidence level. The BMIPF₆-biosensor demonstrated long-term stability (300 days; 920 determinations) and reproducibility, with a relative standard deviation of 0.56%.     

Development and evaluation of a diffusive gradients in a thin film technique for measuring ammonium in freshwaters

A new diffusive gradients in a thin film (DGT) technique, using Microlite PrCH cation exchange resin, was developed and evaluated for measuring NH₄–N in freshwaters. Microlite PrCH had high uptake (>92.5%) and elution efficiencies (87.2% using 2 mol L⁻¹ NaCl). Mass vs. time validation experiments over 24 h demonstrated excellent linearity (R² ≥ 0.996). PrCH-DGT binding layers had an extremely high intrinsic binding capacity for NH₄–N (∼3000 μg). NH₄–N uptake was quantitative over pH ranges 3.5–8.5 and ionic strength (up to 0.012 mol L⁻¹ as NaCl) typical of freshwater systems. Several cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺) were found to compete with NH₄–N for uptake by PrCH-DGT, but NH₄–N uptake was quantitative over concentration ranges typical of freshwater (up to 0.012 mol L⁻¹ Na⁺, 0.006 mol L⁻¹ K⁺, 0.003 mol L⁻¹ Ca²⁺ and 0.004 mol L⁻¹ Mg²⁺). Effective diffusion coefficients determined from mass vs. time experiments changed non-linearly with electrical conductivity. Field deployments of DGT samplers with varying diffusive layer thicknesses validated the use of the technique in situ, allowed deployment times to be manipulated with respect to NH₄–N concentration, and enable the calculation of the diffusive boundary layer thickness. Daily grab sample NH₄–N concentrations were observed to vary considerably independent of major rainfall events, but good agreements were obtained between PrCH-DGT values and mean grab sample measurements of NH₄–N (C_DGT:C_SOLN 0.83–1.3). Reproducibility of DGT measurements in the field was good (relative standard deviation < 11%). Limit of detection was 0.63 μg L⁻¹ (equivalent to 0.045 μmol L⁻¹) based on 24 h deployments.     

Corrosion and Anodic Behaviors of Pure Aluminum in a Novel Alkaline Electrolyte

The corrosion and anodic dissolution behaviors of pure aluminum in Na₂SnO₃-containing 4 mol·L⁻¹ KOH methanol-water mixed solutions with a methanol/water volume ratio of 4:1 were investigated. This was carried out by means of hydrogen collection, polarization curve, galvanostatic discharge, scanning electron microscopy (SEM), and energy dispersive analysis of X-ray (EDAX). The experimental results indicated that the addition of stannate inhibited the corrosion of aluminum in the 4 mol·L⁻¹ KOH methanol-water solutions by the deposition of tin with a higher hydrogen evolution overpotential on the electrode surface. In the electrolytes with higher stannate contents the inhibiting effect decreased because of the occurrence of some cracks on the tin deposition film. The results of galvanostatic discharge showed that the discharge of aluminum in the Na₂SnO₃-containing 4 mol·L⁻¹ KOH methanol-water solutions were obviously improved. In addition, the improvement effect enhanced with the increase of stannate content. It was noted that the aluminum anode showed a very flat discharge plateau at relatively low potentials in the electrolyte with 10.0 mmol·L⁻¹ Na₂SnO₃ at 20 mA·cm⁻² discharge current density.     

二甲醚电氧化增强电化学表面积的研究(英)

0IntroductionFuel cells em ploying polym er(e.g.,N afion m em-branes)as the electrolyte are receiving increasing at-tention.The m em brane-electrode assem bly(M EA),com prising of a proton conducting m em brane sand-wiched between tw o gas diffusion elect…     

In situ selective determination of methylmercury in river water by diffusive gradient in thin films technique (DGT) using baker's yeast (Saccharomyces cerevisiae) immobilized in agarose gel as binding phase

Saccharomyces cerevisiae immobilized in agarose gel as binding phase and polyacrylamide as diffusive layer in the diffusive gradient in thin films technique (DGT) was used for selective determination of methylmercury (MeHg). Deployment tests showed good linearity in mass uptake up to 48 h (3276 ng). When coupling the DGT technique with Cold Vapor Atomic Fluorescence Spectrometry, the method has a limit of detection of 0.44 ng L⁻¹ (pre concentration factor of 11 for 48 h deployment). Diffusion coefficient of 7.03 ± 0.77 × 10⁻⁶ cm² s⁻¹ at 23 °C in polyacrylamide gel (pH = 5.5 and ionic strength = 0.05 mol L⁻¹ NaCl) was obtained. Influence of ionic strength (from 0.0005 mol L⁻¹ to 0.1 mol L⁻¹ NaCl) and pH (from 3.5 to 8.5) on MeHg uptake were evaluated. For these range, recoveries of 84–105% and 84–98% were obtained for ionic strength and pH respectively. Potential interference due to presence of Cu, Fe, Mn, Zn was also assessed showing good recoveries (70–87%). The selectivity of the proposed approach was tested by deployments in solutions containing MeHg and Hg(II). Results obtained showed recoveries of 102–115 % for MeHg, while the uptake of Hg(II) was insignificant. The proposed approach was successfully employed for in situ measurements in the Negro River (Manaus-AM, Brazil).     

Enabled Efficient Ammonia Synthesis and Energy Supply in a Zinc–Nitrate Battery System by Separating Nitrate Reduction Process into Two Stages

The aqueous electrocatalytic reduction of NO₃⁻ into NH₃ (NitrRR) presents a sustainable route applicable to NH₃ production and potentially energy storage. However, the NitrRR involves a directly eight-electron transfer process generally required a large overpotential (<−0.2 V versus reversible hydrogen electrode (vs. RHE)) to reach optimal efficiency. Here, inspired by biological nitrate respiration, the NitrRR was separated into two stages along a [2+6]-electron pathway to alleviate the kinetic barrier. The system employed a Cu nanowire catalyst produces NO₂⁻ and NH₃ with current efficiencies of 91.5 % and 100 %, respectively at lower overpotentials (>+0.1 vs. RHE). The high efficiency for such a reduction process was further explored in a zinc-nitrate battery. This battery could be specified by a high output voltage of 0.70 V, an average energy density of 566.7 Wh L⁻¹ at 10 mA cm⁻² and a power density of 14.1 mW cm⁻², which is well beyond all previously reported similar concepts.     

水热法制备NiS/Cd1-xZnxS及其高效光催化产氢性能

利用水热法制备 NiS 负载的 Cd1-xZnxS 光催化剂.结果表明：在0.35 mol?L-1 Na2SO3和0.25 mol?L-1 Na2S牺牲剂下,0.5%(摩尔分数, y) NiS/Cd0.3Zn0.7S (1840μmol?h-1)获得最好活性,是Cd0.3Zn0.7S (884μmol?h-1)的2.1倍,高于0.5%(质量分数, w) Pt (1390μmol?h-1)的产氢活性.测得其在λ=420 nm附近的表观量子效率为36.8%. X射线衍射(XRD)、紫外-可见漫反射光谱(UV-Vis DRS)、透射电子显微镜(TEM)以及X射线光电子能谱(XPS)的表征结果表明, NiS作为产氢活性位,转移光生电子,因此提高了光催化产氢活性.     

A fully automated effervescence assisted dispersive liquid–liquid microextraction based on a stepwise injection system. Determination of antipyrine in saliva samples

A first attempt to automate the effervescence assisted dispersive liquid–liquid microextraction (EA-DLLME) has been reported. The method is based on the aspiration of a sample and all required aqueous reagents into the stepwise injection analysis (SWIA) manifold, followed by simultaneous counterflow injection of the extraction solvent (dichloromethane), the mixture of the effervescence agent (0.5 mol L⁻¹ Na₂CO₃) and the proton donor solution (1 mol L⁻¹ CH₃COOH). Formation of carbon dioxide microbubbles generated in situ leads to the dispersion of the extraction solvent in the whole aqueous sample and extraction of the analyte into organic phase. Unlike the conventional DLLME, in the case of EA-DLLME, the addition of dispersive solvent, as well as, time consuming centrifugation step for disruption of the cloudy state is avoided. The phase separation was achieved by gentle bubbling of nitrogen stream (2 mL min⁻¹ during 2 min).