Nickel ion removal by porous potassium magnesium titanate made from plate-like crystals

Plate-like potassium magnesium titanate (KMTO) powder prepared by molten salt growth method and the KMTO porous ceramic synthesised by polymeric sponge replication method were used as sorbents to remove nickel ions from wastewater. Both powder and porous ceramic were characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The maximum adsorption capacities of powder and porous ceramic were 96 and 24?mg?g^??1 respectively at a pH value of 6 (25°C). However, the removal efficiencies of both could reach up to 99%. Moreover, the adsorption kinetics for the KMTO powder and the porous ceramics followed the pseudo-second-order kinetic model, and the equilibrium data for the KMTO powder fitted the Langmuir isothermal model well, while the porous ceramics fitted with the Freundlich model. The mechanism of the adsorption by the KMTO powder and the porous ceramic was ion exchange. It was also shown that the nickel saturated KMTO powder and the porous ceramics were stable in leaching tests.     

Amino acid sensing by impedance of porous monolith-type ion exchanger

A biological and chemical sensor with rapid response at the microlevel is required for health and environmental monitoring. To develop a high-performance sensor, we use a porous monolith-type ion exchanger having three-dimensional acceptors to sense chemical substances. This porous monolith-type ion exchanger has an open-cellular structure with 5-50-μm diameter pores. The concentration of amino acids in the solution can be detected by measuring the impedance of the monolith-type ion exchanger. The novel ion exchanger has a high-exchange rate and high-electrical conductivity compared with that of the conventional ion-exchange resins. It is found that the impedance of the porous ion exchanger varies widely, depending on the amino acids such as glycine, asparatic acid, lysine, and phenylalanine. The impedance of anion exchanger had the highest value for phenylalanine with a benzene ring. OH-ion conduction is suppressed possibly due to the phenylalanine molecules stabilized by the hydrophobic interaction with the anion exchanger. In addition, we succeeded in sensing amino acid ions with concentration as low as 10⁻⁷ mol. The porous ion exchanger has the potential of a high-performance device for biological and chemical sensing.     

Template-assisted syntheses of porous metal methylphosphonates

Neutral dibutyl methylphosphonate (DBMP) is used as a template to prepare porous metal methylphosphonates (metal = aluminum, titanium, zirconium). The removal of DBMP in the as-synthesized materials could be easily achieved by evaporation under vacuum without destroying the hybrid structure, as evidenced by elemental analyses, FT-IR spectra, ¹³C CP/MAS NMR and nitrogen adsorption-desorption isotherms. Thermal analyses show that three porous hybrid samples have high thermal stability in air. The exothermic weight losses due to oxidation combustion of organic species occluded in samples appear after 730 K. Furthermore, the templating effect of DBMP is also confirmed by comparing the hybrid materials synthesized in the presence or the absence of the template.     

Modeling of the impedance response of porous metal hydride electrodes

Porous metal hydride electrodes of the alloy MmNi_3.5-3.7Co_0.7-0.8 Mn_0.3-0.4Al_0.3-0.4 have been characterized by means of impedance spectroscopy. A mathematical model for the impedance response, including effects of diffusion of hydrogen, surface kinetics, conductivity in the metal phase and the solution phase, as well as a continuous, lognormal, particle size distribution, was implemented and fitted to the experimental results by application of a least square fitting routine. The model is based on physical parameters, thus avoiding problems related to the conventional interpretation of impedance spectra in terms of equivalent circuits. Very good agreement between experimental results and model results was obtained for a wide range of frequencies, indicating that physical parameters to a great extent can be determined under realistic operating conditions. The latter was confirmed by independent measurements of the variation in open circuit voltage with respect to the state of charge of the electrode. The model provides an improved methodology for the determination of diffusion coefficients based on electrochemical impedance data. Furthermore, the model can be applied for parametric studies of metal hydride electrodes.     

One-pot dual product synthesis of hierarchical Co3O4@N-rGO for supercapacitors,N-GDs for label-free detection of metal ion and bio-imaging applications

Cobalt oxide nanoparticles@nitrogen-doped reduced graphene oxide (Co₃O₄@N-rGO) composite and nitrogen-doped graphene dots (N-GDs) were synthesized by a one-pot simple hydrothermal method. The average sizes of the synthesized bare cobalt oxide nanoparticles (Co₃O₄ NPs) and Co₃O₄ NPs in the Co₃O₄@N-rGO composite were around 22 and 24 nm, respectively with an interlayer distance of 0.21 nm, as calculated using the XRD patterns. The Co₃O₄@N-rGO electrode exhibits superior capacitive performance with a high capability of about 450 F g^?1 at a current density of 1 A g^?1 and has excellent cyclic stability, even after 1000 cycles of GCD at a current density of 4 A g^?1. The obtained N-GDs exhibited high sensitivity and selectivity towards Fe²⁺ and Fe³⁺, the limit of detection was as low as 1.1 and 1.0 μM, respectively, representing high sensitivity to Fe²⁺ and Fe³⁺. Besides, the N-GDs was applied for bio-imaging. We found that N-GDs were suitable candidates for differential staining applications in yeast cells with good cell permeability and localization with negligible cytotoxicity. Hence, N-GDs may find dual utility as probes for the detection of cellular pools of metal ions (Fe³⁺/Fe²⁺) and also for early detection of opportunistic yeast infections in biological samples.     

Direct electrodeposition of metal nanowires on electrode surface

A method for decorating the surface of disk electrodes with metal nanowires is presented. Cu and Ni nanowires with diameters from 1.0 μm to 0.2 μm are directly deposited on the electrode surface using a polycarbonate membrane filter template maintained in contact with the metal substrate by the soft homogeneous pressure of a sponge soaked with electrolyte. The morphologic and structural properties of the deposit are characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The latter shows that the head of nanowires with diameter of 0.4 μm is ordinarily polycrystalline, and that of nanowires with diameter of 0.2 μm is almost always monocrystalline for Cu and frequently also for Ni. Cyclic voltammetries and impedance investigations recorded in alkaline solutions at representative Ni electrodes decorated with nanowires provide consistent values of roughness factor, in the range 20–25.     

Heavy metal removal by ion exchanger based on hydroxyethyl cellulose

In the present work, ion exchange resin based on hydroxyethyl cellulose has been synthesized to remove the heavy metals, such as iron, cobalt, copper, and zinc from their aqueous solutions. The conditions in the column and batch modes were investigated for this purpose. The resin, having an average swelling percentage of 75.94 and an exchange capacity of 2.57 meq g⁻¹ resin, is being introduced as a new ion exchange resin in the heavy metal removal process. An investigation of the column operations using aqueous solutions of heavy metal ions indicated that the resin prepared has some advantages, including high total exchange capacity and good chemical stability. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3501–3506, 1999     

Axial dispersion in metal foams and streamwise-periodic porous media

We present a study on the axial dispersion in metal foams and laser sintered reactors. Commercially available metal foams of 20 and 30 ppi are compared to a designed streamwise-periodic structure in terms of axial dispersion coefficients and pressure drops. Therefore tracer pulse experiments were performed and post processed by means of a deconvolution method. The Peclet number Pe_p based on the pore size is ranging from 5×10⁴ to 8×10⁵ which is attributed to the increased velocities due to the high porosity of the material compared to fixed bed reactors. The attained dispersion coefficients ranging from 1.3×10⁻⁴ to demonstrate the trend of packed beds and common packing materials and increase monotone with the Peclet number Pe_p. The pressure drop versus the interstitial bulk velocity follows the Forchheimer equation and can be described by the conventional Ergun model for all investigated porous media. The parameters obtained correspond to values found in literature. The results of this study show the high potential of foam reactors for catalyst driven reactions. They provide the same or even a higher surface area per volume of catalyst bed while inducing a much smaller pressure drop than corresponding fixed beds.     

In situ wetting of aluminium during the growth of porous alumina by anodic oxidation

The growth of nanoporous alumina at an aluminium surface which is not completely covered by an electrolyte has been investigated. At one point the electrolyte forms three interfaces: oxide/electrolyte, metal/electrolyte, electrolyte/air. At this three-interfaces-point a self-wetting induced oxide growth occurs. The wetting increases up to 7 mm from the electrolyte contact edge. At this final stage of wetting an equilibrium between the wetting induced flow (bottom-up) and the gravity-driven flow (top-down) is reached. The thickness of the nonporous layer decreases with the distance from the starting point.     

Si nanopatterning by reactive ion etching through an on-chip self-assembled porous anodic alumina mask

Abstract

We report on Si nanopatterning through an on-chip self-assembled porous anodic alumina (PAA) masking layer using reactive ion etching based on fluorine chemistry. Three different gases/gas mixtures were investigated: pure SF₆, SF₆/O₂, and SF₆/CHF₃. For the first time, a systematic investigation of the etch rate and process anisotropy was performed. It was found that in all cases, the etch rate through the PAA mask was 2 to 3 times lower than that on non-masked areas. With SF₆, the etching process is, as expected, isotropic. By the addition of O₂, the etch rate does not significantly change, while anisotropy is slightly improved. The lowest etch rate and the best anisotropy were obtained with the SF₆/CHF₃ gas mixture. The pattern of the hexagonally arranged pores of the alumina film is, in this case, perfectly transferred to the Si surface. This is possible both on large areas and on restricted pre-defined areas on the Si wafer.

PACS

78.67.Rb, 81.07.-b, 61.46.-w     

In situ spectroscopic ellipsometric study of porous alumina film dissolution

Porous alumina films have been synthesised by anodisation of high purity aluminium in 0.4 M phosphoric acid at constant current density. The dissolution process of those coatings in 2 M phosphoric acid has been investigated by in situ spectroscopic ellipsometry (SE) combined with electrochemical measurements. A sharp drop of the open current potential is observed due to film removal. The dissolution time depends on total barrier layer thickness. Those results are confirmed by SE measurements. A three layer optical model has been used to interpret SE spectra. During the dissolution process, the porous top layer has a quasi-constant thickness, whereas porosity increases significantly. The dissolution proceeds within the pores. Only the thickness of pure alumina barrier layer (upper part) decreases during the dissolution process whereas the interface barrier layer (lower part) does not change.     

纳米金检测有毒有害物质的研究进展

随着人们对含有重金属的食品,农作物中的农药残留,动物源食品的兽药残留以及包装材料中迁移等有害污染物的关注,开发一个快速、灵敏,经济的对这些有毒有害物质检测方法是非常必要的。纳米金材料凭借其特有的物理和化学性质在此方面显示出巨大的潜力,将纳米金材料用于有毒有害物质的检测领域,成为近几年的一个研究热点。本文介绍了金纳米粒子的基本特征,分析了有害的污染物,其来源和种类,介绍并讨论了金纳米颗粒对有毒有害污染物的检测和应用。     

In situ diffraction studies of electrode surface structure during gold electrodeposition

Surface X-ray scattering (SXS) in transmission geometry provides a valuable tool for in situ structural studies of electrochemical interfaces under reaction conditions, as illustrated here for homoepitaxial electrodeposition on Au(1 0 0) and Au(1 1 1) electrodes. Employing diffusion-limited deposition conditions to separate the effects of potential and deposition rate, a mutual interaction between the interface structure and the growth behavior is found. Time-dependent SXS measurements during Au(1 0 0) homoepitaxy show with decreasing potential transitions from step flow to layer-by-layer growth, then to multilayer growth, and finally back to layer-by-layer growth. This complex growth behavior can be explained within the framework of kinetic growth theory by the effect of potential, Cl adsorbates and the Au surface structure, specifically the presence of the surface reconstruction, on the Au surface mobility. Conversely, the electrodeposition process influences the structure of the reconstructed Au surface, as illustrated for Au(1 1 1), where a significant deposition-induced compression of the Au surface layer as compared to Au(1 1 1) surfaces under ultrahigh vacuum conditions or in Au-free electrolyte is found. This compression increases towards more negative potentials, which may be explained by a release of potential-induced surface stress.     

DNA-immobilized porous polysulfone beads for organic compounds and heavy metal ion removal

Sorption and pervaporation experiments were carried outwith PVA/PAA cross-linked membranes for the separation of azeotropic methyl tert-butyl ether and methanol mixtures. The influence of the PVA/PAA ratio and liquid mixture composition were investigated. With increasing PAA content in the membranes, solubilities and fluxes decreased and selectivities increased. Total sorption and fluxes increased with increasing concentration of McOH. Increasing the concentration of McOH resulted in decreasing selectivities. Because of polarity, McOH permeated selectively through the membranes. Sorption results showed the same tendency with pervaporation results.     

碘电极测定饮用水中的碘和碘离子

应用碘电极 ,采用亚砷酸钠为碘的还原剂进行前处理 ,选用磷酸二氢钠为总离子强度缓冲液 ,测定了总碘及碘离子含量。建立的方法对三碘树脂净水器净化后的水进行了测定 ,结果良好。当总碘和碘离子的浓度在 10 -7～ 10 -4范围内时 ,相关系数为 0 .9999,回收率大于 98.1%。由实验测定的电位选择系数可见 ,该法选择性好 ,检测下限低。     

Electrochemical detection of copper ion using a modified copolythiophene electrode

This paper studies the detection of copper ions by using an iminodiacetatic acid (IDA) modified conducting copolymer electrode. The copolymer film comprising 3-methyl thiophene (3MT) and 3-thiophene acetic acid (3TA) was chosen as the selective metal cation sensing electrode. The carboxylic group of the copolymer was modified to produce IDA group for metal ion capture. The modified electrode was used for the electrochemical analysis of trace copper ions by square wave voltammetry (SWV) technique. The electrode was found to be highly selective to Cu²⁺ in the range of 0.1-10 μM. The modified electrode offered an excellent way, with a high stability and reusability, for selective determination of Cu²⁺ in a solution of mixed metal ions.     

In situ FT-IR spectroelectrochemical study of electrooxidation of pyridoxol on a gold electrode

The electrochemical oxidation of pyridoxol (PN) on a polycrystalline gold electrode was investigated by cyclic voltammetry and in situ Fourier transform infrared spectroscopy (FTIRS). In 0.1 M aqueous NaOH solution, the gold electrode showed a high catalytic activity for the irreversible oxidation process of PN. The individual ionic species and the major tautomeric equilibria of PN molecules in aqueous solutions were evidenced well from the pH-dependent attenuated total reflectance (ATR) spectra, and the results were in good agreement with the voltammetric observations. In situ single potential alteration infrared reflectance spectroscopy (SPAIRS) demonstrated that a lactone form of PN, rather than pyridoxal aldehyde, was likely formed, which was subsequently diffused into the thin layer solution and underwent hydrolysis slowly to pyridoxic acid (PA) as the final product. In addition, the adsorption of PN at Au electrode was characterized by in situ subtractively normalized interfacial Fourier transform infrared reflectance spectroscopy (SNIFTIRS) method, which revealed that the adsorption of deprotonated PN, via nitrogen atom in vertical configuration on electrode surface, occurred from −0.5 V versus Ag?AgCl?KCl(sat), which was much lower than the potential of PN electrooxidation observed from ca. 0 V.     

Nanostructured materials prepared by use of ordered porous alumina membranes

We report on three different methods to prepare nanostructured materials using highly ordered porous alumina membranes as templates: (1) firstly, a new and simple method, termed as the paired cell method, was developed for the preparation of inorganic nanowires. Several kinds of inorganic nanowires were synthesized using this method. The structure and composition of these nanowires were determined by field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. (2) Secondly, highly ordered platinum nanowire arrays were prepared by electrochemical method with the help of porous alumina membrane templates. The structure and composition of these nanowire arrays were also characterized by various experimental techniques. The electrochemically active surface area of the nanowire arrays was determined by cyclic voltammetry based on hydrogen adsorption. Results showed that the platinum nanowire arrays exhibited a large surface area. (3) Finally, we also present a simple and reliable procedure for the preparation of highly ordered metal nanohole and nanopillar arrays, based on the anodic oxidation of aluminum and vacuum evaporation technology. The field emission scanning electron microscopic images revealed that these metal nanostructure arrays were highly ordered over a large area. The nanoimprinting of aluminum surfaces using the as-prepared chromium nanopillar arrays was demonstrated, resulting in periodic indentation on the aluminum surface.     

Enhanced high rate properties of ordered porous Cu2O film as anode for lithium ion batteries

Highly ordered porous Cu₂O film is electrodeposited on copper foil through a self-assembled polystyrene sphere template. Compared with the dense Cu₂O film and the octahedral Cu₂O powder, the ordered porous Cu₂O film exhibits an improved electrochemical cycling stability. The capacity of the porous Cu₂O film can maintain 336 mAh g⁻¹ and 213 mAh g⁻¹ after 50 cycles at the rate of 0.1 C and 5 C, respectively. The reversible capacity holds 63.4% as the discharge-charge rate even increases by 50 times. The enhanced high rate properties of the ordered porous film should be attributed to the sufficient contact surface of Cu₂O/electrolyte and the short diffusion length of Li⁺. Moreover, the direct contact between Cu₂O and current collector and the decreasing inactive interfaces of Cu₂O/polymer binder are also suggested as being responsible for the enhanced high rate property.     

Electrochemical detection of dopamine and cytochrome c at a nanostructured gold electrode

A nanostructured gold surface consisting of closely packed outwardly growing spikes is investigated for the electrochemical detection of dopamine and cytochrome c. A significant electrocatalytic effect for the electrooxidation of both dopamine and ascorbic acid at the nanostructured electrode was found due to the presence of surface active sites which allowed the detection of dopamine in the presence of excess ascorbic acid to be achieved by differential pulse voltammetry. By simple modification with a layer of Nafion, the enhanced electrocatalytic properties of the nanostructured surface was maintained while increasing the selectivity of dopamine detection in the presence of interfering species such as excess ascorbic and uric acids. Also, upon modification of the nanostructured surface with a monolayer of cysteine, the electrochemical response of immobilised cytochrome c in two distinct conformations was observed. This opens up the possibility of using such a nanostructured surface for the characterisation of other biomolecules and in bio-electroanalytical applications.