Abstract  Two new alkoxido-bridged heterometallic complexes of formula [(CoCo3Cu3II)-Co-II-Cu-III(dea)(6)(CH3COO)(3)] (ClO4)(0.75)(CH3COO)(1.25) (1) and [(Co2Co2Zn3II)-Co-II-Zn-III(tea)(2)(piv)(6)(CH3O)(2)(OH)(2)(CH3OH)(2)]center dot H2O 2 (H(2)dea = diethanolamine, H3tea = triethanolamine and Hpiv = pivalic acid) have been assembled using aminoalcohol ligands. The cationic core in 1 possesses a threefold crystallographic axis, and it exhibits a set of three copper(II), one cobalt(II) and three cobalt(III) ions arranged as a hexagon of alternating copper(II) and cobalt(III) ions around the central cobalt(II) ion. Each edge of the hexagon is defined by a double alkoxido bridge, the outer one being bis-monodentate with copper(II)-cobalt(III) pair whereas the inner one adopts a tris-monodentate coordination mode linking the Cu(II)-Co(III) pair with the central cobalt(II) ion. The acetate groups act as bidentate ligands towards the copper(II) ions. The intramolecular cobalt(II)-copper(II) separation is 3.157 angstrom. A hexagon of two cobalt(II), two cobalt(II) and two zinc(II) ions distributed along three types of edges with a central zinc(II) ion occurs in 2. A tris-modentate alkoxido bridge is involved in all edges together with another bis-monodentate alkoxido bridge (Co-III-Co-II and Co-II-Zn-II pairs) and a carboxylatepivalate bridge in the syn-syn conformation. The five coordination at each peripheral zinc(II) ion is completed by a monodentate carboxylate-pivalate ligand whereas a methoxo group allows to achieve the six-coordination at each cobalt(III) ion. The intramolecular cobalt(II)-cobalt(II) separation through the inner zinc(II) ion is 6.309 A. The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9-300 K. The exchange interaction between the six-coordinate cobalt(II) and copper(II) ions through the double alkoxido bridges in 1 and that between the six-coordinate cobalt(II) ions across the diamagnetic zinc (II) ion in 2 are found to be ferromagnetic [J = +5.39(5) (1) and + 1.05(2) cm(-1) (2)], the accidental orthogonality between the interacting magnetic orbitals accounting for this behaviour in the two cases. (C) 2017 Elsevier B. V. All rights reserved.

Abstract  The pentanuclear heterotrimetallic complex [Cu2CoNi2(Me(2)Ea)(6)Cl-4] (1) has been prepared in a one-pot reaction of zerovalent copper with cobalt and nickel chlorides in an acetonitrile solution of 2-(dimethylamino) ethanol (HMe(2)Ea) in open air. The crystal structure displays a rare planar arrangement of the metal atoms. The possible pentanuclear molecular structure types corresponding to the planar and non-planar "butterfly-like'' arrangements, as well as their derivatives, are analyzed and their statistical abundance is discussed. The thermogravimetric behaviour of 1 is investigated and compared with literature examples.

Abstract  A sandwich-type tungstophosphate, (1,3-H(2)dap)(2)H-4[Co-4 (1,3-Hdap)(2)(alpha-B-PW9O34)(2)]center dot 3H(2)O (1,3-dap = 1,3-diaminopropane), was hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, elemental and thermo-gravimetric analysis, and IR and UV spectroscopy. The compound presents a classical tetra-transition metal-substituted sandwich framework, [Co-4(1,3-Hdap)(2)(alpha-B-PW9O34)(2)](8-), which contains two lacunary alpha-B-[PW9O34](9-) Keggin units linked by a rhomb-like Co4O14(1,3-dap)(2) cluster lying across an inversion center. The Co2+ ions are coordinated by a mono-protonated dap ligand. Isolatedly protonated 1,3-dap units act as counter-ions interacting with the [PW9O34](9-) polyanions via hydrogen bonds forming a three-dimensional framework.

Abstract  The tribological profile of alumina (99.7%) mated against rotating disks made in binder-less niobium carbide (NbC) and cobalt-bonded NbC were determined under unidirectional sliding tests (0.1 m/s to 8.0 m/s; 22 degrees C and 400 degrees C) as well as in oscillation tests (f = 20 Hz, Delta x = 0.2 mm, 2/50/98% rel. humidity, n = 10(5)/10(6) cycles) under unlubricated (dry) conditions. In addition, the microstructure and mechanical properties of binderless NbC and NbC bonded with 8% cobalt were determined as well. The reason for testing hot-pressed NbC was to avoid side effects generated by sintering additives and/or second phases. The tribological data obtained were benchmarked with different ceramics, cermets and thermally sprayed coatings. NbC and cobalt-bonded NbC exhibited low wear rates under dry sliding associated with high load carrying capacity. The tribological profile established revealed a strong position of NbC bearing materials under tribological considerations and for closed tribo-systems against traditional references, such as WC, Cr3C2 and (Ti,Mo)(C,N). (C) 2014 Elsevier Ltd. All rights reserved.

Abstract  A single-chain cobalt phosphonate complex [Co(phen)(4,4'-bpy)(PhPO(3)H)(2)](n)center dot 0.5H(2)O 1 (phen = 1,10-phenanthroline, 4,4'-bpy = 4,4'-bipyridine) and a mononuclear cobalt complex [Co(pic)(2)(H(2)O)(2)]center dot 0.5H(2)O 2 (picH = picolinic acid) have been synthesized with identical procedure from similar system containing phenylphosphonic acid and N-containing ligands. Both complexes have been characterized by single crystal X-ray diffraction, IR spectroscopy, magnetic measurement and thermal analysis. Compound 1 crystallizes in the tetragonal system with a P4(3)2(1)2 space group, and exhibits a 1-D cobalt chain connected by 4,4'-bpy bridges propagated along a axis direction, and the chains are linked by strong hydrogen bonds to form a two-dimensional grid like coordination network, whereas compound 2 crystallizes in the monoclinic system with space group P2(1)/n, and the mononuclear molecules in 2 are linked by hydrogen bonds to form infinite double-chains and the double-chains are further crosslinked to create a two-dimensional supramolecular network. The magnetic measurement reveals overall weak antiferromagnetic exchange interactions between the cobalt ions in both complexes 1 and 2. (C) 2008 Elsevier B.V. All rights reserved.

Abstract  Perovskite-type oxide (PTO) of LaFeO3 supported Ni-Co bimetallic catalysts were prepared by citric acid complexation-impregnation method and were used for the steam reforming of ethanol (SRE) to produce hydrogen. The anti-sintering and anti-coking properties of the catalysts for the reaction have been investigated and compared with the monometal catalysts. The catalysts were characterized by using temperature programmed reduction, Xray diffraction, transmission electron microscopy and thermal analysis techniques. The results indicate that the catalyst was both highly selective to hydrogen and very stable for SRE reaction. Characterization results indicated that Ni-Co was in the state of solid solution alloy. Comparing with corresponding monometal catalysts, the bimetal catalyst exhibited better anti-sintering ability and similar anti-carbon deposition ability. The valuable information indicated in this work is that based on the special characters of PTO, bimetal nano-particles can be supported on metal oxides, which should be a new and promising method for preparing supported bimetal catalysts. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Abstract  In this work, an urchin-like yolk-shell Fe3O4@SiO2@Co3O4 catalyst with a diameter of 300 nm has been synthesized for photocatalytic water oxidation to oxygen with excellent activity and recyclability in the Ru(bpy) (3) (2+) -S2O8 (2-) system. In order to compare under identical conditions, we introduced Co3O4 nanoparticles with a diameter of 80 nm as a reference catalyst, the O-2 yield of Fe3O4@SiO2@Co3O4 (93 mu mol) is 2.7 times higher as compared with it after 60 min of photoirradiation. Magnetic properties of Fe3O4 nanoparticles are helpful to recover the catalyst from the solutions after reaction by magnetic separation. In addition, the amount of evolved oxygen reaches 87 % of initial yield for the third run. We believe that urchin-like Fe3O4@SiO2@Co3O4 has broad prospects for photocatalytic water oxidation.

Abstract  Air-formed surface oxide films on four types of Co-Cr-alloys were characterized using X-ray photoelectron spectroscopy (XPS) and five types of Co-Cr alloys were anodically polarized, to identify the effects of the addition of N, Mo, and W to Co-Cr alloys containing high Cr on the surface composition and corrosion resistance. Co-20Cr-15W-10Ni (ASTM P90), Co-30Cr-6Mo, Co-33Cr-5Mo-0.3N, and Co-33Cr-9W0.3N were employed for XPS and the above four alloys and another Co-30Cr-6Mo (ASTM F75) were employed for anodic polarization. The surface oxide film on the Co-Cr alloys consisted of oxide species of Co, Cr, Mo, W and/or Ni contains a large amount of OH-with a thickness of 2.6-3.2 nm. Cations existed in the oxide as Co2+, Cr3+, Mo4+, Mo6+, W6+ and Ni2+. Cr and Mo are enriched and Co and Ni are depleted in the surface oxide film. W was enriched in the case of Co-20Cr-15W-10Ni but depleted in the case of Co-33Cr-9W-0.3N. On the other hand, Cr, Mo, W and Ni were enriched and Co was depleted in the substrate alloy just under the surface oxide film in the polished alloy. During rapid formation of the surface oxide film, Cr was preferentially oxidized and the oxidation of Co and Ni delayed, according to the oxidation and reduction potentials of these elements, The Co-Cr alloys essentially have high localized corrosion resistance that is not easily affected by a small change of composition. Co-33Cr5Mo-0.3N shows higher corrosion resistance compare than conventional Co-Cr alloys.

Abstract  This study conducts a critical review on the studies of material corrosion and deposition on the secondary circuit of a pressurized water reactor, especially on the steam generators (SGs). Available knowledge has shown that the structural materials in the environment of the secondary circuit are susceptible to flow-accelerated corrosion and deposition-induced degradation. The deposition of the non-volatile impurities, especially the corrosion products, on the SG surfaces can be a primary cause of material degradations, including stress corrosion cracking. The review will analyze the fouling mechanisms and behaviors, the source of impurities, corrosion mechanisms, and the factors that affect the deposition and corrosion behaviors.

Abstract  This study examined the release of toxic metal ions from, and the cell response to, a cobalt-chromium (Co-Cr) alloy fabricated using either traditional casting or selective laser melting (SLM) techniques. The releases of Co, Cr, and Molybdenum (Mo) were examined using inductively coupled plasma mass spectroscopy (ICP-AES) for specimens immersed in artificial saliva solution at 37 degrees C for 7 days. Cell response to samples was evaluated by investigating the morphology of mouse 3T3 fibroblasts. Cell proliferation was assessed using an MIT assay. The cell culture medium exposed to specimens was also tested for metal ion release using ICP-AES. Concentrations of Co and Mo were significantly lower in the SLM group in comparison with the traditional casting group. Cells exposed to both SLM and traditional cast samples showed normal cell morphology; however, cell proliferation on SLM samples was higher. In conclusion, the ion release of Co-Cr alloy prepared by selective laser melting was lower and showed better biocompatibility than samples prepared by a traditional casting technique. (C) 2012 Elsevier B.V. All rights reserved.

Abstract  Metal-organic frameworks (MOFs) have attracted much attention in the areas of biomedicine and medicine owing to their versatile porous structure. However, the oversize and high cellular toxicity of some metal-based MOF particles have hindered their development. Therefore, a series of small Ti-based MOFs are prepared with the introduction of tetraethyl orthosilicate (TEOS) into the reaction system. Compared with the Ti-based MOFs prepared by traditional methods, the size of the Ti-based MOFs prepared with this method is decreased by 42.78%. Meanwhile, the good biocompatibility of the prepared Ti-based MOF particles toward the L929 cell lines is proven using CCK-8 assays. Furthermore, the controlled release property of the Ti-based MOFs is evaluated by using ibuprofen (IBU) as a model drug. The amount of drug loaded in the samples is shown to be approximately 10%, and approximately 95% of the IBU is released from the MOFs after exposure to PBS for 24 h. We conclude that the size-decreased Ti-based MOFs prepared with the introduction of TEOS into the reaction systems are potential drug carriers in terms of their good biocompatibility and effective performance in the controlled release of a drug.

Abstract  A water-soluble polypyridine copper complex Cu(dpp)(ClO4)(2) (1, dpp = 2,9-di(pyridin-2-yl)1,10-Phenanthroline) enables to electrocatalyze H-2 generation from neutral phosphate buffer solution at a relatively low overpotential of 520 mV vs. SHE. Sustained proton reduction catalysis occurs at glassy carbon electrode at -1.4 V vs. SHE for 2 h to give H-2 with TONs of 734 mol H-2 (mol catalyst)(-1) cm(-2) and 95% Faradaic yield. CVs, UV-Vis spectra, SEM, EDX and Tyndall analysis reveals that 1 has the desired stability and functions as a molecular electrocatalyst under the conditions. Due to the relatively low over potential and high stability, light-driven hydrogen production based on 1 were also carried out with a TONs of 6 mol H-2 (mol catalyst)(-1) in an aqueous solution. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Abstract  Sodium borohydride (NaBH4) hydrolysis offers significant advantages in hydrogen storage for fuel cells, but the hydrolysis requires the use of expensive catalysts, such as Ru and Pt alloys, or various supports. To explore low-cost and high activity catalysts, we use ZnCl2 to promote the hydrolysis rate of sodium borohydride. The mechanisms and apparent activation energy of these composites are discussed. Compared to the hydrolysis of pure NaBH4 (523 mL/g hydrogen in 2 h at 298 K), NaBH4 with 20 wt% ZnCl2 has the best hydrolysis performance with the hydrogen generation rates of 844 mL/g in 5 min, 1039 mL/g in 10 min and 1933 mL/g in 2 h at 298 K. The apparent activation energies of NaBH4 hydrolysis decreased from 79.5 kJ/mol in deionized water to 47.7 kJ/mol with the addition of 20 wt% ZnCl2. These results demonstrated that ZnCl2 could be a promising reagent to promote NaBH4 hydrolysis in a hydrogen generation system to replace noble metal catalysts. (C) 2017 Elsevier B.V. All rights reserved.

Abstract  Discovery of a chemically stable, light absorbing and low resistivity metal oxide with band edges aligned to the water redox potentials has been a goal of physical scientists for the past forty years. Despite an immense amount of effort, no solution has been uncovered. We present a combined theoretical and experimental exploration of a series of unconventional ternary cobalt spinel oxides, which offer chemical functionality through substitution on the octahedral spinel B site. First-principles predictions of the substitution of group 13 cations (Al, Ga, In) in Co3O4 to form a series of homologous CoX2O4 spinel compounds are combined with experimental synthesis and photoelectrochemical characterization. Ultimately, while tunable band gaps in the visible range can be obtained, the material performance is limited by poor carrier transport properties associated with small polaron carriers. Future design pathways for metal oxide exploration are discussed.

Abstract  Incoloy 903 overlays have been used to provide hydrogen environment embrittlement (HEE) resistance to welds in nickel alloy 718 structures. This is problematic because application of the required overlays has a history of high rejection and rework due to interpass microfissuring. Kovar has been identified as a potential hydrogen resistant replacement for Incoloy 903. A weldability study was initiated to compare the hot crack (microfissure) resistance of the two alloys to determine if substitution of Kovar for Incoloy 903 has the potential to improve the fabricability of HEE overlays. Varestraint testing indicates that Kovar has much higher crack initiation strains for both HAZ and weld metal cracking. Crack initiation strains were approximately 2% for Kovar while Incoloy 903 crack initiation strains were only 0.25%. Maximum crack lengths (MCL) observed on Kovar Varestraint tests were 0.12mm and 0.58mm for base and weld metal respectively, while 903 MCLs were 0.56mm and 2.3mm. Gleeble hot ductility testing indicates that Kovar has a nil ductility range of 7 degrees C while Incoloy 903 has a range of approximately 45 degrees C. The larger range observed for 903 is an indication of its greater crack susceptibility. Fabricability was correlated to material microstructure using optical microscopy, scanning electron microscopy and microprobe analysis.

Abstract  In this study, the synthesis, spectroscopic and catalytic properties of PdLn (n = 1-6) complexes with tetradentate -ONNO- and -SNNS- type Schiff base ligands (LH2)-H-n (n = 1-6) were investigated. The PdLn (n = 1-6) complexes were synthesized by the thermal reactions of the Schiff bases and Pd(OAc)(2) in acetonitrile and characterized by elemental analysis, FT-IR, H-1 NMR, UV-visible and TGA/DTG. The spectroscopic studies suggest that all of the ligands are coordinated to the central metal as a tetradentate ligand coordinating via the central azomethine nitrogens (C=N) and phenolic oxygen/sulfur atoms. On the palladium-catalyzed Suzuki cross-coupling reactions employing PdLn (n = 1-6) complexes toward a various substituted arylbromides and boronic acids were pursued. The conversions were obtained and yields with different arylbromides were calculated and discussed. All the complexes were thermally stable and were not sensitive to air or the moisture. The complexes were easily prepared from low cost precursors that could be used as versatile and catalysts for different C-C coupling reactions (Suzuki-Miyaura reactions). Moreover steady state fluorescence emission and excitation spectra were measured. These studies have been shown that PdL2 and PdL3 dyes exhibited high fluorescence intensity and selective and efficient response to cobalt ions over other metal ions in buffered solutions.

Abstract  Fully epitaxial magnetic tunnel junctions (MTJs) with Co-based Heusler alloy Co(2)MnSi electrodes and a MgO tunnel barrier were fabricated with various values of Mn composition α for Co(2)Mn(α)Si in Co(2)Mn(α)Si/MgO/Co(2)Mn(α)Si MTJs. The tunnel magnetoresistance (TMR) ratios at both 4.2 K and room temperature (RT) increased systematically with increasing α in Co(2)Mn(α)Si electrodes from Mn-deficient compositions (α < 1) up to a certain Mn-rich composition (α > 1), demonstrating high TMR ratios of 1135% at 4.2 K and 236% at RT for MTJs with Mn-rich Co(2)Mn(α)Si electrodes with α = 1.29. Identically fabricated Co(2)Mn(β)Ge(δ)/MgO/Co(2)Mn(β)Ge(δ) (δ = 0.38) MTJs showed similar dependence of the TMR ratio on Mn composition β, demonstrating relatively high TMR ratios of 650% at 4.2 K and 220% at RT for β = 1.40. The Mn composition dependence of the TMR ratio at both 4.2 K and RT observed commonly for both Co(2)MnSi/MgO/Co(2)MnSi and Co(2)MnGe/MgO/Co(2)MnGe MTJs can be attributed to suppressed minority-spin in-gap states around the Fermi level for Mn-rich Co(2)MnSi and Co(2)MnGe electrodes.

Abstract  We performed high-field magnetotransport and magnetization measurements on a single crystal of the 122-phase iron pnictide Ba(Fe1-xCox)(2)As-2. Unlike the high-temperature superconductor cuprates and 1111-phase oxypnictides, Ba(Fe1-xCox)(2)As-2 showed practically no broadening of the resistive transitions under magnetic fields up to 45 T. We report the temperature dependencies of the upper critical field H-c2 both parallel and perpendicular to the c-axis, the irreversibility field H-irr(c)(T), and a rather unusual symmetric volume pinning force curve F-p(H) suggestive of a strong pinning nanostructure. The anisotropy parameter gamma=H-c2(ab)/H-c2(c) deduced from the slopes of dH(c2)(ab)/dT=4.9 T/K and dH(c2)(c)/dT=2.5 T/K decreases from similar to 2 near T-c, to similar to 1.5 at lower temperatures, much smaller than gamma for 1111pnictides and high-T-c cuprates.

Abstract  MgO has several advantageous characteristics and has been applied in various fields. In this study, we deposited Co nanoparticles in an island pattern on a Si substrate using an arc plasma gun (APG). We subsequently formed a MgO thin film on this substrate by metal-organic decomposition (MOD), which enables the formation of films in the atmosphere, thereby yielding a double-layer structure. The MgO thin film formed on Co nanoparticles deposited using the APG with 500 pulses of arc discharge exhibited improved crystallinity and photoelectron emission at least threefold higher than that of a MgO thin film formed directly without depositing Co nanoparticles. Although the transmittance of the specimen formed by depositing Co nanoparticles was initially 30% or lower, it increased to greater than 90% after the formation of the MgO thin film and the dispersion of the Co nanoparticles in the MgO thin film during heat treatment at 900 degrees C. Our results clarify that the characteristics of MgO thin films are markedly improved by depositing Co nanoparticles before forming the films. The results of Kelvin probe force microscopy (KPFM) indicate that the outermost surface of the Co material had become CoO (cobalt oxide) with the dispersion of Co nanoparticles in the MgO thin film. The lattice parameter of CoO nanoparticles (an-axis lattice parameter of 4.2615 angstrom) after heating matches well with that of MgO (4.2126 angstrom). The MgO thin films that grew in conjunction with the CoO nanoparticles were highly crystallized. We successfully established a high-performance, cost-effective bottom-up process that requires no ion injection by dispersing Co nanoparticles in a MgO thin film through heat treatment. (C) 2015 The Japan Society of Applied Physics

Abstract  Co-W-P films were prepared by a pulse plating method on a copper substrate. Effects of different duty ratios on composition, microstructure and magnetic properties of films were investigated. With the increase in duty ratios, the deposition speed increased gradually during the pulse plating process. It was found that the higher ratio duty could improve contents of cobalt and reduce amounts of phosphorus in the film. Almost all the deposited films were crystalline and formed tetrahedral structures Co(3)W with preferred crystallographic orientation (200) and (201). Dissimilar surface morphology could be detected under different duty ratios. Atomic force microscopy showed that lower duty ratios could form typical nodular structures and the dense surface. However, the films with rough and agglomerate nodular structures would be detected with higher duty ratios. Vibration sample magnetometer results showed that higher duty ratio induced larger saturation magnetisation and lower coercivity of Co-W-P films.

Abstract  The energetics, electronic structure and mechanical property Of Co-3(Al,W) precipitates with different ratio of Al to W in Co base alloys were investigated by the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. The calculated results show that the L1(2) Co-3(Al,W) precipitate is the most stable when the ratio of Al to W is equal to 1. When the content of W is higher than 18.5 at%, the L1(2) and hexagonal structures co-exist in Co-3(Al,W) precipitates at 1173 K. It is also shown that the L1(2) ordered Co-3(Al,W) precipitates have an obvious strengthening effect in the disordered fcc cobalt matrix.

Abstract  The effects of Mn addition on the structures, magnetic properties and phase transformation of mechanically alloyed SmCo6.7-xMnxCr0.3 (x = 0-0.6) magnets have been studied systematically. The results show that a small amount of Mn addition facilitates the formation of Th2Zn17-type 2:17 phase and significantly improves the intrinsic coercivities and the maximum energy products of the SmCo6.7-xMnxCr0.3 alloys. The phase transformation from Th2Ni17-type to Th2Zn17-type structure is observed in annealing the alloys. More Mn addition leads to the enhancement of the critical annealing temperature above which the magnetically soft Co phase appears, leading to an improvement in thermal stability of the magnetically hard 2:17 phase. The highest H-i(c) of 17.2 kOe and the largest (BH)(max) of 7.1 MGOe are achieved for the SmCo6.1Mn0.6Cr0.3 alloy annealed at 800 degrees C for 30 min. (C) 2008 Elsevier B.V. All rights reserved.

Abstract  The adsorptive stripping voltammetric detection of nickel and cobalt in water samples at metal film electrodes has been extensively studied. In this work, a novel, environmentally friendly, metal-free electrochemical probe was constructed for the ultra-trace determination of Ni2+ in water samples by Adsorptive Cathodic Stripping Voltammetry (AdCSV). The electrochemical platform is based on the adsorptive accumulation of Ni2+ ions directly onto a glassy carbon electrode (GCE) modified with dimethylglyoxime (DMG) as chelating agent and a Nafion-graphene (NGr) nanocomposite to enhance electrode sensitivity. The nafion-graphene dimethylglyoxime modified glassy carbon electrode (NGr-DMG-GCE) shows superior detection capabilities as a result of the improved surface-area-to-volume ratio and enhanced electron transfer kinetics following the incorporation of single layer graphene, while limiting the toxic effects of the sensor by removal of the more common mercury, bismuth and lead films. Furthermore, for the first time the NGr-DMG-GCE, in the presence of common interfering metal ions of Co2+ and Zn2+ demonstrates good selectivity and preferential binding towards the detection of Ni2+ in water samples. Structural and morphological characterisation of the synthesised single layer graphene sheets was conducted by Raman spectrometry, HRTEM and HRSEM analysis. The instrumental parameters associated with the electrochemical response, including accumulation potential and accumulation time were investigated and optimised in addition to the influence of DMG and graphene concentrations. The NGr-DMG-GCE demonstrated well resolved, reproducible peaks, with RSD (%) below 5% and a detection limit of 1.5 µg L-1 for Ni2+ reduction at an accumulation time of 120 s., the prepared electrochemical sensor exhibited good detection and quantitation towards Ni2+ detection in tap water samples, well below 0.1 mg L-1 set by the WHO and EPA standards. This comparable to the South African drinking water guidelines of 0.15 mg L-1.

Abstract  A selective and sensitive method for simultaneous determination of lead, zinc and copper by adsorptive differential pulse cathodic stripping voltammetry is presented. The method is based on adsorptive accumulation of the complexes of Pb(II), Zn(II), and Cu(II) ions with dopamine onto hanging mercury drop electrode (HMDE), followed by reduction of adsorbed species by differential pulse cathodic stripping voltammetry. The effect of experimental parameters such as pH, dopamine concentration, accumulation time and potential and scan rate were examined. Under the optimized conditions, linear calibration curves were established for the concentration of Pb, Zn, and Cu in the ranges of 5-150, 5-250, and 1-150 ng/mL, respectively. Detection limits of 0.06, 0.25, and 0.04 ng/mL for Pb, Zn, and Cu were obtained. An application of the proposed method is reported for the determination of these elements in some real samples such as natural waters and alloys.

Abstract  The direct CH-alkylation of indoles using carboxylic acids is presented for the first time. The catalytic system based on the combination of Co(acac)3 and 1,1,1-tris(diphenylphosphinomethyl)-ethane (Triphos, L1), in the presence of Al(OTf)3 as co-catalyst, is able to perform the reductive alkylation of 2-methyl-1H-indole with a wide range of carboxylic acids. The utility of the protocol was further demonstrated through the C3 alkylation of several substituted indole derivatives using acetic, phenylacetic or diphenylacetic acids. In addition, a careful selection of the reaction conditions allowed to perform the selective C3 alkenylation of some indole derivatives. Moreover, the alkenylation of C2 position of 3-methyl-1H-indole was also possible. Control experiments indicate that the aldehyde, in situ formed from the carboxylic acid hydrogenation, plays a central role in the overall process. This new protocol enables the direct functionalization of indoles with readily available and stable carboxylic acids using a non-precious metal based catalyst and hydrogen as reductant.