We propose a new formula for the mineral nickelskutterudite, based on our observation that either (or both) Co or Fe3+ are essential structure constituents. The crystal structure of nickelskutterudite, (Ni,Co,Fe) As-3, cubic, Im (3) over bar, Z = 8: a = 8.2653(6) angstrom, V = 564.65(7) angstrom, has been refined to R-1 = 1.4% for 225 unique reflections I > 2 sigma(1) collected on a Bruker X8 four-circle diffractometer equipped with fine-focus, sealed tube MoKa radiation and an APEX-II CCD detector. This is the first report of the crystal structure of nickelskutterudite. Nickelskutterudite, a member of the skutterudite group of isostructural minerals, adopts a distorted perovskite structure with notably tilted octahedra and an unoccupied to partially occupied icosahedral metal site. In the structure of nickelskutterudite, there is one metal (B) site occupied by Ni, Co, or Fe in octahedral coordination with six As atoms. Procrystal electron density analysis shows each As anion is bonded to two cations and two As anions, resulting in a four-membered ring of bonded As with edges 2.547 and 2.475 angstrom. The extreme tilting of BAs6 octahedra is likely a consequence of the As-As bonding. The nickelskutterudite structure differs from the ideal perovskite structure (A(4)B(4)X(12)) in that As4 anion rings occupy three of the four icosahedral cages centered on the A sites. There are reported synthetic phases isomorphous with skutterudite with the other A site completely occupied by a cation (AB(4)X(12)). Electron microprobe analyses of nickelskutterudite gave an empirical chemical formula of (Ni0.62Co0.28Fe0.12)(Sigma 1.02)(AS(2.95)S(0.05))(Sigma 3.00) normalized to three anions. Pure NiAs3 nickelskutterudite, natural or synthesized, has not been reported. In nature, nickelskutterudite is always observed with significant Co and Fe, reportedly because all non-bonded valence electrons must be spin-paired. This suggests that nickelskutterudite must contain Co3+ and Fe2+, consistent with previous models since Ni4+ cannot spin-pair its seven non-bonded electrons, Co3+ and Fe2+, which can spin-pair all non-bonded electrons, are required to stabilize the structure. No anion deficiencies were found in the course of this study so, including the structurally necessary Co and Fe, the chemical formula of nickelskutterudite (currently given as NiAs3-x, by the IMA) should be considered (Ni,Co,Fe)As-3.

M.Tech. (Chemistry, Faculty of Applied and Computer Science), Vaal University of Technology. / Complexes of alkyldithiocarbamate and thiuram have been extensively explored for various applications in the medical field. Thiuram and dithiocarbamate ligands were used to prepared complexes of cobalt and copper. The high abundance of sulfur in these ligands has resulted to be the preferred complexes for the synthesis of metal sulfide nanoparticles. All the prepared complexes were characterized using techniques such as IR and 1HNMR spectroscopy, elemental analysis, and thermogravimetric analysis. All the spectra data obtained were consistent with the coordination of the ligands through sulfur atom to the metal ion. The thermogravimetric analysis of all complexes decomposed to form metal sulfide, which really confirmed that all the complexes could be used to metal sulfide nanoparticles. All the prepared complexes were used to synthesize MxSy nanoparticles. The metal sulfide nanoparticles were successful prepared by thermal decomposition of the single-source precursor in hexadecylamine solution. The reaction parameter such as the concentration (1.0, 0.5, 0.25 and 0.125 g), reaction temperature (80, 130, 200, 250 °C) and the time (5, 10, 15, 20, 25 and 30) of the reactionwere varied to see their effect on the preparation of the nanoparticles. The prepared metal sulfide nanoparticles were characterized using techniques such as UV spectroscopy, photoluminescence spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The concentration was found to have a profound effect in size and shape of the prepared nanoparticles. The nanoparticles prepared at various concentrations were dominated by sphere with an average size of 2-30 nm. The XRD pattern confirmed that the composition is not affected by the temperature. Thetemperature has a dramatic effect in size, shape and the stoichiometry of the reaction. This was confirmed by an increase in size as the temperature was increased, with the exception of cobalt sulfide nanoparticles that decrease in size while temperature was increase. The XRD pattern showed different composition as the temperature was varied. Time of the reaction was found to affect the particles size of the nanoparticle. The sizes of the nanoparticles were increase as the time of the reaction was prolonged.

<p>Obtaining a greater understanding of photo-induced electron-transfer (PET) processes is key to synthesizing photovoltaic materials with enhanced efficiency. Gaining knowledge about the structure property relationship in photo-active donor-bridge-acceptor (<i>D-B-A</i>) dyads will help to optimize electronic and photoelectronic materials. Metal acetylide complexes have attracted increasing interest for their potential applications as building blocks for electronic and photoelectronic materials. Their unique υ(C≡C) (2000-2100 cm^-1) allows for selective excitation, making them an appealing target for attenuating PET processes across a metal acetylide backbone. The following topics will be discussed: i.) an overview of M(cyclam′) alkynyl chemistry, where M = Cr, Fe, Co, or Ni, with a focus on reactivity and spectroscopy, ii.) selective synthesis of dissymmetric species, utilizing a Co^III(cyclam) (1,4,8,11-tetraazacyclotetradecane) alkynyl bridge, iii) synthesis and characterization of metal alkynyl <i>D-B-A</i> dyads <i>trans- </i>[R'₂N-4-C₆H₄C₂-Co^III(cyclam)-C_n-NAP^R]⁺(n = 2 or 4), where the chromophore acceptor is NAP^iPr (<i>N</i>-isopropyl-1,8-napthalimide) and the putative donor is -C₆H₄-4-NR'₂ (R' = Me or Ph-4-OMe), iv.) design and synthesis of <i>D-B-A</i> derivatives, alter NAP^R (R = mesityl, methyl, 1-ethylpropyl, 2-ethylhexyl, or octyl) to tune reactivity and crystallinity, v.) electronic and spectroscopic influence the bridging center on <i>A</i>, and vi.) effect of η² coordination of MX₂ (MX₂ = CuCl₂ or Ag(NO₃)₂) to the alkyne bridge on electron transfer. </p>

>Magister Scientiae - MSc / Microfluidic paper based electrochemical sensing devices (μPEDs) provides a new way for point of care testing (POCT). μPEDs offer an inexpensive, portable, easy to use technology too monitor the environment and diagnose diseases, especially in developing countries in cases where there is not enough infrastructure and a limited trained medical and health professionals. The aim of this work is to develop a paper based electrode which can be further integrated into a microfluidic paper device to develop miniature point of care devices. Paper was used as a substrate for printing of the electrode because it is found everywhere, inexpensive and it is compatible with a number of chemical, biochemical and medical applications. Polyamic acid (PAA) was incorporated into commercial carbon ink and was used to print the working electrode. The first part of the study was conducted using the commercial screen printed carbon electrodes (SPCE) to study and understand the electrochemical behaviour of PAA. Cobalt nanoparticles and cobalt nanoparticles‐polyamic acid composites were electrochemically deposited onto SPCE. The modified electrodes were characterised using cyclic voltammetry. As synthesised polyamic acid were characterised using Scanning Electron Microscopy (SEM) to evaluate the morphology and chemical composition of polyamic acid. Transmission Electron Microscopy (TEM) was used to study the particle size and chemical composition of cobalt nanoparticles. Fourier Transform Infrared Spectroscopy (FTIR) was used to study the chemical nature of polyamic acid and cyclic voltammetry (CV) was used to study the electrochemical behaviour of polyamic acid and cobalt nanoparticle electrodes. The diffusion coefficients and formal potential of the electrodes were calculated. The modified and bare electrodes were also used to electrochemically detect Norfloxacin in an aqueous solution by CV and square wave voltammetry (SWV) and the analytical performance of the electrochemical systems are reported here. The obtained limit of detection for the bare SPCE was 3.7 x 10‐3 M and 14.7 x 10‐3 M for the PAA‐SPCE.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Phllosophy. / A disadvantage of the Fischer-Tropsch synthesis is that a broad product spectrum is obtained. Economic considerations however require an improvement in the optimization of the reaction to maximize the production of high value commercial products, in·particular, short chain olefins and high molecular weight hydrocarbons. [Abbreviated abstract. Open document to view full version] / AC2017

One of the environmental concerns associated with mining waste is the contamination of soil. This study addresses the decontamination of soil, particularly of Co and Ni using Berkheya coddii (B. coddii). B. coddii is a hyperaccumulater plant that is able to decontaminate Co and Ni from the contaminated land. The use of B. coddii to decontaminate soil or waste must be based on a cognizance of the complicated, integrated effects of pollutant sources and soil-plant variables. Phytoextraction pot trials using B. coddii were carried out under green house condition, with controlled watering. A contaminated metallurgical waste residue known as Rustenburg Base Mine Refineries waste (RBMR waste soil) collected from Rustenburg while a serpentine (native) soil (N soil) where B. coddii grows naturally was collected from Mpumalanga. The experiment involved the addition of sulfur doses to both soils in order to test whether acidification and higher sulfur availability could enhance the uptake of both Co and Ni by B. coddii. The results indicate that the addition of sulfur from 2.0 to 8.0 g per kilogram decreased pH in both substrates. RBMR waste soil pH was found to have decreased from 7.8 to 7.4 while the N soil pH was found to have decreased from 6.4 to 4.7. The reduction oxidation potential (redox potential) in both substrates was observed to have decreased along with the increase in sulfur dosage. The mean redox potential for RBMR waste soil was found to be 350 mV and 506 mV for the N soil after the addition of sulfur. Conductivity increased along with the increase in sulfur dosage in both substrates. The mean conductivity for the N soil was found to be 961 μS/cm while that of the RBMR waste soil was found to be 1453 μS/cm after the addition of sulfur. The decrease in soil pH was significant (p = 0.00115) in the N soil than RBMR waste soil. Despite the increase in sulfur dosage and decrease in soil pH in both substrates, B. coddii observed growing. Although it was evident that B. coddii is able to grow in the RBMR waste soil, it was observed that the RBMR waste soil limits the root depth of the B. coddii, reducing chances for the roots to penetrate into the ground especially when dry. The RBMR waste soil becomes more compacted than the N soil when dry. It is therefore crucial to ensure that there is enough moisture to allow for the B. coddii being able to survive effectively in the RBMR waste soil. B. coddii plant height in the RBMR waste soil after four months was observed to be in the range of 190 to 200 mm tall. This was found to be less than the height observed for the B. coddii planted in the N soil, which was in the range of 350 to 400 mm. Nonetheless, plants grown in both substrates were able to absorb Ni and Co into their tissues. More Co and Ni were found to have accumulated into the leaf tissues than in other parts of the plant. This could be an advantage since one would harvest only the leaf part or the canopy (shoots) and allow B. coddii to resprout in order to continue taking up more Co and Ni from the same waste substrate to remediation levels that could be stipulated by Government as desirable for the ecosystem and the protection of human health. Although the accumulated Ni and Co can be recovered from biomass, this alone might not provide sufficient economic justification for phytoextraction due to the low concentrations that could be recovered. B. coddii was found to absorb higher concentrations of Co and Ni from the N soil than from the RBMR waste soil. However, the results found in this study may not be conclusive. This could be due to many variables that could control metal uptake which were not investigated. These include mycorrhizal fungi and metal forms in the soil. Moreover, this study was performed in a green house and not in the outdoor environment. Ni is generally toxic to most plants, hyperaccumulators (i.e. B.coddii) contain elements that nullify the toxic effect of nickel, and in this case the accumulated nickel is bound to malate to form a harmless nickel complex which could be absorbed by the plants as nutrients.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 2014. / The Central African Copperbelt is located in the Lufilian Arc which straddles the border between Zambia and the Democratic Republic of Congo (DRC). Mineralisation of the cupriferous Arc is found in basal Neoproterozoic Katangan Supergroup sedimentary rocks, which in DRC are termed the Mines Series Subgroup. The Mines Series is divided into the dolomitic and carbonaceous GRAT, DStrat RSF, RSC, SD and CMN units. The composition of the units is homogeneous across the Lubumbashi district and potentially across the Katangan basin. This study focussed on the Kinsevere and Ruashi deposits in the Lubumbashi district, which are approximately 50 km apart. The study confirmed that relative eustatic sea level changes resulted in the non-deposition of the RSF and RSC stratigraphic units at Kinsevere. Sedimentation was followed by early pervasive potassic alteration and silicification at the diagenetic stage whilst a magnesian dolomitisation event resulted in alteration of potassic feldspars and recrystallisation of carbonates. Albitisation was veincontrolled and late-stage scapolitisation altered evaporitic nodules. Finally, haematisation by late iron-rich fluids circulating through the Roan Group strata resulted in oxidation of sulphides. The structural analysis of Kinsevere Central pit indicates E-W and N-S shortening whereas the Ruashi pit 1 deposit underwent NE-SW and N-S shortening. Initial shortening, associated with Kolwezian deformation (D1), resulted in the formation of NE-thrust folds and a primary set of joints. The Kolwezian deformation event (D2), reoriented the shortening direction from E-W to N-S, creating interference folds and possibly a second set of joints. The final phase in the structural evolution of the Kinsevere and Ruashi deposits was late-stage brittle deformation (faulting). Mineralisation was a multi-stage process. Disseminated chalcopyrite and carrollite were deposited from formation waters during diagenesis in a stable basin environment. Chalcopyrite, carrollite, chalcocite and bornite are predominantly located at the base of the DStrat, whereas chalcopyrite and pyrite dominate the stratigraphically higher portions of the deposits. Hypogene vein mineralisation began at the syn- to late- orogenic stage with carrollite and chalcopyrite in beddingparallel veins. Possible changes in the compression direction created the perpendicularly oriented veins that host chalcopyrite, carrollite, bornite, covellite, digenite and chalcocite. Finally a late stage of chalcopyrite and pyrite deposition occurred in and around the evaporites, indicating a strong correlation between mineralisation, evaporites and scapolitisation. iii Near-surface supergene alteration of hypogene sulphide ores, resulted in Cu-Co carbonates and oxides, such as malachite, azurite, cobaltiferous malachite, chrysocolla, kolwezite and sphaerocobaltite being deposited in vugs and pore spaces above the meteoric water line. Faulted and brecciated zones tend to have deeper supergene alteration. Between the sulphide facies at depth and the supergene oxide facies at surface is a transition zone which marks the depth to which oxidation has penetrated. Sulphur isotope analysis from the Kinsevere and Ruashi deposits suggests a sulphur contribution from a continental Red-Bed sedimentary source and from an evaporitic source.

O sistema cobalto(II)/tiocianato foi estudado em meio aquoso com o objetivo de se obter dados reais das constantes de formação globais dos complexos. Foram utilizados os métodos potenciométrico indireto e espectrofotométrico em meio de força iônica 2,0 M (NaCl04) a 25,0 &#177; O,l&#176;C. O sistema cádmio(II)/tiocianato foi utilizado como indicador no método potenciométrico indireto com o eletrodo de gota pendente de amálgama de cádmio. As seguintes constantes de equilíbrio foram obtidas para os complexos formados entre o cádmio e o tiocianato, a 25&#176;C e força iônica 2,0 M (NaCl04): &#946;1 = 21,51 &#177; 0,09 M-1, &#946;2 = 123,3 &#177; 1,2 M-2, &#946;3 = 129,9 &#177; 3,1 M-3 e &#946;4 = 173,5 &#177; 1,2 M-4. Valores do número médio de ligantes, &#241;, foram obtidos para várias concentrações de tiocianato, até 2,0 M, pela adição de Co(Cl04)2 (0,1 M) à solução contendo cádmio(II) e tiocianato. A integração da curva de formação e o tratamento das funções de Leden, pelo método dos mínimos quadrados desenvolvido, levou às seguintes constantes de formação globais para o sistema cobalto(II)/tiocianato: &#946;1 = 11,0 M-1, &#946;2 = 22,0 M-2, &#946;3 = 11,2 M-3 e &#946;4 = 1,63 M-4. Um estudo do sistema zinco(II)/tiocianato foi realizado com o objetivo de avaliar o método potenciométrico indireto, visto que esse sistema foi anteriormente estudado por um método direto confiável. A curva de formação obtida apresenta uma boa concordância até &#241; = 1. Depois desse ponto um desvio negativo é observado, com relação a curva obtida pelo método direto, devido à causas não bem compreendidas. Várias curvas de absortividade molar média, &#949; vs. concentração analítica de ligante foram obtidas em três comprimentos de onda (515, 590 e 615 nm) em tres concentraçoes de cobalto(II) diferentes: 0,01, 0,05 e 0,1 M. A análise com base no método das soluções correspondentes permitiu obter a curva &#241; vs. concentração de tiocianato livre, com as seguintes constantes de equilíbrio: &#946;1 = 6,9 M-1, &#946;2 = 28,9 M-2, &#946;3 = 12,1 M-3</SUP e &#946;>SUB>4 = 1,30 M-4. Ambos os métodos revelaram uma tendência à formaçao de duas espécies e uma diminuição acentuada na afinidade com o ligante para formar os complexos &#8204;Co(SCN)3&#8204;- e &#8204;Co(SCN)4&#8204;2-. Uma relação linear entre o número médio de ligantes e a absortividade molar média foi observado em 515 nm, o que permitiu obter o valor de &#949;4. Entretanto, em 590 e 615 nm, observou-se somente uma linearidade entre &#949; e o grau de formação calculado, &#945;4, correspondente a espécie &#8204;Co(SCN)4&#8204;2-, com uma intersecção muito próxima da origem. Isto é uma evidência que &#8204;Co(SCN)4&#8204;2- existe virtualmente como uma espécie tetraédrica com absortividade molar relativamente alta. Foram obtidos os seguintes valores de &#949;n individuais: a) &#949;o = 4,31, &#949;1 = 22,6, &#949;2 = 26,3, &#949;3 = 42,8 e &#949;4 = 50,3 cm-1.M-1 em 515 nm; b) &#949;o = 0,29, &#949;1 = 1,3, &#949;2 = 3,2, &#949;3 = 3,9 e &#949;4 = 215 cm-1.M-1 em 590 nm; c) &#949;o = 0,20, &#949;1 = 0,90, &#949;2 1,5, &#949;3 = 2,2 e &#949;4 = 294 cm-1.M-1 em 615 nm. Especulações com os dados sugerem que somente 1% das espécies tetraédricas estão em equilíbrio com as espécies octaédricas correspondentes com 1,2 e 3 tiocianatos coordenados. Com o emprego de um computador foi realizado um estudo efetuando uma simulação dos métooos espectrofotométricos da razão molar e das variações contínuas. As Simulações, com sistemas reais e hipotéticos, foram muito úteis para mostrar as conclusões ambíguas que podem ser obtidas, a partir de dados experimentais, para se estimar o número de espécies complexas. / The cobalt (II) /thiocyanate system in aqueous medium was studied with the purpose to obtain reliables data of overall stepwise formation constants to complexes. An indirect potentiometric method and a spectrophotometric one were used at 2,0 M ionic strength (NaCl04), at 25,0 &#177; O,l&#176;oC. The cadmium(II)/thiocyanate system was used as indicator in the indirect potentiometric method with hanging drop electrode with cadmium amalgam. The following equilibrium constants of the cadmium(II)/thiocyanate complexes were obtained at 25&#176;C and 2,O M ionic strenght (NaCl04: &#946;1 = 21.51 &#177; 0.09 M-1, &#946;2 = 123.3 &#177; 1,2 M-2, &#946;3 = 129.9 &#177; 3.1 M-3 and &#946;4 = 173.5 &#177; 1.2 M-4. Average 1igands number data, &#241;, were obtained for several thiocyanate concentrations, up to 2 M, by adding Co(Cl04)2 (0.1 M) to the working solution of cadmium (II)/thiocyanate. The integration of the formation curve and treatment of Leden\'s functions by a self developed least square method, lead to the following overall formation constants of the cobalt(II)/thiocyanate system: &#946;1 = 11.0 M-1, &#946;2 = 22.0 M-2, &#946;3 = 11.2 M-3 and &#946;4 = 1.63 M-4. A study of the zinc(II)/thiocyanate system was performed with the purpose to check the indirect potentiometric method inasmuch as this system was formerly studied by a re1iable direct method. The formation curve presented a good agreement until the average ligand number 1. After this point a negative desviation is observed with regard the direct method by not well understood causes. Severa1 curves of average molar absorbtivity, &#949; vs the analytical ligand concentration were obtained at three wave lengths (515, 590 and 615 nm) and three differents cobalt(II) cation concentrations: 0.01, 0.05 and 0.1 M. The analysis on base of corresponding solutions permited to obtain &#241; vs free thiocyanate ion concentrations, with the following equilibrium constants: &#946;1 = 6.9 M-1, &#946;2 = 28.9 M-2, &#946;3 = 12.1 M-3</SUP e &#946; = 1.30 M-4. Both methods revealed a tendency to form two species and a marked decrease in affinity with the 1igand to form &#8204;Co(SCN)3&#8204;<SUP- and &#8204;Co(SCN)4&#8204;2-. A linear relationship between calculated &#241; and &#949; was observed at 515 nm and this permited to obtain &#949;4. However, at 590 and 615 nm linearity of &#949; was achieved only for calculated formation degree, &#945;4, corresponding to specie &#8204;Co(SCN)4&#8204;2-, with an intercept very close to the origin. This is an evidence that the &#8204;CoO(SCN)4&#8204;2- exists virtually as tetrahedra1 specie with relative1y high molar absorbtivity. The fol1owing individual &#949;n were obtained: a) &#949;0 = 4.31, &#949;1 = 22.6, &#949;2 = 26.3, &#949;3 = 42.8 and &#949;4 = 50.3 cm-1.M-1 at 515 nm; b) &#949;0 = 0.29, &#949;1 = 1.3, &#949;2 = 3.2, &#949;3 3.9 and &#949;4 = 215 cm-1.M-1 at 590 nm; c) &#949;0 = 0.20, &#949;1 = 0.90, &#949;2 1.5, &#949;3 = 2.2 and &#949;4 = 294 cm-1 .m-1 at 615 nm. Speculations with the data suggest that on1y 1% of tetrahedral species are in equi1ibrium with the corresponding octahedral ones with 1, 2 and 3 thiocyanate 1igands. An extension of the study was a computer assisted simulation of the molar ratio spectrophotometric titration as well as the continuous variations method. This simulation study with real and hypothetica1 systems,was very usefu1l to show how ambiguous can be the conclusions, taken from experimental data,when the number of species are to be estimated.

Catalisadores de Ni suportados em carbono foram sintetizados por diferentes rotas e avaliados frente a oxidação de glicerol em meio alcalino. O método de impregnação química, seguido de um tratamento térmico em uma atmosfera redutora de H2 por 2 horas, foi escolhido por fornecer um material mais ativo, e através deste método materiais como CoNi, FeNi, FeCoNi contendo 20% de metal foram sintetizados. As amostras foram caracterizadas por Análise Termogravimétrica (TGA-DTA) e Difração de Raios X (XRD) para verificar a quantidade de metal e tamanho de cristalito médio, respectivamente. Ensaios eletroquímicos de Voltametria Cíclica (CV) foram realizados para avaliar a atividade eletroquímica dos catalisadores frente a reação de oxidação do glicerol. Os resultados demonstram que a espécie oxihidróxido de níquel &beta;-NiOOH foi a espécie catalítica ativa frente a oxidação de glicerol em meio alcalino. Como a formação de oxihidróxidos de cobalto e ferro ocorrem em potenciais mais baixos que o níquel, estes elementos adicionaram mudanças no perfil observado para o Ni/C. Estudos em condições controladas também foram feitos através de Voltametria Cíclica. O processo de oxidação do glicerol foi influenciado pela velocidade de varredura, temperatura e concentração do NaOH e glicerol. A relação linear entre a corrente de pico e a raiz quadrada da velocidade de varredura corresponde a um processo controlado por difusão. Verificou-se que ambos os Ipico e Epico são fortemente dependentes da concentração do glicerol. Em um potencial selecionado, experimentos de cronoamperometria foram realizados e os produtos de reação analisados por cromatografia líquida de alta eficiência (HPLC). A conversão do glicerol bem como a seletividade dos produtos formados depende da composição do catalisador. A distribuição de produtos foi correlacionada com os dados de espectroscopia de infravermelho (FTIR), os quais suportam o mecanismo de reação proposto. / Carbon supported nickel nanomaterials were synthesized by different routes and evaluated toward the oxidative transformation of glycerol in alkaline medium. The impregnation method, followed by heat-treatment in reducing H2 atmosphere for 2 hours, was chosen by providing a more active material. This method was used to prepare catalysts with metal loadings of 20 wt. %, such as CoNi/C, FeNi/C and FeCoNi/C. Physical characterizations of the materials were performed by using Thermogravimetric Analysis-Differential Thermal Analysis (TGA-DTA) and X-Ray Diffraction (XRD) to determine their metallic load and the crystallite size, respectively. Cyclic voltammetry was mainly used to evaluate the electrochemical activity of the catalysts for glycerol oxidation reaction. The results demonstrated that nickel oxyhydroxide, &beta;-NiOOH, is the active catalytic specie for the glycerol oxidation reaction in alkaline medium. Since the formation of cobalt and iron oxy-hydroxides occurs at lower potentials than those of nickel, amounts of cobalt and iron were added to modify the Ni material. Studies under several well defined experimental conditions were performed by Cyclic Voltammetry. The process of glycerol oxidation was influenced by the scan rate, temperature, glycerol and NaOH concentration. The linear relationship between the peak current density and square root of scan rate corresponds to a diffusion-controlled process for glycerol oxidation on Ni/C. It was found that both the Ipeak and Epeak are strongly depending on the glycerol concentration. In a selected potential chronoamperometry experiments were carried out and the glycerol oxidation products on the Ni-based anodes were analyzed by High-Performance Liquid Chromatography (HPLC). The glycerol conversion depends on the catalyst composition and the distribution. The products were correlated with those identified by infrared reflectance spectroscopy, which supported the simplified mechanism proposed.

Este trabalho tem por objetivo uma revisão analítica da determinação de cobalto no sangue e/ou urina para fins de monitorização biológica. A proposta de alternativas viáveis para tal metodologia está fundamentada num estudo crítico dos métodos estudados, associados a um Sistema da Qualidade. Os efeitos tóxicos observados nas exposições a diferentes compostos de cobalto, a relação dose-efeito e dose-resposta, bem como os valores de referência para a população sadia e não ocupacionalmente exposta, levou a ACGIH (American Conference of Governmental Industrial Hygienists) dos Estados Unidos a propor desde 1995 a utilização de um BEI (Biological Exposure Indice) para este tipo de exposição. Apesar de o Brasil ainda não ter incluído o cobalto no Programa de Controle Médico de Saúde Ocupacional da Norma Regulamentadora-7, a utilização de um indicador biológico pode constituir-se numa necessidade devido a estudos toxicológicos e analíticos revistos e relatados na literatura. / This work has the purpose of an analytical review of blood and urine\'s cobalt quantification in order to be used in biological monitoring. A proposal of alternatives and feasible methodologies that habe been found are based upon the crutical study associated with a Quality system. The toxic effects observed in exposure to different cobalt compounds, the dose-effect relationship and dose-response, and the reference values in health and non-exposed population, have brought ACGIH (American Conference of Governmental Industrial Hygienists) of the United States to propose since 1995 a BEI (Biological Exposure Indice) to this kind of exposure. Although Brazil has not included cobalt in the PCMSO (Programa de Controle Médico de Saúde Ocupacional), the use of biological indicator can become a necessity due to toxicological and analytical studies here reviewed and reported in the literature