Electron paramagnetic resonance of Ni(II) doped tris(ethylenediamine)zinc(II) dinitrate

Variable temperature electron paramagnetic resonance spectra of tris(ethylenediamine)zinc(II) dinitrate single crystals doped with NI(II) have been measured. The host crystal undergoes a trigonal to monoclinic phase transition at 146 K. Above the transition temperature the zero field splitting tensor is axially symmetric with D = -0.831 cm(-1) and below it becomes rhombic with D = -0.785 cm(-1), E = -0.088 cm(-1). The low temperature spectrum is characterised by the pattern repeating every 60 degrees when the crystal is rotated about the high temperature c axis. The analysis shows that the Zn(II) site retains a C-2 symmetry axis and that the distortion away from the D-3 site symmetry observed for high temperatures is small, the principal axes being tilted by 2.6 degrees. This implies that the phase transition involves the flipping of the C-C backbone in one of the ethylenediamine ligands of the complex, resulting in a A delta delta delta to Lambda delta delta lambda type conformational change.

Effects of oxide promoters on metal dispersion and metal-support interactions in Ni catalysts supported on activated carbon

Various oxide-promoted Ni catalysts supported on activated carbon were prepared, and the effect of promoters on the surface structure and properties of Ni catalysts was studied. Physical adsorption (Na adsorption), thermogravimetric analysis (TGA), temperature-programmed desorption (TPD), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalysts. It is found that nickel is fairly uniformly distributed in the pores of the carbon support. Addition of promoters produces a more homogeneous distribution of nickel ion in carbon. However, distributions of promoters in the pores are varying. Addition of promoters increases the dispersion of nickel in carbon. Promoters also change the interaction between the carbon and Ni, resulting in significantly different behaviors of catalysts under various environments. CaO and MgO promoters improve the reactivity of nickel catalysts with O-2 but retard the interaction between nickel oxide and carbon. La2O3 shows some inhibiting effect on the interactions between nickel oxide and oxygen as well as carbon.

Structural definition of the low-temperature phase transition of tris(ethane-1,2-diamine)zinc(II) dinitrate

The 93 K X-ray crystal structure of tris(ethane-1,2-diamine)zinc(II) dinitrate is reported. As predicted by the spectroscopic studies of other workers, there is a reversible phase transition of the structure at low temperature. We have determined this temperature to be 143 K. The structure at this temperature and below resembles that of the room temperature structure, except the crystallographic D-3 symmetry of the complex cation (296 K) is lowered to C-2 ( below 144 K) by subtle changes in cation-anion hydrogen bonding. No change in the conformation of the cation or its bond lengths and angles was found.

Desenvolvimento de metodologia para determina����o de Co, Cr, Fe, Mn, Ni, Se e V em amostras de ��gua produzida da ind��stria do petr��leo atrav��s da t��cnica ICP OES utilizando digest��o por micro-ondas

O descarte ou reutiliza����o da ��gua produzida da ind��stria do petr��leo �� dif��cil por causa dos impactos ambientais causados devido �� presen��a de alta salinidade e componentes t��xicos, ou pelo risco de obstru����o nas colunas de produ����o devido �� forma����o de incrusta����es que causam redu����o na produ����o de petr��leo e enormes perdas no processo de extra����o. Assim, o conhecimento da composi����o qu��mica da ��gua produzida �� muito importante. O m��todo proposto por este trabalho visa a determina����o de elementos tra��o (Co, Cr, Fe, Mn, Ni, Se e V) em amostras de ��gua produzida de petr��leo por espectrometria de emiss��o ��ptica com plasma indutivamente acoplado (ICP OES) utilizando a digest��o ��cida assistida por micro-ondas para o preparo das amostras (15 g de amostra e 2 mL de HNO3 concentrado). A curva anal��tica constru��da em HNO3 2% v v-1 foi adotada para o m��todo ap��s verificar que n��o �� necess��rio o uso de salinidade para equipara����o de matriz. Para o elemento Ni, n��o h�� necessidade do uso de padr��o interno, para os elementos Co, Cr, Fe, Mn e V os melhores resultados foram obtidos usando Sc como padr��o interno. Para o elemento Se �� recomendado o uso de Y como padr��o interno. Os limites de detec����o obtidos foram Co 0,67, Cr 1,2, Fe 2,3, Mn 0,49, Ni 1,9, Se 3,7 e V 5,5 ��g L-1; e os limites de quantifica����o foram Co 2,2, Cr 4,0, Fe 7,7, Mn 1,6, Ni 6,5, Se 12,4 e V 18,3 ��g L-1. A exatid��o do procedimento foi verificada atrav��s de testes de recupera����o em dois n��veis de concentra����o (40 e 80 ��g L-1) e an��lise dos materiais certificados de refer��ncia de ��gua estuarina SLEW-2 e de ��gua do mar NASS-5. Bons valores de recupera����o foram obtidos e n��o houve diferen��a significativa (95% de confian��a) entre os resultados obtidos e os valores certificados dos materiais de refer��ncia.

S��ntese de precursores de ligando do tipo 5-aril-2-iminopirrole e sua aplica����o na prepara����o de complexos de n��quel

O trabalho apresentado nesta disserta����o centrou-se na s��ntese e caracteriza����o de novos precursores de ligandos do tipo iminopirrolilo, usando como mol��cula de partida a 2-fenil-1-pirrolina. Estes ligandos foram posteriormente usados em tentativas de s��ntese de complexos de Ni(II). Em termos experimentais, este trabalho foi iniciado pelo estudo da s��ntese do 2- fenilpirrole a partir da 2-fenil-1-pirrolina, na tentativa de obter um produto puro, atrav��s de um processo competitivo em termos de efici��ncia e custo em rela����o aos descritos anteriormente pelo grupo de trabalho e pela literatura. Numa segunda fase, estudou-se a s��ntese de dois novos precursores de ligandos iminopirrolilo e, por fim, tentou-se sintetizar dois novos complexos de Ni(II) com base nos referidos ligandos, com vista ao seu uso como catalisadores de polimeriza����o de olefinas. O Cap��tulo 1 apresenta uma introdu����o ao desenvolvimento dos complexos de metais de transi����o como catalisadores de polimeriza����o de olefinas, dando-se ��nfase especial aos catalisadores de n��quel contendo ligandos ��-diimina, fenoxi-imina, anilitropona e iminopirrolilo. Focam-se ainda os m��todos de s��ntese de pirroles substitu��dos na posi����o 2, devido �� import��ncia que apresentam para os objectivos deste trabalho. No Cap��tulo 2 estuda-se a reac����o de desidrogena����o catal��tica de 2-fenil-1-pirrolina a 2-fenilpirrole, catalisada por pal��dio suportado em carv��o ou alumina activados. Posteriormente descreve-se a reac����o de formila����o do 2-fenilpirrole que origina o novo composto 5-fenil-2-formilpirrole. Este �� transformado em novos precursores de ligando do tipo iminopirrolilo, mais especificamente 2-arilimino-5-fenilpirrolilo, por condensa����o com a dimetil- e diisopropilanilina. No Cap��tulo 3 discute-se as tentativas de s��ntese de novos complexos de Ni(II) contendo os ligandos iminopirrolilo sintetizados, a partir da reac����o dos correspondentes sais de s��dio com o complexo [NiCl(Ph)(PPh3)2]. O Cap��tulo 4 apresenta as conclus��es gerais e o Cap��tulo 5 os detalhes experimentais, as s��nteses e as caracteriza����es dos ligandos e dos complexos.

Formation of oriented nickel aggregates in rutile single crystals by Ni implantation

The magnetic and electrical properties of Ni implanted single crystalline TiO2 rutile were studied for nominal implanted fluences between 0.5 x 10(17) cm(-2) and 2.0 x 10(17) cm(-2) with 150 keV energy, corresponding to maximum atomic concentrations between 9 at% and 27 at% at 65 nm depth, in order to study the formation of metallic oriented aggregates. The results indicate that the as implanted crystals exhibit superparamagnetic behavior for the two higher fluences, which is attributed to the formation of nanosized nickel clusters with an average size related with the implanted concentration, while only paramagnetic behavior is observed for the lowest fluence. Annealing at 1073 K induces the aggregation of the implanted nickel and enhances the magnetization in all samples. The associated anisotropic behavior indicates preferred orientations of the nickel aggregates in the rutile lattice consistent with Rutherford backscattering spectrometry-channelling results. Electrical conductivity displays anisotropic behavior but no magnetoresistive effects were detected. (C) 2013 Elsevier B.V. All rights reserved.

Survey of trace elements (Al, As, Cd, Cr, Co, Hg, Mn, Ni, Pb, Se, and Si) in retail samples of flavoured and bottled waters

Concentrations of eleven trace elements (Al, As, Cd, Cr, Co, Hg, Mn, Ni, Pb, Se, and Si) were measured in 39 (natural and flavoured) water samples. Determinations were performed using graphite furnace electrothermetry for almost all elements (Al, As, Cd, Cr, Co, Mn, Ni, Pb, and Si). For Se determination hydride generation was used, and cold vapour generation for Hg. These techniques were coupled to atomic absorption spectrophotometry. The trace element content of still or sparkling natural waters changed from brand to brand. Significant differences between natural still and natural sparkling waters (p<0.001) were only apparent for Mn. The Mann���Whitney U-test was used to search for significant differences between flavoured and natural waters. The concentration of each element was compared with the presence of flavours, preservatives, acidifying agents, fruit juice and/or sweeteners, according to the labelled composition. It was shown that flavoured waters generally increase the trace element content. The addition of preservatives and acidifying regulators had a significant influence on Mn, Co, As and Si contents (p<0.05). Fruit juice can also be correlated to the increase of Co and As. Sweeteners did not provide any significant difference in Mn, Co, Se and Si content.

Growth of (Perylene)(2) [PD(MNT)(2)] crystals

The conditions for [pd(mnt)(2)]he growth of [pd(mnt)(2)]Perylene) [pd(mnt)(2)] [Pd(mnt) [pd(mnt)(2)]] crystals either by chemical oxidation and electrochemical routes are [pd(mnt)(2)]escribed. The electrocrystallisation is limited by close [pd(mnt)(2)]roximity of [pd(mnt)(2)]he oxidation [pd(mnt)(2)]otentials of [pd(mnt)(2)]he [pd(mnt)(2)]erylene [pd(mnt)(2)]onor and [Pd(mnt) [pd(mnt)(2)]] - anion, and [pd(mnt)(2)]epending on [pd(mnt)(2)]he experimental conditions [pd(mnt)(2)]ifferent [pd(mnt)(2)]orphologies can be obtained. [pd(mnt)(2)]Per) [pd(mnt)(2)] [Pd(mnt) [pd(mnt)(2)]] crystals obtained by elecrocrystallisation were found [pd(mnt)(2)]o be [pd(mnt)(2)]ainly of [pd(mnt)(2)]he ��-polymorph with [pd(mnt)(2)]roperties comparable [pd(mnt)(2)]o [pd(mnt)(2)]he Cu, Ni and Pt analogues [pd(mnt)(2)]reviously [pd(mnt)(2)]escribed at variance with [pd(mnt)(2)]hose obtained by chemical oxidation which are [pd(mnt)(2)]ainly of [pd(mnt)(2)]he ��-polymorph.

One-step preparation of optically transparent Ni-Fe oxide film electrocatalyst for oxygen evolution reaction

Optically transparent cocatalyst film materials is very desirable for improved photoelectrochemical (PEC)oxygen evolution reaction (OER) over light harvesting photoelectrodes which require the exciting light to irradiate through the cocatalyst side, i.e., front-side illumination. In view of the reaction overpotential at electrode/electrolyte interface, the OER electrocatalysts have been extensively used as cocatalysts for PEC water oxidation on photoanode. In this work, the feasibility of a one-step fabrication of the transparent thin film catalyst for efficient electrochemical OER is investigated. The Ni-Fe bimetal oxide films, 200 nm in thickness, are used for study. Using a reactive magnetron co-sputtering technique, transparent(> 50% in wavelength range 500-2000 nm) Ni-Fe oxide films with high electrocatalytic activities were successfully prepared at room temperature. Upon optimization, the as-prepared bimetal oxide film with atomic ratio of Fe/Ni = 3:7 demonstrates the lowest overpotential for the OER in aqueous KOH solution, as low as 329 mV at current density of 2 mA cm 2, which is 135 and 108 mV lower than that of as-sputtered FeOx and NiOx thin films, respectively. It appears that this fabrication strategy is very promising to deposit optically transparent cocatalyst films on photoabsorbers for efficient PEC water splitting.

Fitorremedia����o de ��guas residuais contaminadas com Cd e Ni por tr��s gen��tipos de Miscanthus

Fitorremedia����o, o uso de vegeta����o para a descontamina����o de diferentes matrizes, �� uma estrat��gia de baixo custo e tem sido apontada como uma metodologia pass��vel de atenuar e estabilizar ��guas residuais. Neste contexto, este estudo tem como principal objectivo avaliar a capacidade fitorremediadora de tr��s gen��tipos de Miscanthus (duas esp��cies - Miscanthus sinensis e Miscanthus floridulus, e um h��brido ��� Miscanthus x giganteus) a ��guas residuais contaminadas com c��dmio e n��quel (2,0 mg Ni/L e 0,2 mg Cd/L). Os resultados demonstraram que a irriga����o com ��guas residuais contaminadas com Cd e Ni n��o afecta a produtividade dos tr��s gen��tipos de Miscanthus em estudo e que o M. x giganteus e o M. floridulus registaram produtividades mais elevadas que o M. sinensis. Contudo, o M. x giganteus, demonstrou tendencialmente uma redu����o da sua produ����o com a contamina����o de Cd. A biomassa obtida dos ensaios irrigados com ��guas residuais contaminadas apresentaram maior teor de Cd e Ni, do que a biomassa recolhida dos ensaios Controlo. O sistema Miscanthus-solo registou valores de remo����o de Cd de 100%, e de Ni de 96-100%, no caso do M. x giganteus e do M. sinensis. O M. floridulus, contudo, demonstrou menos potencial de fitorremedia����o no que diz respeito �� remo����o de Ni das ��guas residuais: apenas 58% de Ni foi removido pelo sistema ���biofiltrador���. Ainda assim, verificou-se a acumula����o de Cd e Ni no perfil superior do solo devido �� irriga����o com as ��guas residuais contaminadas, o que demonstra a necessidade de controlo desta t��cnica de modo a prevenir poss��veis efeitos negativos no ambiente.

On the influences of the El Ni&#241;o, La ni&#241;a and Atlantic Dipole Paterni on the Amazonian Rainfall during 1960-1998

The influence of the large-scale climatic variability dominant modes in the Pacific and in the Atlantic on Amazonian rainfall is investigated. The composite technique of the Amazon precipitation anomalies is used in this work. The basis years for these composites arc those in the period 1960-1998 with occurrences of extremes in the Southern Oscillation (El Ni&#241;o or La Ni&#241;a) and the north/south warm (or cold) sea surface temperature (SST) anomalies dipole pattern in the tropical Atlantic. Warm (cold) dipole means positive (negative) anomalies in the tropical North Atlantic and negative (positive) anomalies in the tropical South Atlantic. Austral summer and autumn composites for extremes in the Southern Oscillation (El Ni&#241;o or La Ni&#241;a) and independently for north/south dipole pattern (warm or cold) of the SST anomalies in the tropical Atlantic present values (magnitude and sign) consistent with those found in previous works on the relationship between Amazon rainfall variations and the SST anomalies in the tropical Pacific and Atlantic. However, austral summer and autumn composites for the years with simultaneous occurrences of El Ni&#241;o and warm north/south dipole of the SST anomalies in the tropical Atlantic show negative precipitation anomalies extending eastward over the center-eastern Amazon. This result indicates the important role played by the tropical Atlantic in the Amazon anomalous rainfall distribution.

A systematic study of the structural and magnetic properties of Mn-, Co-, and Ni-Doped Colloidal Fe3O4 nanoparticles

A series of colloidal MxFe3-xO4 (M = Mn, Co, Ni; x = 0���1) nanoparticles with diameters ranging from 6.8 to 11.6 nm was synthesized by hydrothermal reaction in aqueous medium at low temperature (200 ��C). Energy-dispersive X-ray microa-nalysis and inductively coupled plasma spectrometry confirms that the actual elemental compositions agree well with the nominal ones. The structural properties of obtained nanoparticles were investigated by using powder X-ray diffraction, Raman scattering, M��ssbauer spectroscopy, and electron microscopy. The results demonstrate that our synthesis technique leads to the formation of chemically uniform single-phase solid solution nanoparticles with cubic spinel structure, confirming the intrinsic doping. Magnetic studies showed that, in comparison to Fe3O4, the saturation magnetization of MxFe3-xO4 (M = Mn, Ni) decreases with increasing dopant concentration, while Co-doped samples showed similar saturation magnetizations. On other hand, whereas Mn- and Ni-doped nanoparticles exhibits superparamagnetic behavior at room temperature, ferromagnetism emerges for CoxFe3-xO4 nanoparticles, which can be tuned by the level of Co doping.

The automorphism group of a free-by-cyclic group in rank 2

Vegeu el resum a l'inici del document del fitxer adjunt

Contractions in the 2-wasserstein lenght space and thermalization of granular media

An algebraic decay rate is derived which bounds the time required for velocities to equilibrate in a spatially homogeneous flow-through model representing the continuum limit of a gas of particles interacting through slightly inelastic collisions. This rate is obtained by reformulating the dynamical problem as the gradient flow of a convex energy on an infinite-dimensional manifold. An abstract theory is developed for gradient flows in length spaces, which shows how degenerate convexity (or even non-convexity) | if uniformly controlled | will quantify contractivity (limit expansivity) of the flow.

Periodic orbits near a heteroclinic loop formed by one dimensional orbit and a 2-dimensional manifold: application to the charged collinear 3-body problem

The paper is devoted to the study of a type of differential systems which appear usually in the study of some Hamiltonian systems with 2 degrees of freedom. We prove the existence of infinitely many periodic orbits on each negative energy level. All these periodic orbits pass near the total collision. Finally we apply these results to study the existence of periodic orbits in the charged collinear 3���body problem.