Marcos Gelesky | FURG - Universidade Federal do Rio Grande (original) (raw)

Papers by Marcos Gelesky

Journal of the American Chemical Society, Jan 6, 2005

Stable Pd(0) and Rh(0) nanoparticles with small and narrow size distribution can be prepared from... more Stable Pd(0) and Rh(0) nanoparticles with small and narrow size distribution can be prepared from relative large and agglomerated transition-metal particles dispersed in 1-n-butyl-3methylimidazolium hexafluorophosphate ionic liquid by simple laser irradiation. The laser irradiation is a complementary method for the generation of stable metal colloids in ionic liquids and also for the regeneration of small-size nanoparticles that may result from their agglomeration after different applications.

Biomacromolecules, Jan 13, 2009

Transition metal-containing membrane films of 10, 20, and 40 μm thickness were obtained by the co... more Transition metal-containing membrane films of 10, 20, and 40 μm thickness were obtained by the combination of irregularly shaped nanoparticles with monomodal size distributions of 4.8 ± 1.1 nm (Rh(0)) and 3.0 ± 0.4 nm (Pt(0)) dispersed in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (BMI·(NTf)(2)) with a syrup of cellulose acetate (CA) in acetone. The Rh(0) and Pt(0) metal concentration increased proportionally with increases in film thickness up to 20 μm, and then the material became metal saturated. The presence of small and stable Rh(0) or Pt(0) nanoparticles induced an augmentation in the CA/IL film surface areas. The augmentation of the IL content resulted in an increase of elasticity and decrease in tenacity and toughness, whereas the stress at break was not influenced. The introduction of IL probably causes an increase in the separation between the cellulose macromolecules that results in a higher flexibility, lower viscosity, and be...

Dalton transactions (Cambridge, England : 2003), Jan 21, 2007

Rh(0) nanoparticles (ca. 4 nm) dispersed in an ionic liquid (1-n-butyl-3-methylimidazolium tetraf... more Rh(0) nanoparticles (ca. 4 nm) dispersed in an ionic liquid (1-n-butyl-3-methylimidazolium tetrafluoroborate) were immobilized within a silica network, prepared by the sol-gel method. The effect of the sol-gel catalyst (acid or base) on the encapsulated ionic liquid and Rh(0) content, on the silica morphology and texture, and on the catalyst alkene hydrogenation activity was investigated. The Rh(0) content in the resulting xerogels (ca. 0.1 wt% Rh/SiO(2)) was shown to be independent of the sol-gel process. However, acidic conditions afforded higher contents of encapsulated ionic liquid and xerogels with larger pore diameters, which in turn might be responsible for the higher catalyst activity in hydrogenation of the alkenes.

Advances in Optical Sciences Congress, 2009

The Journal of Physical Chemistry C, 2008

Physical Chemistry Chemical Physics, 2010

Hydrogen reduction of cationic or neutral Ir(i) compounds, namely [Ir(COD)(2)]BF(4) and [Ir(COD)C... more Hydrogen reduction of cationic or neutral Ir(i) compounds, namely [Ir(COD)(2)]BF(4) and [Ir(COD)Cl](2)respectively. in the ionic liquid (IL) 1-alkyl-3-methylimidazolium tetrafluoroborate affords either irregularly sized spherical (from 1.9 +/- 0.4 to 3.6 +/- 0.9 nm) or worm-like metal nanoparticles, depending on the nature of the imidazolium alkyl group and the type of iridium precursor. The ionic Ir(i) precursor tends to be dissolved and concentrated on the IL polar domains (populated by the imidazolium nucleus and tetrafluoroborate anions) while the neutral precursor dissolves preferentially in the non-polar region of the IL (populated mainly by N-alkyl side chains). The size, or volume, of the nano-region where the Ir(i) precursor is dissolved and reduced, determines the size and, probably, the shape of the formed nanoparticles. The HR-TEM image shows that the Ir(0) with worm-like shape are polycrystalline and formed from aggregation individual &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;spherical&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; nanoparticles of around 1.9 nm. The catalytic activity of Ir(0) NPs on the hydrogenation of cyclohexene (0.01 mol L(-1) of Ir atoms in IL, 75 degrees C, 8 bar of H(2), 500 rpm stirring, 1/1000 Ir(0)/cyclohexene ratio) is always greater in C(1)C(10)I.BF(4) than C(1)C(4)I.BF(4), regardless of the nature of Ir(i) precursor. Moreover, the cyclohexene hydrogenations performed with Ir(0) nanocatalysts made from ionic Ir(i) precursor are approximately twice faster than those NPs obtained from the neutral Ir(i) precursor, in the same IL.

Journal of the Brazilian Chemical Society, 2008

Uma série de líquidos iônicos 1-alquil éter (e 1-alquil)-3-metilimidazólio 2-4 ([C x O y MIm] + [... more Uma série de líquidos iônicos 1-alquil éter (e 1-alquil)-3-metilimidazólio 2-4 ([C x O y MIm] + [Ânion] ou [C x MIm] + [Ânion] , onde MIm = 3-metilimidazólio; C x O y = 1-alquil éter, C 7 O 3 = -(CH 2 ) 2 O(CH 2 ) 2 O(CH 2 ) 2 OCH 3 (A), C 3 O 1 = -(CH 2 ) 2 OCH 3 (B); C x = 1-alquil, C 10 = C 10 H 21 (C), C 4 = C 4 H 9 (D); e [Ânion] = H 3 CSO 3 (2), BF 4 (3) ou PF 6 (4)) foram preparados e caracterizados. A força da ligação de hidrogênio entre o cátion e o ânion dos líquidos iônicos 2-4 depende principalmente do ânion e diminui na ordem H 3 CSO 3 > BF 4 > PF 6 . Todos os líquidos iônicos metanosulfonatos 2 possuem uma forte desblindagem para o próton H 2 do ciclo imidazólio. Os líquidos iônicos funcionalizados com um grupo 1-alquil éter mostram densidades mais altas em comparação com seus equivalentes do grupo 1-alquil. Os sais 2a-b, 3a-d e 4a-b são líquidos iônicos à temperatura ambiente. E, todos os líquidos iônicos 1-alquil éter funcionalizados (exceto 4b) são completamente amorfos. As maiores faixas líquidas foram obtidas com os líquidos iônicos tetrafluoroborato devido as suas solidificações a temperaturas baixas e excelente estabilidade térmica. Estes dados fornecem informações importantes para o entendimento sobre possíveis aplicações e a preparação de líquidos iônicos com tarefas específicas.

Journal of the American Chemical Society, 2005

It is expected that transition-metal nanoparticles of 1-10 nm in size will exhibit physical-chemi... more It is expected that transition-metal nanoparticles of 1-10 nm in size will exhibit physical-chemical properties intermediate between those of the smallest element from which they can be composed and those of the bulk material. 1 However, in solution nanoparticles are solely kinetically stable, and they should be stabilized against aggregation into larger particles and bulk material. The stabilization of nanoparticles in solution can be achieved by electrostatic and/ or steric protection by, for example the use of water-soluble polymers, quaternary ammonium salts, surfactants, or polyoxoanions. In this respect we and others have recently demonstrated that ionic liquids 3 are a suitable medium for the preparation and stabilization of transition-metal nanoparticles and are also ideal for the generation of recyclable biphasic catalytic systems for hydrogenation and C-C coupling reactions. 4 Indeed, the pronounced selforganization of imidazolium ionic liquidssthat can be described as polymeric supramolecules 5 shas been used for the preparation of various highly organized hybrid nanostructures. 6 It has been suggested that the combined intrinsic high charge plus the steric bulk of these salts can create an electrostatic and steric colloidtype stabilization of transition-metal nanoparticles, similar to the proposed model for the stabilization of nanoclusters by polyoxoanions or by tetralkylammonium salts. 7 However, in some cases the transition-metal nanoparticles, in particular those of Rh(0) and Pd(0), dispersed in the ionic liquid tend to aggregate into larger structures with loss of their catalytic activity. 8 It is worth pointing out that the valence band emission for these metal particles occurs at binding energies (measured by XPS analysis with respect to the Fermi level) that are quite similar to that of the pure metals. This suggests that in these cases the development of electron deficiencies at the nanoparticle surface is not sufficient to approximate the ionic liquid and thus to create an effective electronic/steric protection layer. 7 It is also known that laser irradiations of metal particles promote the photoejection of electrons, which induces subsequent fragmentations, and this constitutes an alternative and selective method for the breakup of large or irregular particles into smaller and regular ones. 9 Therefore, the irradiation of nanoparticles dissolved in ionic liquids may provide a new method for the generation of transition-metal nanoparticles with a small and narrow size distribution dispersed in ionic liquids or restructure those particles that tend to aggregate into larger particles after use as, for example, in catalysis. Moreover, since imidazolium ionic liquids possess negligible vapor pressure, it is possible to investigate their size and shape modification before and after radiation by in situ transmission electron microscopy (TEM) experiments, 10 thus avoiding sample treatments such elimination of the solvents, which may be involved in the stabilization of the nanoparticles.

Journal of Sol-Gel Science and Technology, 2009

This article describes the preparation of silica xerogels by the sol-gel technique, using tetraet... more This article describes the preparation of silica xerogels by the sol-gel technique, using tetraethoxysilane as precursor and hydrofluoric acid as catalyst, in the presence of imidazolium ionic liquids (ILs). The applied ILs 1-3 contained the 1-monoethylene glycol monomethyl ether-3-methylimidazolium cation in combination with the methanesulfonate (1), tetrafluoroborate (2) and hexafluorophosphate (3) anions, respectively. Characterization of these materials was performed by photography, scanning electron microscopy, atomic force microscopy, X-ray diffraction, thermogravimetric analysis and nitrogen adsorption-desorption isotherms. The IL anion was identified as a powerful morphology controller. The methanesulfonate anion of IL 1 induced the formation of a compact lamellar monolith with an interlamellar distance of 1.5 nm and a flat surface. A free flowing powder of aggregated spherical particles was obtained in the presence of tetrafluoroborate IL 2, and the hexafluorophosphate anion of IL 3 induced the formation of porcelain like aggregates with honeycomb shapes.

Journal of Molecular Catalysis A: Chemical, 2006

The hydroformylation of 1-alkenes can be performed in solventless conditions using ligand-modifie... more The hydroformylation of 1-alkenes can be performed in solventless conditions using ligand-modified or unmodified Rh(0) nanoparticles prepared in imidazolium ionic liquids as catalyst precursors. There is a strong influence of the nanoparticle size on the hydroformylation reaction. Aldehydes are generated when 5.0nm Rh(0) nanoparticles are used in the hydroformylation of 1-alkenes and l/b selectivities up to 25 can be achieved

Dalton Transactions, 2007

ChemSusChem, 2008

Dedicated to Prof. Martin Schmal on the occasion of his 70th birthday Without doubt, in this cent... more Dedicated to Prof. Martin Schmal on the occasion of his 70th birthday Without doubt, in this century Fischer-Tropsch (FT) technology will play an important role for the generation of high-value, clean-burning fuels. Indeed, syngas (a mixture of CO and H 2 ), produced by the gasification of fossil fuels or biomass, can be converted into a large number of organic compounds that are useful as chemical feedstocks, fuels, and solvents. Currently, several oil companies are researching the large-scale production of FT fuels and at least four major companies have announced plans to build pilot plants to produce synthetically derived FT diesel fuels. [2] Two main characteristics of the Fischer-Tropsch synthesis (FTS) are the unavoidable production of a wide range of hydrocarbon products (olefins, paraffins, and oxygenated products) and the liberation of a large amount of heat from the highly exothermic synthesis reactions. Product distributions are influenced by the temperature, composition of the feed gas (H 2 /CO), pressure, type of catalyst, and catalyst composition. Depending on the types and quantities of desired FT products, either low-(200-240 8C) or high-temperature (300-350 8C) synthesis is employed with either an iron or cobalt catalyst. FTS catalysts can lose their activity as a result of a) conversion of the active metal site into an inactive oxide site, b) sintering, c) loss of active surface area by carbon deposition, and d) chemical poisoning. It is assumed that the catalytic activity, stability, and selectivity may be, to a large extent, modulated by the shape, diameter, and size distribution of the metal catalysts. In this respect, it was recently reported that metal nanoparticles with a small diameter and narrow size distribution can be prepared by reduction with H 2 of metal compounds or decomposition of organometallic species dissolved in ionic liquids. These metal nanoparticles dispersed in ionic liquids are catalysts for various reactions, such as the hydrogenation of alkenes under multiphase conditions. We report herein preliminary results for the synthesis of Co nanoparticles in ionic liquids and their use as efficient catalysts for the FTS. The Co nanoparticles were prepared by simple decomposition of the organometallic precursor [Co 2 (CO) 8 ] dissolved in 1-n-butyl-3-methylimidazolium N-bis(trifluoromethanesulfonyl)imidate (BMI·NTf 2 ), 1-n-decyl-3-methylimidazolium tetrafluoroborate (DMI·BF 4 ), or 1-n-tetradecyl-3methylimidazolium N-bis(trifluoromethanesulfonyl)imidate (TDMI·NTf 2 ). Hence, the addition of a hexane solution of [Co 2 (CO) 8 ] (0.05 mmol) to BMI·NTf 2 , DMI·BF 4 , or TDMI·NTf 2 (0.5 mL) yielded after 20-40 min at 150 8C a black solution. FTIR spectroscopy during the decomposition process showed the disappearance of the bridging carbonyl and the presence of only terminal C=O bands at 2055-2065 cm À1 , indicating that the bimetallic precursor is first broken to form the tetracarbonylcobalt anion [Co(CO) 4 ] À . A drop of this black solution was placed on a carbon grid and analyzed by transmission electron microscopy (TEM, . This black ionic-liquid suspension is composed of Co nanoparticles of (7.7 AE 1.2) nm in size. The diameter of the nanoparticles was estimated from ensembles of 150 particles (300 counts) found in arbitrary chosen areas of the enlarged micrographs, and the obtained size distribution was reasonably fitted to a Gaussian curve . Nanoparticles with a size of (4.5 AE 0.6) nm were obtained by decomposition of [Co 2 (CO) 8 ] in DMI·BF 4 (see in the Supporting Information). This suggests that the size of the Co nanoparticles can be controlled by the choice of counter anion of the ionic liquid.

Journal of Colloid and Interface Science, 2007

A surface-enhanced Raman spectroscopy (SERS) study of imidazolium ionic liquid stabilized gold(0)... more A surface-enhanced Raman spectroscopy (SERS) study of imidazolium ionic liquid stabilized gold(0) nanoparticles (GNPs) furnished previously unknown knowledge about the coordination and stabilization mode of the imidazolium cation. GNPs were prepared by hydrazine reduction of a chloroauric acid solution in 1-triethylene glycol monomethyl ether-3-methylimidazolium methanesulfonate 2 as ether-functionalized roomtemperature ionic liquid (RTIL). UV-vis spectroscopy showed the presence of GNP aggregates as absorptions extended to the NIR region. A parallel coordination mode for the imidazolium cation of RTIL 2 on the GNP surface was observed by SERS, which occurred without the simultaneous coordination of the 1-triethylene glycol monomethyl ether-functionality. Instead of this, the ether-functionality was directed away from the GNP surface and acted as steric barrier between the GNPs/GNP aggregates, thus preventing further aggregation. These new insights suggest that the imidazolium cation is responsible for electrosteric stabilization.