Carbon Nanotube Growth Using Ni Catalyst in Different Layouts

Vertically aligned carbon nanotubes have been grown using Ni as catalyst by plasma enhanced chemical vapor deposition system (PECVD) in various pre-patterned substrates. Ni was thermally evaporated on silicon substrates with anodized alumina mask prepared in different methods including 2 step anodization of porous alumina template and interference lithography assisted array of pores. The templates helped to define Ni nanodots inside the pores which in turn catalyzed the growth of carbon nanotubes inside the PECVD system at temperature of 700-750C using mixture of ammonia and acetylene gases. The resulting well-aligned multi-walled carbon nanotubes were further investigated using SEM, TEM and Raman spectroscopy. The size, shape and structure of the grown carbon nanotubes were also discussed.

Public and student awareness science: recreational science as a catalyst

When discussing the traditional and new missions of higher education (1996 Report to UNESCO of the International Commission on Education for the 21st Century) Jacques Delors stated that "Excessive attraction to social sciences has broken equilibrium of available graduates for workforce, thus causing doubts of graduates and employers on the quality of knowledge provided by higher education". Likewise, when discussing the progress of science and technology, the 1998 UNESCO World Conference on Higher Education concluded that "Another challenge concerts the latest advancements of Science, the sine qua non of sustainable development"; and that “with Information Technology, the unavoidable invasion of virtual reality has increased the distance between industrial and developing countries". Recreational Science has a long tradition all over the Educational World; it aims to show the basic aspects of Science, aims to entertain, and aims to induce thinking. Until a few years ago, this field of knowledge consisted of a few books, a few kits and other classical (yet innovative) ways to popularize the knowledge of Nature and the laws governing it. In Spain, the interest for recreational science has increased in the last years. First, new recreational books are being published and found in bookstores. Second the number of Science-related museums and exhibits is increasing. And third, new television shows are produced and new short science-based, superficial sketches are found in variety programs. However, actual programs in Spanish television dealing seriously with Science are scarce. Recreational Science, especially that related to physical phenomena like light or motion, is generally found at Science Museums because special equipment is required. On the contrary, Science related mathematics, quizzes and puzzles use to gather into books, e.g. the extensive collections by Martin Gardner. However, lately Science podcasts have entered the field of science communication. Not only traditional science journals and television channels are providing audio and video podcasts, but new websites deal exclusively with science podcasts, in particular on Recreational Science. In this communication we discuss the above mentioned trends and show our experience in the last two years in participating at Science Fairs and university-sponsored events to attract students to science and technology careers. We show a combination of real examples (e.g., mathemagic), imagination, use of information technology, and use of social networks. We present as well an experience on designing a computational, interactive tool to promote chemistry among high school, prospective students using computers ("Dancing with Bionanomolecules"). Like the concepts related to Web 2.0, it has been already proposed that a new framework for communication of science is emerging, i.e., Science Communication 2.0, where people and institutions develop new innovative ways to explain science topics to diverse publics – and where Recreational Science is likely to play a leading role

Síntesi de nous macrocicles nitrogenats poliinsaturats. Estudis de coordinació i reactivitat

La síntesi i caracterització estructural d'un nou tipus de macrocicles nitrogenats de 15, 20 i 25 membres, els quals contenen triples i dobles enllaços i diferents unitats aríliques a la seva estructura, ha estat estudiada. S'han preparat els complexos de pal·ladi(0) dels corresponents macrocicles poliinsaturats de 15 membres, els quals són estables a l'aire i a la humitat i en alguns casos presenten quiralitat. La seva caracterització completa s'ha portat a terme mitjançant RMN i difracció de raigs-X. S'ha estudiat també la reacció de cicloisomerització d'aquests macrocicles emprant diferents catalitzadors basats en metalls de transició, observant-se que el catalitzador de Wilkinson, de rodi(I), és el que ha donat més bons resultats. Finalment, s'ha realitzat una introducció a l'estudi del mecanisme d'aquest tipus de reaccions mitjançant ESI-MS, així com també un estudi inicial de la reacció de cicloisomerització enantioselectiva.

Síntesi i Reactivitat de nous Macrocicles Nitrogenats Poliinsaturats

En aquesta tesi s'han sintetitzat macrocicles nitrogenats poliinsaturats de diferents mides i s'ha estudiat la seva reactivitat. S'han preparat macrocicles de quinze i setze baules triacetilènics i de quinze baules contenint dos triples i un doble enllaç a l'estructura. S'ha estudiat la ciclotrimerització [2+2+2] d'aquests macrocicles catalitzada per metalls de transició en dissolvents orgànics convencionals o en sals foses. S'han sintetitzat complexos de rodi contenint un lligand carbènic N-heterocíclic per tal d'utilitzar-los com a catalitzadors alternatius al complex de Wilkinson en les reaccions de ciclotrimerització dels macrocicles poliinsaturats i d'altres anàlegs oberts. Els complexos carbènics sintetitzats han presentat una eficiència lleugerament superior a la del catalitzador de Wilkinson. També s'ha iniciat un estudi mecanístic de la cicloisomerització d'aquests macrocicles induïda tèrmicament. Finalment, s'han preparat macrocicles de catorze i dinou baules contenint un nucli endiínic a més d'altres insaturacions i s'ha estudiat la corresponent ciclació de Bergman en estat sòlid.

Model catalyst studies of the strong metal-support interaction: Surface structure identified by STM on Pd nanoparticles on TiO2(110)

Model catalysts of Pd nanoparticles and films on TiO2 (I 10) were fabricated by metal vapour deposition (MVD). Molecular beam measurements show that the particles are active for CO adsorption, with a global sticking probability of 0.25, but that they are deactivated by annealing above 600 K, an effect indicative of SMSI. The Pd nanoparticles are single crystals oriented with their (I 11) plane parallel to the surface plane of the titania. Analysis of the surface by atomic resolution STM shows that new structures have formed at the surface of the Pd nanoparticles and films after annealing above 800 K. There are only two structures, a zigzag arrangement and a much more complex "pinwheel" structure. The former has a unit cell containing 7 atoms, and the latter is a bigger unit cell containing 25 atoms. These new structures are due to an overlayer of titania that has appeared on the surface of the Pd nanoparticles after annealing, and it is proposed that the surface layer that causes the SMSI effect is a mixed alloy of Pd and Ti, with only two discrete ratios of atoms: Pd/Ti of 1: 1 (pinwheel) and 1:2 (zigzag). We propose that it is these structures that cause the SMSI effect. (c) 2005 Elsevier Inc. All rights reserved.

Interaction of 2-(arylazo)phenols with rhodium. Usual coordination vs. C-H and C-C activation

Reaction of 2-(2'-hydroxyphenylazo)phenol with [Rh(PPh3)(3)Cl] in refluxing benzene in presence of triethylamine afforded a red complex in which the ligand is coordinated to rhodium as a tridentate O,N,O-donor. However, similar reaction of [Rh(PPh3)(3)Cl] with 2-(2'carboxyphenylazo)-4-methylphenol yielded two complexes, viz. a blue one and a green one. In both the complexes the ligand is coordinated as C,N,O-donor. However, in the blue complex orthometallation takes place from the ortho-carbon atom, which bears -COOH group via decarboxylation and in green one orthometallation occurs from the other ortho-carbon. Structures of all the three complexes were determined by X-ray crystallography. In all the three complexes rhodium is sharing the equatorial plane with the tridentate ligand and a chloride, and the two triphenylphosphines are axially disposed. All of the complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation on the positive side of SCE and a reduction of the coordinated azophenolate ligand on the negative side. (c) 2006 Elsevier B.V. All rights reserved.

Rhodium assisted C-H activation of N-(2 '-hydroxyphenyl)benzaldimines. Synthesis, structure and electrochemical properties of a group of organorhodium complexes

Reaction of a group of N-(2'-hydroxyphenyl)benzaldimines, derived from 2-aminophenol and five para-substituted benzaldehydes (the para substituents are OCH3, CH3, H, Cl and NO2), with [Rh(PPh3)(3)Cl] in refluxing toluene in the presence of a base (NEW afforded a family of organometallic complexes of rhodium(III). The crystal structure of one complex has been determined by X-ray crystallography. In these complexes the benzaldimine ligands are coordinated to the metal center, via dissociation of the phenolic proton and the phenyl proton at the ortho position of the phenyl ring in the imine fragment, as dianionic tridentate C,N,O-donors, and the two PPh3 ligands are trans. The complexes are diamagnetic (low-spin d(6), S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry shows a Rh(III)-Rh(IV) oxidation within 0.63-0.93 V vs SCE followed by an oxidation of the coordinated benzaldimine ligand. A reduction of the coordinated benzaldimine is also observed within -0.96 to -1.04 V vs SCE. Potential of the Rh(Ill)-Rh(IV) oxidation is found to be sensitive to the nature of the para-substituent. (c) 2006 Elsevier B.V. All rights reserved.

Molecular aluminum hydrides identified by inelastic neutron scattering during H-2 regeneration of catalyst-doped NaAlH4

Catalyst-doped sodium aluminum hydrides have been intensively studied as solid hydrogen carriers for onboard proton-exchange membrane (PEM) fuel cells. Although the importance of catalyst choice in enhancing kinetics for both hydrogen uptake and release of this hydride material has long been recognized, the nature of the active species and the mechanism of catalytic action are unclear. We have shown by inelastic neutron scattering (INS) spectroscopy that a volatile molecular aluminum hydride is formed during the early stage of H-2 re-eneration of a depleted, catalyst-doped sodium aluminum hydride. Computational modeling of the INS spectra suggested the formation of AlH3 and oligomers (AlH3)(n) (Al2H6, Al3H9, and Al4H12 clusters), which are pertinent to the mechanism of hydrogen storage. This paper demonstrates, for the first time, the existence of these volatile species.

Tin and tin-titanium as catalyst components for reversible hydrogen storage of sodium aluminium hydride

This paper is concerned with the effects of adding tin and/or titanium dopant to sodium aluminium hydride for both dehydrogenation and re-hydrogenation reactions during their reversible storage of molecular hydrogen. Temperature programmed decomposition (TPD) measurements show that the dehydrogenation kinetics of NaAlH4 are significantly enhanced upon doping the material with 2 mol% of tributyltin hydride, Sn(Bu)(3)H but the tin catalyst dopant is shown to be inferior than titanium. On the other hand, in this preliminary work, a significant synergetic catalytic effect is clearly revealed in material co-doped with both titanium and tin catalysts which shows the highest reversible rates of dehydrogenation and re-hydrogenation (after their hydrogen depletion). The re-hydrogenation rates of depleted Sn/Ti/NaAlH4 evaluated at both 9.5 and 140 bars hydrogen are also found to be favourable compared to the Ti/NaAlH4, which clearly suggest the importance of the catalyst choice. Basing on these results some mechanistic insights for the catalytic reversible dehydrogenation and re-hydrogenation processes of Sn/Ti/NaAlH4 are therefore made. (C) 2006 Elsevier Ltd. All rights reserved.

Colloidal stable silica encapsulated nano-magnetic composite as a novel bio-catalyst carrier

A colloidal stable silica-encapsulated magnetic nano-composite of a controlled dimension is, for the first time, employed to carry beta-lactamase via chemical linkage on the silica overlayer: activity study reflects that this new type of immobilisation allows site (enzyme) isolation, accessibility as good as free enzyme and recovery & reusability upon application of magnetic separation.

Tris-(1,3-diaryltriazenide) complexes of rhodium: synthesis, structure and, spectral and electrochemical properties

Reaction of 1,3-diaryltriazenes (abbreviated in general as HL-R, where R stands for the para-substituent in the aryl fragment and H stands for the dissociable hydrogen atom, R = OCH3, CH3, H, Cl, NO2) with [Rh(PPh3)(2)(CO)Cl] in ethanol in the presence of NEt3 produces a series of tris-diaryltriazenide complexes of rhodium of type [Rh(L-R)(3)], where the triazenes are coordinated to rhodium as monoanionic, bidentate N,N-donors. Structure of the [Rh(L-OCH3)(3)] complex has been determined by X-ray crystallography. The complexes are diamagnetic, and show characteristic H-1 NMR signals and intense MLCT transitions in the visible region. They also fluoresce in the visible region under ambient condition while excited at around 400 nm. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation (within 0.84-1.67 V vs SCE), followed by an oxidation of the coordinated tri- and azene ligand (except the R = NO2 complex). An irreversible reduction of the coordinated triazene is also observed for all the complexes below -1.03 V vs SCE.

Silica coated noble metal nanoparticle hydrosols as supported catalyst precursors

Synthesis of well-defined nanoparticles has been intensively pursued not only for their fundamental scientific interest, but also for many technological applications. One important development of the nanomaterial is in the area of chemical catalysis. We have now developed a new aqueous-based method for the synthesis of silica encapsulated noble metal nanoparticles in controlled dimensions. Thus, colloid stable silica encapsulated similar to 5 nm platinum nanoparticle is synthesized by a multi-step method. The thickness of the silica coating could be controlled using a different amount of silica precursor. These particles supported on a high surface area alumina are also demonstrated to display a superior hydrogenation activity and stability against metal sintering after thermal activation.

A new oxidation catalyst system using fluorous cobalt(II) species in water-supercritical carbon dioxide (C-H free environment)

Stabilized water droplet dispersed in supercritical carbon dioxide fluid is demonstrated to be an excellent alternative solvent system to acetic acid for air oxidation of a number of alkyl aromatic hydrocarbons using Co(II) species at mild conditions.

Comparison of new microemulsion prepared "Pt-in-Ceria" catalyst with conventional "Pt-on-Ceria" catalyst for water-gas shift reaction

New "Pt-in-CeO2" catalyst prepared by microemulsion method is shown to give higher activity for a water-gas shift reaction but with no formation of CH4, the side product from hydrogenation of carbon oxides using a hydrogen-rich reformate as compared to conventional "Pt-on-CeO2" catalysts. Detailed characterization by DRIFT analysis and temperature programmed reduction presented in this work clearly suggest the ceria coverage on Pt inhibits the metal from forming a strong CO adsorption.