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Au nanoparticles (AuNPs) were immobilized on S-containing amino acids (cysteine and methionine) Mg/Al hydrotalcite clay in both bulk and exfoliated (colloidal) forms. The Au nanoparticles were prepared by a biomimetic method using an anti-oxidant tea extract to reduce the Au salt solution. The performance of bulk and exfoliated clays with Au nanoparticles in aerobic olefin epoxidation was assessed with very interesting results. Both catalysts were very active towards the epoxide products; selectivity was found to be dependent on the catalyst form. The exfoliated catalysts yielded higher product stereoselectivity in the case of limonene epoxidation. These results can be explained by the existence of a confined environment around the AuNPs structures provided by the clay nanosheets wrapping the nanoparticles, modulating how substrates interact with the catalytic active centres. Based on experimental data mechanistic proposals were also rationalized for these catalysts showing how they assist the catalytic process. more...

A Co/Al layered double hydroxide material was synthesized in both bulk and exfoliated (colloidal) forms. Anion exchange with methionine allowed immobilization of Au nanoparticles previously prepared by a biomimetic method using an anti-oxidant tea aqueous extract to reduce the Au salt solution. The catalytic performance of bulk and exfoliated clays Au-hybrid materials was assessed in aerobic olefin epoxidation. Both catalysts were very active towards the epoxide products and with very interesting substrate conversion levels after 80 h reaction time. The Au-exfoliated material, where the nanosheets work as large ligands, yielded higher product stereoselectivity in the case of limonene epoxidation. This arises from a confined environment around the Au nanoparticles wrapped by the clay nanosheets modulating access to the catalytic active centres by reagents. Mechanistic assessment was also accomplished for styrene oxidation by DFT methods. more...

Poly-aniline (PAn) film can be oxidized by contacting oxygen in an electron-transfer reaction and its redox state, for instance the open circuit potential and the dielectric constant, is quantitatively related to oxygen concentration. This feature may contribute to an improved application of dissolved oxygen (DO) detection with the combined optical and electrochemical sensor. In this paper, PAn is used as a sensing surface to detect DO by the combination sensor composed of electrochemistry and total internal reflection imaging ellipsometry (EC-TIRIE). Results demonstrate that both optical and electrical signals show a logarithmic correlation with DO concentration (0-20ppm). Compared with the results obtained only with the gold surface, both the optical and electrical signals of the EC-TIRIE sensor for DO detection are amplified with the PAn modified gold surface. more...

Reaction of [Co(η 5 -C 5 H 5 )(CO) 2 ], 1 , with 1,1′-bis(diphenylphosphino)ferrocene (dppf) yields the new trinuclear complex [Co(η 5 -C 5 H 5 )(CO)] 2 (μ-dppf), 2 , which was structurally characterised by single crystal X-ray diffraction and showed two Co(η 5 -C 5 H 5 )(CO) moieties covalently linked by a dppf bridge. Electrochemical studies in dichloromethane revealed that both Co(I) and Fe(II) in the precursors were oxidized to Co(II)/Co(III) and Fe(III), respectively. On the other hand, in 2 the two first oxidation waves were assigned to Co, the Fe(II) centre requiring a higher potential than in free dppf. DFT calculations showed that the HOMOs of 2 were localised in the Co fragments, owing to the destabilisation of the Co(η 5 -C 5 H 5 )(CO) orbitals after binding dppf. more...

In this work we report the spontaneous immobilization of n-decane phosphonic acid (n-C10H21PO3H2), a deuteroporphyrin and Cobalt-porphyrin [MPorph(PO3H2)2; M = 2H and Co] phosphonic acid derivatives from butanolic solutions on HOPG electrodes. The electrochemical activation of the graphite surface (HOPGET) prior to layer deposition, has shown to be a requisite for the adsorption of phosphonic acid derivatives onto the newly formed oxide species. HOPG electrode before and after controlled electrochemical oxidation was characterized by Atomic Force Microscopy (AFM) and water contact angle measurements. The formation of phosphonate based layers was confirmed by the study of the blocking properties of the modified surfaces towards the redox conversion of [Fe(CN)6)]3−/[Fe(CN)6)]2−, by reductive desorption studies in NaOH solutions, and also by water contact measurements, where the competitive adsorption of solvent (butanol) molecules is discussed. Further confirmation of the successful immobilization of porphyrin-PO3H2 derivatives on HOPGET is provided by their electrochemical response in organic medium, where the main redox peaks expected for the porphyrin macrocycle are depicted, as well as the cobalt centred ones. Oxygen reduction reaction in acid medium was used to evaluate the electrocatalytic properties of the immobilized deutero and CoPorph(PO3H2)2. more...

This work exploits the electroless precipitation approach for the incorporation of palladium in polypyrrole (PPy). Electrochemical and morphological analysis of PPy films prepared on Pt, under potentiostatic and potentiodynamic control, reveal the influence of the electrosynthesis conditions on the bulk and surface properties of the polymer. It is shown that, besides the pH of the PdCl2 containing solutions, those PPy characteristics play an important role on the rate of the Pd uptake process. The resulting Pd(0)/Pdox ratio, size and surface distribution of the metallic particles on the film surface are analysed in detail and correlated to the electrocatalytic activity disclosed by the modified PPy electrodes towards the oxidation of hydrazine in KCl solution. In comparison to palladium thin coatings, a superior behaviour is achieved for PPy rough surfaces able to create uniform dispersions of sub-micron Pd particles, but the employment of polymer films with less coarse surfaces and/or an increasing in the amount and size of the Pd particles is disadvantageous for catalytic purposes. more...

The purpose of this study was to develop a simple biological method for the synthesis of Ag nanoparticles (AgNPs) using Lippia citriodora leaves aqueous extract as reducing agent. Transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD), and visible absorption spectroscopy (UV-vis) confirmed the reduction of silver ions to AgNPs. Stable, spherical crystalline AgNPs with well defined dimensions (average size of 15-30 nm) were obtained, on treating aqueous silver nitrate with the plant leaf aqueous extract. The kinetic of particles formation was proportional to the effect of reducing agent concentration and was enhanced by the increase of temperature from 25 degrees C to 95 degrees C. Time, temperature and extract concentration did not influence significantly the shape and size of nanoparticles. In order to identify the compounds responsible for the bioreduction of silver ions and stabilization of the AgNPs formed, we investigated the constituents of L. citriodora aqueous extract by high performance liquid chromatography (HPLC) and mass spectrometry (MS). The main compounds found were verbascoside, isoverbascoside, chrysoeriol-7-O-diglucoronide and luteonin-7-O-diglucoronide. The data obtained suggests that the isoverbascoside compound is responsible for Ag(+) ions reduction and act as capping agents of the nanoparticles afterwards. more...

The deposition of palladium as microparticles on electrogenerated polyaniline (PAni) films accomplished by metal electroless precipitation or by electrodeposition has been used to prepare stable polymer-modified electrode systems. Its general morphology, metal particles size and distribution were obtained by AFM analysis. The PAni/Pd microparticles electrodes have been evaluated for their catalytic activity towards hydrogenation reactions upon organic compounds reduction using 4-nitro-benzaldehyde. Studies on rotating ring-disk electrodes have shown that relatively low Pd loadings are required to obtain effective electrocatalytic activity, provided a good metal particles dispersion of about 100 nm diameter is observed. more...

Three new mononuclear oxovanadium(IV) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)imino} acenaphthene, R = H, 1; CH3, 2; Cl, 3) were prepared and characterized. They promoted the catalytic oxidation of olefins such as cyclohexene, cis-cyclooctene, and styrene with both tbhp (tert-butylhydroperoxide) and H2O2, and of enantiopure olefins (S(-)- and R(+)-pinene, and S(-)- and R(+)-limonene) selectively to their epoxides, with tbhp as the oxidant. The TOFs for styrene epoxidation promoted by complex 3 with H2O2 (290 mol mol(-1)V h(-1)) and for cis-cyclooctene epoxidation by 2 with tbhp (248 mol mol(V)(-1) h(-1)) are particularly good. Conversions reached 90% for several systems with tbhp, and were lower with H2O2. A preference for the internal C=C bond, rather than the terminal one, was found for limonene. Kinetic data indicate an associative process as the first step of the reaction and complex [VO(acac)(H-BIAN)](+) (1(+)) was isolated in an FTICR cell after adding tbhp to 1. EPR studies provide evidence for the presence of a V(IV) species in solution, until at least 48 hours after the addition of tbhp and cis-cyclooctene, and cyclic voltammetry studies revealed an oxidation potential above 1 V for complex 1. DFT calculations suggest that a [VO(H-BIAN)(MeOO)](+) complex is the likely active V(IV) species in the catalytic cycle from which two competitive mechanisms for the reaction proceed, an outer sphere path with an external attack of the olefin at the coordinated peroxide, and an inner sphere mechanism starting with a complex with the olefin coordinated to vanadium. more...

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A investiga����o na ��rea da Educa����o real��a como o livro de literatura para a inf��ncia pode contribuir para o desenvolvimento e aprendizagem das crian��as. No ��mbito da Educa����o Pr��-escolar, esta realidade sugere a necessidade de avaliar a perce����o dos educadores sobre o livro de literatura para a inf��ncia. O presente artigo apresenta o processo de constru����o e valida����o de um Question��rio de Conhecimento sobre a Literatura para a Inf��ncia (QCLI), pretendendo assim contribuir com uma resposta a essa necessidade. Participaram no estudo 270 educadores de inf��ncia em Portugal continental, dos quais 99% dos inquiridos s��o do sexo feminino com uma m��dia de idades de 43 anos. As respostas ao question��rio, ap��s diversos procedimentos de valida����o, conduziram pela an��lise fatorial confirmat��ria composta a tr��s dimens��es: uma primeira sobre a perce����o dos educadores sobre a compet��ncia pessoal no uso do livro de literatura para a inf��ncia, uma segunda sobre a perce����o dos educadores acerca da potencialidade do livro de literatura para a inf��ncia na ��rea da express��o e comunica����o, e uma terceira dimens��o sobre a perce����o dos educadores acerca da potencialidade do livro de literatura para a inf��ncia na ��rea da forma����o pessoal e social e conhecimento do mundo. As tr��s dimens��es apresentam um bom ��ndice de consist��ncia interna (respetivamente ��=0,918, ��=0,950 e ��=0,953). O question��rio revela-se ��til e adequado para uso em futuras pesquisas que procurem aprofundar o conhecimento sobre as perce����es dos educadores em rela����o ao potencial do livro de literatura para a inf��ncia., Interac����es, Vol. 17 No. 60 (2021): Cultura e Ci��ncia Perspetivadas na sua Rela����o com a Educa����o more...

Tese de doutoramento, Educação (Psicologia da Educação), Universidade de Lisboa, Instituto de Educação, 2016 Submitted by Amelia Janeiro (ajaneiro@reitoria.ul.pt) on 2016-07-13T15:07:30Z No. of bitstreams: 1 ulsd072907_td_Ana_Mourato.pdf: 3436155 bytes, checksum: 072a3c5a8d51a8dd242d8565f2125c1d (MD5) Made available in DSpace on 2016-07-15T13:07:16Z (GMT). No. of bitstreams: 1 ulsd072907_td_Ana_Mourato.pdf: 3436155 bytes, checksum: 072a3c5a8d51a8dd242d8565f2125c1d (MD5) Previous issue date: 2016 more...