Loading...
23 results
Search Results
Now showing 1 - 10 of 23
- Organic resins functionalized with chiral salen complexes as heterogeneous catalysts for the strecker reactionPublication . Esteves, M. Alexandra; Santos, Célia; Guerreiro, A. Margarida; Baleizão, Carlos
- Synthesis, spectroscopy, photophysics and thermal behaviour of stilbene-based triarylamines with dehydroabietic acid methyl ester moietiesPublication . Gigante, Bárbara; Esteves, M. Alexandra; Pires, N.; Davies, Matthew L.; Douglas, Peter; Fonseca, Sofia M.; Burrows, Hugh D.; Pina, João; Melo, João Seixas deNovel stilbene-based triarylamines with dehydroabietic acid methyl ester moieties have been synthesised by palladium catalysed C–N coupling reactions. The presence of the bulky dehydroabietic acid group increases solubility, hinders crystallisation and permits their sublimation while preserving their electronic and optical characteristics. This makes them good candidates for various molecular electronic applications. We report a detailed characterisation of their electrochemical, spectroscopic and photophysical properties. In addition, the thermal stability and behaviour is discussed with reference to the potential for preparation of stable thin films.
- Enhancing Pt electrocatalytic activity by surface functionalization of carbon support with aromatic sulphonic groupsPublication . Capelo, Anabela; Esteves, M. Alexandra; de Sá, A.I.; Rangel, C. M.Preliminary results are presented for Pt deposited on 4-aminobenzenesulphonic acid-functionalized carbon, Pt/C_ABSA. Vulcan XC-72R was functionalized with the objective of influencing the dispersion of catalyst nanoparticles and to decrease the resistance of three phase boundaries, by introducing sulphonic groups. Electrochemical characterization of the supported catalyst was done in a 0.5 M sulphuric acid solution with added chloride and also using methanol demonstrating well defined features and stable voltammograms after 30 cycles, with apparent higher currents when compared with commercial catalyst. The structure sensitive adsorption of anions on platinum is confirmed by the blocking effect of chloride ions in the hydrogen adsorption-desorption region as well as by the consequent dissolution of platinum, evident in both anodic and cathodic features of the voltammograms regarding surface oxide formation and reduction. The partial reversibility of the effect of chloride ions is discussed. Research is in progress in order to accomplish a comprenhensive characterization of the synthesized catalyst and to ascertain the effect of the sulphonic groups.
- The H2Excellence Project: Fuel Cells and Green Hydrogen Centers of Vocational Excellence towards affordable, secure, and sustainable energy for Europe [Resumo]Publication . Gano, António; Pinto, P.J.R.; Esteves, M. Alexandra; Rangel, C. M.ABSTRACT: The demand for green hydrogen (H2) and related technologies is expected to increase in the coming years mainly framed by drivers such as climate change and energy security of supply amid the European and global energy crises. REpowerEU Plan called for an intensification of hydrogen delivery targets, that will bring large-scale adoption of hydrogen production and applications in various sectors, stressing the need for a skilled workforce in the emergent hydrogen markets. To that end, the Erasmus+ European H2Excellence transnational project[2] has gathered 24 partners across the EU, to establish a Platform of Vocational Excellence in the field of fuel cells and green hydrogen technologies, with an educational and training offer that will tackle identified skill gaps and implement life-long learning opportunities. The project aims to become a benchmark in training and knowledge transfer, contributing to the integration of quality employment into green hydrogen local innovative systems approaching the entire hydrogen value chain.
- New hydroxypyrimidinone-sulfonamides as biatarget ligands for enzyme inhibitionPublication . Esteves, M. Alexandra; Olrtet, Osvaldo; Capelo, Anabela; Santos, Célia; Marques, Sérgio; Supuran, Claudiu; Santos, M. Amélia
- A tripodal hydroxypyriminone-based compund and aluminium decorporationPublication . Chaves, S.; Marques, S.; Areias, Laurinda; Esteves, M. Alexandra; Gano, L.; Santos, M. Amélia; Capelo, Anabela
- Synthesis and photophysical properties of tetraphenylethylene derivatives as luminescent downshifting materials for organic photovoltaic applicationsPublication . Barros, Helio; Esteves, M. Alexandra; Brites, Maria JoãoABSTRACT: Luminescent Down-Shifting (LDS) is an optical approach applied in several photovoltaic (PV) technologies in which high energy solar radiation is converted to a wavelength region where the response of the photovoltaic devices is better. The use of LDS layers on organic photovoltaics (OPV) could serve two purposes: to prevent cell degradation by filtering the incident ultraviolet (UV) radiation and to improve the spectral response of PV cells at short-wavelength. This work reports, the design and synthesis of a series of tetraphenylethylene (TPE) derivatives based on TPE-A or A-pi-TPE-pi-A molecular structure featuring various electron-acceptor (A) groups. The photo-physical properties of the new LDS compounds were systematically studied in 1,4-dioxane solution and film (Zeonex) by UV-visible absorption and fluorescence spectroscopy, and electrochemical properties studied by cyclic voltammetry. Thermal stability of the new LDS compounds was evaluated by Thermogravimetric analysis (TGA). Theoretical computational studies provided evidence of existence of intramolecular charge-transfer (ICT) between frontier orbitals of donor and acceptor moieties. The good photophysical and thermal properties of the synthesized TPE derivatives, associated with high molar absorption coefficients in UV spectrum and emission maximum in the range of 476-531 nm, make them promising candidates for LDS layers in OPV application.
- Deactivation and regeneration of Pt-Titania-reduced graphene oxide nanocomposites as catalysts in the photochemical generation of hydrogen [Resumo]Publication . Esteves, M. Alexandra; Fernandes, Vitor; Rangel, C. M.
- Photocatalytic hydrogen production using noble and transition metals surface modified titania [Resumo]Publication . Capelo, Anabela; Esteves, M. Alexandra; Fernandes, Vitor; Rangel, C. M.ABSTRACT: A large number of photocatalytic materials have been studied for water splitting since the seminal work of Fujishima and Honda1, showing great potential for solar energy conversion, including H2 production. The irradiation of a suspension of semiconductor oxides, as is the case of TiO2, presents attracting features but also stringent requirements regarding materials properties, including the tailoring of the electronic structure. Furthermore, efficient charge transport is necessary, as well as effective charge separation and prevention of electron-hole pair recombination, before the redox reactions can proceed2,3. In this work, the catalytic activity under UV excitation of TiO2-Au photocatalyst for H2 production was undertaken using glycerol and ethanol as sacrificial agents. Furthermore, substitution of Au by transition metal Cu was attempted with good results. Comparison is made with results obtained using TiO2-rGO-Pt catalyst under analogous loading conditions.
- New heterogeneous chiral vanadium (V) salen catalysts for the strecker reactionPublication . Esteves, M. Alexandra; Oliveira, João C.; Guerreiro, Ana Maria; Santos, Célia; Baleizão, Carlos
- «
- 1 (current)
- 2
- 3
- »