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- Analysis of metallic nanoparticles embedded in thin film semiconductors for optoelectronic applicationsPublication . Fantoni, Alessandro; Fernandes, Miguel; Vygranenko, Yuri; Louro, Paula; Vieira, Manuela; Silva, R. P. O.; Teixeira, D.; Da Costa Ribeiro, Ana Paula; Prazeres, Duarte; Alegria, ElisabeteThis paper reports about a study of the local plasmonic resonance (LSPR) produced by metal nanoparticles embedded in a dielectric or semiconductor matrix. It is presented an analysis of the LSPR for different nanoparticle metals, shapes, and embedding media composition. Metals of interest for nanoparticle composition are Aluminum and Gold. Shapes of interest are nanospheres and nanotriangles. We study in this work the optical properties of metal nanoparticles diluted in water or embedded in amorphous silicon, ITO and ZnO as a function of size, aspect-ratio and metal type. Following the analysis based on the exact solution of the Mie theory and DDSCAT numerical simulations, it is presented a comparison with experimental measurements realized with arrays of metal nanospheres. Simulations are also compared with the LSPR produced by gold nanotriangles (Au NTs) that were chemically produced and characterized by microscope and optical measurements.
- The influence of multiwalled carbon nanotubes and graphene oxide additives on the catalytic activity of 3d metal catalysts towards 1-phenylethanol oxidationPublication . Da Costa Ribeiro, Ana Paula; Fontolana, Emmanuele; Alegria, Elisabete; Kopylovich, Maximilian; Bertani, Roberta; Pombeiro, Armando3d metal (Cu, Fe, Co, V) containing composite catalysts for the solvent-free microwave-assisted trans-formation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (TBHP) as oxidant wereprepared by ball milling. The influence of multiwalled carbon nanotubes (CNTs) and graphene oxide (GO)additives on the catalytic activity of the catalysts was studied. CNTs or GO were mixed by ball millingwith the metal salts (CoCl2), oxides (CuO, Fe2O3, V2O5) or binary systems (Fe2O3-CoCl2, CoCl2-V2O5, CuO-Fe2O3). For CoCl2-based catalytic systems, addition of small amounts (0.1–5%) of CNTs or GO leads tosignificant improvement in catalytic activity, e.g. 1% of the CNTs additive allows to rise yields from 28to 77%, under the same catalytic conditions. The CoCl2-5%CNTs composite is the most active among thestudied ones with 85% yield and TON of 43 after 1 h
- Ultrasound and radiation-induced catalytic oxidation of 1-phenylethanol to acetophenone with iron-containing particulate catalystsPublication . Soliman, Mohamed Mostafa Aboelhassan; Kopylovich, Maximilian N.; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Ferraria, Ana Maria; Rego, Ana; Correia, Luís M. M.; Saraiva, Marta S.; Pombeiro, ArmandoIron-containingparticulatecatalystsof0.1–1 µmsizewerepreparedbywetandball-milling procedures from common salts and characterized by FTIR, TGA, UV-Vis, PXRD, FEG-SEM, and XPS analyses. It was found that when the wet method was used, semi-spherical magnetic nanoparticles were formed, whereas the mechanochemical method resulted in the formation of nonmagnetic microscale needles and rectangles. Catalytic activity of the prepared materials in the oxidation of 1-phenylethanol to acetophenone was assessed under conventional heating, microwave (MW) irradiation, ultrasound (US), and oscillating magnetic field of high frequency (induction heating). In general, the catalysts obtained by wet methods exhibit lower activities, whereas the materials prepared by ball milling afford better acetophenone yields (up to 83%). A significant increase in yield (up to 4 times) was observed under the induction heating if compared to conventional heating. The study demonstrated that MW, US irradiations, and induction heating may have great potential as alternative ways to activate the catalytic system for alcohol oxidation. The possibility of the synthesized material to be magnetically recoverable has been also verified.
- N2O-Free single-pot conversion of cyclohexane to adipic acid catalysed by an iron(II) scorpionate complexPublication . Da Costa Ribeiro, Ana Paula; Martins, Luisa; Pombeiro, ArmandoThe highly efficient eco-friendly synthesis of adipic acid (96% yield, 98% selectivity, TONs up to 1.8 × 103) directly from cyclohexane is achieved by using ozone and [FeCl2{κ3-HC(pz)3}] (pz = pyrazol-1-yl) in a solvent-, heating-, radiation- and N2O-free new protocol.
- Supported C-Scorpionate Vanadium(IV) Complexes as Reusable Catalysts for Xylene OxidationPublication . Wang, Jiawei; Martins, Luisa; Da Costa Ribeiro, Ana Paula; Carabineiro, Sonia Alexandra Correia; Figueiredo, José L.; Pombeiro, ArmandoC-Scorpionate vanadium(IV) [VOxCl3-x{k(3)-RC(pz)(3)}] [pz = pyrazol-1-yl; x=0, R = SO3 (1); x = 1, R= CH2OH (2) or CH2OSO2Me (3)] complexes supported on functionalized carbon nanotubes (CNTs) are the first V-scorpionate catalysts used so far for the neat oxidation of o-, m- or p-xylene, with TBHP (70% aqueous solution), to the corresponding toluic acids (main products), tolualdehydes and methylbenzyl alcohols. Remarkably, a p-toluic acid yield of 43% (73% selectivity, TON = 1.34 V 10(3)) was obtained with 2@CNT in a simple microwave-assisted mild oxidation procedure, using a very low catalyst charge (3.2 x 10(-2) mol% vs. substrate). Further, this occurred in the absence of any bromine source, what is significant towards the development of a greener and more sustainable process for oxidation of xylenes. Moreover, reuse of catalysts with preservation of their activity was found for up to six consecutive cycles. The effects of reaction parameters, such as reaction time, temperature, amount of catalyst or type of heating source, on the performance of the above catalytic systems are reported and discussed.
- Ball milling as an effective method to prepare magnetically recoverable heterometallic catalysts for alcohol oxidationPublication . Fontolan, Emmanuele; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Kopylovich, Maximilian; Bertani, Roberta; Pombeiro, ArmandoHeterometallic double Fe2O3–CoCl2, CoCl2–V2O5, MoO3–V2O5, and triple CuO–Fe2O3–CoCl2 3d metal dispersed systems were easily prepared by ball milling at room temperature and characterized by scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energydispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). They catalyze the microwave-assisted solvent-free heterogeneous oxidation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (t-BuOOH) as oxidant, used as a model reaction. In most of the heterometallic systems a significant improvement in the catalytic activity was observed in comparison to homometallic ones. For the tested catalytic systems and experimental conditions, the CuO–Fe2O3–CoCl2 and Fe2O3–CoCl2 systems exhibit the highest activity with maximum 78% yield and TON 39 after 1 h. The possibility of magnetic recovery of the catalysts was demonstrated for the Fe2O3–CoCl2 (3:1) system.
- Tailored 3D foams decorated with nanostructured manganese oxide for asymmetric electrochemical capacitorsPublication . Siwek, K. I.; Eugenio, S.; Aldama, I.; Rojo, J. M.; Amarilla, J. M.; Da Costa Ribeiro, Ana Paula; Moura E Silva, Teresa; Montemor, M.F.Tailored 3D (Ni and NiCo) metallic foam architectures were produced by electrodeposition and decorated via electrochemical routes with manganese oxide (MnOx) to serve as positive electrodes for supercapacitors. For comparative purposes, an electrode made of commercial Ni foam was also prepared. The foam-based electrodes were paired with a carbon cloth electrode and used to assemble asymmetric electrochemical cells. The electrochemical response of these cells was studied by applying different electrochemical techniques. In addition, two different protocols (cycling and floating) were applied to assess cells durability and fade. Despite the significant differences in the decorated foams morphology and structure their electrochemical responses revealed similar trends. The electrodes made of tailored foams showed higher specific capacitance, better capacitance retention at high current load and enhanced cycling stability compared to the electrodes made of commercial foam. The asymmetric cells made with the tailored foams revealed higher (maximum) specific energy (11-14 Wh kg(-1)) and specific power (1.3-1.4 x 10(4 )W kg(-1)) compared to cells assembled with commercial foams (8.4 Wh kg(-1) and 6.3 x 10(3) W kg(-1)). The durability tests evidenced that corrosion of the NiCo electrodeposited foams and electrochemical dissolution of MnOx are possible causes of cells degradation.
- Effect of graphene vs. reduced graphene oxide in gold nanoparticles for optical biosensors: a comparative studyPublication . Carvalho, Ana P. G.; Alegria, Elisabete; Fantoni, Alessandro; Ferraria, Ana Maria; Rego, Ana; Da Costa Ribeiro, Ana PaulaAiming to develop a nanoparticle-based optical biosensor using gold nanoparticles (AuNPs) synthesized using green methods and supported by carbon-based nanomaterials, we studied the role of carbon derivatives in promoting AuNPs localized surface plasmon resonance (LSPR), as well as their morphology, dispersion, and stability. Carbon derivatives are expected to work as immobilization platforms for AuNPs, improving their analytical performance. Gold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4·3H2O using phytochemicals (from tea) which act as both reducing and capping agents. UV–Vis spectroscopy, transmission electron microscopy (TEM), zeta potential (ζ-potential), and X-ray photoelectron spectroscopy (XPS) were used to characterize the AuNPs and nanocomposites. The addition of reduced graphene oxide (rGO) resulted in greater dispersion of AuNPs on the rGO surface compared with carbon-based nanomaterials used as a support. Differences in morphology due to the nature of the carbon support were observed and are discussed here. AuNPs/rGO seem to be the most promising candidates for the development of LSPR biosensors among the three composites we studied (AuNPs/G, AuNPs/GO, and AuNPs/rGO). Simulations based on the Mie scattering theory have been used to outline the effect of the phytochemicals on LSPR, showing that when the presence of the residuals is limited to the formation of a thin capping layer, the quality of the plasmonic resonance is not affected. A further discussion of the application framework is presented.
- Synergistic catalytic action of vanadia-titania composites towards the microwave-assisted benzoin oxidationPublication . Ferretti, Francesco; Da Costa Ribeiro, Ana Paula; Alegria, Elisabete; Ferraria, Ana Maria; Kopylovich, Maximilian; Guedes Da Silva, M. Fátima C.; Marchetti, Fabio; Pombeiro, ArmandoIntensification of chemical processes according to the motto "faster, simpler, greener" is among the main concerns nowadays. One of the ways of intensification is the application of synergistic catalytic effects when the overall efficiency of a composite catalyst is much higher than the sum of the component activities. Here, we report on the preparation of synergistic catalytic materials by a simple and straightforward ball milling procedure. Oxidation of benzoin was selected as a model reaction to demonstrate the viability of the concept. For the V2O5-TiO2 (95 : 5) composite material, the synergistic effect is triggered by low power microwave irradiation with more than a tenfold jump in the catalytic activity in comparison to the activities of the individual components.
- Copper(II) complexes with an arylhydrazone of methyl 2-cyanoacetate as effective catalysts in the microwave-assisted oxidation of cyclohexanePublication . Jlassi, Raja; Da Costa Ribeiro, Ana Paula; Alegria, Elisabete; Naili, Houcine; Tiago, Gonçalo; Rueffer, Tobias; Lang, Heinrich; Zubkov, Fedor; Pombeiro, Armando; Rekik, WalidReaction of sodium (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene) hydrazinyl) benzene-sulfonate (NaHL) with copper(II) nitrate hydrate in the presence of imidazole (im) in methanol affords [CuL(im)(H2O)] (1). Complex 1 is characterized by IR spectroscopy and ESI-MS spectrometry, elemental and single crystal X-ray crystal structural analyses. The coordination environment of the central copper(II) is nearly intermediate between ideal square-based pyramidal and trigonal bipyramidal geometry, three sites being occupied by the L2- ligand, which chelates in the O, N, O fashion, while two other sites are filled with the water and imidazole molecules. Extensive intermolecular hydrogen bonds between the L2-, water and imidazole ligands lead to a 3D supramolecular network. 1 and known Cu(II) complexes [Cu(H2O)(2)L]center dot H2O (2), [Cu(H2O)(py)L]center dot H2O (3) and [Cu-3(mu(3)-OH)(NO3)(CH3OH)(mu(2)-X)(3)(mu(2)-HL)] (4) act as effective catalysts in the oxidation of cyclohexane to cyclohexanol and cyclohexanone, using low power microwave (MW) irradiation, under mild conditions. Without a promoter, the activity of the catalyst reached a turnover number of 1.44 x 10(3) and a turnover frequency of 1.98 x 10(3) h(-1), after 2 h, at 50 degrees C. (C) 2017 Elsevier B.V. All rights reserved.