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Structural and magnetic properties of P25 TiO2 nanoparticles doped by Co

Publication . Morais Lopes, Fernando; Bessergenev, Valentin; J. Lourenço, João Paulo Lourenço; Hantusch, Martin; Burkel, Eberhard; Botelho do Rego, Ana M.; Rajnak, Michal; Timko, Milan; Kopcansky, Peter

The present work reports on the structural and magnetic properties of TiO2 P25 Degussa powder doped with cobalt. Dissolution of cobalt in TiO2 matrix was achieved by precipitation of tris(diethyldithiocarbamato) cobalt (III) (CoDtc - Co[S2CN(C2H5)(2)](3) in chloroform (CHCl3) and consequent thermal treatment. Five different Co atomic percentage contents were chosen, e.g., 0.5%, 1%, 2%, 5% and 10%. It was shown that cobalt atoms are uniformly distributed across TiO2 matrix and exhibit antiferromagnetic interactions at low temperatures.

2020-05Journal article

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Spectroscopic Methods for Quantifying Gabapentin: Framing the Methods without Derivatization and Application to Different Pharmaceutical Formulations

Publication . Fonseca, Frederico; de Barros, Ricardo Brito; Ilharco, Laura M.; Garcia, Ana

This work aimed at analyzing the performance of direct spectroscopic methods for the quantification of gabapentin (GABAp), given the lack of previous studies, in comparison with the more reviewed and complex derivatization techniques, discussing their susceptibility to the pharmaceutical formulations. All of the methods analyzed showed high selectivity for this pharmaceutical analyte, with recoveries close to 100%. Absorption spectroscopy without derivatization yielded better sensitivity and lower limits of detection and quantification of gabapentin in aqueous solution (AqSol method) when compared with other solvents, such as acidic solution or ethanol/water mixture. Derivatization with sodium hypochlorite presented the highest precision, whereas derivatization with vanillin exhibited the highest accuracy. The best method for GABAp quantification in terms of highest sensitivity, lowest limits of detection, and quantification, and also with good precision and accuracy, proved to be fluorescence with derivatization by 4-chloro-7-nitrobenzofurazan. The effect of the pharmaceutical formulation (nature of excipients) was tested for the most robust and sensitive methods, with and without derivatization, on capsules of five commercial brands. Recoveries in the range of 97.9-101.5% proved that there are no matrix interfering effects. Although not presenting the best performance in all the parameters evaluated, the AqSol method, due to its simplicity, proved to be suitable for the quantification of GABAp in capsules and tables containing the molecule as the active ingredient.

2017-11Journal article

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Structure and properties of cork-silica Xerogel nanocomposites: influence of the cork content

Publication . Garcia, Ana; Julio, Maria de Fatima; Ilharco, Laura M.

Environmentally friendly nanocomposites were synthesized from a silica precursor and cork under mild conditions and dried at atmospheric pressure. Because of the covalent bonding between the components, these CorSil nanocomposites are homogeneous, light (apparent density in the range 360-750 kg m(-3)), machinable, with the Shore D hardness up to 67 and compressive strength up to 22.6 MPa. These properties place them as good replacements for wood, other natural products, and thermoplastic polymers, with the advantage of being flame-retardant. The influence of the cork content and grain size on the structure, porosity, and mechanical properties of the nano composites was studied using infrared spectroscopy, sorption isotherms, compressive strength, and Shore D hardness measurements.

2019-01Journal article

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A cork-silica xerogel nanocomposite with unique properties

Publication . Garcia, Ana; Julio, M. F.; Ilharco, L. M.

Taking advantage of the bonding between cork and silica xerogel, environmentally friendly nanocomposites are synthesized by a sol-gel process and dried at ambient pressure, with a superb combination of properties: densities near 600 kg m(-3), surface areas of 200 m(2) g(-1), mechanical strength up to 24 MPa, Shore D hardness up to 58 and, moreover, flame retardant. These properties are tunable by adjusting the synthesis parameters. The effects of cork granulometry and pre-swelling, and of the catalysis conditions are analyzed. Potential applications for these innovative nanocomposites are envisaged as replacement of thermoplastic polymers or hard wood, when non-flammability is desirable. The present approach opens a range of possibilities for developing unique composite materials that use natural and inexpensive raw resources and soft synthesis processes, with little energy requirements. [GRAPHICS]

2017-09Journal article

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