Browsing by Author "Nunes, Manuel R."
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- Enhancing alkane oxidation using Co-doped SnO2 nanoparticles as catalystsPublication . Silva, Telma F.S.; Silvestre, A. J.; Rocha, Bruno G. M.; Nunes, Manuel R.; Monteiro, Olinda; Martins, LuisaA novel eco-friendly KA oil synthesis at room temperature (up to 25% yield) via solvent-free cyclohexane oxidation using Sn1 − xCoxO2 − δ (x = 0, 0.01 or 0.05) nanoparticles as catalyst (TON up to 2 × 103) is here reported. These nanoparticles are the first SnO2-based material able to catalyze the oxidation of alkanes. The most active nanocatalyst was the Sn0.95Co0.05O2 − δ, allowing an easy recovery and reuse, at least for five consecutive cycles, maintaining high selectivity concomitant with 92% of its initial activity.
- Influence of Re and Ru doping on the structural, optical and photocatalytic properties of nanocrystalline TiO2Publication . Barrocas, Beatriz; Monteiro, Olinda; Nunes, Manuel R.; Silvestre, António JorgeTiO2 and TM-doped TiO2 (TM = Re, Ru) anatase crystalline nanopowders were synthesized by a simple hydrothermal method. Samples with nominal TM/Ti ratio of 0.01 were prepared for this study. Their structural, microstructural and optical properties were studied. The lattice parameters of the different prepared samples were calculated and their mean crystallite sizes determined to be in the range 15–7 nm, the lower values being obtained for the doped crystallites. The samples’ specific surface areas were determined and correlated with their mean crystallite sizes. The incorporation of the dopant elements results in an increase of the optical absorption in the visible range. The samples’ optical bandgap and Urbach energies were calculated from UV–Vis diffuse reflectance spectra. The photocatalytic behavior of the synthesized samples was investigated for the rhodamine B and phenol degradation processes, the kinetics of the different photo-oxidation reactions being also studied. The results showed that doping either with Re or Ru can lead to enhancement of the TiO2 photocatalytic efficiency and that, among the synthesized samples Ru-doped TiO2 is the most efficient photocatalyst for both the Rhodamine B and phenol photodegradation reactions.
- A new chemical route to synthesise TM-doped (TM = Co, Fe) TiO2 nanoparticlesPublication . Nunes, Manuel R.; Monteiro, Olinda C.; Castro, Ana L.; Vasconcelos, Duarte A.; Silvestre, António JorgeSince the discovery of ferromagnetism well above room temperature in the Co-doped TiO2 system, diluted magnetic semiconductors based on TiO2 doped with transition metals have generated great interest because of their potential use in the development of spintronic devices. The purpose of this paper is to report on a new and swift chemical route to synthesise highly stable anatase single-phase Co- and Fe-doped TiO2 nanoparticles, with dopant concentrations of up to 10 at.-% and grain sizes that range between 20 and 30 nm. Complementary structural, microstructural and chemical analyses of the different nanopowders synthesised strongly support the hypothesis that a homogeneous distribution of the dopant element in the substitutional sites of the anatase structure has been achieved. Moreover, UV/Vis diffuse reflectance spectra of powder samples show redshifts to lower energies and decreasing bandgap energies with increasing Co or Fe concentration, which is consistent with n-type doping of the TiO2 anatase matrix. Films of Co-doped TiO2 were successfully deposited onto Si (100) substrates by the dip-coating method, with suspensions of Ti1-xCOxO2 nanoparticles in ethylene glycol. ((C)Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).