Olinda C. Monteiro

Photocatalytic decolorization of methylene blue in the presence of TiO2/ZnS nanocomposites.

The synthesis of distinct nanocrystalline TiO2 capped ZnS samples was carried out using a chemical deposition method. The materials characterization showed that the presence of ZnS onto TiO2 surface results in a red shift of the material band edge when compared with the initial semiconductor. The photocatalytic activity of the prepared nanocomposites was tested on the decolorization of methylene blue (MB) aqueous solutions. The dye photodecolorization process was studied considering the influence of experimental parameters such as catalyst concentration, TiO2/ZnS ratio, pH and methylene blue adsorption rate. The material with the best catalytic activity towards the methylene blue photodecolorization was the TiO2 doped with 0.2% of ZnS. The complete photodecolorization of a 20ppm methylene blue solution, at natural pH was achieved in less than 20min, nearly 70min faster than the TiO2 photoassisted process.

Synthesis of PbSe nanocrystallites using a single-source method. The X-ray crystal structure of lead (II) diethyldiselenocarbamate

Abstract The compounds Pb{Se2CN(C2H5)2}2 and Pb{Se2CN(CH3)(C6H13)}2 were synthesised and characterised. The X-ray crystal structure of Pb{Se2CN(C2H5)2}2 is reported. The use of these compounds as single-molecule precursors to produce PbSe by thermolysis in tri-n-octylphosphine oxide was investigated. The optical and morphological properties of the PbSe particulates were analysed; strong quantum confinement effects were observed in the optical spectra of nanodispersed PbSe in organic solvents.

Magnetic properties of Co-doped TiO2 anatase nanopowders

This letter reports on the magnetic properties of Ti1−xCoxO2 anatase phase nanopowders with different Co contents. It is shown that oxygen vacancies play an important role in promoting long-range ferromagnetic order in the material studied in addition to the transition-metal doping. Furthermore, the results allow ruling out the premise of a strict connection between Co clustering and the ferromagnetism observed in the Co:TiO2 anatase system.

Aerosol-assisted metallo-organic chemical vapour deposition of Bi2Se3 films using single-molecule precursors. The crystal structure of bismuth(III) dibutyldiselenocarbamate

The complexes [Bi{Se2CN(C2H5)2}3], [Bi{Se2CN(C4H9)2}3], [Bi{Se2CN(CH3)(C4H9)}3] and [Bi{Se2CN(CH3)(C6H13)}3] have been synthesized and characterized structurally using IR, 1H and 13C NMR. In addition, the crystal structure of [Bi{Se2CN(C4H9)2}3] was determined by single-crystal X-ray diffraction, showing the bismuth centre coordinated to three dialkyldiselenocarbamate ligands through the selenium donor atoms. The Bi(III) compounds were used as precursors for the deposition of Bi2Se3 films on glass substrates through aerosol-assisted metallo-organic chemical vapour deposition (AA-MOCVD).

The LP-MOCVD of CdS/Bi2S3 bilayers using single-molecule precursors

Abstract The single-molecule precursors [Cd(S 2 CNMe n -Hex) 2 ] and [Bi(S 2 CNMe n -Hex) 3 ] (Me=methyl; n -Hex= n -hexyl) were used to prepare CdS/Bi 2 S 3 layers by low-pressure metal organic chemical vapour deposition (LP-MOCVD). The bilayers were deposited onto glass substrates at 400–450 °C for varying growth conditions. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical measurements. The results were compared with those obtained for the single phases.

Novel one-pot synthesis and sensitisation of new BiOCl–Bi2S3 nanostructures from DES medium displaying high photocatalytic activity

A novel route to synthesise Bi2S3-sensitised BiOCl nanoparticles from deep eutectic solvent medium at room temperature by a one-pot approach is reported. The influence of the temperature, sulphur source, concentration of reactants and presence of water, on the morphological, structural and microstructural, optical and photocatalytic properties of the synthesised nanoparticles is analysed and discussed. Stable and crystalline BiOCl hybrid structures with shapes from sheet-like to flower-like hierarchical aggregates and (001) and (110) dominant crystallographic orientation were obtained. The sensitisation of BiOCl with Bi2S3 was successfully achieved in situ during synthesis by an ion-exchange process and the relative proportion of the components (BiOCl and Bi2S3) was controlled by the Bi : S ratio in the synthesis medium and by the sulphur precursor. The sensitiser nanomaterial (Bi2S3) extends the BiOCl photoactive region to the visible range. Also it favours charge separation and reducing the electron/hole pair recombination and therefore increasing the photocatalytic performance. The prepared composite materials show high ability to adsorb rhodamine B cationic dye and the complete photocatalytic degradation was achieved within 45 min (75 mg per g of catalyst).

Corrosion of silver alloys in sulphide environments: a multianalytical approach for surface characterisation

Sterling silver samples, prepared to simulate cultural heritage surfaces, were subjected to accelerated ageing tests through exposure to sulphide containing environments. Data obtained by X-ray diffraction, ultraviolet-visible spectrophotometry, contact angle goniometry, ellipsometry and scanning electron microscopy revealed, contrarily to what has been suggested, that the colour of corroded surfaces is related to the thickness of the corrosion layer and to the multi-layer structure of various corrosion products. At the early stages of corrosion, Cu prevails over the Ag compounds. In subsequent stages, AgCuS complexes were also detected. Ag2S is the prevailing corrosion product after longer periods of time.

Biotechnologically obtained nanocomposites: A practical application for photodegradation of Safranin-T under UV-Vis and solar light

This research was undertaken to determine the potential of biologically obtained ZnS-TiO2 nanocomposites to be used as catalysts in the photodegradation of organic pollutants, namely, Safranin-T. The photocatalysts were prepared by modifying the surface of commercial TiO2 particles with naturally produced ZnS, using sulfide species produced by sulfate-reducing bacteria and metal contaminated wastewaters. Comparative studies using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), prior and after photodegradation, were carried out in order to monitor possible structural and morphological changes on the particles. Adsorption properties and specific areas were determined by the Brunauer–Emmet–Teller (BET) method. The final solutions were characterized by UV-Vis and chemical oxygen demand (COD) content in order to determine Safranin-T concentration and toxicity. The influence of the catalyst amount, initial pH and dye concentration was also evaluated. Finally, the efficiency of the precipitates as catalysts in sunlight-mediated photodegradation was investigated, performing two scale experiments by using different volumes of dye-contaminated water (150 mL and 10 L). All tested composites showed potential to be used as photocatalysts for the degradation of Safranin-T, although the ZnS-TiO2_0.06 composite (0.06 g of TiO2 per 50 mL of the zinc solution) was the most effective. This substantiates the applicability of these biologically obtained materials as efficient photocatalysts for the degradation of organic pollutants, in laboratorial conditions and under direct sunlight.

Enhanced photocatalytic degradation of psychoactive substances using amine-modified elongated titanate nanostructures

Many thousands of pharmaceuticals and personal care products (PPCPs) are used worldwide and disposed in the environment after use. Several removal methodologies have been proposed but clear improvements in effectiveness and efficiency are needed. In this work, new hybrid photocatalytic nanomaterials were obtained through sensitization of titanate nanotubes (TNT) and nanowires (TNW) with ethylenediamine (EDAmine). The prepared materials, NTNT and NTNW respectively, were morphologically, structurally, and optically characterized by XRD, TEM, DRS and XPS. No modifications in the structure and morphology were detected after EDAmine incorporation. However, an increase in the visible light absorption and in the point of zero charge was observed. The application of these novel hybrid nanomaterials in the catalytic photodegradation of emergent pollutants was studied. Terephthalic acid was used as a probe for hydroxyl radical photocatalytic production evaluation. The highest catalytic activity was achieved by the NTNT sample. The photocatalytic ability of the hybrid materials for the degradation of psychoactive substances, caffeine and theophylline, and for phenol removal was evaluated and the secondary products identified. After 60 min under UV-vis radiation, the NTNT sample was the best catalyst, achieving 98% photodegradation efficiency for phenol and theophylline and 60% for caffeine (20 ppm solutions). A mechanism for charge transfer in irradiated NTNT is proposed and discussed.

The influence of the constituent elements on the corrosion mechanisms of silver alloys in sulphide environments: the case of sterling silver

The corrosion of copper and silver in sulphide environments was assessed by several analytical techniques to investigate the influence of each one on the corrosion of sterling silver. The surface colour changes with the immersion time due to the formation of corrosion products composed of particles with distinct sizes and shapes and the consequent layer thickening. Ag2S is the main corrosion product of silver. At early stages of corrosion, Cu develops Cu2O and Cu2S, and later Cu2O again. After the corrosion of sterling silver, pure Cu and Ag are compared, and the predominant influence of Cu at the first stages may be suggested whilst Ag mainly contributes to longer corrosion stages. The layer-by-layer corrosion structure observed for the sulphidation of sterling silver was not observed for its constituent elements.