M.H. Mendonça

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.

Effect of the partial replacement of Fe by Ni and/or Mn on the electrocatalytic activity for oxygen evolution of the CoFe2O4 spinel oxide electrode

Abstract The study of the electrochemical behaviour of mixed spinel oxide electrodes, obtained by the partial replacement of Fe by Ni and/or Mn in the cobalt ferrite CoFe 2 O 4 is presented. The electrodes were prepared by brush painting of iron substrates with a suspension of the respective oxide, prepared by solid-state reaction. The influence of the substituent on the electrodes electrocatalytic activity towards the OER is analysed in terms of the kinetic parameters obtained by steady state measurements and the cationic distribution proposed for the oxides. The data show that the introduction of Ni brings about the presence of Co 3+ tetrahedrally coordinated in addition to the Co 3+ /Co 2+ couple in octahedral sites, giving rise to a better electrocatalyst for the OER. In contrast the presence of Mn produces electrodes with lower catalytic activity.

XPS and voltammetric studies on Ni1-xCuxCo2O4 spinel oxide electrodes

Abstract Spinel oxide electrodes of Ni 1− x Cu x Co 2 O 4 (0.00≤ x ≤0.75) layers were prepared by thermal decomposition of the corresponding nitrate solutions on Ni mesh at 350°C. The surface analysis was carried out by XPS and shows that the oxides surface is rich in copper for all the studied compositions, and when x ≤0.10 an enrichment in nickel was also observed. The surface electrochemical properties were studied by cyclic voltammetry and correlated with XPS data.

Preparation and characterisation of spinel oxide ferrites suitable for oxygen evolution anodes

Abstract The effect of the partial substitution of iron by Ni and also by Mn on the properties of the CoFe2O4 spinel type oxide has been studied. The oxide powders CoFe2–xMxO4 were prepared by the standard ceramic method, and the respective structural characterisation performed by X-ray powder diffraction. In particular, the electric, magnetic and electrochemical behaviour of the monophasic mixed oxides have been analysed. From the synthesised oxide samples, iron coated electrodes were fabricated and tested as anode for the oxygen evolution reaction in alkaline medium.

Hyperthermia studies of ferrite nanoparticles synthesized in the presence of cotton

MFe2O4 (M = Co, Fe, Mn) compounds were synthesized using hydrothermal treatment in the presence of medicinal cotton. Two sets of nanoparticles were produced for each composition and subsequently characterized by XRD, TEM and SEM. The nanoparticles obtained from the solution display the expected spinel structure and different mean sizes (below 16 nm); the nanoparticles embedded in cotton were subjected to a calcination process for cotton elimination. Regarding these calcinated samples, the spinel structure was maintained for CoFe2O4, a mixture of phases was identified for the M = Mn sample and, in the case of iron, the magnetite phase was converted to hematite (α-Fe2O3). After cotton elimination the samples exhibit a morphology which evidences the role of cotton as a template. To evaluate the quality of the nanoparticles for hyperthermia, SQUID magnetometry and Mossbauer spectroscopy were used to perform the magnetic characterization of all products, and the specific loss power (SLP) was determined by induction heating measurements. All the ferrite NP obtained by hydrothermal synthesis in the presence of cotton display good hyperthermia performance. MnFe2O4 nanoparticles exhibit the highest SLP value, 90 W g−1, followed by Fe3−xO4, and CoFe2O4. In the case of CoFe2O4, the specific loss power of the NP obtained after cotton elimination is enhanced by 50% which is explained by the NP morphology adopted from the cotton template during the synthesis.

Phenol electrooxidation on Fe–Co3O4 thin film electrodes in alkaline medium

Fe-Co(3)O(4) thin film with different amounts of Fe have been used for the electro-oxidation of phenol in alkaline medium at room temperature. The electrodes were prepared by coating stainless steel supports with successive layers of the oxides, obtained by thermal decomposition at 673 K. The electrolysis was carried out at constant potential and the phenol disappearance, during the electrolysis, was monitored by UV-Vis absorbance measurements between 250 and 500 nm. After 3 h of electrolysis, the intermediates were identified by comparing the HPLC data and UV-Vis spectra to those from pure standards. The results indicate that the same oxidation products are formed on the different prepared electrodes, namely the decomposition products of phenol such as benzoquinone, hydroquinone and cathecol in basic medium. Simulated results show clearly the decrease of the amount of phenolic species with the electrolysis time. An enhancement of the phenol removal is observed with the presence of iron in the oxide. Under the operating conditions, around 30% of the initial phenol has been removed at ca. 3 h and the complete degradation is obtained after 54 h of electrolysis, when Fe-Co(3)O(4) thin film with 10% of Fe is used as anode.

Effect of the substrate on the electrodeposition of iron sulphides

The electrodeposition of iron sulphides films on titanium and Ebonex®, in aqueous solutions containing iron(II) ions and colloidal sulphur, has been assessed at 333 K, using periodic pulse electrolysis. Mackinawite was the only crystalline iron sulphide phase identified on the deposit. The structural and morphological characterization of the sulphide films obtained on both substrates was accomplished by X-ray powder diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDS). The results show that the film structure and morphology are sensitive to the substrate material.

Gelatine-assisted synthesis of magnetite nanoparticles for magnetic hyperthermia

Magnetite nanoparticles were synthesized by the co-precipitation method exploring the use of gelatine and agar as additives. For comparison, magnetite nanoparticles were also prepared by standard co-precipitation, by co-precipitation with the addition of a surfactant (sodium dodecyl sulphate) and by the thermal decomposition method. The structure and morphology of the synthesized nanoparticles were investigated by powder X-ray diffraction and transmission electron microscopy. Their magnetic properties were studied by SQUID magnetometry and 57Fe Mössbauer spectroscopy. The nanoparticles potential for applications in magnetic hyperthermia was evaluated through heating efficiency under alternating magnetic field. The results show that all synthesis methods produce Fe3−xO4 nanoparticles with similar sizes. The nanoparticles synthesized in the gelatine medium display the narrowest particle size distribution, the lowest oxidation degree, one of the highest saturation magnetization values and the best hyperthermia efficiency, proving that this gelatine-assisted synthesis is an efficient, environmental friendly, and low-cost method to produce magnetite nanoparticles.Graphical AbstractA new gelatine-assisted method is an efficient and low-cost way to synthesize magnetite nanoparticles with enhanced magnetic hyperthermia.

New Ceramic Products from Slate and Aluminium Sludge Wastes

Previous studies had shown that a promising material could be obtained by mixing aluminium-rich sludge with slate powder (with Al2O3:SiO2 molar proportion of 2:1), shaping by uniaxial pressing and sintering at 1300oC, in order both to detoxify the sludge by fixing the metals in a leach-resistant ceramic matrix and to yield a new material from the reactions of the above compounds at high temperature. In view of potential applications, since this material was also found to be inert after leaching tests, a further systematic study, reported in the present paper, was carried out, in order to determine its mechanical properties and discuss them in function of the microstructure. The average values of Vickers hardness HV3 (683), bend strength (126 MPa), Youngs modulus (161GPa) and fracture toughness (3.35 MPa.m1/2) are significantly higher than those found for the as sintered slate powders, which is attributed to the increased fraction of α- alumina and reduced content of glassy phase in the microstructure of the material with sludge addition.

Caracterização através de análise química da escultura portuguesa sobre madeira de produção erudita e de produção popular da época barroca

Making use of several analytical techniques, four erudite and four popular Portuguese baroque wooden sculptures were studied. The materials and techniques employed were identified and the relationship between their artistic quality and the materials used was investigated. In general, the pigments were common at the time, but one pigment discovered in the beginning of the 18th century and two rare arsenic pigments were also identified. In popular sculptures cost-saving was detected, particularly concerning the gold leaf. Regarding some technical procedures identified, recommendations found in historical documents did not seem to have been entirely followed, neither in erudite nor in popular sculptures.