Photocatalytic activity of Portland cement pastes blended with nanoparticles of titanium oxynitride (TiO2−xNy) was studied. Samples with different percentages of TiO2−xNy (0.0%, 0.5%, 1%, 3%) and TiO2 (1%, 3%) were evaluated in order to study their self-cleaning properties. The presence of nitrogen in the tetragonal structure of TiO2 was evidenced by X-ray diffraction (XRD) as a shift of the peaks in the 2θ axis. The samples were prepared with a water/cement ratio of 0.5 and a concentration of Rhodamine B of 0.5 g/L. After 65 h of curing time, the samples were irradiated with UV lamps to evaluate the reduction of the pigment. The color analysis was carried out using a Spectrometer UV/Vis measuring the coordinates CIE (Commission Internationale de l'Eclairage) L*, a*, b*, and with special attention to the reddish tones (Rhodamine B color) which correspond to a* values greater than zero. Additionally, samples with 0.5%, 1%, 3% of TiO2−xNy and 1%, 3% of TiO2 were evaluated under visible light with the purpose of determining the Rhodamine B abatement to wavelengths greater than 400 nm. The results have shown a similar behavior for both additions under UV light irradiation, with 3% being the addition with the highest photocatalytic efficiency obtained. However, TiO2−xNy showed activity under irradiation with visible light, unlike TiO2, which can only be activated under UV light. OPEN ACCESSCoatings 2015, 5 466

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El efecto puzolánico de partículas de nanosílice (NS) combinadas con Nanotubos de Carbono de Pared Múltiple (MWCNT) fue estudiado en pastas de Ca(OH)2 y morteros de cemento Pórtland. Técnicas de diseño experimental fueron aplicadas para planear los experimentos e identificar el efecto de las nanopartículas sobre las propiedades de las matrices cementantes usando Análisis de Varianza (ANOVA). Se prepararon muestras con diferentes combinaciones de NS y MWCNT. Las pastas de Ca(OH)2 fueron usadas para estudiar el efecto de las naopartículas en la producción de Silicato de Calcio Hidratado (C-S-H), y los morteros de cemento Pórtland se usaron para estudiar el efecto de las nanopartículas en las resistencias a compresión y flexo-tracción de las matrices. Se encontró que solo la NS tuvo un efecto significativo sobre la producción de C-S-H hasta 21 días de hidratación, y que los MWCNT no presentaron un efecto positivo sobre las propiedades mecánicas de los morteros debido a efectos de reagomeración.

a b s t r a c tIn this work, rare-earth orthoferrites polycrystalline compounds REFeO 3 (REFO) with RE = rare-earth La, Pr, Nd and Sm were synthesized by the self-combustion method. A direct correlation between the magnitude of the magnetic hyperfine field and the FeAO 1 AFe bond angles was observed. From transmission Mössbauer spectra recorded at room-temperature, relative recoilless F-factors for these REFO compounds were estimated. The method applied to perform this calculation was based on the determination of two subspectral areas present in a mixture of known amounts of the compound under study and a standard sample (a-Fe). For that purpose spectra were thickness-corrected and fitted using lorentzian lines. The so obtained factors were F-REFeO3 (RE = rare-earth La, Pr, Nd and Sm): 1.30 ± 0.02, 1.08 ± 0.04, 1.15 ± 0.05, 1.18 ± 0.08 respectively. The absolute recoilless factors obtained by this method had an average relative error around 11% in comparison with the values predicted by the Debye model.