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Listado de Artículos Publicados en 2014

Los artículos están ordenados por el factor de impacto reflejado en el 'Journal Citation Reports 2013'.
  1. EELS analysis of Nylon 6 nanofibers reinforced with nitroxide-functionalized graphene oxide
    César Leyva-Porras, C Ornelas-Gutiérrez, M. Miki-Yoshida, Yazmín I. Ávila-Vega, Javier Macossay, José Bonilla-Cruz
    Carbon 70, (2014), 164–172 F. I. 6.16
    A detailed analysis by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) of nitroxide-functionalized graphene oxide layers (GOFT) dispersed in Nylon 6 nanofibers is reported herein. The functionalization and exfoliation process of graphite oxide to GOFT was confirmed by TEM using electron diffraction patterns (EDP), wherein 1–4 graphene layers of GOFT were observed. The distribution and alignment of GOFT layers within a sample of Nylon 6 nanofiber reveals that GOFT platelets are mainly within the fiber, but some were partially protruding from it. Furthermore, Nylon 6 nanofibers exhibited an average diameter of 225 nm with several microns in length. GOFT platelets embedded into the fiber, the pristine fiber, and amorphous carbon were analyzed by EELS where each spectra [corresponding to the carbon edge (C-K)] exhibited changes in the fine structure, allowing a clear distinction between: (i) GOFT single-layers, (ii) Nylon-6 nanofibers, and (iii) the carbon substrate. EELS analysis is presented here for the first time as a powerful tool to identify functionalized graphene single-layers (< 4 layers of GOFT) into a Nylon 6 nanofiber composite.
  2. Influence of ZnO sol–gel electron transport layer processing on BHJ active layer morphology and OPV performance
    Diego Barrera , Yun-Ju Lee, Julia W.P. Hsu
    Solar Energy Materials and Solar Cells 125, (2014), 27–32 F. I. 5.03
    We report that thermal annealing of P3HT:PCBM bulk heterojunctons (BHJs) on top of a commonly used sol–gel ZnO electron transport layer can lead to the formation of PCBM clusters, which significantly decreased short circuit current density (up to 45%), open circuit voltage (up to 35%), and fill factor (up to 15%). To understand the cause of this phenomenon, we deposited ZnO films using different sol–gel recipes and systematically studied the correlation between sol–gel ZnO processing and the morphology of the P3HT:PCBM BHJ. We showed that higher amounts of monoethanolamine (MEA), a stabilizer in the ZnO sol–gel precursor, lead to higher densities of PCBM clusters in the BHJ. In addition, we correlated the cluster area fraction with bimolecular recombination at 100 mW/cm2, as quantified by white-light biased external quantum efficiency measurements. Finally, we show that rinsing off residual organics from the ZnO surface after pyrolysis eliminated PCBM cluster formation, avoiding poor organic photovoltaic device performance.
  3. Removal of Total Organic Carbon from Sewage Wastewater Using Poly(ethylenimine)-Functionalized Magnetic Nanoparticles
    Lakshmanan, R; Sánchez- Domínguez, M; Matutes-Aquino, JA; Wennmalm, S; Rajarao, GK.
    Langmuir 30, (2014), 1036-1044 F. I. 4.384
    The increased levels of organic carbon in sewage wastewater during recent years impose a great challenge to the existing wastewater treatment process (WWTP). Technological innovations are therefore sought that can reduce the release of organic carbon into lakes and seas. In the present study, magnetic nanoparticles (NPs) were synthesized, functionalized with poly(ethylenimine) (PEI), and characterized using TEM (transmission electron microscopy), X-ray diffraction (XRD), FTIR (Fourier transform infrared spectroscopy), CCS (confocal correlation spectroscopy), SICS (scattering interference correlation spectroscopy), magnetism studies, and thermogravimetric analysis (TGA). The removal of total organic carbon (TOC) and other contaminants using PEI-coated magnetic nanoparticles (PEI-NPs) was tested in wastewater obtained from the Hammarby Sjostadsverk sewage plant, Sweden. The synthesized NPs were about 12 nm in diameter and showed a homogeneous particle size distribution in dispersion by TEM and CCS analyses, respectively. The magnetization curve reveals superparamagnetic behavior, and the NPs do not reach saturation because of surface anisotropy effects. A 50% reduction in TOC was obtained in 60 min when using 20 mg/L PEI-NPs in 0.5 L of wastewater. Along with TOC, other contaminants such as turbidity (89%), color (86%), total nitrogen (24%), and microbial content (90%) were also removed without significant changes in the mineral ion composition of wastewater. We conclude that the application of PEI-NPs has the potential to reduce the processing time, complexity, sludge production, and use of additional chemicals in the WWTP.
  4. Local structure and nanoscale homogeneity of CeO2-ZrO2: differences and similarities to parent oxides revealed by luminescence with temporal and spectral resolution
    Tiseanu, C; Parvulescu, V; Avram, D; Cojocaru, B; Boutonnet, M; Sánchez Domínguez, M.
    Physical Chemistry Chemical Physics 16, (2014), 703-710 F. I. 4.198
    Although homogeneity at the atomic level of CeO2-ZrO2 with a Ce/Zr atomic ratio close to unity is considered to be one of the main causes for the increased total oxygen storage capacity (OSC), the characterization approaches of homogeneity remain a major challenge. We propose a simple, yet effective method, to assess both structural and compositional homogeneity of CeO2-ZrO2 by using Eu3+ luminescence measured with time and dual spectral resolution (emission and excitation). For Eu3+-CeO2-ZrO2 calcined at 750 degrees C, the X-ray diffraction, Raman and High-Resolution Transmission Electron Microscopy data converge to a single pseudo-cubic phase. However, the evolution of Eu3+-delayed luminescence from cubic ceria-like to tetragonal zirconia-like emission reveals the formation of CeO2- and ZrO2-rich nanodomains and provides evidence for early phase separation. For Eu3+-CeO2-ZrO2 calcined at 1000 degrees C, the emission of Eu3+ reveals both structural and compositional inhomogeneity. Our study identifies the differences between the local structure properties of CeO2 and ZrO2 parent oxides and CeO2-ZrO2 mixed oxide, also confirming the special chemical environment of the oxygen atoms in the mixed oxide as reported earlier by Extended X-ray Absorption Fine Structure investigations.
  5. Structural, down- and phase selective up-conversion emission properties of mixed valent Pr doped into oxides with tetravalent cations
    Tiseanu, C ; Parvulescu, V; Avram, D ; Cojocaru, B ; Apostol, N ; Vela-González, AV ; Sánchez- Domínguez, M
    Physical Chemistry Chemical Physics 12, (2014), 5793-5802 F. I. 4.198
    We report on structure-property relationships in Pr-doped CeO2 and ZrO2 using X-ray diffraction (XRD), Raman, UV to Vis Diffuse Reflectance (DR-UV/Vis), X-ray Photoelectron (XPS), and luminescence (PL) spectroscopies. Both 3+ and 4+ valence states of Pr are evidenced, irrespective of the host and calcination temperature, T (T = 500 and 1000 degrees C) with consequences on absorption, surface, vibrational and luminescence properties. Only zirconia represents a suitable host for Pr3+ luminescence. The distinct trivalent Pr centers and their excitation mechanism are identified in relation to the tetragonal and monoclinic phases of ZrO2. A near-infrared to visible up-conversion (UPC) emission of Pr3+ is observed upon excitation at 959 nm which occurs, most probably, via a two-photon excited state process. By using a multi-wavelength, time-gated excitation, the UPC process is established as phase selective, i.e. only Pr3+ located in the monoclinic sites of the mixed phase, monoclinic and tetragonal ZrO2 (T = 1000 degrees C) contribute to the UPC emission. We believe that, besides the local symmetry, a key role in phase selective UPC is played by the presence of Pr3+ low-lying 4f 5d levels. To the best of our knowledge, this is the first report of phase selective up-conversion emission in a lanthanide doped multi-phase host

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