Hydrothermal synthesis of 1D TiO2 nanostructures for dye sensitized solar cells

El pdf del artículo es la versión pre-print.Mono-dimensional titanium oxide nanostructures (multi-walled nanotubes and nanorods) were synthesized by the hydrothermal method and applied to the construction of dye sensitized solar cells (DSCs). First, nanotubes (TiNTs) and nanotubes loaded with titanium oxide nanoparticles (TiNT/NPs) were synthesized with specific surface areas of 253 m2/g and 304 m2/g, respectively. After that, thermal treatment of the nanotubes at 500 °C resulted in their transformation into the corresponding anatase nanorods (TiNT-Δ and TiNT/NPs-Δ samples). X-ray diffraction and Raman spectroscopy data indicated that titanium oxide in the pristine TiNT and TiNT/NP samples was converted into anatase phase TiO2 during the heating. Additionally, specific surface areas and water adsorption capacities decreased after the heat treatment due to the sample agglomeration and the collapse of the inner nanotube channels. DSCs were fabricated with the nanotube TiNT and TiNT/NP samples and with the anatase nanorod TiNT-Δ and TiNT/NPs-Δ samples as well. The highest power conversion efficiency of η = 3.12% was obtained for the TiNT sample, despite its lower specific surface compared with the corresponding nanoparticle-loaded sample (TiNT/NP). © 2011 Elsevier B.V. All rights reserved.This work was funded by the Government of Aragon and La Caixa (project ref. GA-LC-041/2008) and by the Spanish MICINN (projects ref. EUI2008-00152 and ENE2008-04373). We thank the Spanish National Research Council (CSIC) for the JAE-Doc contracts awarded to Y.Y. and A.A. To the Xarxa de Referència en Materials Avanc¸ ats per a l’Energia, XaRMAE (Reference Center for Advanced Materials for Energy) of the Catalonia Government.Peer Reviewe

New insights into the properties of pubescent surfaces: the peach fruit (prunus persica batsch) as a model

The surface of peach (Prunus persica ‘Calrico’) is covered by a dense indumentum, which may serve various protective purposes. With the aim of relating structure to function, the chemical composition, morphology, and hydrophobicity of the peach skin was assessed as a model for a pubescent plant surface. Distinct physicochemical features were observed for trichomes versus isolated cuticles. Peach cuticles were composed of 53% cutan, 27% waxes, 23% cutin, and 1% hydroxycinnamic acid derivatives (mainly ferulic and p-coumaric acids). Trichomes were covered by a thin cuticular layer containing 15% waxes and 19% cutin and were filled by polysaccharide material (63%) containing hydroxycinnamic acid derivatives and flavonoids. The surface free energy, polarity, and work of adhesion of intact and shaved peach surfaces were calculated from contact angle measurements of water, glycerol, and diiodomethane. The removal of the trichomes from the surface increased polarity from 3.8% (intact surface) to 23.6% and decreased the total surface free energy chiefly due to a decrease on its nonpolar component. The extraction of waxes and the removal of trichomes led to higher fruit dehydration rates. However, trichomes were found to have a higher water sorption capacity as compared with isolated cuticles. The results show that the peach surface is composed of two different materials that establish a polarity gradient: the trichome network, which has a higher surface free energy and a higher dispersive component, and the cuticle underneath, which has a lower surface free energy and higher surface polarity. The significance of the data concerning water-plant surface interactions is discussed within a physiological context.The surface of peach (Prunus persica ‘Calrico’) is covered by a dense indumentum, which may serve various protective purposes. With the aim of relating structure to function, the chemical composition, morphology, and hydrophobicity of the peach skin was assessed as a model for a pubescent plant surface. Distinct physicochemical features were observed for trichomes versus isolated cuticles. Peach cuticles were composed of 53% cutan, 27% waxes, 23% cutin, and 1% hydroxycinnamic acid derivatives (mainly ferulic and p-coumaric acids). Trichomes were covered by a thin cuticular layer containing 15% waxes and 19% cutin and were filled by polysaccharide material (63%) containing hydroxycinnamic acid derivatives and flavonoids. The surface free energy, polarity, and work of adhesion of intact and shaved peach surfaces were calculated from contact angle measurements of water, glycerol, and diiodomethane. The removal of the trichomes from the surface increased polarity from 3.8% (intact surface) to 23.6% and decreased the total surface free energy chiefly due to a decrease on its nonpolar component. The extraction of waxes and the removal of trichomes led to higher fruit dehydration rates. However, trichomes were found to have a higher water sorption capacity as compared with isolated cuticles. The results show that the peach surface is composed of two different materials that establish a polarity gradient: the trichome network, which has a higher surface free energy and a higher dispersive component, and the cuticle underneath, which has a lower surface free energy and higher surface polarity. The significance of the data concerning water-plant surface interactions is discussed within a physiological context

Action of transcription factors in the control of transferrin receptor expression in human brain endothelium

Brain endothelium has a distinctive phenotype, including high expression of transferrin receptor, p-glycoprotein, claudin-5 and occludin. Dermal endothelium expresses lower levels of the transferrin receptor and it is absent from lung endothelium. All three endothelia were screened for transcription factors that bind the transferrin receptor promoter and show different patterns of binding between the endothelia. The transcription factor YY1 has distinct DNA-binding activities in brain endothelium and non-brain endothelium. The target-sites on the transferrin receptor promotor for YY1 lie in close proximity to those of the transcription initiation complex containing TFIID, so the two transcription factors potentially compete or interfere. Notably, the DNA-binding activity of TFIID was the converse of YY1, in different endothelia. YY1 knockdown reduced transferrin receptor expression in brain endothelium, but not in dermal endothelium implying that YY1 is involved in tissue-specific regulation of the transferrin receptor. Moreover a distinct YY1 variant is present in brain endothelium and it associates with Sp3. A model is presented, in which expression from the transferrin receptor gene in endothelium requires the activity of both TFIID and Sp3, but whether the gene is transcribed in different endothelia, is related to the balance between activating and suppressive forms of YY1

Carbon nanotube networks as gas sensors for NO2 detection

Networks of different carbon nanotube (CNT) materials were investigated as resistive gas sensors for NO2 detection. Sensor films were fabricated by airbrushing dispersions of double-walled and multi-walled CNTs (DWNTs and MWNTs, respectively) on alumina substrates. Sensors were characterized by resistance measurements from 25 to 250 °C in air atmosphere in order to find the optimum detection temperature. Our results indicate that CNT networks were sensitive to NO2 concentrations as low as 0.1 ppm. All tested sensors provided significantly lower response to interfering gases such as H2, NH3, toluene and octane. We demonstrate that the measured sensitivity upon exposure to NO2 strongly depends on the employed CNT material. The highest sensitivity values were obtained at temperatures ranging between 100 and 200 °C. The best sensor performance, in terms of recovery time, was however achieved at 250 °C. Issues related to the gas detection mechanisms, as well as to CNT network thermal stability in detection experiments performed in air at high operation temperatures are also discussed.This work has been supported by MEC (Spain, projects TEC2004-05098-C02-01/MIC and TEC2004-05098-C02-02/MIC, Programa I3 2006 8 0I 060) and the European Regional Development Fund (ERDF).Peer reviewe

Combined modification of a TiO2 photocatalyst with two different carbon forms

9 pages, 11 figures, 2 tablesHydrothermally synthesized titanate nanotubes were carbon-doped through a thermal treatment in the presence of glucose followed by blending with single-walled carbon nanotubes (SWCNTs). A series of TiO2-based materials was prepared with various initial glucose contents and two SWCNT types, resulting in total carbon contents from 0.3 wt.% to nearly 26 wt.%. Electron microscopy observations indicated that titanate nanotubes were converted into nanorods during the thermal treatment, and X-ray diffraction patterns confirmed that all the treated materials mostly consisted of anatase TiO2. Glucose pyrolisis caused changes in the infrared and X-ray photoelectron spectra of the titania material, indicating an interaction between the inserted carbon atoms and titanium atoms. Raman spectra of SWCNT/C/TiO2 hybrids showed characteristic bands of both the SWCNT and anatase TiO2 phases. SWCNT/C/TiO2 multicomponent materials demonstrated substantially better photocatalytic activities than P25 TiO2 for methylene blue degradation under visible light irradiation. Independently from its origin, the presence of carbon caused a strong increase in the TiO2 visible light absorption. However, the results obtained with the C/TiO2 and SWCNT/C/TiO2 photocatalysts clearly showed different photocatalysis mechanisms depending on the carbon form.This work was funded by the Government of Aragon and “La Caixa” under project GA-LC-041/2008, the Spanish MINECO under the projects EUI2008-00152, TEC2010-15736, and PRI-PIBAR-2011-1, and the Government of Aragon (DGA) and the European Social Fund (ESF) under Project DGA-ESF-T66 CNN.Peer reviewe

Composite C/TiO2 nanocatalysts: Synergy and doping

Resumen del trabajo presentado a la International Conference on Nanostructured Systems for Solar Fuel Production (Solar Fuel Conference), celebrada en Mallorca del 25 al 27 de marzo de 2012.Peer reviewe

SWCNTs as electron withdrawers in nanocrystalline anatase photocatalysts

Single-walled carbon nanotube (SWCNT)/anatase TiO2 composite materials were prepared by successive sol–gel and hydrothermal processes. The composites contained thin SWCNT bundles embedded in aggregates of ~ 12 nm anatase crystallites. A series of SWCNT/TiO2 photocatalysts was prepared with various SWCNT contents; a SWCNT content of ~ 8 wt.% was found to be optimal for methylene blue (MB) degradation under combined UV/visible radiation. The optimized SWCNT/TiO2 composite demonstrated substantially higher photocatalytic activity than pure nanocrystalline anatase (5.2 times) and Degussa P-25 TiO2 powder (2.7 times). The MB degradation and mineralization processes were separately evaluated and complete decomposition of MB was shown to take place. The presence of SWCNTs caused an increase in the visible light absorbance of TiO2; however, SWCNT/TiO2 composites did not show any photocatalytic activity when the UV part of the UV/visible light source was filtered. Therefore SWCNTs worked as acceptors for the TiO2 photoexcited electrons, but did not act as sensitizers for TiO2.Peer reviewe

Preparación de nanostructuras de TiO2 y aplicaciones

Trabajo presentado al XI Congreso Nacional de Materiales, celebrado en Zaragoza del 23 al 25 de junio de 2010.Peer reviewe

Anatase nanotubes synthesized by a template method and their application as a green photocatalyst

Anatase nanotubes were synthesized by a template method from four different titanium precursors. Anodized aluminium oxide membranes with a 200-nm pore diameter were used as templates. The resulting nanostructures were characterized by electron microscopies, Raman spectroscopy, X-ray diffraction and nitrogen adsorption. Their photoactivities towards methylene blue dye decomposition were measured and compared with commercial anatase powder (Aldrich, >99%, −325 mesh). Anatase nanotubes obtained from Ti isopropoxide exhibited the longest hollow tubular structures with less amorphous material and the highest surface area, 56 m2 g−1. Despite TiO2 nanotubes showing lower photocatalytic activity than commercial anatase, the possibility of their recovery through several cycles and the feasibility of their utilization in continuous cycling processing make them potential materials of interest in green chemistry.Authors sincerely acknowledge J. Sanchez for his helpful contribution to the experimental work. This study was funded by the Government of Aragon and “La Caixa” Ref. GA-LC-041/2008 and by the Spanish Ministry of Science and Innovation Ref. EUI2008-00152Peer reviewe

Preparation of a TiO2–MoS2 nanoparticle-based composite by solvothermal method with enhanced photoactivity for the degradation of organic molecules in water under UV light

The MoS2 nanocrystals coupled with anatase nanoparticles were prepared by the solvothermal method at relatively low temperatures. It was determined that the materials consisted of 15–20 nm diameter anatase nanoparticles with highly dispersed MoS2 nanocrystals of approximately 3–7 nm in size. Visible light absorption in the MoS2–TiO2 samples increased with the MoS2 content. However, their lambda edges (λedge) remained almost identical at approximately 390 nm, meaning that MoS2 did not cause a red shift in the anatase bandgap energy. The hybrid MoS2-anatase materials had higher surface area (70–124 m2 g−1) than commercial TiO2 (P25) (50 m2 g−1). The MoS2-anatase hybrid nanocrystals showed enhanced activity in the oxidation of methylene blue in water under UV light irradiation. A photomechanism able to elucidate the observed dye decolourisation was suggested.This work was funded by the Government of Aragon and ‘La Caixa’ Ref. GA-LC-041/2008 and by the Spanish Ministry of Science and Innovation Ref. EUI2008-00152.Peer reviewe