Suchergebnisse

Resumen del trabajo presentado a la XXXVII Reunión Bienal de la Real Sociedad Española de Química, celebrada en Donostia-San Sebastián del 26 al 30 de mayo de 2019. ; Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) and European Regional Development Fund (MAT2016-77290-R), ESF and the Aragón Government (T43-17R) is gratefully acknowledged. ; Peer reviewed

5 Figuras.- 1 Tabla.- Información complementaria disponible en línea en la página web del editor. ; The emission of a bright blue fluorescence is a unique feature common to the vast variety of polymer carbon dots (CDs) prepared from carboxylic acid and amine precursors. However, the difficulty to assign a precise chemical structure to this class of CDs yet hampers the comprehension of their underlying luminescence principle. In this work, we show that highly blue fluorescent model types of CDs can be prepared from citric acid and ethylenediamine through low temperature synthesis routes. Facilitating controlled polycondensation processes, the CDs reveal sizes of 1–1.5 nm formed by a compact network of short polyamide chains of about 10 monomer units. Density functional theory calculations of these model CDs uncover the existence of a spatially separated highest occupied molecular orbital and a lowest unoccupied molecular orbital located at the amide and carboxylic groups, respectively. Photoinduced charge transfer between these groups thus constitutes the origin of the strong blue fluorescence emission. Hydrogen-bond-mediated supramolecular interactions between the polyamide chains enabling a rigid network structure further contribute to the enhancement of the radiative process. Moreover, the photoinduced charge transfer processes in the polyamide network structure easily explain the performance of CDs in applications as revealed in studies on metal ion sensing. These findings thus are of general importance to the further development of polymer CDs with tailored properties as well as for the design of technological applications. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 642742. A.M.B. and W.K.M. further acknowledge Spanish MINEICO (project ENE2016-79282-C5-1-R), the Gobierno de Aragón (Grupo Reconocido DGA T03_17R), and associated EU Regional Development Funds. E.P.U. acknowledges Gobierno de Aragón (Grupo Reconocido DGA E19_17R) and associated EU Regional Development Funds. ; Peer reviewed

The emission of a bright blue fluorescence is a unique feature common to the vast variety of polymer carbon dots (CDs) prepared from carboxylic acid and amine precursors. However, the difficulty to assign a precise chemical structure to this class of CDs yet hampers the comprehension of their underlying luminescence principle. In this work, we show that highly blue fluorescent model types of CDs can be prepared from citric acid and ethylenediamine through low temperature synthesis routes. Facilitating controlled polycondensation processes, the CDs reveal sizes of 1 - 1.5 nm formed by a compact network of short polyamide chains of about ten monomer units. Density functional theory calculations of these model CDs uncover the existence of spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital located at the amide and carboxylic groups, respectively. Photoinduced charge-transfer between these groups thus constitutes the origin of the strong blue fluorescence emission. Hydrogen-bond mediated supramolecular interactions between the polyamide chains enabling a rigid network structure further contribute to the enhancement of the radiative process. Moreover, the photoinduced charge-transfer processes in the polyamide network structure easily explain the performance of CDs in applications as revealed in studies on metal ion sensing. These findings thus are of general importance to the further development of polymer CDs with tailored properties as well as for the design of technological applications. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 642742. AMB, and WKM further acknowledge Spanish MINEICO (project ENE2016-79282-C5-1-R), the Gobierno de Aragón (Grupo Reconocido DGA T03_17R), and associated EU Regional Development Funds). EPU acknowledges Gobierno de Aragón (Grupo Reconocido DGA E19_17R) and associated EU Regional Development Funds. Technical and human support provided by IZO-SGI, SGIker (UPV/EHU, MICINN, GV/EJ ERDF and ESF) is gratefully acknowledged for assistance and generous allocation of computational resources. ; Peer reviewed

The self-assembly of novel core-shell nanoensembles consisting of regioregular poly(3-hexylthiophene) nanoparticles (P3HTNPs) of 100 nm as core and semiconducting CdTe quantum dots (CdTeQDs) as shell with a thickness of a few tens of nanometres was accomplished by employing a re-precipitation approach. The structure, morphology and composition of CdTeQDs/P3HTNPs nanoensembles were confirmed by high-resolution scanning transmission microscopy and dynamic light scattering studies. Intimate interface contact between the CdTeQDs shell and the P3HTNPs core leads to the stabilization of the CdTeQDs/P3HTNPs nanoensemble as probed by steady-state absorption spectroscopy. Effective quenching of the characteristic photoluminescence of CdTeQDs at 555 nm, accompanied by simultaneous increase of emission of P3HTNPs at 660 and 720 nm, reveals photoinduced charge-transfer processes. Probing the redox properties of films of CdTeQDs/P3HTNPs further proves the formation of a stabilized core-shell system in the solid-state. Photoelectrochemical assays on CdTeQDs/P3HTNPs films show a reversible on-off photoresponse at a bias voltage of +0.8 V with a three times increased photocurrent compared to CdTeQDs. The improved charge separation is directly related to the unique core-shell configuration, in which the outer CdTeQDs shell forces the P3HTNPs core to effectively act as electron acceptor. The creation of novel donor-acceptor core-shell hybrid materials via self-assembly is transferable to other types of conjugated polymers and semiconducting nanoparticles. This work, therefore, opens new pathways for the design of improved optoelectronic devices. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 642742. AMB and WKM gratefully acknowledge financial support from Spanish MINECO under project ENE206-79282-C5-1-R and its associated European Regional Development Fund, as well as the Government of Aragon under project DGA-T66 and associated European Social Fund. RA gratefully acknowledges financial support from Spanish MINECO under project MAT2016 79776-P and its associated European Regional Development Fund, as well as the Government of Aragon under project DGA-E26 and associated European Social Fund. The STEM studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon Universidad de Zaragoza, Spain. The authors would like to thank Esteban Urriolabeitía for carrying out the NMR studies. ; Peer reviewed

Resumen del trabajo presentado al HeteroNanoCarb: "Advances and Applications in Carbon Related Nanomaterials: From pure to doped structures including heteroatom layers", celebrado en Benasque (España) del 7 al 11 de diciembre de 2015. ; This work has been funded by the Spanish Ministry MINECO and the European Regional Development Fund under the project ENE2013-48816-C5-5-R, and the Government of Aragon and the European Social Fund (DGA-ESF-T66 Grupo Consolidado). ; Peer reviewed

We report on the modification of graphene oxide (GO) with poly(vinyl alcohol) (PVA) leading to the mechanical improvement of GO based materials. First, GO was covalently functionalised with PVA by esterification of carboxylic groups on GO with hydroxyl groups of PVA resulting in functionalised f-(PVA)GO. This was carried out for PVA of six different molecular weights. This functionalised graphene oxide could be formed into a paper-like material by vacuum filtration. Papers prepared from f-(PVA)GO showed significant increases in mechanical properties compared to those prepared with GO or with simple mixtures of GO and PVA. The best performance was achieved for PVA functional groups with molecular weights between 50 and 150 kg/mol. Improvements in Young's moduli of 60% and tensile strength of 400% were observed relative to GO-only paper. The improved mechanical properties are attributed to enhanced inter-flake stress transfer due to the covalently bonded PVA. Second, functionalised f-(PVA)GO was used as filler in * Corresponding author. Tel/Fax: +34 976 73-3977 / -3318. E-mail address: wmaser@icb.csic.es (W.K. Maser) 2 PVA-based composites. The application of a pre-selection method allowed the use of only the largest functionalised f-(PVA)GO flakes. This resulted in substantially reinforced PVA-f-(PVA)GO composites. Both modulus and strength increased by 40% relative to the pure polymer for f- (PVA)GO loadings below 0.3 vol.%. ; The authors would like to acknowledge Science Foundation Ireland, (grant number 07/IN.7/I1772), Spanish Ministry of Science and Innovation (MICINN) under project MAT2010-15026, Spanish Research Council CSIC under project 201080E124 and the Government of Aragon (DGA) under Project DGA-T66 CNN. M.C. thanks MICINN for her PhD contract and funding for research stay at TCD under FPI Programme BES-2008-003503. ; Peer reviewed

The robust adhesion of single-walled carbon nanotubes (SWCNTs) to plastic substrates is a key issue toward their use in flexible electronic devices. In this work, semitransparent SWCNT films were prepared by spray-coating on two different plastic substrates, specifically poly(ethylene terephthalate) and poly(vinylidene fluoride). The deposited SWCNT films were treated by dipping in suitable solvents separately, namely, 53% nitric acid (HNO3) and N-methyl pyrrolidone. Direct evidence of SWCNT adhesion to the substrate was obtained by a peel-off test carried out with an adhesive tape. Moreover, these treatments caused enhanced film transparency and electrical conductivity. Electron microscopy images suggested that SWCNTs were embedded in the plastic substrates, forming a thin layer of conductive composite materials. Raman spectroscopy detected a certain level of doping in the SWCNTs after the chemical treatments, which particularly affected metallic nanotubes in the case of the HNO3 treatment. The microscopic adhesion and hardness of the SWCNT films were studied through a nanoscratch test. Overall, the efficiency of selected chemical postdeposition treatments for improving the SWCNT adhesion and the robustness of the resulting SWCNT films are demonstrated on flexible substrates of different chemical compositions. ; This work has been funded by the MINECO and the European Regional Development Fund (ENE 2016-79282-C5-1-R), the Government of Aragón (T03-17R and E14-17R), and the European Commission (H2020-MSCA-ITN-2014-ETN 642742 "Enabling Excellence"). ; Peer reviewed

Hybrid film electrodes were made of nanocrystalline titanium dioxide (TiO2) and various percentages of single‐walled carbon nanotube (SWCNT) fillers up to 5.5 wt%. A complete photoelectrochemical study was performed in both alkaline and acidic conditions by using cyclic voltammetry, potentiostatic photocurrent measurements, and open‐circuit‐potential measurements under UV/Vis irradiation. Dark voltammograms show a transition from a capacitive to a resistive behavior in the TiO2 accumulation region upon increasing SWCNT percentages. In addition, the energy levels of deep electron traps change inside the TiO2 bandgap. The new peak positions correspond to the reduction potentials of SWCNTs, and their associated charge capacities increase with the SWCNT percentage. The modifications observed in dark experiments directly impact on the shape profile of cyclic voltammograms under irradiation. As a consequence, reduction potentials of SWCNTs appear near the cathodic peaks of certain water oxidation intermediates, and may be interacting with them. On the other hand, open‐circuit photopotentials reach maximum values for small SWCNTs percentages around 0.02 wt%. An increase in potentiodynamic and potentiostatic photocurrents is observed for the electrode containing 0.02 wt% SWCNTs, compared to reference TiO2 in acidic conditions. ; The authors thank the Institute for Biocomputation and Physics of Complex Systems (BIFI) for the centrifugation laboratory. This work has been funded by MINECO and European Regional Development Fund (ENE 2016-79282-C5-1-R), Government of Aragon and European Social Fund (DGA-ESF-T66 "Grupo Consolidado") and European Commission (H2020-MSCA-ITN-2014-ETN 642742 "Enabling Excellence"). ; Peer reviewed

Resumen del trabajo presentado al Nanomath, celebrado en Toulouse (Francia) del 27 al 30 de junio de 2016. ; This work has been funcled by MINECO ancl Europea.n Regional Development Funcl (ENE2013-48816-C5-5-R "NANOSOL-MAT"), CSIC (project 2015801011 "Int.ramural"), Government of Aragón and European Social Fund (DGA-ESF-T66 "Grupo Consolidado") ancl European Commission (H2020-MSCA-ITN-2014-ETN 642742 "Enabling Excellcnce"). ; Peer reviewed

9 pages, 9 figures.-- Available online 21 February 2014 ; The effect of -irradiation on the structure and composition of chemically synthesized few-layered graphene materials was studied. Fully oxidized graphene oxide and graphene nanoribbons, as well as their respective chemically post-reduced forms, were treated under -irradiation in an air-sealed environment. Three different irradiation doses of 60, 90 and 150 kGy were applied. Structure and composition of the irradiated materials were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Raman spectroscopy and Xray photoelectron spectroscopy (XPS). The XRD patterns were not affected by - irradiation, and small changes were observed in the FTIR and TGA results. However, significant modifications were detected by Raman spectroscopy and XPS, particularly in the Raman G/D band intensity ratios and in the C 1s XPS profiles. Comparatively, the changes in Raman and XPS spectra after -irradiation were even greater than those occurring during the chemical reduction of graphene oxides. Our results indicate that the graphene carbon lattice was strongly affected by -irradiation, but the materials experienced small variations in their oxygen content. ; This work was funded by the Spanish MINECO under the projects TEC2010-15736, MAT2010-15026, MAT2010-16175 (CICYT) and PRI-PIBAR-2011-1, CSIC under Project 201080E124 and the Government of Aragon (DGA) and the European Social Fund (ESF) under Project DGA-ESF-T66 CNN. ; Peer reviewed

1 figure.-- Comunicación oral presentada en el congreso ChemOnTubes 2022, celebrado en San Sebastián, del 24 al 28 abril. ; Carbon Dots (CDs) have attracted considerable attention due to their excellent photoluminescence (PL), high photochemical stability, easy functionalization, water solubility, low toxicity and good biocompatibility, among others. All these properties elevate CDs as a potential alternative to conventional quantum dots, thus overcoming issues of toxicity due to the presence of heavy metals [1]. The outstanding properties of CDs have enabled their application in many research fields, such as biomedicine [2], photocatalysis, photovoltaics, photoelectrochemistry [3], and sensing. Actually, most of the reported CDs show intrinsic blue emission, whose PL mechanism has been studied in depth [4]. However, there is increased research activity to obtain CDs with longer emission wavelengths. Herein, we present the bottom-up microwave synthesis, optimization and characterization of water-soluble CDs with high PL quantum yield and green emission. Moreover, the intense PL is maintained even in the solid state, when embedded in a biopolymer matrix. Finally, we demonstrate that the CDs show great promise as sensitizers in TiO2 photoanodes, integrated into a photoelectrochemical cell for the production of green hydrogen. ; Spanish MICINN/AEI: PID2019-104272RB-C51/AEI/10.13039/501100011033; Government of Aragón: Grupos Reconocidos DGA T03_20R and PhD grant of MAA IIU/796/2019. ; Peer reviewed

5 Tablas, 7 Figuras.-- Material suplementario disponible en línea en la página web del editor. ; Controlling the physicochemical properties of nanoparticles in fluids directly impacts on their liquid phase processing and applications in nanofluidics, thermal engineering, biomedicine and printed electronics. In this work, the temperature dependent viscosity of various aqueous nanofluids containing carbon nanotubes (CNTs) or graphene oxide (GO), i.e. 1D and 2D nanoparticles with extreme aspect ratios, is analyzed by empirical and predictive physical models. The focus is to understand how the nanoparticle shape, concentration, motion degrees and surface chemistry affect the viscosity of diluted dispersions. To this end, experimental results from capillary viscosimeters are first examined in terms of the energy of viscous flow and the maximum packing fraction applying the Maron-Pierce model. Next, a comparison of the experimental data with predictive physical models is carried out in terms of nanoparticle characteristics that affect the viscosity of the fluid, mostly their aspect ratio. The analysis of intrinsic viscosity data leads to a general understanding of motion modes for carbon nanoparticles, including those with extreme aspect ratios, in a flowing liquid. The resulting universal curve might be extended to the prediction of the viscosity for any kind of 1D and 2D nanoparticles in dilute suspensions. ; This work has been funded by the Spanish MINEICO under the project ENE 2016-79282-C5-1-R (AEI/FEDER, UE), the Government of Aragón (Grupo reconocido T03-20R) and associated EU Regional Development Funds (DGA/FEDER, UE). SVR thanks Spanish MINEICO for her PhD grant (BES2014-068727 and associated EU Social Funds). J.M.G.-D. greatly acknowledges Spanish Ministry of Science, Innovation and Universities (MICINN, formerly MINEICO) for his "Juan de la Cierva – incorporación" grant (Ref. JCI-2016-27789). We also acknowledge institutional support from the Unit of Information Resources for Research at the "Consejo Superior de Investigaciones Científicas" (CSIC) for the article-processing charges contribution. ; Peer reviewed

The game-changing role of graphene oxide (GO) in tuning the excitonic behavior of conjugated polymer nanoparticles is described for the first time. This is demonstrated by using poly(3-hexylthiophene) (P3HT) as a benchmark conjugated polymer and employing an in-situ re-precipitation approach resulting in P3HT nanoparticles (P3HTNPs) with sizes of 50 - 100 nm in intimate contact with GO. During the self-assembly process, GO changes the crystalline packing of P3HT chains in the forming P3HTNPs from H to H/J aggregates exhibiting exciton coupling constants as low as 2 meV, indicating favorable charge separation along the P3HT chains. Concomitantly, π-π interface interactions between the P3HTNPs and GO sheets are established resulting in the creation of P3HTNPs-GO charge-transfer complexes whose energy bandgaps are lowered by up to 0.5 eV. Moreover, their optoelectronic properties, pre-established in the liquid phase, are retained when processed into thin films from the stable aqueous dispersions, thus eliminating the critical dependency on external processing parameters. These results can be transferred to other types of conjugated polymers. Combined with the possibility of employing water based "green" processing technologies, charge-transfer complexes of conjugated polymer nanoparticles and GO open new pathways for the fabrication of improved optoelectronic thin film devices. ; This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 642742. AMB, and WKM acknowledge Spanish MINEICO (project ENE2016-79282-C5-1-R) and the Gobierno de Aragón (Grupo Reconocido DGA T03_17R), and associated EU Regional Development Funds). ; Peer reviewed

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Low Temperature Physics 43, 383 (2017) and may be found at https://doi.org/10.1063/1.4979362 ; The kinetics of the sorption and the subsequent desorption of 4He by the starting graphite oxide (GtO) and the thermally reduced graphene oxide samples (TRGO, Treduction = 200, 300, 500, 700 and 900 °C) have been investigated in the temperature interval 1.5–20 K. The effect of the annealing temperature on the structural characteristics of the samples was examined by the x-ray diffraction (XRD) technique. On lowering the temperature from 20 to 11–12 K, the time of 4He sorption increased for all the samples, which is typically observed under the condition of thermally activated diffusion. Below 5 K the characteristic times of 4He sorption by the GtO and TRGO-200 samples were only weakly dependent on temperature, suggesting the dominance of the tunnel mechanism. In the same region (T < 5 K) the characteristic times of the TRGOs reduced at higher temperatures (300, 500, 700 and 900 °C) were growing with lowering temperature, presumably due to the defects generated in the carbon planes on removing the oxygen functional groups (oFGs). The estimates of the activation energy (Ea) of 4He diffusion show that in the TRGO-200 sample the Ea value is 2.9 times lower as compared to the parent GtO, which is accounted for by GtO exfoliation due to evaporation of the water intercalated in the interlayer space of carbon. The nonmonotonic dependences Ea(T) for the GtO samples treated above 200 °C are determined by a competition between two processes—the recovery of the graphite carbon structure, which increases the activation energy, and the generation of defects, which decreases the activation energy by opening additional surface areas and ways for sorption. The dependence of the activation energy on Treduction correlates well with the contents of the crystalline phase in GtO varying with a rise of the annealing temperature. ; Financial support from Spanish Ministry MINECO and the European Regional Development Fund (Project No. ENE2013-48816-C5-5-R), the Regional Government of Aragon and the European Social Fund DGA-ESF (Project No. T66) and Targeted Comprehensive Fundamental Research Program of NASU (Project No. 6/16-H) is gratefully acknowledged. ; Peer reviewed

5 figures.-- Supporting information available.-- This ACS article is provided under the terms of this ACS AuthorChoice/Editors' Choice via Creative Commons CC-BY agreement: https://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html ; Developing highly efficient and stable photoelectrochemical (PEC) water-splitting electrodes via inexpensive, liquid phase processing is one of the key challenges for the conversion of solar energy into hydrogen for sustainable energy production. ZnO represents one the most suitable semiconductor metal oxide alternatives because of its high electron mobility, abundance, and low cost, although its performance is limited by its lack of absorption in the visible spectrum and reduced charge separation and charge transfer efficiency. Here, we present a solution-processed water-splitting photoanode based on Co-doped ZnO nanorods (NRs) coated with a transparent functionalizing metal–organic framework (MOF). The light absorption of the ZnO NRs is engineered toward the visible region by Co-doping, while the MOF significantly improves the stability and charge separation and transfer properties of the NRs. This synergetic combination of doping and nanoscale surface functionalization boosts the current density and functional lifetime of the photoanodes while achieving an unprecedented incident photon to current efficiency (IPCE) of 75% at 350 nm, which is over 2 times that of pristine ZnO. A theoretical model and band structure for the core–shell nanostructure is provided, highlighting how this nanomaterial combination provides an attractive pathway for the design of robust and highly efficient semiconductor-based photoanodes that can be translated to other semiconducting oxide systems. ; A.G.-G., A.K.S., F.M., A.G., D.A.Z., and D.A. acknowledge funding received from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No 722176. W.K.M., A.M.B., and J.H.F. acknowledge financial support from Spanish Ministry MINEICO under Project ENE2016-79282-C5-1-R (AEI/UE/FEDER) and the Gobierno de Aragón (Grupo Reconocido DGA T03_17R, FEDER/UE y DGA T03_20R). ; Peer reviewed