Showing papers by "Alice Scarpellini published in 2016"

Fully Solution-Processed Conductive Films Based on Colloidal Copper Selenide Nanosheets for Flexible Electronics

Abstract: A novel colloidal synthesis of copper selenide nanosheets (NSs) with lateral dimensions of up to 3 μm is developed. This material is used for the fabrication of flexible conductive films prepared via simple drop-casting of the NS dispersions without any additional treatment. The electrical performance of these coatings is benchmarked against copper selenide spherical nanocrystals (SNCs) in order to demonstrate the advantage of 2D morphology of the NSs for flexible electronics. In this contest, Cu2−xSe SNC films exhibit higher conductivity but lower reproducibility due to the formation of cracks leading to discontinuous films. Furthermore, the electrical properties of the films deposited on different flexible substrates following their bending, stretching and folding are studied. A comparison of Cu2−xSe SNC and CuSe NS films reveals an increased stability of the CuSe NS films under mechanical stress applied to the samples and their improved long-term stability in air.

Co2+ and Ho3+ doped CuS nanocrystals with improved photocatalytic activity under visible light irradiation

Abstract: In this work, Co2+ and Ho3+ doped CuS nanostructured assemblies have been synthesized by means of a surfactant free hydrothermal method and investigated as photocatalysts in the degradation of methylene blue (MB) dye under visible light irradiation in the presence of H2O2. Firstly, it is found that the nature of dopants (M = Co2+, Ho3+) plays an important role in controlling the morphology of CuS structures as observed in FESEM and TEM analysis. Secondly, the band gap values of the M doped CuS structures showed a red shift. As a result, the M doped CuS structures exhibited enhanced photocatalytic activities compared to the pristine CuS structures. Among the different photocatalysts tested, 2.5 mol% cobalt doped CuS (CC samples) showed the best activity (∼52% more than CuS) in the photocatalytic degradation of dyes (almost complete degradation (∼99%) of MB dye in 20 min). In addition, these CC samples showed good catalyst stability for the degradation of dyes. The overall differences in the catalytic activity of the samples tested are discussed in terms of their band gap, surface area, porosity, defect surface, and morphology.

A High Voltage Olivine Cathode for Application in Lithium-Ion Batteries

Abstract: A new olivine composition (i.e., LiFe0.25 Mn0.5 Co0.25 PO4) is proposed as electrode material with increased energy density for application in lithium-ion batteries. The new formulation increases the working voltage and induces different electrochemical behavior with respect to bare olivine materials based on Fe. The study provides deep insight into the features of the Fe(3+) /Fe(2+), Mn(3+)/Mn(2+), and Co(3+)/Co(2+) redox couples within the olivine lattice in terms of electrochemical activity, Li(+) transport properties, and Li-cell behavior. The electrochemical characterization clearly reveals the voltage signatures corresponding to the various metals; however, the Mn(3+)/Mn(2+) process has higher intrinsic polarization with respect to Fe(3+)/Fe(2+) and Co(3+)/Co(2+). This issue is efficiently mitigated by carbon coating the material, resulting in enhanced electrochemical performances.

Low-cost and effective fabrication of biocompatible nanofibers from silk and cellulose-rich materials

Abstract: Here, we show the production of nanofibrous mats with controlled mechanical properties and excellent biocompatibility by combining fibroin with pure cellulose and cellulose-rich parsley powder agro-waste. To this end, trifluoroacetic acid was used as a common solvent for all of the involved biomaterials, achieving highly homogeneous blends that were suitable for the electrospinning technique. Morphological analysis revealed that the electrospun composite nanofibers were well-defined and defect-free, with a diameter in the range of 65–100 nm. Mechanical investigations demonstrated that the fibrous mats exhibited an increased stiffness when pure fibroin was combined with cellulose, whereas they possessed an increased flexibility when the parsley waste was added to fibroin. Lastly, the produced mats were highly biocompatible, as demonstrated by the promoted proliferation of fibroblast cells. The characteristics of the hybrid fibroin–cellulose nanofibers, in terms of nanoscale topography, mechanical propertie...

Antimicrobial Lemongrass Essential Oil—Copper Ferrite Cellulose Acetate Nanocapsules

Abstract: Cellulose acetate (CA) nanoparticles were combined with two antimicrobial agents, namely lemongrass (LG) essential oil and Cu-ferrite nanoparticles. The preparation method of CA nanocapsules (NCs), with the two antimicrobial agents, was based on the nanoprecipitation method using the solvent/anti-solvent technique. Several physical and chemical analyses were performed to characterize the resulting NCs and to study their formation mechanism. The size of the combined antimicrobial NCs was found to be ca. 220 nm. The presence of Cu-ferrites enhanced the attachment of LG essential oil into the CA matrix. The magnetic properties of the combined construct were weak, due to the shielding of Cu-ferrites from the polymeric matrix, making them available for drug delivery applications where spontaneous magnetization effects should be avoided. The antimicrobial properties of the NCs were significantly enhanced with respect to CA/LG only. This work opens novel routes for the development of organic/inorganic nanoparticles with exceptional antimicrobial activities.

Dumbbell-like Au0.5Cu0.5@Fe3O4 Nanocrystals: Synthesis, Characterization, and Catalytic Activity in CO Oxidation

Abstract: We report the colloidal synthesis of dumbbell-like Au0.5Cu0.5@Fe3O4 nanocrystals (AuCu@FeOx NCs) and the study of their properties in the CO oxidation reaction. To this aim, the as-prepared NCs were deposited on γ-alumina and pretreated in an oxidizing environment to remove the organic ligands. A comparison of these NCs with bulk Fe3O4-supported AuCu NCs showed that the nanosized support was far more effective in preventing the sintering of the metal domains, leading thus to a superior catalytic activity. Nanosizing of the support could be thus an effective, general strategy to improve the thermal stability of metallic NCs. On the other hand, the support size did not affect the chemical transformations experienced by the AuCu NCs during the activation step. Independently from the support size, we observed indeed the segregation of Cu from the alloy phase under oxidative conditions as well as the possible incorporation of the Cu atoms in the iron oxide domain.

Single step in situ formation of porous zinc oxide/PMMA nanocomposites by pulsed laser irradiation: kinetic aspects and mechanisms

Abstract: The simultaneous in situ formation of zinc oxide nanoparticles and controlled porosity in poly(methyl methacrylate) films is presented herein as an innovative method for the preparation of polymer based porous nanocomposites. The process is based on the conversion of zinc acetate in spherical zinc oxide nanoparticles of 9 nm on average, by pulsed laser activated precursor decomposition. The kinetics of the nanoparticles formation, followed by UV-visible spectroscopy, show a remarkable increase of the reaction rate with respect to the conventional thermally activated process. Most importantly, as revealed by scanning electron microscopy investigations, the laser treatment leads to the simultaneous formation of a porous structure in the polymer matrix, which can be ascribed to the yielded gaseous by-products during the zinc oxide nanoparticle formation. The combination of all these characterizations allowed a deeper insight in the kinetic aspects and mechanisms involved in the single step formation of porous poly(methyl methacrylate)/zinc oxide nanocomposites with tailored characteristics that cannot be achieved by the conventional thermal treatment.

Self-Assembled Dense Colloidal Cu2Te Nanodisk Networks in P3HT Thin Films with Enhanced Photocurrent

Abstract: The integration of colloidal nanocrystals with polymers adds optoelectronic functionalities to flexible and mechanically robust organic films. In particular, self-assembled structures of nanocrystals in polymers can act as functional components enhancing, for instance, transport or optical properties of the hybrid material. This study presents Cu2Te hexagonal nanodisks that assemble into ribbons with a face-to-face configuration in poly(3-hexylthiophene-2,5-diyl) through a controlled solvent evaporation process. The ribbons form weaving patterns that create 3D networks fully embedded in the thin polymer film at high nanodisk concentration. The photoresponse of these composite films measured in a layered vertical geometry demonstrates increased photocurrent with increasing nanocrystal loading. This study attributes this behavior to the presence of networks of Cu2Te nanodisks that form a bulk heterojunction with the semiconducting polymer, which improves exciton dissociation and the overall photoelectric response.

Effect of Anderson localization on light emission from gold nanoparticle aggregates.

Abstract: The localization of light known as Anderson localization is a common phenomenon characterizing aggregates of metallic nanostructures. The electromagnetic energy of visible light can be localized inside nanostructures below the diffraction limit by converting the optical modes into nonradiative surface plasmon resonances. The energy of the confined photons is correlated to the size and shape of the nanostructured system. In this work, we studied the photoluminescence dependence of aggregates of 14 nm diameter gold nanoparticles (AuNPs) synthesized by drop-casting a liquid suspension on two different substrates of glass and quartz. The AuNP aggregates were characterized by electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The dielectric constant of the surrounding medium plays a crucial role in determining the aggregate geometry, which affects the Anderson localization of light in the aggregates and hence causes a red-shift in the plasmonic resonance and in the photoluminescence emission. The geometry of the gold nanoparticle aggregates determine the strength of the Anderson localization, and hence, the light emission from the aggregates. The photoluminescence lifetime was found to be dependent on the AuNP aggregate geometry and the dielectric constant of the medium.

High-performance flexible nanoporous Si-carbon nanotube paper anodes for micro-battery applications.

Abstract: Nanoporous Si has been grown by pulsed laser deposition on a free-standing carbon nanotube (CNT) paper sheet for micro-battery anodes The Si deposition shows conformal coverage on the CNT paper, and the Si-CNT paper anodes demonstrate high areal capacity of ∼1000 μAh cm(-2) at a current density of 54 μA cm(-2), while 69% of its initial capacity is preserved when the current density is increased by a factor 10 Excellent stability without capacity decay up to 1000 cycles at a current density of 1080 μA cm(-2) is also demonstrated After bending along the diameter of the circular paper disc many times, the Si-CNT paper anodes preserve the same morphology and show promising electrochemical performance, indicating that nanoporous Si-CNT paper anodes can find application for flexible micro-batteries

Laser-induced in situ synthesis of Pd and Pt nanoparticles on polymer films

Abstract: We present the localized in situ formation of Pd and Pt nanoparticles embedded in chitosan solid films. This is achieved by the photo-induced reduction of metallic precursors, previously incorporated in chitosan films, through controlled UV pulsed laser irradiation. Interestingly, at high number of laser pulses, Pd and Pt follow different formation pathways, contrary to their common photoreduction mechanism occurring at low irradiation pulses. Specifically, in the case of the Pd, a photofragmentation process takes place fracturing the previously formed nanoparticles into smaller ones; whereas in the case of Pt, the prolonged irradiation promotes the nanoparticles agglomeration. The combination of both precursors in a binary solid system results in the combined formation of both Pd and Pt nanoparticles in the polymer film upon laser irradiation. The herein reported approach is an efficient and precise tool to generate size- and density-controlled Pd and Pt nanoparticles in desired areas of polymeric films, rendering this method a potential candidate for the fabrication of flexible polymeric devices for gas-sensing or electro-catalysis applications. Schematic representation of Pd, Pt and Pd–Pt combined NPs formation mechanisms under pulsed laser irradiation

Biomimetic Locomotion on Water of a Porous Natural Polymeric Composite

Abstract: Observation of the natural world can provide invaluable information on the mechanisms that semiaquatic living organisms or bacteria use for their self-propulsion. Microvelia, for example, uses wax excreted from its legs to move on water in order to escape from predators or reach the bank of the river. Mimicking such mechanism, few self-propelled materials on water, as camphor, have been previously developed, but weak points like slow locomotion, short movement duration or shape-restrictions still need to be improved. Herein we present a totally green self-assembled porous system, formed by the combination of a natural polymer with an essential oil, that spontaneously moves on water for hours upon expulsion of the oil, with high velocities reaching 15 cm/s. The structural characteristics of the natural polymeric composite are carefully analyzed and associated to its spontaneous movement. Surface tension change experiments are also presented that connect the essential oil release with the locomotion of the porous composite films. This research work opens novel routes towards bio-inspired natural materials that can be used for mimicking and studying the motion of bio-organisms and microorganisms, and for applications such as energy harvesting, aquatic pollution monitoring, drug delivery, to name few.

A High Voltage Olivine Cathode for Application in Lithium‐Ion Batteries.

Abstract: A new olivine composition (i.e., LiFe0.25 Mn0.5 Co0.25 PO4) is proposed as electrode material with increased energy density for application in lithium-ion batteries. The new formulation increases the working voltage and induces different electrochemical behavior with respect to bare olivine materials based on Fe. The study provides deep insight into the features of the Fe(3+) /Fe(2+), Mn(3+)/Mn(2+), and Co(3+)/Co(2+) redox couples within the olivine lattice in terms of electrochemical activity, Li(+) transport properties, and Li-cell behavior. The electrochemical characterization clearly reveals the voltage signatures corresponding to the various metals; however, the Mn(3+)/Mn(2+) process has higher intrinsic polarization with respect to Fe(3+)/Fe(2+) and Co(3+)/Co(2+). This issue is efficiently mitigated by carbon coating the material, resulting in enhanced electrochemical performances.