1,721,084 research outputs found
RuO2 Nanostructure as an Efficient and Versatile Catalyst for H2 Photosynthesis
Full text linkPhotocatalytic H-2 generation holds promisein the greenproduction of alternative fuels and valuable chemicals. Seeking alternative,cost-effective, stable, and possibly reusable catalysts representsa timeless challenge for scientists working in the field. Herein,commercial RuO2 nanostructures were found to be a robust,versatile, and competitive catalyst in H-2 photoproductionin several conditions. We employed it in a classic three-componentsystem and compared its activities with those of the widely used platinumnanoparticle catalyst. We observed a hydrogen evolution rate of 0.137mol h(-1) g(-1) and an apparent quantumefficiency (AQE) of 6.8% in water using EDTA as an electron donor.Moreover, the favorable employment of l-cysteine as the electronsource opens possibilities precluded to other noble metal catalyst.The versatility of the system has also been demonstrated in organicmedia with impressive H-2 production in acetonitrile. Therobustness has been proved by the recovery of the catalyst by centrifugationand reusage alternatively in different media
Decorated and Modified Graphenes as Electrodes in Na and Li-Ion Batteries
Full text linkNowadays, rechargeable Li-ion batteries represent the state of the art for the power supply in technological devices. However, the wide-scale implementation of this technology, for example in the automotive field or for large stationary applications, could raise issues, i.e. concerning the limited lithium mineral reserves. The investigation of alternatives to lithium is hence highly desirable, although it requires the identification of new materials suitable as components for new batteries, displaying similar or possibly even better performances with respect to the current systems. Here we show that electrodes based on graphene derivatives are able not only to support the insertion of Li+, but also of Na+ ions, with high capacity and stability upon cycling, leading to the development of novel Na-ion batteries
Advances in Focused Ion Beam Tomography for Three-Dimensional Characterization in Materials Science
Full text linkOver the years, FIB-SEM tomography has become an extremely important technique for the three-dimensional reconstruction of microscopic structures with nanometric resolution. This paper describes in detail the steps required to perform this analysis, from the experimental setup to the data analysis and final reconstruction. To demonstrate the versatility of the technique, a comprehensive list of applications is also summarized, ranging from batteries to shale rocks and even some types of soft materials. Moreover, the continuous technological development, such as the introduction of the latest models of plasma and cryo-FIB, can open the way towards the analysis with this technique of a large class of soft materials, while the introduction of new machine learning and deep learning systems will not only improve the resolution and the quality of the final data, but also expand the degree of automation and efficiency in the dataset handling. These future developments, combined with a technique that is already reliable and widely used in various fields of research, are certain to become a routine tool in electron microscopy and material characterization
Hydrogen Desorption below 150 °c in MgH2-TiH2 Composite Nanoparticles: Equilibrium and Kinetic Properties
Full text linkReversible hydrogen sorption coupled with the MgH2 <-> Mg phase transformation was achieved in the remarkably low 340-425 K temperature range using MgH2-TiH2 composite nanoparticles obtained by reactive gas-phase condensation of Mg Ti vapors under He/H-2 atmosphere. The equilibrium pressures determined by in situ measurements at low temperature were slightly above those predicted using enthalpy Delta H and entropy Delta S of bulk magnesium. A single van't Hoff fit over a range extended up to 550 K yields the thermodynamic parameters Delta H = 68.1 0.9 kJ/molH(2) and Delta S = 119 2 J/(Kmo1H2) for hydride decomposition. A desorption rate of 0.18 wt % H-2/min was measured at T = 423 K and p(H-2) approximate to 1 mbar, i.e., close to equilibrium, without using a Pd catalysts. The nanoparticles displayed a small absorption desorption pressure hysteresis even at low temperatures. We critically discuss the influence exerted by nanostructural features such as interface free energy, elastic clamping, and phase mixing at the single nanopartide level on equilibrium and kinetic properties of hydrogen sorption
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Au-based catalysts: Optimization of active phase and metal-support interaction
Full text linkIn the present work, a series of Au- and Au-Cu-containing catalysts based on different carriers such as TiO2 and CeO2 were studied with a view to increasing the activity and selectivity in 5-hydroxymethylfurfural oxidation by optimizing the interaction both between the metals and with the support. The results obtained demonstrated the high activity in HMF oxidation of gold supported on ceria and titania. Nevertheless, although the particle size of gold on both supports was comparable, Au/CeO2 showed significantly higher activity than Au/TiO2, thus corroborating the theory that not only the gold particle size, but the support also, plays a key role in HMF oxidation in the aqueous phase. Indeed, pre-made uniform nanoparticles, used for catalyst preparation, were surface-bound by poly(N-vinyl-2-pyrrolidone) - the stabilizer used during nanoparticle synthesis - whose presence proved to prevent the interaction of active phases with CeO2, while worsening the catalytic activity of both monometallic and bimetallic systems. The pre-treatment of the prepared catalysts was necessary to activate the materials, by maximizing the contact between the metal and the support and thus suggesting an important role of the ceria defects on 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid
Novel electrochemical biosensors based on a biomimetic graphene-lipid bilayer interface
No full textIn our work we investigate the development of a novel electrochemical biosensor that integrates a graphene layer as the transducer element for the analysis of electroactive membrane proteins. Graphene is used as transducer because of its unique properties (high surface area, electrical conductivity, ultra-high electron mobility, wide electrochemical potential window, low charge-transfer resistance, reduction of overvoltage), all of which are responsible for the enhancement of the direct electron transfer between graphene and the membrane proteins. However, in biosensors for membrane proteins a major problem is the denaturation of such proteins when they are in contact with the electrode solid surface. To avoid this, membrane proteins are normally embedded in a biological system mimicking their native environment, the supported lipid bilayer (SLB). This study is focused on the synthesis of the graphene interface through chemical vapour deposition, on its surface treatments through a mild oxidation to improve its biocompatibility, and on the investigation of the graphene interface with SLBs. The obtained films of graphene are characterized using scanning electron microscopy, Raman spectroscopy and measuring the water contact angles before and after surface treatments. The interaction of the graphene surface with liposomes and the formation of the graphene-supported lipid bilayer are investigated using electrochemical impedance spectroscopy
Biological application of Compressed Sensing Tomography in the Scanning Electron Microscope
No full textThe three-dimensional tomographic reconstruction of a biological sample, namely collagen fibrils in human dermal tissue, was obtained from a set of projection-images acquired in the Scanning Electron Microscope. A tailored strategy for the transmission imaging mode was implemented in the microscope and proved effective in acquiring the projections needed for the tomographic reconstruction. Suitable projection alignment and Compressed Sensing formulation were used to overcome the limitations arising from the experimental acquisition strategy and to improve the reconstruction of the sample. The undetermined problem of structure reconstruction from a set of projections, limited in number and angular range, was indeed supported by exploiting the sparsity of the object projected in the electron microscopy images. In particular, the proposed system was able to preserve the reconstruction accuracy even in presence of a significant reduction of experimental projections
Tracking graphene by fluorescence imaging: A tool for detecting multiple populations of graphene in solution
No full textMost methods used for the characterization of graphene produced by liquid phase exfoliation require the deposition of the liquid sample on a substrate and subsequent drying. Because of this or other post-synthetic treatments, the reliability of the data in describing the actual features of the graphene particles in the pristine solution becomes questionable. Hence there is a need for new methods that permit the study of graphene directly in solution. Fluorescence imaging is at present the most convenient and sensitive method to visualize nanosized objects in solution. Here we report the development of a new method for visualizing and tracking exfoliated graphene directly in solution using a conventional set-up for fluorescence microscopy. We functionalized a fluorescent surfactant typically used for exfoliating graphite in aqueous phase (Pluronic P123) with two different fluorophores, in order to make graphene detectable by fluorescence microscopy. The photophysical interactions between the fluorescent surfactant and graphene were investigated at the bulk level. Finally, fluorescence microscopy allowed us to track the carbon particles produced and to identify two different populations of particles with sizes of 265 ± 25 and 1100 ± 200 nm respectively. The correlation of these results with TEM and DLS data is discussed
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