The Exfoliation of Graphene in Liquids by Electrochemical,Chemical, and Sonication‐Assisted Techniques: A Nanoscale Study

The different exfoliation routes of graphite to produce graphene by sonication in solvent, chemical oxidation and electrochemical oxidation are compared. The exfoliation process and roughening of a flat graphite substrate is directly visualized at the nanoscale by scanning probe and electron microscopy. The etching damage in graphite and the properties of the exfoliated sheets are compared by Raman spectroscopy and X‐ray diffraction analysis. The results show the trade‐off between exfoliation speed and preservation of graphene quality. A key step to achieve efficient exfoliation is to couple gas production and mechanical exfoliation on a macroscale with non‐covalent exfoliation and preservation of graphene properties on a molecular scale.     

Photoconductive and supramolecularly engineered organic field-effect transistors based on fibres from donor-acceptor dyads

We report on the formation of photoconductive self-assembled fibres by solvent induced precipitation of a HBC-PMI donor-acceptor dyad. Kelvin Probe Force Microscopy revealed that upon illumination with white light the surface potential of the fibres shifted to negative values due to a build-up of negative charge. When integrated in a field-effect transistor (FET) configuration, the devices can be turned 'on' much more efficiently using light than conventional bias triggered field-effect, suggesting that these structures could be used for the fabrication of light sensing devices. Such a double gating represents an important step towards bi-functional organic FETs, in which the current through the junction can be modulated both optically (by photoexcitation) and electrically (by gate control).     

Optimizing Single‐Walled‐Carbon‐Nanotube‐Based Saturable Absorbers for Ultrafast Lasers

The application of single‐walled carbon nanotubes (SWCNTs) as saturable absorbers (SA) in a Nd:glass femtosecond laser is verified as a promising alternative to traditional semiconductor saturable‐absorber mirrors (SESAMs). The shortest laser pulses achieved with a SWCNT‐SA fabricated by the slow‐evaporation method are reported herein. Nearly Fourier‐limited 288 fs pulses are obtained with negative‐dispersion soliton mode‐locking. The importance of the properties of the starting material, such as the degree of purity and the chirality, and the successive slow‐evaporation deposition method is proven by using a multitechnique approach based on X‐ray diffractometry, scanning electron microscopy, and μ‐Raman spectroscopy. The high degree of nanotube alignment on the glass substrate and also the slight metallic character due to electron transfer between the glass matrix and the nanotubes themselves are identified as the main features responsible for the good laser response.     

Effect of modified atmosphere and active packaging on the shelf-life of fresh bluefin tuna fillets

The aim of this work was to study the influence of the combined use of MAP and antioxidant-based active packaging on the shelf-life of fresh bluefin tuna fillets stored at 3 °C. Active packaging films were produced by embedding α-tocopherol into an unstabilized low density polyethylene (LDPE) matrix at three concentrations (0.1%, 0.5%, 1%). α-Tocopherol release kinetics, in vitro antioxidant activity, oxygen permeability and crystallinity degree were determined to characterize the film. Preliminary shelf-life tests were performed to select critical quality indices, the best gas composition and the best α-tocopherol concentrations in the active film. Then, the effectiveness of the chosen active packaging film in combination with MAP was assessed by monitoring critical quality indices of fresh bluefin tuna fillet during storage at 3 °C for 18 days. Obtained results showed that (i) 100% N₂ atmosphere has a protective effect on haemoglobin and lipid oxidation processes monitored, (ii) active film is able to reduce fat oxidation, (iii) the combined effect of MAP and active packaging can be considered a valuable tool to increase the shelf-life of raw fish products.     

Perspective on hydrogen energy carrier and its automotive applications

The paper outlines the concept of energy carrier with a particular reference to hydrogen, in view of a more disseminated employment in the field of automotive applications. In particular hydrogen production is analyzed considering the actual state of the art and recent technologies applied in production from the primary sources (fossil fuels, renewable energies, and water electrolysis). Then the problem of hydrogen storage is considered both from technical and economical point of views. In particular, differences between physical and chemical storage are here considered with a particular glance to the most innovative technologies including carbon nanostructures. A review on the main problems in storage and transportation is then shown with a particular attention given to infrastructures costs that perhaps will address particular choices for the technologies of the next future. Automotive applications are called out, accounting the main current technologies and notes on fueling station for hydrogen fed vehicle. The discussion of hydrogen safety in automotive put in evidence the needs for sophisticated sensors, but a comparison with the safety of gasoline and fire risks, evidences that some common incertitudes on hydrogen usage should be overcome. Some other safety issues are introduced in the section of hydrogen transportation. An overview of costs related hydrogen production, storage and transportation is finally given. This aspect is of a capital importance for the future dissemination of the hydrogen energy carrier.     

Analysis of capillary flow driven model for water transport in PEFC cathode catalyst layer: Consideration of mixed wettability and pore size distribution

The solid matrix of the porous cathode catalyst layer (CCL) of a polymer electrolyte fuel cell is made of two different materials (carbon with supported Pt and ionomer), which are characterized by different wettability (i.e. contact angles). This paper discusses the need for considering the combined consideration of the mixed wettability and the distributed pore structure of CCL in modelling the transport of liquid water and oxygen gas. A simple 1-D model that considers two different pore size distributions, derived from experimental capillary pressure–saturation literature data, for the hydrophobic and hydrophilic pores is presented. The results indicate that for water to be transported in liquid-state through the CCL, the liquid saturation is such that only very small hydrophobic pores remain available for gas transport such that Knudsen diffusion will dominate and must be considered in CCL models.     

Optimization of the operating conditions for steam reforming of slow pyrolysis oil over an activated biochar-supported Ni–Co catalyst

Highly performing activated biochar-based catalysts were produced for steam reforming of slow pyrolysis oil. The raw biochar obtained from the slow pyrolysis step was physically activated with CO₂ at 700 °C and 1.0 MPa and then employed as support. Preliminary tests on steam reforming of acetic acid at 600 °C showed that using activated biochar-supported catalysts containing 10 wt % Ni and 7 wt % Co led to a conversion above 90% with a relatively slow deactivation rate. When a representative organic model compounds mixture was used as feed, relatively fast deactivation of the catalyst was observed, probably due to the adsorption of heavy organic compounds, which could subsequently react to form not easily desorbable reaction intermediates. However, the dual Ni–Co catalysts exhibited a good performance during the steam reforming of a real slow pyrolysis oil at 750 °C, showing long stability and a constant carbon conversion of 65%.     

Poly‐left‐lactic acid tubular scaffolds via diffusion induced phase separation: Control of morphology

In this work, tubular poly‐left‐lactic acid scaffolds for vascular tissue engineering applications were produced by an innovative two‐step method. The scaffolds were obtained by performing a dip‐coating around a nylon fiber, followed by a diffusion induced phase separation process. Morphological analysis revealed that the internal lumen of the as‐obtained scaffold is equal to the diameter of the fiber utilized; the internal surface is homogeneous with micropores 1–2 μm large. Moreover, a porous open structure was detected across the thickness of the walls of the scaffold. An accurate analysis of the preparation process revealed that it is possible to tune up the morphology of the scaffold (wall thickness, porosity, and average pore dimension), simply by varying some experimental parameters. Preliminary in vitro cell culture tests were carried out inside the scaffold. The results showed that cells are able to grow within the internal surface of the scaffolds and after 3 weeks they begin to form a “primordial” vessel‐like structure. Modeling predictions of the dip‐coating process display always an underestimate of experimental data (dependence of wall thickness upon extraction rate). POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

High‐frequency sampling and kernel estimation for continuous‐time moving average processes

Interest in continuous‐time processes has increased rapidly in recent years, largely because of high‐frequency data available in many applications. We develop a method for estimating the kernel function g of a second‐order stationary Lévy‐driven continuous‐time moving average (CMA) process Y based on observations of the discrete‐time process Y^Δ obtained by sampling Y at Δ, 2Δ, …, nΔ for small Δ. We approximate g by g^Δ based on the Wold representation and prove its pointwise convergence to g as Δ → 0 for continuous‐time autoregressive moving average (CARMA) processes. Two non‐parametric estimators of g^Δ, on the basis of the innovations algorithm and the Durbin–Levinson algorithm, are proposed to estimate g. For a Gaussian CARMA process, we give conditions on the sample size n and the grid spacing Δ(n) under which the innovations estimator is consistent and asymptotically normal as n → ∞. The estimators can be calculated from sampled observations of any CMA process, and simulations suggest that they perform well even outside the class of CARMA processes. We illustrate their performance for simulated data and apply them to the Brookhaven turbulent wind speed data. Finally, we extend results of Brockwell et al. (2012) for sampled CARMA processes to a much wider class of CMA processes.     

Bread crust melanoidins as potential prebiotic ingredients

Melanoidins are the final products of the Maillard reaction. They are a heterogeneous mixture of compounds characterized by brown color and high molecular weight. The physiological properties of melanoidins have been widely investigated and there is a general consensus on their poor digestibility and bioavailability. In vitro studies on food melanoidins are in many cases limited by their poor water solubility. This problem was recently overcome for bread melanoidins using an enzymatic digestion procedure. Bread melanoidins are constituted by low-molecular-weight, colored compounds linked to the gluten polymer. In this work, melanoidins from different bread types were investigated for their potential prebiotic activity by a static batch culture. Results showed that anaerobic bacteria, particularly Bifidobacteria strains, are able to use bread melanoidins as carbon source. The bacterial growth is different for the various types of melanoidins samples indicating that starting materials and processing conditions have a strong influence on the prebiotic potential of bread melanoidins. In all cases the bacterial growth obtained using bread melanoidins is lower than that previously observed using melanoidins from other sources, such as coffee silverskin.