• Energy Research
• Restricted close
• Embargo close
• ES close
• National Research Council close

Hydrogen generation from water using solar energy has grown into a promising approach for sustainable energy production. Over the last years, graphitic carbon nitrides (g-C3N4, CN), polymers based on the heptazine-group, have been widely applied as photocatalysts for H2 evolution. The poor charge separation efficiency of CN is considered the major drawback. Here, we investigated the effect of coupling CN with different types of carbon nanotubes on the charge transfer properties and the photocatalytic H2 evolution. We used carbon nanotubes (CNTs) of different wall number (single (SWCNTs), double (DWCNTs) and multi-walled (MWCNTs) CNTs) for the development of full-organic CN based composite photocatalysts. Photoactivity was drastically affected by the content but more importantly by the nature of the CNTs. The SWCNTs functionalized CN composites were the most active presenting approximately 2-5 times higher H2 evolution than the corresponding DWCNTs and MWCNTs functionalized CN under both solar and pure visible light irradiation. Photoactivity was primarily controlled by the improved electronic properties linked with the abundance and stability of photogenerated charges as evidenced by electron paramagnetic resonance spectroscopy. Transient absorption spectroscopy verified the transfer of reactive electrons from CN to CNTs. CNTs functioned as electron acceptors improving charge separation. The data suggest that charge transfer is inversely proportional to the wall number of the CNTs and that photoactivity is directly controlled by the size at the nanoscale of the CNTs used. In the CNTs/CN nanocomposites, photogenerated electrons are transferred more efficiently from CN when SWCNTs are used, providing more available electrons for H2 production.

Heterofermentative lactic acid bacteria (76 strains) belonging to Lactobacillus, Leuconostoc and Weissella species which are important in fermentation, spoilage or as probiotics were screened in a factorial experiment for their ability to grow, produce catalase and consume oxygen in aerobiosis or in anaerobiosis, with or without supplementation with hemin and/or menaquinone in a medium containing glucose as a carbohydrate source. Aerobiosis improved growth with a few exceptions. The effect of supplementation with heme and/or menaquinone was strain specific and clear evidence of heme-boosted respiration was found in some cases. Heme-catalase was produced by strains of L. brevis, W. minor and Leuc. mesenteroides; some strains of the latter species produced non-heme catalase. Shaken flasks experiments showed that aerobic growth resulted in increased maximum growth rate and in a limited increase in biomass. Heme supplementation during aerobic growth resulted in a further increase in growth rate and final biomass only for a few strains; this was often related to catalase, which was also responsible for increased tolerance of H2O2. In both experiments we found evidence of heme toxicity, especially in anaerobiosis and in absence of menaquinone. Dose response curves for aerobic growth in the presence of combinations of hemin and menaquinone were non-monotonic, with growth stimulation at low doses of heme (<2.5 mg/l) and toxicity at higher doses. Menaquinone at 0.25-8 mg/l increased growth stimulation and partially reduced toxicity.

Phase change material emulsions (PCMEs) were largely investigated as potential working fluids for various applications as in HVAC systems, solar thermal storage, and heat transfer. They basically contain water and phase change materials, possess much larger energy storage capacity than currently used chilled water based systems and exploit higher thermal conductivity than bulk PCM reservoirs. Main barriers to their application are the difficulty in maintaining emulsion stability and the undercooling effect. In this work, a new solvent-assisted route was developed to produce nano-emulsions of commercial paraffin waxes in water. Concentrations from 2 to 10 wt% were obtained starting from two commercial paraffin waxes, with nominal melting temperatures around 55 °C and 70 °C. The droplet dimensions were verified and resulted below 100 nm for lower concentrations and around 180-220 nm for 10 wt%. The stability of emulsions was verified by long-term tests. An undercooling effect was verified and strongly reduced by testing some nucleating agents (a paraffin melting at 70 °C in the paraffin melting at 55 °C or a carbon nanostructure, single wall carbon nanohorns). The heat of melting was lower than expected, probably due to PCM molecules on the surface of the nanoparticles anchored to the surfactant. However, calculating the thermal capacity of PCMEs with respect to pure water, a gain up to 40% for operating temperatures close to PCM melting temperature was estimated. Optical properties of single wall carbon nanohorns/paraffin composites were also measured.

An ultracapacitor (UCap) based on carbon xerogel electrodes and sodium sulfate electrolyte was investigated in the voltage range between 0 and 1.8 V. Notwithstanding the high value of maximum voltage (1.8 V) the UCap exhibited excellent stability during 20000 of cycling test. Moreover, the achievement of this high voltage made possible to obtain high value of specific energy. The stability was possible because the potential limits of electrode-electrolyte decomposition at positive and negative electrodes were never achieved. This is because an asymmetric UCap with different amounts of carbon xerogel in the electrodes was used. The UCap with the carbon xerogel of BET specific surface area of 3100 m(2) g(-1) demonstrated a specific energy of 17.5 Wh kg(-1) and a specific capacitance of 156 F g(-1) and, retained 91% of initial capacitance after 20000 cycles of duration test. (C) 2012 Elsevier B.V. All rights reserved.

This work reports results of an experimental investigation carried out on a multihole injector for direct injection spark ignition engines by using phase Doppler anemometry (PDA). Results of droplet size and velocity were compared testing n-butanol and gasoline injected at 5 and 10 MPa in a vessel at atmospheric pressure and ambient temperature. Experiments were focused on the characterization of the dynamic behavior of droplet size and velocity acquired on the axis and the edge of one of the jets at different distances from the nozzle hole. The effect of the injection interval and the photomultiplier voltage on the sample distribution was investigated. It was found that these parameters have a strong influence on data validation and their fine tuning can avoid the occurrence of time intervals with lack of validated data. Different post-processing filtering methods were applied in order to evaluate differences linked to the data statistical distributions. Results have highlighted that the different fuel properties have an influence on the droplet size and velocity and affect the jet dynamic behavior.

One of the most fascinating characteristics of perovskite solar cells (PSCs) is the retrieved obtainment of outstanding photovoltaic (PV) performances withstanding important device configuration variations. Here we have analyzed CH3NH3PbI3-xClx in planar or in mesostructured (MS) configurations, employing both titania and alumina scaffolds, fully infiltrated with perovskite material or presenting an overstanding layer. The use of the MS scaffold induces to the perovskite different structural properties, in terms of grain size, preferential orientation, and unit cell volume, in comparison to the ones of the material grown with no constraints, as we have found out by X-ray diffraction analyses. We have studied the effect of the PSC configuration on photoinduced absorption and time-resolved photoluminescence, complementary techniques that allow studying charge photogeneration and recombination. We have estimated electron diffusion length in the considered configurations observing a decrease when the material is confined in the MS scaffold with respect to a planar architecture. However, the presence of perovskite overlayer allows an overall recovering of long diffusion lengths explaining the record PV performances obtained with a device configuration bearing both the mesostructure and a perovskite overlayer. Our results suggest that performance in devices with perovskite overlayer is mainly ruled by the overlayer, whereas the mesoporous layer influences the contact properties.

CuxO-TiO2 (x = 1, 2) nanomaterials are synthesized on polycrystalline Ti substrates by a convenient chemical vapor deposition (CVD) approach, based on the initial growth of a CuxO matrix (at 400 and 550 °C for x = 1 and 2, respectively) and the subsequent overdispersion of TiO2 at 400 °C. All CVD processes are carried out in an oxygen atmosphere saturated with water vapor. The obtained systems are investigated by means of glancing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and electrochemical experiments. Galvanostatic charge/discharge measurements indicate that Cu2O-TiO2 nanomaterials exhibit very attractive high-rate capabilities (∼400 mA h g(-1) at 1 C; ∼325 mA h g(-1) at 2 C) and good stability after 50 operating cycles, with a retention of 80% of the initial capacity. This phenomenon is mainly due to the presence of TiO2 acting as a buffer material, i.e., minimizing volume changes occurring in the electrochemical conversion. In a different way, CuO-TiO2 systems exhibit worse electrochemical performances as a consequence of their porous morphology and higher thickness. In both cases, the obtained values are among the best ever reported for CuxO-based systems, candidating the present nanomaterials as extremely promising anodes for eventual applications in thin film lithium batteries.

An experimental study has been performed for identifying the role of injector nozzle hole convergence and cavitation in diesel engine combustion and pollutant emissions. For doing so, five nozzles were tested under different operating and experimental conditions. The critical cavitation number of each nozzle was analyzed. With this value, an estimation of the mixing process at different conditions obtained. This data is used to explain the combustion results which are analyzed in terms of the apparent combustion time, rate of heat release, in-cylinder pressures, adiabatic temperatures and soot and NO, emissions. Special emphasis is put in developing an expression to explicitly link the mixing process and the injection rate with the rate of heat release. The results show that the fuel-air mixing process can be improved by the use of both convergent and cavitating nozzles, thus lowering the soot emissions. The NO, production, being dependent of the injection rate and the mixing process, does not necessarily increase with the use of more convergent nozzles. (c) 2007 Elsevier Ltd. All rights reserved.