Decoupling of soil nutrient cycles as a function of aridity in global drylands

The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems. It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes. Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability. The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients. Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. We find a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition. Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems.

A long marine history of carbon cycle modulation by orbital-climatic changes

Pacing of the marine carbon cycle by orbital forcing during the Pliocene and Pleistocene Ice Ages [past 2.5 million years (Myr)] is well known. As older deep-sea sediment records are being studied at greater temporal resolution, it is becoming clear that similar fluctuations in the marine carbon system have occurred throughout the late Mesozoic and Tertiary, despite the absence of large continental ice sheets over much of this time. Variations in both the organic and the calcium carbonate components of the marine carbon system seem to have varied cyclically in response to climate forcing, and carbon and carbonate time series appear to accurately characterize the frequency spectrum of ancient climatic change. For the past 35 Myr, much of the variance in carbonate content carries the “polar” signal of obliquity [41,000 years (41 kyr)] forcing. Over the past 125 Myr, there is evidence from marine sediments of the continued role of precessional (≈21 kyr) climatic cycles. Repeat patterns of sedimentation at about 100, 400, and 2,400 kyr, the modulation periods of precession, persistently enter into marine carbon cycle records as well. These patterns suggest a nonlinear response of climate and/or the sedimentation of organic carbon and carbonates to precessional orbital perturbations. Nonlinear responses of the carbon system may help to amplify relatively weak orbital insolation anomalies into more significant climatic perturbations through positive feedback effects. Nonlinearities in the carbon cycle may have transformed orbital-climatic cycles into long-wavelength features on time scales comparable to the residence times of carbon and nutrient elements in the ocean.

Self-sensing properties of alkali activated blast furnace slag (BFS) composites reinforced with carbon fibers

In recent years, several researchers have shown the good performance of alkali activated slag cement and concretes. Besides their good mechanical properties and durability, this type of cement is a good alternative to Portland cements if sustainability is considered. Moreover, multifunctional cement composites have been developed in the last decades for their functional applications (self-sensing, EMI shielding, self-heating, etc.). In this study, the strain and damage sensing possible application of carbon fiber reinforced alkali activated slag pastes has been evaluated. Cement pastes with 0, 0.29 and 0.58 vol % carbon fiber addition were prepared. Both carbon fiber dosages showed sensing properties. For strain sensing, function gage factors of up to 661 were calculated for compressive cycles. Furthermore, all composites with carbon fibers suffered a sudden increase in their resistivity when internal damages began, prior to any external signal of damage. Hence, this material may be suitable as strain or damage sensor.

Asymmetric hybrid capacitors based on activated carbon and activated carbon fibre–PANI electrodes

Composites consisting of polyaniline (PANI) coatings inside the microporosity of an activated carbon fibre (ACF) were prepared by electrochemical and chemical methods. Electrochemical characterization of both composites points out that the electrodes with polyaniline show a higher capacitance than the pristine porous carbon electrode. These materials have been used to develop an asymmetric capacitor based on activated carbon (AC) as negative electrode and an ACF–PANI composite as positive electrode in H2SO4 solution as electrolyte. The presence of a thin layer of polyaniline inside the porosity of the activated carbon fibres avoids the oxidation of the carbon material and the oxygen evolution reaction is produced at more positive potentials. This capacitor was tested in a maximum cell voltage of 1.6 V and exhibited high energy densities, calculated for the unpackaged active materials, with values of 20 W h kg−1 and power densities of 2.1 kW kg−1 with excellent cycle lifetime (90% during the first 1000 cycles) and high coulombic efficiency.

Biodiesel production by acid catalysis with heteropolyacids supported on activated carbon fibers

Different catalysts, based on heteropolyacids supported on activated carbon fibers, have been prepared for palmitic acid esterification reaction. The influence of the catalyst (heteropolyacid) and the support on the catalytic activity have been analyzed. The results prove that an adequate combination of both is required to achieve the most suitable catalysts. Regarding to the heteropolyacid, phosphomolybdic acid seems to be the most suitable appropriate taking into account its lowest leaching. About the support, it must show an optimum microporosity, which must be wide enough to allow the entrance and exit of the reagents and products but not too wide in order to avoid the leaching of the catalyst. In addition, both decreasing of the catalytic activity and its recovery over several cycles have been analyzed.

Palladium and Bimetallic Palladium–Nickel Nanoparticles Supported on Multiwalled Carbon Nanotubes: Application to Carbon–Carbon Bond-Forming Reactions in Water

Palladium and bimetallic Pd–Ni nanoparticles (NPs) protected by polyvinylpyrrolidone were prepared by the reduction-by-solvent method and deposited on multiwalled carbon nanotubes (MWCNTs). The catalytic activity of these NPs to carbon–carbon bond-forming reactions was studied by using 0.1 mol % Pd loading, at 120 °C for 1 h and water as a solvent under ligand-free conditions. The Suzuki–Miyaura reaction took place quantitatively for the cross-coupling of 4-bromoanisole with phenylboronic acid, better than those obtained with potassium phenyltrifluoroborate, with Pd50Ni50/MWCNTs as a catalyst and K2CO3 as a base and TBAB as an additive, with good recyclability during 4 cycles with some Ni leaching. The Hiyama reaction of 4-iodoanisole with trimethoxyphenylsilane, under fluoride-free conditions using 50 % aqueous NaOH solution, was performed with Pd/MWCNTs as a catalyst in 83 % yield with low recyclability. For the Mizoroki-Heck reaction 4-iodoanisole and styrene gave the corresponding 4-methoxystilbene quantitatively with Pd50Ni50/MWCNTs using K2CO3 as a base and TBAB as an additive although the recycle failed. In the case of the Sonogashira-Hagihara reaction, Pd/MWCNTs had to be used as a catalyst and pyrrolidine as a base for the coupling of 4-iodoanisole with phenylacetylene under copper-free conditions. The corresponding 4-methoxytolane was quantitatively obtained allowing the recycling of the catalyst during 3 cycles.

The effect of carbon nanofillers on the performance of electromechanical polyaniline-based composite actuators

Different types of crystalline carbon nanomaterials were used to reinforce polyaniline for use in electromechanical bilayer bending actuators. The objective is to analyze how the different graphitic structures of the nanocarbons affect and improve the in situ polymerized polyaniline composites and their subsequent actuator behavior. The nanocarbons investigated were multiwalled carbon nanotubes, nitrogen-doped carbon nanotubes, helical-ribbon carbon nanofibers and graphene oxide, each one presenting different shape and structural characteristics. Films of nanocarbon-PAni composite were tested in a liquid electrolyte cell system. Experimental design was used to select the type of nanocarbon filler and composite loadings, and yielded a good balance of electromechanical properties. Raman spectroscopy suggests good interaction between PAni and the nanocarbon fillers. Electron microscopy showed that graphene oxide dispersed the best, followed by multiwall carbon nanotubes, while nitrogen-doped nanotube composites showed dispersion problems and thus poor performance. Multiwall carbon nanotube composite actuators showed the best performance based on the combination of bending angle, bending velocity and maximum working cycles, while graphene oxide attained similarly good performance due to its best dispersion. This parallel testing of a broad set of nanocarbon fillers on PAni-composite actuators is unprecedented to the best of our knowledge and shows that the type and properties of the carbon nanomaterial are critical to the performance of electromechanical devices with other conditions remaining equal.

Carbon Leakage: Options for the EU. CEPS Special Report, March 2014

This CEPS Special Report builds on the first deliverable of the project entitled “Carbon leakage: Options for the EU”. It identifies carbon costs, and the ability to pass through carbon costs, as the main risk factors that could lead from asymmetrical carbon policies to carbon leakage. It also outlines and evaluates, based on criteria discussed in the paper, options for detecting and mitigating the risk of carbon leakage in three jurisdictions, with special attention to the EU ETS (Emissions Trading Scheme). Based on the analysis of approaches currently used in a number of existing carbon pricing systems, it identifies the balance between the number of sectors identified as being at risk, and the amount of compensation provided as a risk mitigation measure, as the critical element in providing an optimum approach to address carbon leakage risks. It also identifies a risk-based approach to identifying sectors at risk as allowing for a better reflection of reality in a counterfactual argument. Finally, the paper concludes that while, with some exceptions, there has been limited carbon leakage until now, the past may not be a good reflection of the future and that measures need to be put in place for the post-2020 period. While examining a number of approaches, it identifies free allocation as the most likely way forward for mitigating the risk of carbon leakage. While other approaches may provide interesting options, they also present challenges for implementation, from a market functioning, to international trade and relations, points of view. A number of challenges will need to be addressed in the post-2020 period, with many of them part of the EU ETS structural reform package. Some of these challenges include, among others, the need to recognise, and provide for individual sectoral characteristics, as well as for changes in production patterns, due to economic cycles, and other factors. Finally, the paper emphasises the need for an open dialogue regarding the post-2020 provisions for carbon leakage as no overall Energy and Climate Package is likely to be agreed on until this matter is addressed.