Caratterizzazione di membrane metalliche e ionomeriche per applicazioni energetiche

The work of this thesis has been focused on the characterization of metallic membranes for the hydrogen purification from steam reforming process and also of perfluorosulphonic acid ionomeric (PFSI) membranes suitable as electrolytes in fuel cell applications. The experimental study of metallic membranes was divided in three sections: synthesis of palladium and silver palladium coatings on porous ceramic support via electroless deposition (ELD), solubility and diffusivity analysis of hydrogen in palladium based alloys (temperature range between 200 and 400 °C up to 12 bar of pressure) and permeation experiments of pure hydrogen and mixtures containing, besides hydrogen, also nitrogen and methane at high temperatures (up to 600 °C) and pressures (up to 10 bar). Sequential deposition of palladium and silver on to porous alumina tubes by ELD technique was carried out using two different procedures: a stirred batch and a continuous flux method. Pure palladium as well as Pd-Ag membranes were produced: the Pd-Ag membranes’ composition is calculated to be close to 77% Pd and 23% Ag by weight which was the target value that correspond to the best performance of the palladium-based alloys. One of the membranes produced showed an infinite selectivity through hydrogen and relatively high permeability value and is suitable for the potential use as a hydrogen separator. The hydrogen sorption in silver palladium alloys was carried out in a gravimetric system on films produced by ELD technique. In the temperature range inspected, up to 400°C, there is still a lack in literature. The experimental data were analyzed with rigorous equations allowing to calculate the enthalpy and entropy values of the Sieverts’ constant; the results were in very good agreement with the extrapolation made with literature data obtained a lower temperature (up to 150 °C). The information obtained in this study would be directly usable in the modeling of hydrogen permeation in Pd-based systems. Pure and mixed gas permeation tests were performed on Pd-based hydrogen selective membranes at operative conditions close to steam-reforming ones. Two membranes (one produced in this work and another produced by NGK Insulators Japan) showed a virtually infinite selectivity and good permeability. Mixture data revealed the existence of non negligible resistances to hydrogen transport in the gas phase. Even if the decrease of the driving force due to polarization concentration phenomena occurs, in principle, in all membrane-based separation systems endowed with high perm-selectivity, an extensive experimental analysis lack, at the moment, in the palladium-based membrane process in literature. Moreover a new procedure has been introduced for the proper comparison of the mass transport resistance in the gas phase and in the membrane. Another object of study was the water vapor sorption and permeation in PFSI membranes with short and long side chains was also studied; moreover the permeation of gases (i.e. He, N2 and O2) in dry and humid conditions was considered. The water vapor sorption showed strong interactions between the hydrophilic groups and the water as revealed from the hysteresis in the sorption-desorption isotherms and thermo gravimetric analysis. The data obtained were used in the modeling of water vapor permeation, that was described as diffusion-reaction of water molecules, and in the humid gases permeation experiments. In the dry gas experiments the permeability and diffusivity was found to increase with temperature and with the equivalent weight (EW) of the membrane. A linear correlation was drawn between the dry gas permeability and the opposite of the equivalent weight of PFSI membranes, based on which the permeability of pure PTFE is retrieved in the limit of high EW. In the other hand O2 ,N2 and He permeability values was found to increase significantly, and in a similar fashion, with water activity. A model that considers the PFSI membrane as a composite matrix with a hydrophilic and a hydrophobic phase was considered allowing to estimate the variation of gas permeability with relative humidity on the basis of the permeability in the dry PFSI membrane and in pure liquid water.

Role of reactive oxygen and nitrogen species in the response of Prunus spp. to bicarbonate

In calcareous soils, which are a large share of agricultural soils worldwide, iron availability is limited. Consequently, the whole plant physiology is affected, because of the key role of iron in redox metabolism, resulting in reduced crop yield and quality. Peach cultivation is economically important in northern Italy, and is easily subjected to iron chlorosis. The management of iron nutrition in peach includes grafting on bicarbonate-tolerant rootstocks; other forms of management may be expensive and environmentally impacting. Four genotypes, used as rootstocks for peach and characterized by different degrees of tolerance to chlorosis, were tested in vitro on optimal and bicarbonate-enriched medium. Their redox status and antioxidant responses were assayed; the production and possible roles of nitric oxide (NO) and related compounds were also studied. The most sensitive genotypes show a stronger reduction of the antioxidant enzymatic activities and an increased oxidative stress. A high production of NO was found to be associated to resistant genotypes, whereas sensitive genotypes reacted to stress by downregulating nitrosoglutathione reductase activity. Therefore, NO is proposed to improve the internal iron availability, or to stimulate iron intake.

Modelling the effects of nitrogen deposition and carbon dioxide enrichment on forest carbon balance

Atmospheric CO2 concentration ([CO2]) has increased over the last 250 years, mainly due to human activities. Of total anthropogenic emissions, almost 31% has been sequestered by the terrestrial biosphere. A considerable contribution to this sink comes from temperate and boreal forest ecosystems of the northern hemisphere, which contain a large amount of carbon (C) stored as biomass and soil organic matter. Several potential drivers for this forest C sequestration have been proposed, including increasing atmospheric [CO2], temperature, nitrogen (N) deposition and changes in management practices. However, it is not known which of these drivers are most important. The overall aim of this thesis project was to develop a simple ecosystem model which explicitly incorporates our best understanding of the mechanisms by which these drivers affect forest C storage, and to use this model to investigate the sensitivity of the forest ecosystem to these drivers. I firstly developed a version of the Generic Decomposition and Yield (G’DAY) model to explicitly investigate the mechanisms leading to forest C sequestration following N deposition. Specifically, I modified the G’DAY model to include advances in understanding of C allocation, canopy N uptake, and leaf trait relationships. I also incorporated a simple forest management practice subroutine. Secondly, I investigated the effect of CO2 fertilization on forest productivity with relation to the soil N availability feedback. I modified the model to allow it to simulate short-term responses of deciduous forests to environmental drivers, and applied it to data from a large-scale forest Free-Air CO2 Enrichment (FACE) experiment. Finally, I used the model to investigate the combined effects of recent observed changes in atmospheric [CO2], N deposition, and climate on a European forest stand. The model developed in my thesis project was an effective tool for analysis of effects of environmental drivers on forest ecosystem C storage. Key results from model simulations include: (i) N availability has a major role in forest ecosystem C sequestration; (ii) atmospheric N deposition is an important driver of N availability on short and long time-scales; (iii) rising temperature increases C storage by enhancing soil N availability and (iv) increasing [CO2] significantly affects forest growth and C storage only when N availability is not limiting.

Organic fertilization of peach trees: implication on nitrogen availability, root growth and carbon distribution within plant

In the last years, sustainable horticulture has been increasing; however, to be successful this practice needs an efficient soil fertility management to maintain a high productivity and fruit quality standards. For this purpose composted organic materials from agri-food industry and municipal solid waste has been used as a source to replace chemical fertilizers and increase soil organic matter. To better understand the influence of compost application on soil fertility and plant growth, we carried out a study comparing organic and mineral nitrogen (N) fertilization in micro propagated plants, potted trees and commercial peach orchard with these aims: 1. evaluation of tree development, CO2 fixation and carbon partition to the different organs of two-years-old potted peach trees. 2. Determination of soil N concentration and nitrate-N effect on plant growth and root oxidative stress of micro propagated plant after increasing rates of N applications. 3. Assessment of soil chemical and biological fertility, tree growth and yield and fruit quality in a commercial orchard. The addition of compost at high rate was effective in increasing CO2 fixation, promoting root growth, shoot and fruit biomass. Furthermore, organic fertilizers influenced C partitioning, favoring C accumulation in roots, wood and fruits. The higher CO2 fixation was the result of a larger tree leaf area, rather than an increase in leaf photosynthetic efficiency, showing a stimulation of plant growth by application of compost. High concentrations of compost increased total soil N concentration, but were not effective in increasing nitrate-N soil concentration; in contrast mineral-N applications increased linearly soil nitrate-N, even at the lowest rate tested. Soil nitrate-N concentration influenced positively plant growth at low rate (60- 80 mg kg-1), whereas at high concentrations showed negative effects. In this trial, the decrease of root growth, as a response to excessive nitrate-N soil concentration, was not anticipated by root oxidative stress. Continuous annual applications of compost for 10 years enhanced soil organic matter content and total soil N concentration. Additionally, high rate of compost application (10 t ha-1 year-1) enhanced microbial biomass. On the other hand, different fertilizers management did not modify tree yield, but influenced fruit size and precocity index. The present data support the idea that organic fertilizers can be used successfully as a substitute of mineral fertilizers in fruit tree nutrient management, since they promote an increase of soil chemical and biological fertility, prevent excessive nitrate-N soil concentration, promote plant growth and potentially C sequestration into the soil.

Influence of nitrogen and soil physical characteristics on belowground carbon flux dynamics of woody plants

At ecosystem level soil respiration (Rs) represents the largest carbon (C) flux after gross primary productivity, being mainly generated by root respiration (autotrophic respiration, Ra) and soil microbial respiration (heterotrophic respiration, Rh). In the case of terrestrial ecosystems, soils contain the largest C-pool, storing twice the amount of C contained in plant biomass. Soil organic matter (SOM), representing the main C storage in soil, is decomposed by soil microbial community. This process produces CO2 which is mainly released as Rh. It is thus relevant to understand how microbial activity is influenced by environmental factors like soil temperature, soil moisture and nutrient availability, since part of the CO2 produced by Rh, directly increases atmospheric CO2 concentration and therefore affects the phenomenon of climate change. Among terrestrial ecosystems, agricultural fields have traditionally been considered as sources of atmospheric CO2. In agricultural ecosystems, in particular apple orchards, I identified the role of root density, soil temperature, soil moisture and nitrogen (N) availability on Rs and on its two components, Ra and Rh. To do so I applied different techniques to separate Rs in its two components, the ”regression technique” and the “trenching technique”. I also studied the response of Ra to different levels of N availability, distributed either in a uniform or localized way, in the case of Populus tremuloides trees. The results showed that Rs is mainly driven by soil temperature, to which it is positively correlated, that high levels of soil moisture have inhibiting effects, and that N has a negligible influence on total Rs, as well as on Ra. Further I found a negative response of Rh to high N availability, suggesting that microbial decomposition processes in the soil are inhibited by the presence of N. The contribution of Ra to Rs was of 37% on average.

Soil application of Meliaceae derivatives: effect on carbon and nitrogen dynamics in the soil-plant system

The effect of soil incorporation of 7 Meliaceae derivatives (6 commercial neem cakes and leaves of Melia azedarach L.) on C and N dynamics and on nutrient availability to micropropagated GF677 rootstock was investigated. In a first laboratory incubation experiment the derivatives showed different N mineralization dynamics, generally well predicted by their C:N ratio and only partly by their initial N concentration. All derivatives increased microbial biomass C, thus representing a source of C for the soil microbial population. Soil addition of all neem cakes (8 g kg-1) and melia leaves (16 g kg-1) had a positive effect on plant growth and increased root N uptake and leaf green colour of micropropagated plants of GF677. In addition, the neem cakes characterized by higher nutrient concentration increased P and K concentration in shoot and leaves 68 days after the amendment. In another experiment, soil incorporation of 15N labeled melia leaves (16 g kg-1) had no effect on the total amount of plant N, however the percentage of melia derived-N of treated plants ranged between 0.8% and 34% during the experiment. At the end of the growing season, about 7% of N added as melia leaves was recovered in plant, while 70% of it was still present in soil. Real C mineralization and the priming effect induced by the addition of the derivatives were quantified by a natural 13C abundance method. The real C mineralization of the derivatives ranged between 22% and 40% of added-C. All the derivatives studied induced a positive priming effect and, 144 days after the amendment, the amount of C primed corresponded to 26% of added-C, for all the derivatives. Despite this substantial priming effect, the C balance of the soil, 144 days after the amendment, always resulted positive.

New techniques for the remote sensing of foliar nitrogen concentration in forest ecosystems.

During my Doctoral study I researched about the remote detection of canopy N concentration in forest stands, its potentials and problems, under many overlapping perspectives. The study consisted of three parts. In S. Rossore 2000 dataset analysis, I tested regressions between N concentration and NIR reflectances derived from different sources (field samples, airborne and satellite sensors). The analysis was further expanded using a larger dataset acquired in year 2009 as part of a new campaign funded by the ESA. In both cases, a good correlation was observed between Landsat NIR, using both TM (2009) and ETM+ (2000) imagery, and N concentration measured by a CHN elemental analyzer. Concerning airborne sensors I did not obtain the same good results, mainly because of the large FOV of the two instruments, and to the anisotropy of vegetation reflectance. We also tested the relation between ground based ASD measures and nitrogen concentration, obtaining really good results. Thus, I decided to expand my study to the regional level, focusing only on field and satellite measures. I analyzed a large dataset for the whole of Catalonia, Spain; MODIS imagery was used, in consideration of its spectral characteristics and despite its rather poor spatial resolution. Also in this case a regression between nitrogen concentration and reflectances was found, but not so good as in previous experiences. Moreover, vegetation type was found to play an important role in the observed relationship. We concluded that MODIS is not the most suitable satellite sensor in realities like Italy and Catalonia, which present a patchy and inhomogeneous vegetation cover; so it could be utilized for the parameterization of eco-physiological and biogeochemical models, but not for really local nitrogen estimate. Thus multispectral sensors similar to Landsat Thematic Mapper, with better spatial resolution, could be the most appropriate sensors to estimate N concentration.

Synthesis and aplication of linear and macrocyclic nitrogen ligand

Linear and macrocyclic nitrogen ligands have been found wide application during the years. Nitrogen has a much strong association with transition-metal ions because the electron pair is partucularly available for complexing purposes. We started our investigation with the synthesis of new chiral perazamacrocycles containing four pyrrole rings. This ligand was synthesized by the [2+2]condensation of (R,R)-diaminocyclohexane and dipirranedialdehydes and was tested, after a complexation with Cu(OAc)2, in Henry reactions. The best yields (96%) and higher ee’s (96%) were obtained when the meso-substituent on the dipyrrandialdehyde was a methyl group. The positive influence of the pyrrole-containing macrocyclic structure on the efficiency/enantioselectivity of the catalytic system was demonstrated by comparison with the Henry reactions performed using analogous ligands. Henry product was obtain in good yield but only 73% of ee, when the dialdehyde unit was replaced by a triheteroaromatic dialdehye (furan-pyrrol-furan). Another well known macrocyclic ligand is calix[4]pyrrole. We decided to investigate, in collaboration with Neier’s group, the metal-coordinating properties of calix[2]pyrrole[2]pyrrolidine compounds obtained by the reduction of calix[4]pyrrole. We focused our attention on the reduction conditions, and tested different Pd supported (charcoal, grafite) catalysts at different condition. Concerning the synthesis of linear polyamine ligands. We focused our attention to the synthesis of 2-heteroaryl- and 2,5-diheteroarylpyrrolidines. The reductive amination reaction of diarylketones and aryl-substitutedketo-aldehydes with different chiral amines was exploited to prepare a small library of diastereo-enriched substituted pyrrolidines. We have also described a new synthetic route to 1,2-disubstituted 1,2,3,4-tetrahydropyrrole[1,2-a]pyrazines, which involves the diastereoselective addition of Grignard reagents to chiral oxazolidines. The best diastereoselectivity (98:2) was dependent on the nature of both the chiral auxiliary, (S)-1-phenylglycinol, and the nature of the organometallic reagent (MeMgBr).

Crystal Engineering of bright luminescent copper iodide clusters with phosphorus and nitrogen-based ligands

Copper(I) halide clusters are recently considered as good candidate for optoelectronic devices such as OLEDs . Although the copper halide clusters, in particular copper iodide, are very well known since the beginning of the 20th century, only in the late ‘70s the interest on these compounds grew dramatically due their particular photophysical behaviour. These complexes are characterized by a dual triplet emission bands, named Cluster Centred (3CC) and Halogen-to-Ligand charge transfer (3XLCT), the intensities of which are strictly related with the temperature. The CC transition, due to the presence of a metallophylic interactions, is prevalent at ambient temperature while the XLCT transition, located preferentially on the ligand part, became more prominent at low temperature. Since these pioneering works, it was easy to understand the photophysical properties of this compounds became more interesting in solid-state respect to solution with an improvement in emission efficiency. In this work we aim to characterize in SS organocopper(I)iodide compounds to valuate the correlation between the molecular crystal structure and the photophysical properties. It is also considered to hike new strategies to synthesize CuI complexes from the wet reactions to the more green solvent free methods. The advantages in using these strategies are evident but, obtain a single crystal suitable for SCXRD analysis from these batches is quite impossible. The structure solution still remains the key point in this research so we tackle this problem solving the structure by X-ray powder diffraction data. When the sample was fully characterized we moved to design and development of the associated OLED-device. Since copper iodide complexes are often insoluble in organic solvents, the high vacuum deposition technique is preferred. A new non-conventional deposition process have also been proposed to avoid the low complex stability in this practice with an in-situ complex formation in a layer-by layer deposition route.

Structural and biochemical studies of Sporosarcina pasteurii UreE: a nickel-chaperone involved in the urease activation process

Urease is a nickel-dependent enzyme that catalyzes hydrolysis of urea in the last step of organic nitrogen mineralization. Its active site contains a dinuclear center for Ni(II) ions that must be inserted into the apo-enzyme through the action of four accessory proteins (UreD, UreE, UreF, UreG) leading to activation of urease. UreE, acting as a metallo-chaperone, delivers Ni(II) to the preformed complex of apo-urease-UreDFG and has the capability to enhance the GTPase activity of UreG. This study, focused on characterization of UreE from Sporosarcina pasteurii (SpUreE), represents a piece of information on the structure/mobility-function relationships that control nickel binding by SpUreE and its interaction with SpUreG. A calorimetric analysis revealed the occurrence of a binding event between these proteins with positive cooperativity and a stoichiometry consistent with the formation of the (UreE)2-(UreG)2 hetero-oligomer complex. Chemical Shift Perturbations induced by the protein-protein interaction were analyzed using high-resolution NMR spectroscopy, which allowed to characterize the molecular details of the protein surface of SpUreE involved in the complex formation with SpUreG. Moreover, backbone dynamic properties of SpUreE, determined using 15N relaxation analysis, revealed a general mobility in the nanoseconds time-scale, with the fastest motions observed at the C-termini. The latter analysis made it possible for the first time to characterize of the C-terminal portions, known to contain key residues for metal ion binding, that were not observed in the crystal structure of UreE because of disorder. The residues belonging to this portion of SpUreE feature large CSPs upon addition of SpUreG, showing that their chemical environment is directly affected by protein-protein interaction. Metal ion selectivity and affinity of SpUreE for cognate Ni(II) and non cognate Zn(II) metal ions were determined, and the ability of the protein to select Ni(II) over Zn(II), in consistency with the proposed role in Ni(II) cations transport, was established.