Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

In this review, the progress made in the last ten years concerning the synthesis of porous carbon materials is summarized. Porous carbon materials with various pore sizes and pore structures have been synthesized using several different routes. Microporous activated carbons have been synthesized through the activation process. Ordered microporous carbon materials have been synthesized using zeolites as templates. Mesoporous carbons with a disordered pore structure have been synthesized using various methods, including catalytic activation using metal species, carbonization of polymer/polymer blends, carbonization of organic aerogels, and template synthesis using silica nanoparticles. Ordered mesoporous carbons with various pore structures have been synthesized using mesoporous silica materials such as MCM-48, HMS, SBA-15, MCF, and MSU-X as templates. Ordered mesoporous carbons with graphitic pore walls have been synthesized using soft-carbon sources that can be converted to highly ordered graphite at high temperature. Hierarchically ordered mesoporous carbon materials have been synthesized using various designed silica templates. Some of these mesoporous carbon materials have successfully been used as adsorbents for bulky pollutants, as electrodes for supercapacitors and fuel cells, and as hosts for enzyme immobilization. Ordered macroporous carbon materials have been synthesized using colloidal crystals as templates. One-dimensional carbon nanostructured materials have been fabricated using anodic aluminum oxide (AAO) as a template.

Recent Progress in the Synthesis of Porous Carbon Materials

Graphene sheets, which possess unique nanostructure and a variety of fascinating properties, can be considered as promising nanoscale building blocks of new composites, for example, a support material for the dispersion of nanoparticles. Here, we present a general approach for the preparation of graphene−metal particle nanocomposites in a water−ethylene glycol system using graphene oxide as a precursor and metal nanoparticles (Au, Pt and Pd) as building blocks. These metal nanoparticles are adsorbed on graphene oxide sheets and play a pivotal role in catalytic reduction of graphene oxide with ethylene glycol, leading to the formation of graphene−metal particle nanocomposites. The typical methanol oxidation of graphene−Pt composites in cyclic voltammograms analyses indicated its potential application in direct methanol fuel cells, bringing graphene−particle nanocomposites close to real technological applications.

Graphene−Metal Particle Nanocomposites

Polyaniline (PANI) shows electrical as well as optical property changes when it is in contact with oxidant/reductor gas. In this work, the optical transmittance changes in PANI coatings originated by their exposure to the ammonia gas were detected by a nulling optical transmittance bridge. The adsorption and desorption curves were carefully analysed using Langmuir kinetic theory for the adsorption of ammonia gas on PANI single and PANI–PMMA composite coatings. Because of the inhomogeneous nature of the PANI film surface adsorption isotherms were the best described by Freundlich model. From the numerical fitting equations it is suggested that there may be two energetically different adsorption sites on the PANI surface for NH 3 molecules, which corroborates with the no-uniform positive charge distribution on the nitrogen atoms of the PANI backbone chains. The activation energy of adsorption and the heat of adsorption were estimated to be about 0.3–0.5 eV at a NH 3 gas concentration of 10–1000 ppm.

Adsorption kinetics of optochemical NH3 gas sensing with semiconductor polyaniline films

One-step room-temperature synthesis of nanocrystalline Mn3O4 hausmannite, without heating posttreatment, was carried out from a simple dissolution of manganese(II) acetate in a mixture of N,N'-dimethylformamide (DMF) and water. Homogeneous nanocrystals like rods were obtained, with an average width and length of 6.6+/-1.2 nm and 17.4+/-4.1 nm, respectively, and a preferential growth along the 001 direction. Magnetization measurements on a powdered sample showed ferrimagnetic behavior at low temperatures. Under zero-field cooling (ZFC) measurement at 100 Oe, the observed blocking temperature (T(B)) was 37 K.

One-step synthesis of Mn3O4 nanoparticles: structural and magnetic study.

Gold nanoparticles were deposited on the surface of multiwalled carbon nanotubes (MWNTs) functionalized with aliphatic bifunctional thiols (1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, and 2-aminoethanethiol) through a direct solvent-free procedure. Small gold particles, with a narrow particle size distribution around 1.7 nm, were obtained on 1,6-hexanedithiol-functionalized MWNTs. For MWNTs functionalized with the aminothiol, the average Au particle size was larger, 5.5 nm, apparently due to a coalescence phenomenon. Gatan image filter (GIF) observations show that sulfur is at the nanotube surface with a non-homogeneous distribution. A higher sulfur concentration was observed around the gold nanoparticles' location.

Deposition of Gold Nanoparticles onto Thiol-Functionalized Multiwalled Carbon Nanotubes

Gold nanoparticles supported on reducible (TiO 2 and CeO 2 ) and non-reducible oxides (Al 2 O 3 and SiO 2 ) with comparable gold particle size (2.5–3.5 nm) were studied as catalysts in the WGS reaction. Deposition–precipitation with urea (DP Urea) was used to prepare gold nanoparticles supported on TiO 2 , CeO 2 and Al 2 O 3 . Cationic adsorption was used as preparation method in the case of SiO 2 . Metal loading was fixed to 4 and 8 wt.%. The WGS reaction was studied in the temperature range from 50 to 400 °C in a flow reactor at atmospheric pressure. Before reaction the samples were calcined at 200, 300 or 400 °C to study the effect of calcination temperature in the catalyst activity. The Au/CeO 2 catalyst showed an enhanced reduction at low-temperatures as evidenced by the H/Au ratio. The lowest reduction temperature was observed for gold in the Au/TiO 2 catalyst. When supported on TiO 2 and CeO 2 , the activity of gold nanoparticles was much higher than the one observed when supported on Al 2 O 3 and SiO 2 being the Au/SiO 2 catalyst practically inactive. For samples calcined at 300 °C and reaction temperatures below 225 °C the activity varied as follows: TiO 2  > CeO 2  ≫ Al 2 O 3 . CO adsorption in the presence of H 2 O was followed by DRIFT. Bands coming from C–H stretching associated to formate species were clearly observed on CeO 2 . Intensity of these bands decreased when Au is present on the supports. Au 0 -CO adsorption band was evidenced when Au is supported on TiO 2 , CeO 2 and Al 2 O 3 . Fast conversion of formate species in Au/TiO 2 and Au/CeO 2 takes place and this explains the higher activity displayed by these catalysts.

Gold nanoparticles: Support effects for the WGS reaction

Multibranched carbon nanotubes were grown by pyrolysis of acetylene in an anodic aluminum oxide (AAO) template with and without catalytic Co particles at the pore bottom. HRTEM structure analysis shows that both types of carbon nanotubes (CNTs) exhibit the same multiwall features, which consist of cylindrically stacked flakes, and the channel structures, either straight or multi branched, have no effect on the tube wall structure. The pore internal surface of the AAO template plays a catalytic role for the decomposition of acetylene. Due to the poor crystallinity of the present CNTs, their thermal stability in air is lower than that of CNTs by the carbon arc method, but it is better than that of the refined mixed fullerenes. AFM examination reveals that the CNTs can be easily squashed by the interaction between the tip and sample; the height profile can be used to measure the tube wall thickness under contact mode. The formation of CNTs without catalyst deposition gives a reliable and convenient way to st...

José M. Saniger

Papers

Adsorption kinetics of optochemical NH3 gas sensing with semiconductor polyaniline films

One-step synthesis of Mn3O4 nanoparticles: structural and magnetic study.

Deposition of Gold Nanoparticles onto Thiol-Functionalized Multiwalled Carbon Nanotubes

Gold nanoparticles: Support effects for the WGS reaction

Structure, Thermal Stability, and Deformation of Multibranched Carbon Nanotubes Synthesized by CVD in the AAO Template