Matteo Ceppatelli

Fourier transform infrared study of the pressure and laser induced polymerization of solid acetylene

The polymerization of solid acetylene under pressure has been studied by Fourier transform infrared (FTIR) spectroscopy. Controlled laser irradiation cycles and the employment of infrared sensors to measure the sample pressure, allowed to separate the photochemical and the pressure effect on the injection and on the evolution of the reaction. The careful assignment of all the spectral features and analysis of their relative intensities and frequencies gave evidence to the specific effect of pressure and laser irradiation on the reaction products. Pressure induces an ordered growth of trans-polyenic species, while irradiation produces the opening of the double bonds and a consequent branching of the chains. Constant pressure measurements allowed to obtain precise information on the kinetics of the reaction. A monodimensional growth geometry, involving the molecules on the bc plane, agrees with the parameters extracted by the kinetic curves. Comparison between experiments at different temperatures suggests ...

High pressure reactivity of solid furan probed by infrared and Raman spectroscopy

The behavior of crystalline furan has been investigated, at room temperature, along the 0–47–0 GPa pressure cycle by using IR and Raman spectroscopy. These data, joint to high pressure low temperature IR data, allow the identification of two solid phases in the 1.2–12 GPa pressure range: the low-pressure orientationally disordered phase IV and the high-pressure ordered phase III. Above 10–12 GPa solid furan starts to chemically transform. The threshold pressure for the transformation is much lower than in benzene, as expected according to the minor stability of the heteroaromatic ring. The reaction proceeds continuously along the compression path, but it becomes complete only with releasing pressure, and a yellow–brownish sample is recovered. This compound was identified as an amorphous hydrogenated carbon (a-C:H) containing alkylpolyether type segments, alcoholic functions, and C=O bonds. The presence of these new chemical species attests to the opening of the original furan rings and to the transfer of hydrogen atoms. The reaction seems to be very similar to that induced in crystalline benzene. This comparison indicates a general behavior for the reactivity under ultrahigh pressures of the whole class of aromatic compounds.

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry.

High-pressure methods have been demonstrated to be efficient in providing new routes for the synthesis of materials of technological interest. In several molecular compounds, the drastic pressure conditions required for spontaneous transformations have been lowered to the kilobar range by photoactivation of the reactions. At these pressures, the syntheses are accessible to large-volume applications and are of interest to bioscience, space, and environmental chemistry. Here, we show that the short-lived hydroxyl radicals, produced in the photodissociation of water molecules by near-UV radiation at room temperature and pressures of a few tenths of a gigapascal (GPa), can be successfully used to trigger chemical reactions in mixtures of water with carbon monoxide or nitrogen. The detection of molecular hydrogen among the reaction products is of particular relevance. Besides the implications in fundamental chemistry, the mild pressure and irradiation conditions, the efficiency of the process, and the nature of the reactant and product molecules suggest applications in synthesis.

High‐Pressure Chemistry of Red Phosphorus and Water under Near‐UV Irradiation

Phosphorus is a key element in chemistry, physics, and biology, as well as in Earth and planetary sciences. Among the allotropes of phosphorus, the white molecular form (P4), despite its extreme reactivity and toxicity, is currently preferred in industrial and research chemistry over the more-stable and less-toxic red polymeric one (Pred), because it is easily obtained and functionalized. The less-reactive red phosphorus has had much less importance so far and has been employed in the industry of matches and, to a lesser extent, to produce flame retardants in plastics and aluminum phosphide. In view of the intrinsic reduced toxicity, particularly for aquatic organisms, switching from the extremely toxic white to red phosphorus would benefit any industrial procedure for organophosphorus compounds, from an environmental viewpoint, and could attract a large interest from organophosphorus manufactories. High-pressure conditions are often used in chemistry to control the equilibrium constant and the reaction rate of a chemical reaction. Pressure is indeed the most effective tool for modifying intermolecular interactions to induce unexpected and amazing chemical transformations in condensed molecular systems, typically occurring in the GPa range. Despite the very attractive possibility of synthesizing new materials in the absence of solvents and catalysts, according to the principles of green chemistry, at the moment the application of these reactions is strongly limited by the high pressures required, which can not be achieved by large volume apparatuses. However, the combination of high pressure and electronic photoexcitation has been demonstrated to be very efficient in selecting preferential reaction paths and in reducing the threshold pressure for the reaction, even to a few tenths of a GPa, where applications can be envisaged. Recently, the two-photon dissociation of water molecules by near-UV radiation at moderate pressures has been used to generate H atoms and COH radicals and to induce chemical reactions in fluid mixtures and in clathrate hydrates. This approach is employed herein to trigger a very efficient reactivity between red phosphorus and water at room temperature and a few tenths of a GPa, leading to the formation of a large amount of H2 and to a pressure-tuned quantitative oxidation and/or disproportionation of phosphorus to different phosphorus oxyacids and PH3. The reaction occurs in the total absence of solvents, catalysts, and radical initiators. Beyond the fundamental and applicative interest related to the chemistry of phosphorus under non-conventional conditions, obtaining H2 from water is also relevant to the current goal of environmentally friendly synthetic methods based on renewable sources to produce the energy vector of the future. Finally, being that phosphorus is an essential element in the life cycle and in minerals, abiotic formation of phosphorus-containing compounds in terrestrial and space environments could also be relevant. 22] The stability of the mixture of Pred and water was checked on compression up to 0.6 GPa using a diamond anvil cell (DAC; Supporting Information Sections 1.1 and 2). Irradiation of the sample at this pressure for five hours, using the UV multi-line (UVML) emission of an Ar ion laser centered at appoximately 350 nm, resulted in the occurrence of a chemical reaction, as evidenced by the formation of bubbles and by the almost complete consumption of the red phosphorus (Figure 1). Three different areas were roughly identified by visual inspection of the sample as bubbles, transparent, and dark areas. For the three areas, the two most informative frequency regions of the Raman spectrum at 200– 1200 cm 1 and 2100–2500 cm 1 are separately presented and discussed herein. The Raman spectra of the bubbles in the 200–1200 cm 1 frequency region (Figure 2A) are dominated by four sharp bands, identified as the S0(0) (355 cm ), S0(1) (589 cm ), S0(2) (816 cm ), and S0(3) (1033.5 cm ) rotational bands of H2. [23] Other product bands, broader and weaker, which are the only signals observed in the transparent areas, also appears in some bubbles (traces e, h, and l). The Raman spectra of the transparent areas in the 200–1200 cm 1 frequency region show product bands with peak frequencies measured at 428, 526, 805, 898, 941, 1005 (shoulder), 1022, and 1135 cm 1 (Figure 2 B, traces d, x, y, and z). Finally, the Raman spectra measured in the dark areas of the sample (Figure 2C, traces u, v, and w) only show the bands of amorphous red phosphorus. Excluding the rotational bands of H2, all the product bands observed in the 200–1200 cm 1 spectral region [*] Dr. M. Ceppatelli, Dr. M. Caporali, Dr. M. Peruzzini ICCOM-CNR, Istituto di Chimica dei Composti OrganoMetallici Consiglio Nazionale delle Ricerche Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze (Italy) E-mail: matteo.ceppatelli@iccom.cnr.it ceppa@lens.unifi.it

Pressure Induced Reactivity of Solid CO by FTIR Studies

The pressure induced reactivity of carbon monoxide was investigated in a wide temperature range (100-400 K) completely avoiding any irradiation of the sample with visible or higher frequency light. FTIR spectroscopy was employed to monitor the reaction and infrared sensors for measuring the pressure. With this approach we have been able to separate the effects of the three variables (P, T and hnu) that establish the conditions for the occurrence of the chemical reaction. A new instability boundary, not affected by the photoactivation of the reaction, is provided. The reaction has been studied in three different crystal phases (epsilon, delta, and beta), but the small differences in the reaction products are ascribable to the temperature changes rather than to the crystalline arrangement. For T<300 K the analysis of the IR spectra reveals the formation of an extended amorphous material formed, according to the vibrational assignment and to the kinetic data, by polycarbonyl linear chains containing a large amount of anhydride groups. For T>or=300 K the formation of carbon dioxide and epoxy rings, and the simultaneous decrease of carbonyl species, let suppose a decarboxylation of the extended solid product. Once exposed to the atmosphere, the reaction product readily and irreversibly reacts with water giving rise to carboxylic groups.

The high-pressure chemistry of butadiene crystal

FTIR spectroscopy was applied to the study of the high-pressure reactivity of solid butadiene. The chemical transformation from the ordered phase I was observed to occur only above 270 K. The existence of a threshold temperature for the reaction reveals the central role of the lattice phonons in the activation of the transformation. Below 4.0 GPa only dimerization to 4-vinylcyclohexene occurs, while above this pressure an increasing amount of polymer forms with rising pressure. Room temperature kinetic studies have been performed at different pressures, from 2.1 up to 6.6 GPa, and the sign of the activation volume for the dimerization has been obtained. The dimerization reaction is found to follow a first-order mechanism. A reaction pathway for this process is proposed where the internal rearrangement of a diradical intermediate specie is identified as the rate limiting step. An acceleration of the dimerization process is observed above 4.0 GPa and is ascribed to the simultaneous polymer formation. This effect causes the laser assisted reaction, where a large amount of polymer is produced at any pressure, to be not as selective on polymerization as it is in the liquid phase, since also the dimerization rate is enhanced.

High-pressure photochemistry of furane crystal

The role of light absorption in triggering the high-pressure reaction of solid furane is investigated. When the sample is irradiated with the 458.0-nm line of an Ar+ ion laser the reaction is found to occur just above 3 GPa, well below the pressure value (10 GPa) where it takes place without irradiation. The pressure threshold of the transformation increases as the excitation line is shifted to the red. The analysis of the pressure evolution of the UV-VIS absorption spectrum allows us to identify the injection mechanism as a two-photon absorption process to the lowest excited states of furane. The aromatic ring opening shows, in this case, additional reaction paths with respect to the purely pressure induced reaction, as attested by the presence of CO2 and by the larger amount of carbonyl groups found in the recovered product. These results suggest the ring opening mechanism to be mainly controlled by the relative molecular orientation both in the disordered phase IV and in the ordered phase III.

“Click” on Tubes: a Versatile Approach towards Multimodal Functionalization of SWCNTs

Organic functionalization of carbon nanotube sidewalls is a tool of primary importance in material science and nanotechnology, equally from a fundamental and an applicative point of view. Here, an efficient and versatile approach for the organic/organometallic functionalization of single-walled carbon nanotubes (SWCNTs) capable of imparting multimodality to these fundamental nanostructures, is described. Our strategy takes advantage of well-established Cu-mediated acetylene-azide coupling (CuAAC) reactions applied to phenylazido-functionalized SWCNTs for their convenient homo-/heterodecoration with a number of organic/organometallic frameworks, or mixtures thereof, bearing terminal acetylene pendant arms. Phenylazido-decorated SWCNTs were prepared by chemoselective arylation of the CNT sidewalls with diazonium salts under mild conditions, and subsequently used for the copper-mediated cycloaddition protocol in the presence of terminal acetylenes. The latter reaction was performed in one step by using either single acetylene derivatives or equimolar mixtures of terminal alkynes bearing either similar functional groups (masked with orthogonally cleavable protecting groups) or easily distinguishable functionalities (on the basis of complementary analytical/spectroscopic techniques). All materials and intermediates were characterized with respect to their most relevant aspects/properties by TEM microscopy, thermogravimetric analysis coupled with MS analysis of volatiles (TG-MS), elemental analysis, cyclic voltammetry (CV), Raman and UV/Vis spectroscopy. The functional loading and related chemical grafting of both primary amino- and ferrocene-decorated SWCNTs were spectroscopically (UV/Vis, Kaiser test) and electrochemically (CV) determined, respectively.

High-Pressure Reactivity of Model Hydrocarbons Driven by Near-UV Photodissociation of Water

The ambient temperature photoinduced reactivity of mixtures containing water and some of the simplest model hydrocarbons has been studied in a diamond anvil cell below 1 GPa. The near-UV 350 nm emission of an Ar ion laser has been employed to photodissociate water molecules through two-photon absorption processes. The hydroxyl radicals generated through this process are able to trigger a chemical reaction in the mixtures containing ethane and acetylene, which are otherwise stable under the same P-T-hnu conditions, whereas the contribution of water has no effect or is very limited in the case of the ethylene and propene mixtures, respectively. The reaction evolution and the reaction products were characterized by using FTIR spectroscopy. The formation of fluorescent products limits or prevents, as in the case of acetylene, the characterization by Raman spectroscopy. Particularly relevant is the in situ efficient sequestration of the CO(2) formed during the reaction, through the formation of a clathrate hydrate, in the mixtures where water is largely in excess.

Chemical functionalization of N-doped carbon nanotubes: a powerful approach to cast light on the electrochemical role of specific N-functionalities in the oxygen reduction reaction

In this paper, we describe the combination of two different synthetic approaches to carbon nanotube N-decoration/doping: the chemical functionalization with tailored N-pyridinic groups and the classical Chemical Vapor Deposition (CVD) technique. Accordingly, CVD-prepared N-doped CNMs (NMWs) and their N-decorated (chemically functionalized) counterparts (NMW@N1,2) have been prepared and used as metal-free electrocatalysts for the oxygen reduction reaction (ORR). It has been demonstrated that chemical functionalization occurs on the NMW surface sites responsible for their inherent electrochemical properties and “switches them off”. As a result, the ORR promoted by NMW@N1,2 is fully controlled by the appended N-heterocycles. A comparative analysis of N-functionalized samples and N-doped (CVD prepared) materials is used to foster the hypothesis of a unique N-configuration (N-pyridinic) responsible for the overall electrochemical performance in NMWs. In addition to that, original electrochemical insights unveiled during the study are discussed and the truly metal-free action of NMW in ORR catalysis is demonstrated.