Solid-state reaction of alkylamines with CO2 in ambient air.

This paper explores possible procedures to accelerate CO2 capture from ambient air by a crystalline alkylamine surfactant (octadecylamine), leading to the corresponding crystalline ammonium-carbamate. Conversion of the amine to the carbamate, in different conditions, is studied by four different techniques: WAXD, FTIR, TGA, and DSC. The WAXD study also gives relevant information on the crystal structures of both amine and derived carbamate. Kinetics of reactions of the crystalline amine are mainly studied by DSC scans, by evaluating melting enthalpies of residual amine. The kinetics of conversion of the amine in ambient CO2 is strongly accelerated by ball milling with full conversion achieved after only 4h, while the reaction kinetics of amine powder simply exposed to ambient CO2 is complete only after nearly 103 h. A substantial increase in kinetics of the solid-state amine reaction with ambient CO2 can be also achieved by increasing the temperature up to 50°C, i.e. at a temperature slightly lower than amine melting. However, the time for full conversion remains much higher than for room-temperature ball-milled amine (roughly 102h vs 4h). Hence, suitable ball-milling procedures can lead to complete and relatively fast conversion of the crystalline amine to the crystalline ammonium-carbamate, even with ambient CO2.

Mechano Chemical Compatibilization of Polyethylene with Graphite by Means of a Suitable Ester.

An effective non-covalent compatibilization method for graphite and low-density polyethylene is reported. To obtain this result, pyren-1-yl-stearate (P1S) was synthesized, characterized and mixed with graphite to provide a better dispersion in polyethylene matrix. The P1S improves the dispersion of carbon filler in polyethylene through non-covalent compatibilization: the pyrenyl group gives π-π stacking interactions with graphite and the stearyl chain provides van der Waals interaction with the polymer chain (specifically London dispersion forces). In this study, different P1S/graphite fillers were prepared with a ratio by weight of 90/10 and 50/50, respectively, by using manual and ball-milling mixing. Their stability, interaction and morphology were evaluated through TGA, RX, and SEM. Thermogravimetric analyses showed that ball-milling mixing is more effective than manual mixing in promoting π-π stacking interactions of molecules such as P1S ester containing an alkyl chain and aromatic rings. The role of ball milling is confirmed by X-ray diffraction measurements since it was possible to observe both exfoliation and intercalation phenomena when this technique was used to mix the P1S ester with graphite. SEM analyses of polyethylene containing 1% of the carbon fillers again highlighted the importance of ball milling to promote the interaction of the ester with graphite and, simultaneously, the importance of the alkyl chain in order to achieve polyethylene-graphite compatibilization.

Hydrogen Bonded Dimer of an Alcohol with the Derived Carboxylic Acid Triggering their Sorption by Nanoporous-crystalline PPO Films.

Films exhibiting nanoporous-crystalline (NC) phases of poly(2,6-dimethyl-1,4-phenylene) oxide (PPO), which are highly effective to absorb apolar organic guest molecules, are also able to absorb polar molecules (like alcohols and carboxylic acids) but only from concentrated organic solutions. NC PPO films, which do not absorb alcohols and carboxylic acids from diluted aqueous solutions, exhibits a huge uptake (even above 30 wt %) of benzyl alcohol (BAL) and benzoic acid (BA), if BA is obtained by spontaneous room temperature oxidation of BAL in aqueous solution. This phenomenon is rationalized by an easy uptake, mainly by the PPO intrahelical crystalline empty channels, of a BAL/BA 1/1 hydrogen-bonded dimer. This huge uptake of BAL/BA dimer by NC PPO films, which is also fast for films exhibiting the orientation of the crystalline helices perpendicular to the film plane (c⊥ orientation), can be exploited for purification of water from BAL, when present in traces. High and fast sorption of a hydrogen bonded dimer and negligible sorption of the two separate compounds is possibly unprecedented for absorbent materials.

Catalytic Applications for Oxidized Carbon Materials: New Perspectives for the Special Issue in Materials.

This Special Issue from Materials, entitled "Catalytic Applications for Oxidized Carbon Materials", aims to publish original papers on new scientific and applied research, providing great contributions to the understanding of oxidized carbon materials and related synthesis, characterization and applications [...].

Basified Graphene Oxide and PPO Composite Aerogel with Basified Graphene Oxide for Henry Reaction in Solvent-Free Conditions: A Green Approach.

Novel basified graphene oxide and high-porosity monolithic composite aerogels of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) containing basified graphene oxide (b-eGO) have been prepared as recoverable and reusable catalysts for the Henry reaction in solvent-free conditions at room temperature. The results showed that, although b-eGO was able to promote the reaction, it suffered from reduced stability. On the other hand, PPO/b-eGO aerogels were able to efficiently promote the Henry reaction in solvent-free conditions. The product could be obtained pure without a purification step, and the catalyst was stable for over 15 months and could be easily recycled without losing catalytic efficiency. The stereochemical outcome was further investigated in the presence of PPO/b-eGO. Despite its negligible influence on diastereoselectivity, better efficiency and a sensible reduction of reaction time were observed.

Nanoporous Crystalline Composite Aerogels with Reduced Graphene Oxide.

High-porosity monolithic composite aerogels of syndiotactic polystyrene (sPS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) containing reduced graphene oxide (r-GO) were prepared and characterized. The composite aerogels obtained by supercritical carbon dioxide (scCO2) extraction of sPS/r-GO and PPO/r-GO gels were characterized by a fibrillar morphology, which ensured good handling properties. The polymer nanoporous crystalline phases obtained within the aerogels led to high surface areas with values up to 440 m2 g-1. The role of r-GO in aerogels was studied in terms of catalytic activity by exploring the oxidation capacity of composite PPO and sPS aerogels toward benzyl alcohol in diluted aqueous solutions. The results showed that, unlike sPS/r-GO aerogels, PPO/r-GO aerogels were capable of absorbing benzyl alcohol from the diluted solutions, and that oxidation of c.a. 50% of the sorbed benzyl alcohol molecules into benzoic acid occurred.

Graphene Oxide and Oxidized Carbon Black as Catalyst for Crosslinking of Phenolic Resins.

Influence of different graphite-based nanofillers on crosslinking reaction of resorcinol, as induced by hexa(methoxymethyl)melamine, is studied. Curing reactions leading from low molecular mass compounds to crosslinked insoluble networks are studied by indirect methods based on Differential Scanning Calorimetry. Reported results show a catalytic activity of graphene oxide (eGO) on this reaction, comparable to that one already described in the literature for curing of benzoxazine. For instance, for an eGO content of 2 wt %, the exothermic crosslinking DSC peak (upon heating at 10 °C/min) shifted 6 °C. More relevantly, oxidized carbon black (oCB) is much more effective as catalyst of the considered curing reaction. In fact, for an oCB content of 2 wt %, the crosslinking DSC peak can be shifted more than 30 °C and a nearly complete crosslinking is already achieved by thermal treatment at 120 °C. The possible origin of the higher catalytic activity of oCB with respect to eGO is discussed.

Release of Cationic Drugs from Charcoal.

The goal of this research is to improve preparation of charcoal adducts in a manner suitable for cationic drug release, possibly using an eco-friendly procedure. Charcoal, widely commercialized for human ingestion, is oxidized by hydrogen peroxide in mild conditions. Adducts of a cationic drug (lidocaine hydrochloride, a medication used as local anesthetic) with charcoal are prepared after basification of charcoal and characterized mainly by elemental analysis, wide-angle X-ray diffraction, infrared spectroscopy and thermogravimetry. The drug in the prepared adducts is present in amount close to 30% by weight and can be readily released to both neutral and acidic aqueous solutions. Cation release, as studied by UV spectra of aqueous solutions, is faster in acidic solutions and is faster than for adducts with graphite oxide, which can be prepared only in harsh conditions.

Edge-Oxidation of Graphites by Hydrogen Peroxide.

A simple and eco-friendly procedure of edge oxidation of high-surface area graphites, based on hydrogen peroxide treatments at 60 °C, is presented. Already, short-term treatments lead to O/C weight ratios higher than 0.1, leaving unaltered interlayer spacing and correlation length. This clearly indicates that all oxidized groups are located on exposed sites (mainly on lateral edges) of the graphitic layers. Short-term H2O2 treatments, as expected, increase hydrophilicity and reduce thermal stability with respect to the starting graphite. Long-term treatments, on the contrary, reduce hydrophilicity and increase thermal stability with respect to the starting graphite, mainly due to surface area reduction associated with the oxidation procedure. Exfoliation of a substantial fraction of the obtained edge-oxidized graphite can be achieved by simple procedures of dispersion and sonication in water.

PLA Melt Stabilization by High-Surface-Area Graphite and Carbon Black.

Small amounts of carbon nanofillers, specifically high-surface-area graphite (HSAG) and more effectively carbon black (CB), are able to solve the well-known problem of degradation (molecular weight reduction) during melt processing, for the most relevant biodegradable polymer, namely poly(lactic acid), PLA. This behavior is shown by rheological measurements (melt viscosity during extrusion experiments and time sweep-complex viscosity) combined with gel permeation chromatography (GPC) experiments. PLA's molecular weight, which is heavily reduced during melt extrusion of the neat polymer, can remain essentially unaltered by simple compounding with only 0.1 wt % of CB. At temperatures close to polymer melting by compounding with graphitic fillers, the observed stabilization of PLA melt could be rationalized by scavenging traces of water, which reduces hydrolysis of polyester bonds. Thermogravimetric analyses (TGA) indicate that the same carbon fillers, on the contrary, slightly destabilize PLA toward decomposition reactions, leading to the loss of volatile byproducts, which occur at temperatures higher than 300 °C, i.e., far from melt processing conditions.

Catalytic Activity of Oxidized Carbon Black and Graphene Oxide for the Crosslinking of Epoxy Resins.

This article compares the catalytic activities of oxidized carbon black (oCB) and graphene oxide (eGO) samples on the kinetics of a reaction of diglycidyl ether of bisphenol A (DGEBA) with a diamine, leading to crosslinked insoluble networks. The study is mainly conducted by rheometry and Differential Scanning Calorimetry (DSC). Following the same oxidation procedure, CB samples are more efficiently oxidized than graphite samples. For instance, CB and graphite samples with high specific surface areas (151 and 308 m²/g), as oxidized by the Hummers' method, exhibit O/C wt/wt ratios of 0.91 and 0.62, respectively. Due to the higher oxidation levels, these oCB samples exhibit a higher catalytic activity toward the curing of epoxy resins than fully exfoliated graphene oxide.

Oxidized Carbon Black as an Activator of Transesterification Reactions under Solvent-Free Conditions.

A metal-free procedure for oxidation of carbon black (CB), under mild and ecofriendly conditions, is described. The procedure, based on 5/1 w/w H2O2/H2SO4, when applied to high-surface-area CB, leads to oxidation contents (O/C = 0.66) comparable to those obtained for graphite with the more aggressive and metal-based Hummers method (O/C 0.63). Oxidized nanocarbons are able to activate transesterification reactions under solvent-free conditions. Activation of transesterification reactions is much more effective by oxidized CB than by graphene oxide.

Regio- and enantioselective friedel-crafts reactions of indoles to epoxides catalyzed by graphene oxide: a green approach.

Graphene oxide efficiently promotes high regio- and enantioselective ring opening reactions of aromatic epoxides by indoles addition, in solvent- and metal-free conditions. The Friedel-Crafts products were obtained with enantioselectivity up to 99 % ee. The complete inversion of stereochemistry indicates the occurrence of SN 2-type reaction, which assures high level of enantioselectivity.

Asymmetric Friedel-Crafts alkylation of indole with chalcones catalyzed by chiral phosphoric acids.

The reaction of indole with chalcones, to give Michael-type adducts, was found to occur with good efficiency (up to 98% yield) and moderate enantioselectivity (up to 52% e.e.) in the presence of a chiral BINOL-based phosphoric acid. Furthermore, the alkylation products can be obtained in much higher e.e.s after one only crystallization.

Organocatalytic asymmetric hydroxylation of beta-keto esters: metal-free synthesis of optically active anti-diols.

The organocatalytic alpha-hydroxylation of beta-keto esters using cinchona-alkaloid derivatives as the catalyst and peroxides as the terminal oxidant has been investigated and is shown to proceed in high yields and with good enantioselectivity. The scope of the reaction is demonstrated for various substrates, and furthermore, the preparation of optically active anti-diols is presented.

Easy approach to chiral Michael adducts by Eu+3-catalyzed conjugate addition.

Michael addition of enantiopure N-acetoacetyl-oxazolidin-2-ones is shown to take place in the presence of catalytic amounts of Eu(+3) salts and complexes in high yields, very reduced reaction times, and moderate diastereoselectivity. The level of diastereoselectivity can be significantly enhanced by the suitable exploitation of the easy epimerization of the adducts in the presence of silica gel.