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[EN] The synthesis of dihydroxybenzenes (DHBZ), essential chemical reagents in numerous industrial processes, with a high degree of selectivity and yield from the hydroxylation of phenol is progressively attracting great interest in the catalysis field. Furthermore, the additive manufacturing of catalysts to produce 3D printed monoliths would provide additional benefits to enhance the DHBZ synthesis performance. Herein, 3D cellular Fe/γ-Al2O3 monoliths with a total porosity of 88% and low density (0.43 g·cm-3) are printed by Robocasting from pseudoplastic Fe-metal-organic frameworks (Fe-MOF)-based aqueous boehmite inks to develop catalytic monoliths containing a Fe network of dispersed clusters (≤5 μm), nanoclusters (, This work was supported by the following agencies and grants: Spanish Government under the project RTI2018-095052-BI00 (MICINN/AEI/FEDER, UE), Community of Madrid under project S2018/EMT-4341, and CSIC project I–COOP+ 2019 (ref. COOPB20405). P.L. acknowledges the Community of Madrid and the European Social Fund for the financing received through the contract PEJ-2019-AI/IND-14385.

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[EN] The aim of this work is to evaluate the performance of the stirring 3D Fe/AlO monolithic reactor in batch operation applied to the liquid-phase hydroxylation of phenol by hydrogen peroxide (HO ). An experimental and numerical investigation was carried out at the following operating conditions: C = 0.33 M, CO,0 = 0.33 M, T = 75–95C, P = 1 atm, ω = 200–500 rpm and W ~ 1.1 g. The kinetic model described the consumption of the HO by a zero-order power-law equation, while the phenol hydroxylation and catechol and hydroquinone production by Eley–Rideal model; the rate determining step was the reaction between the adsorbed HO, phenol in solution with two active sites involved. The 3D CFD model, coupling the conservation of mass, momentum and species together with the reaction kinetic equations, was experimentally validated. It demonstrated a laminar flow characterized by the presence of an annular zone located inside and surrounding the monoliths (u = 40–80 mm s ) and a central vortex with very low velocities (u = 3.5–8 mm s ). The simulation study showed the increasing phenol selectivity to dihydroxybenzenes by the reaction temperature, while the initial HO concentration mainly affects the phenol conversion., This work was funded by the following agencies and grants: Spanish Government under project RTI2018-095052-BI00 (MICINN/AEI/FEDER, UE), Community of Madrid under project S2018/EMT-4341, and CSIC project I-COOP+ 2019 (Ref. COOPB20405). P. Lopez acknowledges the Community of Madrid and the European Social Fund for the financing received through the contract PEJ-2019-AI/IND-14385

Furfural is a toxic compound that can be found in a wide variety of everyday food and beverages, notably espresso coffee. Given the toxicity of furfural, exposure could lead to liver and skin cancer. Recently, graphene oxide (GO) has been used for application in Solid Phase Micro-Extraction (SPME) due to its large surface area and wide variety of oxygenated functional groups, which makes it an excellent support for the adsorption of different organic compounds. Therefore, in this work a thermally reduced graphene oxide coating (rGOC) was synthetized for the micro-extraction of furfural in espresso coffee. This rGOC was able to absorb the furfural from espresso coffee despite having thickness of around only 1.9 μm. An analysis and optimization of extraction conditions of the furfural in the espresso coffee was carried out and then applied to the quantification of furfural. The furfural was quantified using a Gas Chromatograph coupled to a Mass Spectrometer (GC–MS). The concentration of furfural found was 2.1724 ± 0.0837 mg/L using rGOC whereas with commercial DVB/CAR/PDMS fiber was 2.0766 ± 0.0444 mg/L. The present work attempts to expand the applications of GO in SPME through the analysis of furfural in complex matrix foodstuffs such as espresso coffee. The application of rGOC, as presented in this article, has the advantage of being easy to prepare, requires a low quantity of material and together with its low cost, such application can easily be used instead of commercial fibers.

Three-dimensional graphene materials (3D) have attracted great interest in recent years due to the outstanding properties that are product of the combination between graphene intrinsic properties and 3D materials macroscopic properties, such as porosity and easy manipulation due to their macroscopic scale dimensions. These characteristics have given them notorious advantage for various applications over other materials. This study reports a methodology to obtain a 3D material made with reduced graphene oxide (rGO) using spherical particles of calcium carbonate (CaCO3) as sacrificial template. CaCO3 particles were coated with graphene oxide (GO), using a layer-by-layer procedure (LbL) and later, templates were removed using acid solution. The obtained monolith retains the shape of the templates. The morphology, thermal stability and chemical composition of the monolith were characterized by several techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray photoemission spectroscopy (XPS), Raman spectroscopy and infrared spectroscopy (FTIR). The results showed that the obtained monolith has spherical hollow spaces distributed throughout the 3D structure. In addition, physisorption analysis using N2 revealed that the obtained monolith increased 40% its surface area compared to a conventional rGO aerogel prepared without using sacrificial templates.

Graphene oxide (GO) is a carbon material with wide chemistry, and its functionalization represents the main challenge to develop multi-functional materials for different applications. Besides to epoxide and carboxyl groups, the alkenes that arise during the graphite oxidation seem to provide an excellent approach for developing selective reactions. In specific, α,β-unsaturated acids can be functionalized by thiol-ene Michael addition (TEMA) using base catalysts. However, when base catalysts are used, the thiol-epoxide ring opening reaction (TEROR) has been considered as the predominant and unique reaction. Therefore, there is a need to understand the reactivity of the GO when TEMA and TEROR take place from a qualitative and quantitative point of view. Herein, we studied the functionalization of GO and reduced graphene oxide (RGO) with cysteamine (CA) using different base catalysts. XPS results revealed that despite the thermal reduction of GO, the functionalization was possible confirming the coupling reaction between the CA and α,β-unsaturated acids of RGO by TEMA. In addition, a quantitative analysis was conducted via fluorescent labelling corroborating that TEMA produced more CA molecules bonded to GO than TEROR.

Graphene oxide (GO) is an important platform that can be functionalized due notably to its wide variety of functional groups. The functionalization is a critical step leading the production of GO b...

A semi-crystalline iron-based metal-organic framework (MOF), in particular Fe-BTC, that contained 20 wt.% Fe, was sustainably synthesized at room temperature and extensively characterized. Fe-BTC nanopowders could be used as an efficient heterogeneous catalyst for the synthesis of dihydroxybenzenes (DHBZ), from phenol with hydrogen peroxide (H2O2), as oxidant under organic solvent-free conditions. The influence of the reaction temperature, H2O2 concentration and catalyst dose were studied in the hydroxylation performance of phenol and MOF stability. Fe-BTC was active and stable (with negligible Fe leaching) at room conditions. By using intermittent dosing of H2O2, the catalytic performance resulted in a high DHBZ selectivity (65%) and yield (35%), higher than those obtained for other Fe-based MOFs that typically require reaction temperatures above 70 °C. The long-term experiments in a fixed-bed flow reactor demonstrated good Fe-BTC durability at the above conditions., The authors thank the financial support by Consejo Nacional de Ciencia y Tecnología (CONACYT) for the grant number 764635 and the project 256296; and to TNM for the supporting project 5627.19.P. Also, to the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN) and FEDER program (EU) through the projects: CTM2016-76454-R (MICINN) and RTI2018-095052-B-I00 ((MCIU/AEI/FEDER, UE).

Hydrogen peroxide (H2O2) is an alternative oxidant and green method for the purification and functionalization of carbon nanotubes (CNTs), which works more efficiently in combination with UV radiation. In this paper, we investigated and monitored the oxidation mechanism of ethanol-synthesized and standard multi-walled carbon nanotubes. Characterization was carried out by high-resolution transmission electron microscopy (HRTEM), X-ray photo electron spectroscopy (XPS), acid/base titrations, thermo-gravimetric analysis (TGA) and Raman spectroscopy. Interestingly, we found a close correlation between oxidation time and the nature of the nanotubes. For the first time, a unique cyclic peeling of layers within MWNTs, termed “onion effect” was found. In this process, the degree of crystallinity of the outer layers significantly changed for the different peeling stages. We explain the process and how the number of layers within nanotubes gradually decreases when reaching critical acid concentrations. This method now allows the synthesis of MWCNTs with specific numbers of walls, diameter and controlled degree of crystallinity that could be effectively used for applications in biology and composites.

Graphene oxide is widely-used for many applications because of its surface area and the variety of oxygen functional groups that possess. This latter feature allows it to be a good candidate for polar compounds adsorption such as furfural. Furfural is a toxic compound that has been detected in a wide variety of foods of daily consumption. Frequent exposure in high doses can represent a risk to human health. In the present work, it is proposed an easy procedure to obtain reduced graphene oxide based coatings through dip-coating for Solid Phase Micro-Extraction (SPME) of furfural. The coatings were made with graphene oxide and carboxylated graphene oxide. These coatings were thermally reduced and then tested using a furfural standard. The thermally reduced graphene oxide coatings were characterized using FT-IR, Raman spectroscopy and SEM. SEM micrographs revealed that graphene oxide based fibers had thickness values between 1.5 and 2.5 μm approximately. Subsequently the results of furfural extraction were compared with those obtained from the Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) commercial fibers.

Cleavage of the β C H bond of ethanol during its dehydrogenation on TiO 2 -supported gold samples was investigated by the combined use of infrared (IR) spectroscopy and mass spectrometry. IR spectra characterizing the samples during ethanol adsorption shows that the alcohol was adsorbed both molecularly and dissociatively in the form of ethoxy species bonded to Ti 4+ sites. When a supported gold sample was exposed to consecutive pulses of ethanol 1,1-D 2 (CH 3 CD 2 OH) at 220 °C, mass spectra of the products indicated the formation of acetaldehyde 1-D 1 (CH 3 CDO) and three forms of hydrogen, namely H 2 , HD and D 2 . Because the formation of H 2 was much higher than those of HD and D 2 , it was inferred that cleavage of the β C H bond did not necessarily occur on the gold particles, but on sites of the support. Bolstering this idea, IR spectra measured under reaction conditions indicate the appearance of a band at 2712 cm −1 , assigned to the υ OD vibration mode of deuteroxyl groups on TiO 2 . The data are consistent with the abstraction of deuterium atoms from the ethoxy species by basic sites of the support. It is proposed that the presence of gold particles enhances the diffusion of hydrogen atoms on the sample, as evidenced by marked changes in the absorbance of IR and UV–vis radiation during the reaction, which indicate the presence of electrons trapped at defect sites on the metal oxide near the bottom of the conduction band. Those electrons might have been formed during the reverse spillover of hydrogen from the support to the gold particles, on which they were readily recombined and desorbed as H 2 .

Amino acids are important compounds for GO functionalization because they can improve GO properties for many applications ranging from biomedicine to depollution. However, amino acids can act as nucleophiles or as reducing agents for GO functionalization or reduction, respectively. Hence, we systematically studied the GO functionalization/reduction using glycine as a model amino acid under basic conditions at room temperature. Attenuated total reflectance–Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy, and Raman spectroscopy were used to characterize the modified GO with glycine. We found that low glycine concentrations produced an epoxide ring opening reaction, whereas an increase in glycine concentration led to GO reduction. The basic medium allowed to conserve the carboxylic acid groups, whereas the GO reduction mechanism was governed by the partial hydrolysis of epoxide groups and the subsequent reduction of carboxylic acids to carbonyls. This article opens up the opportunity to study and control the conditions in which different amino acids could be used for either GO functionalization or GO reduction.

[EN] The promising applications of metal-organic frameworks (MOF) can be widened if these materials were additive manufactured to develop three-dimensional (3D) MOF architectures. In this work, iron-based MOF/silicon carbide (SiC) composite aqueous inks with a high solids content (64 ​wt%) are printed into 3D periodic lattices by a direct ink writing technique (Robocasting). MOF appear fully integrated within the cellular architectures, which display total porosities in the range of 74–78% depending on the scaffold design. The 3D MOF-Fe/SiC structures exhibit good mechanical strength (~4.6 ​MPa) and a semiconductor-like behaviour. The structures show a remarkable response in the hydroxylation of phenol with hydrogen peroxide, demonstrating high selectivity and yield to dihydroxybenzene species., This work was supported by the following funding organisms and projects: Spanish Government under the project RTI2018-095052-BI00 (MICINN/AEI/FEDER, UE), Community of Madrid under the project S2018/EMT-4341, CSIC project I-COOPþ 2019 (Ref. COOPB20405), TNM projects 7936.20-P and 9063.20-P, and CONACYT under the project 764635. Authors thank Dr. D. Pérez-Coll for his experimental assistance in the electrical measurements.

Full intralayer potassium intercalation in multiwalled carbon nanotubes MWCNTs was achieved by carefully engineering the nanotube morphology (length, width, and number of layers). The complete intercalation induced a high doping resulting in metallic nanotubes with a bright golden color. The successful intercalation of MWCNTs serves as a first step for obtaining controlled graphene nano-ribbons through exfoliation and potentially preparing superconducting nanotubes.

We demonstrated that the ball-milled slag-SiC mixture is an effective catalyst to grow pyrrolic nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) by aerosol assisted chemical vapor deposition (AACVD) method. N-MWCNTs synthesized at 800 °C, 850 °C and 900 °C were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, x-ray powder diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). TEM characterizations revealed the presence of a bamboo-like structure, a typical feature of nitrogen-doped carbon nanotubes. The presence of nitrogen was confirmed by the N1s XPS spectrum. Furthermore, a deconvolution of the N1s spectra revealed the presence of N-pyrrolic defects. This nitrogen functionality is investigated concerning the presence of silicon carbide material. Giant nanotubes with large diameters were obtained when SiC was added to the slag to be used as a substrate for N-MWCNTs synthesis. From Raman spectroscopy, the appearance of the D-band was observed, indicating the presence of topological defects that were also observed by TEM. XRD and TEM characterizations demonstrated the presence of Fe3C and α-Fe nanoparticles. The N-MWCNTs fabricated here could be used into (electro)catalytic applications or for reinforcing ceramic nanomaterial or polymers.

Three types of multi-walled carbon nanotubes are investigated as electrodes in the positive half-cell of a vanadium redox flow battery (VRFB). Pure (MWCNTs), nitrogen-doped (CNxMWNTs) and oxygen functionalized (MWCNT-Cs) carbon nanotubes exhibit significant structural differences at the nanoscale, as well as different chemical and physical properties. The influence of such different characteristics on the electrochemical behavior towards the VO2+/VO2+ redox reactions is investigated by cyclic voltammetry, electrochemical impedance spectroscopy and charge/discharge experiments. MWCNT-Cs exhibit the best performance despite not having the largest specific surface area, neither the greatest amount of oxygen nor nitrogen functional groups on their surface. Therefore, their enhanced performance in terms of electrochemical activity and kinetic reversibility towards the vanadium reactions and energy efficiency of the corresponding static battery, are attributed to the highest sp2 carbon content, which brings the highest electrical conductivity. These results represent a significant advance in the fundamental understanding and design of effective electrode materials that will lead to more efficient batteries.

Silicon carbide (SiC) cellular ceramic skeletons based on ceramic pillars of ∼250 μm in diameter and porous micro-channels of ∼700 μm were used as support to grow long and aligned crystalline carboxyl functionalized carbon nanotubes (COx) by floating catalyst chemical vapor deposition. The resulting hybrid COx/SiC material retained water and allowed the flow of oils and gasoline through the specimen, showing, thus, superhydrophobic and superoleophilic properties. In addition, the developed hybrid material exhibited high electrical conductivity with a good ohmic contact at the COx–SiC interface.

Nitrogen-doped multiwalled carbon nanotube (CNT) bundles exhibiting pine-tree-like morphologies were synthesized on silicon–silicon oxide (Si/SiO2) substrates using a pressure-controlled chemical vapor deposition process. Electron field emission (FE) measurements showed a notable emission improvement at low turn-on voltages for the CNT pine-like morphologies (e.g., 0.59 V/µm) in comparison with standard aligned N-doped CNTs (>1.5 V/µm). We envisage that these pine-tree-like structures could be potentially useful in the fabrication of efficient FE and photonic devices.

Nitrogen-doped multi-walled carbon nanotubes (CNxMWNTs) with multiple morphological defects were produced using a modified chemical vapor deposition (CVD) method. In a typical CNxMWNTs synthesis by CVD, an acetone trap is used to catch organic by-products from pyrolysis. In the present work, an aqueous solution of NaCl (26.82 wt%) was used in the trap, instead of acetone. Carbon nanotubes with sharp tips and lumps were found in the products. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy showed the formation of nanoparticles of different shapes inside the nanotubes. The electronic and magnetic properties were studied using a physical properties measurement Evercool system (PPMS). With this simple change in the CVD-trap, it is possible to control the morphology of carbon nanotubes and metallic nanoparticles. Differences in gas flow are proposed as a possible mechanism to produce these changes in both nanoparticles and CNxMWNTs.

Graphene oxide (GO) has recently become an attractive building block for fabricating graphene-based functional materials. GO films and fibers have been prepared mainly by vacuum filtration and wet spinning. These materials exhibit relatively high Young's moduli but low toughness and a high tendency to tear or break. Here, we report an alternative method, using bar coating and drying of water/GO dispersions, for preparing large-area GO thin films (e.g., 800-1200 cm(2) or larger) with an outstanding mechanical behavior and excellent tear resistance. These dried films were subsequently scrolled to prepare GO fibers with extremely large elongation to fracture (up to 76%), high toughness (up to 17 J/m(3)), and attractive macroscopic properties, such as uniform circular cross section, smooth surface, and great knotability. This method is simple, and after thermal reduction of the GO material, it can render highly electrically conducting graphene-based fibers with values up to 416 S/cm at room temperature. In this context, GO fibers annealed at 2000 °C were also successfully used as electron field emitters operating at low turn on voltages of ca. 0.48 V/μm and high current densities (5.3 A/cm(2)). Robust GO fibers and large-area films with fascinating architectures and outstanding mechanical and electrical properties were prepared with bar coating followed by dry film scrolling.

Novel highly electrically conducting nanocomposites consisting of a silicon nitride (Si 3 N 4 ) ceramic matrix containing up to 13.6 vol.% of nitrogen-doped multi-walled carbon nanotubes (CNx) were fabricated. As-synthesized CNx were treated with hydrogen peroxide in order to efficiently detach/isolate the nanotubes from bundles, then they were mixed with the ceramic powders and fully densified using the spark plasma sintering (SPS) technique. Composites containing 13.6 vol.% CNx reached an electrical conductivity of 2174 S m −1 that is the highest value reported hitherto for carbon nanotubes/Si 3 N 4 nanocomposites. The nitrogen doping also favored a strong mechanical interlocking between the nanotubes and the Si 3 N 4 matrix; when compared to the undoped carbon nanotubes. These novel nanocomposites could be used in devices associated to power generation or telecommunications.

Two types of Si 3 N 4 composites containing graphene nanostructures using two different graphene sources, pristine graphene nanoplatelets and graphene oxide layers were produced by Spark Plasma Sintering. The maximum toughness of 10.4 MPa m 1/2 , measured by flexure testing of pre-cracked bars, was achieved for a composite (∼60β/40α-Si 3 N 4 , ∼300 nm grain size) with 4 vol.% of reduced graphene oxide, indicating a toughening enhancement of 135% when compared to a similar Si 3 N 4 . This was also accompanied by a 10% increase in flexure strength (1040 MPa). For the composites with thicker graphene nanoplateletes only a 40% of toughness increase (6.6 MPa m 1/2 ) without strength improvement was observed for the same filler content. The large difference in the maximum toughness values accomplished for both types of composites was attributed to variations in the graphene/Si 3 N 4 interface characteristics and the extent of monolayer graphene exfoliation.

We report the preparation of hybrid paperlike films consisting of alternating layers of graphene (or graphene oxide) and different types of multiwalled carbon nanotubes (N-doped MWNTs, B-doped MWNTs, and pristine MWNTs). We used an efficient self-assembly method in which nanotubes were functionalized with cationic polyelectrolytes in order to make them dispersible in water, and subsequently these suspensions were mixed with graphene oxide (GO) suspensions, and the films were formed by casting/evaporation processes. The electronic properties of these films (as produced and thermally reduced) were characterized, and we found electrical resistivities as low as 3 × 10(-4) Ω cm. Furthermore, we observed that these films could be used as electron field emission sources with extraordinary efficiencies; threshold electric field of ca. 0.55 V/μm, β factor as high as of 15.19 × 10(3), and operating currents up to 220 μA. These values are significantly enhanced when compared to previous reports in the literature for other carbon nanostructured filmlike materials. We believe these hybrid foils could find other applications as scaffolds for tissue regeneration, thermal and conducting papers, and laminate composites with epoxy resins.

The complex melting behavior of isotactic polypropylene, after isothermal crystallization, was studied within the context of step-like melting mechanisms which were previously proposed for high temperature polymers. The morphological characteristics of the melting process were also studied as a function of molecular weight, and close similarities were observed with respect to high temperature polymers. Positive birefringence crystals of low molecular weight samples developed double melting behavior in three steps. The first melting step was assigned to continuous melting of secondary crosshatch reversing lamellae, together with recrystallization of the remaining isothermal crystals. In the second melting step (first melting endotherm), crystals tended to lose their original coarse negative birefringence due to melting of secondary reversing branching. This effect rendered new, finer texture, but still negative birefringence crystals. In the third melting step (second melting endotherm), there was a combination of melting of two crystal populations, one consisting of the remaining fraction of reversing primary crystals, and the other consisting of nonreversing primary crystals. A crosshatch secondary branching model was therefore proposed to explain the overall results. Mixed birefringence spherulites of high molecular weight samples displayed similar, although proportional, behavior under identical crystallization and melting conditions corroborating the proposed melting mechanism.

Chemical vapor deposition (CVD) is a preferential method to fabricate carbon nanotubes (CNTs). Several changes have been proposed to obtain improved CNTs. In this work we have fabricated nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) by means of a CVD which has been slightly modified. Such modification consists in changing the content of the by-product trap. Instead of acetone, we have half-filled the trap with an aqueous solution of NaCl (0–26.82 wt.%). Scanning electron microscope (SEM) characterization showed morphological changes depending upon concentration of NaCl included in the trap. Using high resolution transmission electron microscopy several shape changes on the catalyst nanoparticles were also observed. According to Raman spectroscopy results N-MWCNTs fabricated using pure distillate water exhibit better crystallinity. Resistivity measurements performed on different samples by physical properties measurement Evercool system (PPMS) showed metallic to semiconducting temperature dependent transitions when high content of NaCl is used. Results of magnetic properties show a ferromagnetic response to static magnetic fields and the coercive fields were very similar for all the studied cases. However, saturation magnetization is decreased if aqueous solution of NaCl is used in the trap.

The complex crystallization and melting behavior of neat Nylon-6 and two Nylon-6-nanoclay hybrids with different montmorillonite concentration was studied using several experimental techniques. The differential scanning calorimetry (DSC) traces were taken as a reference and experiments were made at several isothermal crystallization temperatures followed by linear heating. The results, depending on the crystallization temperature, indicated two sequences of melting for neat Nylon-6 and four for the nanoclay hybrids. After isothermal crystallization at low temperatures, neat Nylon-6 behaved different from the hybrids, however, after high crystallization temperatures there was a common melting behavior for all samples. Molecular orientation, molecular weight, and nanoclay concentration were sequentially considered in order to determine the origin of the regimes behavior in the DSC traces. Molecular weight was found as the main cause of the thermal behavior with a minimum influence of molecular orientation a...

CO2 adsorption has been measured in different types of graphitic nanostructures (MWCNTs, acid treated MWCNTs, graphene nanoribbons and pure graphene) in order to evaluate the effect of the different defective regions/conformations in the adsorption process, i.e., sp3 hybridized carbon, curved regions, edge defects, etc. This analysis has been performed both in pure carbon and nitrogen-doped nanostructures in order to monitor the effect of surface functional groups on surface created after using different treatments (i.e., acid treatment and thermal expansion of the MWCNTs), and study their adsorption properties. Interestingly, the presence of exposed defective regions in the acid treated nanostructures (e.g., uncapped nanotubes) gives rise to an improvement in the amount of CO2 adsorbed; the adsorption process being completely reversible. For N-doped nanostructures, the adsorption capacity is further enhanced when compared to the pure carbon nanotubes after the tubes were unzipped. The larger proportion of defect sites and curved regions together with the presence of stronger adsorbent–adsorbate interactions, through the nitrogen surface groups, explains their larger adsorption capacity. Financial support from the MICINN (project PLE2009-0052) and Generalitat Valenciana (PROMETEO/2009-002). SMVD, FTL, HM, TH, RCS, MT, and ME acknowledge support from the Research Center for Exotic Nanocarbons, Japan regional Innovation Strategy Program by the Excellence, JST. AMG acknowledges support from NEDO for postdoctoral position.

In this work, we carried out chemical oxidation studies of nitrogen-doped multiwalled carbon nanotubes (CNx-MWCNTs) using potassium permanganate in order to obtain nitrogen-doped graphene nanoribbons. Reaction parameters such as oxidation reaction, reaction time, the oxidizer to nanotube mass ratio, and the temperature were varied, and their effect was carefully analyzed. The presence of nitrogen atoms makes CNx-MWCNTs more reactive toward oxidation when compared to undoped multiwalled carbon nanotubes (MWCNTs). High-resolution transmission electron microscopy studies indicate that the oxidation of the graphitic layers within CNx-MWCNTs results in the unzipping of large diameter nanotubes and the formation of a disordered oxidized carbon coating on small diameter nanotubes. The nitrogen content within unzipped CNx-MWCNTs decreased as a function of the oxidation time, temperature, and oxidizer concentration. By controlling the degree of oxidation, the N atomic % could be reduced from 1.56% in pristine CNx-MWCNTs down to 0.31 atom % in nitrogen-doped oxidized graphene nanoribbons. A comparative thermogravimetric analysis reveals a lower thermal stability of the (unzipped) oxidized CNx-MWCNTs when compared to MWCNT samples. The oxidized graphene nanoribbons were chemically and thermally reduced and yielded nitrogen-doped graphene nanoribbons (N-GNRs). The thermal reduction at relatively low temperature (300 °C) results in graphene nanoribbons with 0.37 atom % of nitrogen. This method represents a novel route to preparation of bulk quantities of nitrogen-doped unzipped carbon nanotubes, which is able to control the doping level in the resulting reduced GNR samples. Finally, the electrochemical properties of these materials were evaluated.

Graphene/silicon nitride (Si3N4) composites with high fraction of few layered graphene are synthesized by an in situ reduction of graphene oxide (GO) during spark plasma sintering (SPS) of the GO/Si3N4 composites. The adequate intermixing of the GO layers and the ceramic powders is achieved in alcohol under sonication followed by blade mixing. The reduction of GO occurs together with the composite densification in SPS, thus avoiding the implementation of additional reduction steps. The materials are studied by X-ray photoelectron and micro-Raman spectroscopy, revealing a high level of recovery of graphene-like domains. The SPS graphene/Si3N4 composites exhibit relatively large electrical conductivity values caused by the presence of reduced graphene oxide (similar to 1 S cm(-1) for similar to 4 vol.%, and similar to 7 S cm-1 for 7 vol.% of reduced-GO). This single-step process also prevents the formation of highly curved graphene sheets during the thermal treatment as the sheets are homogeneously embedded in the ceramic matrix. The uniform distribution of the reduced GO sheets in the composites also produces a noticeable grain refinement of the silicon nitride matrix. (C) 2013 Elsevier Ltd. All rights reserved.

We report a novel physicochemical route to produce highly crystalline nitrogen-doped graphene nanoribbons. The technique consists of an abrupt N 2 gas expansion within the hollow core of nitrogen-doped multiwalled carbon nanotubes (CN x-MWNTs) when exposed to a fast thermal shock. The multiwalled nanotube unzipping mechanism is rationalized using molecular dynamics and density functional theory simulations, which highlight the importance of open-ended nanotubes in promoting the efficient introduction of N 2 molecules by capillary action within tubes and surface defects, thus triggering an efficient and atomically smooth unzipping. The so-produced nanoribbons could be few-layered (from graphene bilayer onward) and could exhibit both crystalline zigzag and armchair edges. In contrast to methods developed previously, our technique presents various advantages: (1) the tubes are not heavily oxidized; (2) the method yields sharp atomic edges within the resulting nanoribbons; (3) the technique could be scaled up for the bulk production of crystalline nanoribbons from available MWNT sources; and (4) this route could eventually be used to unzip other types of carbon nanotubes or intercalated layered materials such as BN, MoS 2, WS 2, etc. © 2012 American Chemical Society., We acknowledge the support from the Program for Fostering Regional Innovation in Nagano from the Ministry of Education, Culture, Sports, Science and Technology of Japan. M.T., S.V.-D., F.T.-L., R.C.-S., and M.E. acknowledge support from the Research Center for Exotic Nanocarbons, Japan regional Innovation Strategy Program by the Excellence, JST. A.M.-G. acknowledges support from CONACYT for postdoctoral visit. B.G.S. was supported by the Center for Nanophase Materials Sciences, which is sponsored by the Office of Basic Energy Sciences at Oak Ridge National Laboratory, U.S. Department of Energy.

The dispersibility in a DNA solution of bundled multiwalled carbon nanotubes (MWCNTs), having different chemical functional groups on the CNT sidewall, was investigated by optical spectroscopy. We observed that the dispersibility of nitrogen (N)-doped MWCNTs was significantly higher than that of pure MWCNTs and MWCNTs synthesized in the presence of ethanol. This result is supported by the larger amount of adsorbed DNA on N-doped MWCNTs, as well as by the higher binding energy established between nucleobases and the N-doped CNTs. Pure MWCNTs are dispersed in DNA solution via van der Waals and hydrophobic interactions; in contrast, the nitrogenated sites within N-doped MWCNTs provided additional sites for interactions that are important to disperse nanotubes in DNA solutions.

The thermal stability of nitrogen (N) functionalities on the sidewalls of N-doped multi-walled carbon nanotubes was investigated at temperatures ranging between 1000 °C and 2000 °C. The structural stability of the doped tubes was then correlated with the electrical conductivity both at the bulk and at the individual tube levels. When as-grown tubes were thermally treated at 1000 °C, we observed a very significant decrease in the electrical resistance of the individual nanotubes, from 54 kΩ to 0.5 kΩ, which is attributed to a low N doping level (e.g. 0.78 at% N). We noted that pyridine-type N was first decomposed whereas the substitutional N was stable up to 1500 °C. For nanotubes heat treated to 1800 °C and 2000 °C, the tubes exhibited an improved degree of crystallinity which was confirmed by both the low R value (I(D)/I(G)) in the Raman spectra and the presence of straight graphitic planes observed in TEM images. However, N atoms were not detected in these tubes and caused an increase in their electrical resistivity and resistance. These partially annealed doped tubes with enhanced electrical conductivities could be used in the fabrication of robust and electrically conducting composites, and these results could be extrapolated to N-doped graphene and other nanocarbons.

Graphene constitutes a two dimensional sp² hybridized carbon material with outstanding electrical and mechanical properties. To date, novel methods for producing large quantities of graphene and its derivatives (doped or functionalized graphenes, nanoribbons and nanoplatelets) are emerging, and research dedicated to the fabrication of polymer nanocomposites using graphenes has started. In this Research News, we summarize the synthesis and properties of graphene and its derivatives, and provide an overview of the latest research dedicated to the fabrication of polymer composites for different applications, including mechanical, electrical, optical and thermal. Some of the recently fabricated composites exhibit outstanding properties, however, it is vital to understand the chemistry and physics of the interphases established between the polymer and the graphene surfaces. The challenges in the fabrication of super robust and highly conducting composites using graphenes are also discussed. It is believed that graphene-based polymer composites will result in commercial products if their interphases and reactivity are carefully controlled. Authors wish to thank Ministerio de Ciencia e Innovación (SPAIN) for financial support under grant MAT2010-17091. MT and SMVD acknowledge support from the Research Center for Exotic NanoCarbon Project, Japan regional Innovation Strategy Program by the Excellence, JST.