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•A catalytic effect of nitrogen doped graphenic support is observed.•Catalytic properties are also affected by the sizes of Ru nanoparticles.•The Ru(CO)/NrGO catalyst yields 46% of ...benzaldehyde under mild reaction conditions.•This catalyst can be reused or easily reactivated just by a drying treatment.
The catalytic performance of a series of Ru-based catalysts was evaluated for the selective aerobic oxidation of benzyl alcohol to benzaldehyde under base-free mild conditions. The effect of metal precursor (RuCl3, RuNO(NO3)3 and Ru3(CO)12) and support on catalyst performance was investigated by comparing undoped (rGO) and N-doped (NrGO) reduced graphene oxide with commercial activated carbon and high surface area graphite supports. The surface chemistry and structure of materials were characterized by nitrogen physisorption (BET), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The average Ru nanoparticle sizes were in the range from 1.4 to 2.4 nm, with the smallest particle sizes obtained on rGO support owing to its highest surface area.
Catalysts prepared from RuNO(NO3)3 and Ru3(CO)12 precursors exhibit the highest benzyl alcohol conversion to the corresponding aldehyde, with highest conversions observed when NrGO support is employed. Catalysts prepared from Ru3(CO)12 on NrGO support exhibit the highest activity for benzaldehyde formation, which is over three times that of commercial activated carbon supported Ru catalysts.
The differences in catalytic performance are attributed to interactions between the acidic product of the reaction and the basic surface sites of the NrGO support, and modification of the surface hydrophobicity. These factors confer a significant rate enhancement in the selective oxidation of benzyl alcohol over Ru/NrGO compared to Ru/rGO. Ru/NrGO is stable under reaction conditions, however progressive deactivation is observed owing to water accumulation at the active site. Catalysts are easily reactivated via heating, with >90% of the original activity recovered on reuse.
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•Fish skin-based wound dressing systems are promising scaffolds for burns treatment.•The coating of fish skin with graphenic materials inhibits biofilm formation.•The electrostatic ...repulsion of skin and bacteria improves the antibiofilm activity.
Wound dressings based on natural materials, such as fish skin, represent an important strategy for the treatment of burns. Despite their utility, contamination of these natural materials with bacteria (planktonic and biofilm forms) introduces significant risks to patients under treatment. This disadvantage can be overcome by modifying the material’s surface to prevent bacterial deposition through chemical or physical interactions. In this work, functional graphenic materials (FGM) with tunable surface charges were incorporated into tilapia (Oreochromis niloticus) fish skin as a part of a strategy to control the biofilm adhesion on surfaces. The antibiofilm activity was evaluated against S. aureus and K. pneumoniae due to the biofilm-forming properties of these bacterial strains. FGM-modified tilapia skin samples possess a strong capacity to reduce biofilm formation on the tilapia fish skin with a higher antibiofilm activity against Gram-positive bacteria, compared to Gram-negative bacteria. Negatively charged FGMs were more effective than positively charged FGMs in preventing biofilm formation on the impregnated tilapia skin xenografts: negatively charged Claisen graphene achieved an 88.8% reduction in biofilm formation on the tilapia skin. Overall, this study demonstrates the utility of FGM-impregnated tilapia skins as a treatment for burn wounds due to their ability to modulate bacterial adhesion.
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•Photocatalytic treatment of saline produced water by reduced graphene oxide/titania.•Graphenic-TiO2 nanocomposites (rGO-TiO2) are prepared via hydrothermal routes.•rGO-TiO2 ...nanocomposites are more efficient for removing high hydrophobic organics.•The rGO/TiO2 weight ratio affect the photocatalytic activity of hybrid nanocomposites.
Graphene like-TiO2 nanocomposites (rGO-TiO2) are prepared via hydrothermal route by following different synthetic protocols. The as-prepared nanostructured materials exhibit higher photocatalytic activity than bare TiO2 in the treatment of synthetic produced water containing high salinity levels and different compositions of recalcitrant dissolved organic matter. The effect of the preparation method on the physico-chemical properties is assessed by performing a wide characterization combining different analyses, such as nitrogen physic-adsorption (BET), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), UV-VIS Diffuse Reflectance Spectroscopy (DRUV) and Electron Paramagnetic Resonance (EPR). The effect of several operative variables (i.e., TiO2/rGO weight ratios, and addition of hydrogen peroxide) on the photocatalytic activity is also critically evaluated.
The highest photocatalytic activity is obtained for a rGO/TiO2 weight ratio of about 10%, for which a good compromise between uniformity of dispersion of the TiO2 particles on the rGO layers and covering degree of the titania photoactive surface is achieved.
This study can contribute to open new perspectives in the design of high performance graphene like-based TiO2 photocatalysts for removing hydrophobic bio-recalcitrant pollutants from saline water.
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•Properties of graphenic materials are crucial to understand adsorption interactions.•The study of adsorption effect is required to understand the posterior catalysis.•The XRD, ATR ...and DRIFT results prove intercalation compounds between GO layers.•Cooperative interactions between pollutants were detected using GO.•Synergetic effects between pollutants were developed with rGO and N-rGO.
Graphenic materials have been recently applied for adsorption processes due to their high efficiency and their easy capability of surface modification. In the present study two different graphene oxides, two reduced graphene oxides under inert atmosphere and one reduced graphene oxide under ammonia atmosphere were used as adsorbents for removing two chloroaromatic compounds from water: 2,4-dichlorophenol and 2,4-dichlorophenoxyacetic acid. Hydrogen bonds and ππ interactions have been detected by Attenuated Total Reflectance infrared spectroscopy in the solids with adsorbed species. Besides, two direct relationships between their adsorption capacities and graphenic surface, textural and structural properties were found. In order to obtain real adsorption information, some experiments with the presence of both pollutants at the same time were performed. From these mixture experiments, when graphene oxide was used as adsorbent some cooperative effects between pollutants were detected. Based on XRD results and an innovative comparison between different infrared techniques, the importance of interlayer spaces during adsorption was demonstrated. Otherwise, synergetic interactions between pollutants were revealed as the main adsorption forces when reduced graphene oxides were used, being their aromatic structures a decisive factor in their final adsorption capacity.
The reinforcement of elastomers is essential in the rubber industry in order to obtain the properties required for commercial applications. The addition of active fillers in an elastomer usually ...leads to an improvement in the mechanical properties such as the elastic modulus and the rupture properties. Filled rubbers are also characterized by two specific behaviors related to energy dissipation known as the Payne and the Mullins effects. The Payne effect is related to non-linear viscoelastic behavior of the storage modulus while the Mullins or stress-softening effect is characterized by a lowering in the stress when the vulcanizate is extended a second time. Both effects are shown to strongly depend on the interfacial adhesion and filler dispersion. The basic mechanisms of reinforcement are first discussed in the case of conventional rubber composites filled with carbon black or silica usually present in the host matrix in the form of aggregates and agglomerates. The use of nanoscale fillers with isotropic or anisotropic morphologies is expected to yield much more improvement than that imparted by micron-scale fillers owing to the very large polymer-filler interface. This work reports some results obtained with three types of nanoparticles that can reinforce rubbery matrices: spherical, rod-shaped and layered fillers. Each type of particle is shown to impart to the host medium a specific reinforcement on account of its own structure and geometry. The novelty of this work is to emphasize the particular mechanical behavior of some systems filled with nanospherical particles such as in situ silica-filled poly(dimethylsiloxane) networks that display a strong polymer-filler interface and whose mechanical response is typical of double network elastomers. Additionally, the potential of carbon dots as a reinforcing filler for elastomeric materials is highlighted. Different results are reported on the reinforcement imparted by carbon nanotubes and graphenic materials that is far below their expected capability despite the development of various techniques intended to reduce particle aggregation and improve interfacial bonding with the host matrix.
The removal by adsorption of methylene blue dye from water using two‐dimensional (2D) (graphene oxide and reduced graphene oxide) and three‐dimensional (3D) (graphite and graphite oxide) carbon ...structures was studied. Two graphites with different degrees of graphitization were used to evaluate the significance of the carbon structural order in the adsorption efficiency, and therefore, the economic repercussions, because the degree of graphitization is related with the cost. Graphene oxides showed the best performance in methylene blue adsorption, with a removal of around 90%. The adsorption process was strongly influenced by the surface oxygenated groups, and electrostatic interaction was the main mechanism of adsorption. The degree of graphitization of the precursor does not have a strong influence on the adsorption results of methylene blue. Thus, graphene oxide with a lower degree of graphitization represents an economical and efficient adsorbent for the removal of methylene blue from water. The kinetic study was realized in pseudo‐first order, pseudo‐second order, and Elovich kinetic models in their linear and non‐linear forms. According to the determination coefficient and the standard deviation, the experimental data were best fitted to the Elovich model in its non‐linear form.
Exhibiting a very high surface area, a good electrical conductivity and a high density of active sites, nitrogen-doped graphenic materials are considered as promising catalysts for the oxygen ...reduction reaction (ORR). Seldom studied in acidic media, N-doped graphenic foams were tested here as the cathode catalysts of a polymer electrolyte membrane fuel cell (PEMFC). The materials were prepared via a solvothermal-based process, by reacting either cyclohexanol and ethanolamine or 1-(2-hydroxyethylethyl) piperidine with metallic sodium, under high pressure and temperature. Membrane electrode assemblies were prepared with a Pt/C anode, 212 Nafion membrane, and an 8 mm disk cathode based on the graphenic materials. The performance exhibited by the PEMFC was evaluated using chronopotentiometry and impedance spectroscopy, depending on the synthesis conditions. The kinetic parameters of the ORR were estimated by interpretation of the experimental data: the high Tafel slope found might express the partial control of oxygen diffusion through the graphenic microporous structure. Relationships between the electrochemical behavior of the materials and their structural properties are discussed. Moderately crystallized materials with a low oxygen content showed the highest catalytic properties, with a current density larger than 30 mA cm
−2
and a maximum power density at 2.3 mW cm
−2
.
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The effects caused by the interaction with graphene-like layers on the 1H NMR spectra of water molecules adsorbed onto porous carbon materials were investigated by a combination of shielding ...calculations using density functional theory (DFT) and 1H NMR experiments. Experimental 1H NMR spectra were recorded for different water-containing carbon materials (activated carbons and milled graphite samples); the 1H NMR signals due to adsorbed water in these materials showed a strong shielding effect caused by the electron currents present in the graphene-like layers. This effect was enhanced for activated carbons prepared at high heat treatment temperatures and for milled graphite samples with short milling times, evidencing that the structural organization of the graphene-like layers was the key feature defining the magnitude of the shielding on the 1H nuclei in the water molecules adsorbed by the analyzed materials. The DFT calculations of the shielding sensed by these 1H nuclei showed an increased interaction with the graphitic layers as the distance between these layers (representing the pore size) was reduced. A continuous decrease of the 1H NMR chemical shift was then predicted for pores of smaller sizes, in good agreement with the experimental findings. These calculations also showed a large dispersion of chemical shifts for the several 1H nuclei in the water clusters, attributed to intermolecular interactions and to shielding variations within the pores. This dispersion, combined with the effects due to the locally anisotropic diamagnetic susceptibility of graphite-like crystallites, are the main contributions to the broadening of the 1H NMR signals associated with water adsorbed onto porous carbon materials.
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•Interactions between adsorbed water molecules and graphene-like layers are studied.•DFT calculations of the shielding on the 1H nuclei in adsorbed water are reported.•1H NMR peaks move to lower chemical shifts as the pore size is reduced.•Experimental results are reported for activated carbons and milled graphite samples.•1H NMR spectra are largely affected by the structural organization of the material.
Graphenic materials have excited the scientific community due to their exciting mechanical, thermal, and optoelectronic properties for a potential range of applications. Graphene and graphene ...derivatives have demonstrated application in areas stretching from composites to medicine; however, the environmental and health impacts of these materials have not been sufficiently characterized. Graphene oxide (GO) is one of the most widely used graphenic derivatives due to a relatively easy and scalable synthesis, and the ability to tailor the oxygen containing functional groups through further chemical modification. In this paper, ecological and health impacts of fresh and ultrasonically altered functional graphenic materials (FGMs) were investigated. Model organisms, specifically Escherichia coli, Bacillus subtilis, and Caenorhabditis elegans, were used to assess the consequences of environmental exposure to fresh and ultrasonically altered FGMs. FGMs were selected to evaluate the environmental effects of aggregation state, degree of oxidation, charge, and ultrasonication. The major findings indicate that bacterial cell viability, nematode fertility, and nematode movement were largely unaffected, suggesting that a wide variety of FGMs may not pose significant health and environmental risks.
•High-throughput screening system for assessing environmental impact of 2D nanomaterials.•Model bacteria viability not impacted by functional graphenic material (FGMs) exposure.•Nematode fertility and movement unaffected upon FGM exposure.•Artificial aging of graphenic materials did not alter health impacts on model organisms.•Nematodes safely ingested graphenic materials with no adverse effects.
Graphene oxide and functionalized graphenic materials (FGMs) have promise as platforms for imparting programmable bioactivity to poly(methyl methacrylate) (PMMA)‐based bone cement. To date, however, ...graphenic fillers have only been feasible in PMMA cements at extremely low loadings, limiting the bioactive effects. At higher loadings, graphenic fillers decrease cement strength by aggregating and interfering with curing process. Here, these challenges are addressed by combining bioactive FGM fillers with a custom cement formulation. These cements contain an order of magnitude more graphenic filler than previous reports. Even at 1 wt% FGM, these cements have compressive strengths of 78– 88 MPa, flexural strengths of 74–81 MPa, and flexural stiffnesses of 1.8–1.9 GPa, surpassing the ASTM requirements for bone cement and competing with traditional PMMA cement. Further, by utilizing designer FGMs with programmed bioactivity, these cements demonstrate controlled release of osteogenic calcium ions (releasing a total of 5 ± 2 µmol of Ca2+ per gram of cement over 28 d) and stimulate a 290% increase in expression of alkaline phosphatase in human mesenchymal stem cells in vitro. Also, design criteria are described to guide creation of future generations of bone cements that utilize FGMs as platforms to achieve dynamic biological activity.
Bioactive additives, including functionalized graphenic materials (FGMs), could lend bone cement the ability to improve wound healing—but compromise cement strength by aggregating and quenching cure. Here, this is addressed with a custom cement formulation that allow cements to carry higher loads of bioactive, ion‐releasing FGMs without sacrificing strength. Also, design criteria for future generations of FGM‐loaded cements are described.
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