This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
This work describes a novel route for the preparation of pitches by oxidative polymerization of a... more This work describes a novel route for the preparation of pitches by oxidative polymerization of an industrial anthracene oil (AO) in a microwave semi-pilot equipment consisting in a multimode applicator having a 2.45 GHz magnetron with variable microwave power. The experimental five variables of microwave heating of AO air-blowing range between 320-380 ˚C (temperature), 0.2-3.9 ˚C min-1 (heating rate), 1.5-5 h (soaking time), 16-20.5 % (air/AO ratio) and 200-1500 g (initial weight). Their effect on the overall microwave air-blowing process is evaluated by means of a statistical analysis. A detailed characterization of the pitches has been carried out in terms of ultimate analysis, softening point, solubility parameters (toluene insolubles (TI) and quinoline insolubles (QI)) and thermogravimetric analysis. The experiments were also carried out by using conventional heating for comparative purposes. The detailed study of the electric energy consumption of the overall microwave treatment allows estimating a significant electric energy saving of about 20 % when compared to conventional heating thus representing an excellent result in the production of carbon precursors.
Index 1.-NMR and IR spectra of 1 and 2 S-2 2.-1 H-PRESAT NMR of CNT-1 and CNT-2 S-4 3.-NMR and IR... more Index 1.-NMR and IR spectra of 1 and 2 S-2 2.-1 H-PRESAT NMR of CNT-1 and CNT-2 S-4 3.-NMR and IR spectra of 1-Ir and 3-Ir S-5 4.-XPS characterization of CNT-2, and Elemental analysis and XPS data of parent and functionalized CNT samples S-9 5.-TGA characterization of CNT-1, CNT-2, and CNT-2-Ir S-10 6.-TEM characterization of CNT, CNT-1-Ir, CNT-2-Ir and EDX of CNT-2-Ir S-10 7.-XPS characterization of CNT-1-Ir and CNT-2-Ir S-12 8.-CAN-driven water oxidation by the homogeneous catalysts 1-Ir and 3-Ir. S-12 9.-Electrocatalytic water oxidation experiments S-13
The development of more efficient electrode materials is essential to obtain vanadium redox flow ... more The development of more efficient electrode materials is essential to obtain vanadium redox flow batteries (VRFBs) with enhanced energy densities and to make these electrochemical energy storage devices more competitive. A graphene-modified graphite felt synthesized from a raw graphite felt and a graphene oxide water suspension by means of electrophoretic deposition (EPD) is investigated as a suitable electrode material in the positive side of a VRFB cell by means of cyclic voltammetry, impedance spectroscopy and charge/discharge experiments. The remarkably enhanced performance of the resultant hybrid material, in terms of electrochemical activity and kinetic reversibility towards the VO 2+ /VO 2 + , and mainly the markedly high energy efficiency of the VRFB cell (c.a. 95.8 % at 25 mA cm-2) can be ascribed to the exceptional morphological and chemical characteristics of this tailored material. The 3D architecture consisting of fibers interconnected by graphene-like sheets positively contributes to the proper development of the vanadium redox reactions and so represents a significant advance in the design of effective electrode materials.
Brief C4F8plasma exposure on platelet carbon nanofibers can lead to fabrication of novel LIB anod... more Brief C4F8plasma exposure on platelet carbon nanofibers can lead to fabrication of novel LIB anodes with enhanced rate performances.
This paper reports on the development of novel Ti-doped 3D carbon fibre composites (CFCs) and the... more This paper reports on the development of novel Ti-doped 3D carbon fibre composites (CFCs) and their performance when exposed to transient thermal loads (disruptions) in the electron beam facility JUDITH at different conditions. Depending on the applied load, the CFCs showed three steps of erosion: 1) breaking of PAN fibres with pull out from the surface; 2) cracking and ablation of pitch fibres close to the interface of PAN/pitch fibre-bundles; 3) finally, erosion of pitch fibres in the centre of the bundle. The addition of titanium carbide resulted in a significant improvement in thermal shock behaviour of these materials compared to their undoped counterparts.
Biological membranes are currently used in Ophthalmology in order to treat different ocular disor... more Biological membranes are currently used in Ophthalmology in order to treat different ocular disorders. These membranes have different properties such as cellular biocompatibility and promoting wound healing. Moreover, intrinsic antimicrobial properties could also be desirable because it would allow their use reducing the risk of infections. Graphene and its derivatives are promising biomaterials that already proved their bactericidal effect. However, their clinical use is limited due to the controversial results regarding their toxicity. In this work, we have developed and characterized a reduced graphene oxide membrane (rGOM) for its use in ocular Regenerative Medicine, and studied its in vitro and in vivo biocompatibility and genotoxicity with different types of human ocular cells. We proved that rGOM allowed the growth of different ocular cells without inducing in vitro or in vivo cytotoxicity or genotoxicity in the short-term. These results indicate that rGOM may be a promising candidate in Regenerative Medicine for the treatment of different ocular pathologies.
A commercial impregnating coal-tar pitch was thermally treated at 4308C for 2-5 h in nitrogen. Re... more A commercial impregnating coal-tar pitch was thermally treated at 4308C for 2-5 h in nitrogen. Resultant pitches, which contained mesophase ranging from 10 to 46 vol.%, were filtered to separate the isotropic phases, in order to study their contribution to the rheology of the whole pitches. The parent pitch, thermally treated pitches and the individual isotropic phases were characterized by measuring their elemental composition, softening point, carbon yield, solubility in toluene and in N-methyl-2-pyrrolidone, mesophase content (by optical microscopy) and X-ray diffraction parameters. The rheological behavior of the pitches and the isotropic phases was studied using steady shear rheometry. Results showed that not only had the whole pitches, which were partially anisotropic, a non-Newtonian behavior, but also the single isotropic phases.
The phase-mineral and chemical composition of magnetic (MCs) and char (CCs) concentrates recovere... more The phase-mineral and chemical composition of magnetic (MCs) and char (CCs) concentrates recovered from five fly ashes (FAs) produced in four large Spanish thermo-electric power stations was characterized. The MCs and CCs were isolated by magnetic ...
The current work investigates the performance of petroleum coke (PC) as a blended fuel under pulv... more The current work investigates the performance of petroleum coke (PC) as a blended fuel under pulverized-fuel combustion conditions. Three full-scale combustion experiments were carried out: a pure Carboniferous, high volatile bituminous coal and two blends of this coal with different proportions of PC. The samples studied included feed fuels and blends, fly ashes, chars taken at different positions of the combustion chamber, and chars prepared in a drop tube reactor to test the performance of the individual fuels. The addition of PC led to a substantial increase in the unburned carbon of the fly ashes. The petrographic analysis of the granulometric fractions of the fuels revealed that this increase cannot be attributed to an enrichment in coke of the coarser fractions, as reported in the literature. On the contrary, the finer fraction contained slightly more coke than the raw blend. The petrographic analysis of the chars collected with the suction probe and the fly ashes showed that the two blended fuels were strongly enriched in PC-derived material, indicating a poorer combustibility compared to the high volatile bituminous coal. It is concluded that the reactivity of the blends in the later stages of combustion is related with the contents of PC-derived chars and the burnout itself.
A comparative study of several screen-printed electrodes modified with electrochemically reduced ... more A comparative study of several screen-printed electrodes modified with electrochemically reduced graphene oxides (ERGO) by means of a constant current has been carried out. The ERGOs were produced from graphene oxides (GO) with different controlled functional groups contents and locations. The experimental reduction conditions were optimized for each particular GO to generate ERGO-modified electrodes with the aim of improving the performance of the dopamine redox process. The ERGO-modified electrodes exhibited a larger electroactive area, a higher reversibility of the redox process, faster kinetics, and greater double-layer capacitance. Analysis of the reduction degree and residual functional groups by means of X-ray photoelectron spectroscopy (XPS) after and before reduction enabled us to determine the relation between the electrochemical behavior and morphology of the electrodes. A hydrazine-reduced graphene oxide showed the best analytical performance with a higher sensitivity (0.259 μA/μM vs. 0.090 μA/μM in the case of a bare electrode), and a linear range from 1-100 μM. It was found that both the experimental reduction conditions and starting graphene material are critical for obtaining a modified electrode with a suitable electrochemical behavior and properties and that a constant current is a suitable technique for the reduction of graphene oxides, especially for screen-printed electrodes. Graphene, a two-dimensional carbon material with highly useful properties including a large surface area and high mechanical, thermal and chemical stabilities, has emerged as a very interesting material for electrochemical applications, especially in (bio)sensors due to its excellent properties such as high electron conductivity, fast heterogeneous electron-transfer rate at the graphene sheet edges and basalplane defect sites, large surface area and good biocompability. 1-4 The most suitable graphene material for modifying electrochemical sensors is graphene oxide (GO) due to its high capacity to be dispersed in aqueous solvents that allows a more efficient electrode modification. GO is usually produced by the oxidation of graphite, a methodology based on the Hummers 5 or Brodie method, 6 which is considered to be the best alternative for the preparation of graphene on a large scale. 7 Additionally, the preparation of GO can be modified by using graphites with different crystalline structures or by different preparation methods 8 giving rise to graphene materials of different sheet size, structure and properties, variables that can also be tuned to improve the electrochemical performance of electrodes. Although several studies on GO improving electrode properties have been reported, 9,10 in most cases a previous GO reduction is carried out in order to decrease the number of oxygen-based functional groups to obtain better electrochemical properties. 13 Several authors have reported that the electrocatalysis is influenced by the orientation of the graphene sheets with respect to the electrode surface, the C/O atomic ratio, or the synthesis route of the material. 14 For instance, graphene nanoribbons with different oxidation degrees were employed for the optimization of the detection of several analytes, showing how the graphene structure had a significant effect on the electrochemical detection. For the development of sensors and biosensors, screen-printed electrodes (SPEs) are among the most widely used platforms due to the low cost of their fabrication, high sensitivity, and their easily modified surfaces with compounds such as proteins or nanomaterials, that increase their active area and electrocatalytical properties. 22 These nanostructured SPEs have been used for several (bio)sensing applications. The aim of this work was to study the electrochemical performace of ERGO-modified screen-printed electrodes and, particularly, the effect of different graphenes on the electrochemical behavior of dopamine using the modified electrodes. Dopamine was selected because it is one of the most widely used model analytes for the characterization of electrodes and would facilitate a comparison between our results and the results obtained with other graphene or electrode materials. Screen-printed carbon electrodes (SPCEs) were modified using three GOs with different content and location of defects and functional groups. Electrochemically reduced graphene oxides were obtained by in situ electrochemical reduction using a constant current and the effect on the electrochemical process of dopamine was studied under several experimental conditions (reduction current, reduction time, pH, GO amount) by a multifactorial design. The main
Graphene materials have recently attracted increasing interest due to the excellent physico-chemi... more Graphene materials have recently attracted increasing interest due to the excellent physico-chemical properties that they can exhibit.[1] One interesting application is as electrodes in vanadium redox flow batteries (VRFBs). These are promising large-scale energy storage devices in which the electrodes must be carefully selected since they support the chemical reactions necessary for the operation of the battery. In this regard, graphenes obtained by thermal treatment of graphite oxide exhibited an excellent performance due to their high electrical conductivity and a high mechanical stability.[2]
Ana M. Pérez-Mas, Laura Fernández-García, Patricia Álvarez, Patricia Blanco, Ricardo Santamaría, ... more Ana M. Pérez-Mas, Laura Fernández-García, Patricia Álvarez, Patricia Blanco, Ricardo Santamaría, Marcos Granda, Clara Blanco, Rosa Menéndez Instituto Nacional del Carbón, CSIC, P.O.: 73, 33080 Oviedo, Spain [email protected] Abstract The morphology, size and height of graphene sheets are currently analysed by AFM without much difficulty. However, when dealing with graphenes obtained by thermal reduction of graphene oxides, the sheets cannot be easily visualized by this technique, mainly because of their shape, roughness and typical wrinkles, which difficult their AFM monitorization at the different temperatures. The aim of this work is to evaluate the effect of the thermal treatment on the graphene oxide (GO) sheet morfology in different substrates by means of AFM. For that, a GO obtained by a modified Hummer’s method [1] and subsequently sonicated (exfoliated) for 8h [2], was initially drop casted into silicon and HOPG substrates. After that, the whole systems were heated in a...
Multifunctional elastomer nanocomposites have been applied in several high-tech fields. The desig... more Multifunctional elastomer nanocomposites have been applied in several high-tech fields. The design of materials with tailored properties capable of tuning their performance is a topical challenge. Here, we demonstrate that it is possible to modulate the mechanical and transport properties of silicone rubber nanocomposites by controlling the structure, chemical composition and morphology of the graphene material. Intrinsic graphene properties, such as remaining oxygen groups, specific surface area, and aspect ratio, among others, have a profound effect on the final properties of the nanocomposite. Thus, the thermal conductivity benefits from larger filler size and high aromatic restoration. Whereas mechanical properties and electrical conductivity require a proper balance between filler/polymer matrix interaction and a partial aromatic restoration.
A proper design of heterogeneous molecular catalysts supported on carbon materials requires a sys... more A proper design of heterogeneous molecular catalysts supported on carbon materials requires a systematic study of "metal−carbon support interactions" and their influence on catalytic activity. In this study, hybrid materials containing covalently anchored iridium N-heterocyclic carbene (NHC) organometallic complexes have been successfully prepared from oxidized and partially reduced carbon nanotubes (CNTs). The preparation method for these supported materials relies on the selective functionalization of the superficial hydroxylic groups using the imidazolium salt, 1-(3hydroxypropyl)-3-methyl-1H-imidazol-3-ium chloride. The hydrogen transfer catalysis activity of these nanotube-based hybrid catalysts was tested by the reduction of cyclohexanone to cyclohexanol with 2-propanol, and the results of the tests were compared with those obtained using similar hybrid graphene-based catalysts. While EXAFS analysis revealed a common first coordination shell of the iridium atom for all the hybrid materials examined, independently of whether they were either supported on carbon nanotubes or graphene materials, catalytic activity in all the reduced materials was significantly superior. Moreover, catalytic systems based on reduced
A coal-tar-derived mesophase was chemically activated to produce a high surface area (3,200 m 2 ... more A coal-tar-derived mesophase was chemically activated to produce a high surface area (3,200 m 2 /g) carbon with a porosity made up of both micropores and mesopores. Its adsorption capacities were found to be among the highest ever reported in literature, reaching values of 860 mg/g and 1,200 mg/g for the adsorption of benzene and toluene, respectively, and 1,200 mg/g for the combined adsorption of benzene and toluene from an industrial wastewater. Such high values imply that the entire pore system, including the mesopore fraction, is involved in the adsorption process. The almost complete pore filling is thought to be due to the high relative concentrations of the tested solutions, resulting from the low saturation concentration values for benzene and toluene, which were obtained by fitting the adsorption data to the BET equation in liquid phase. The kinetics of adsorption in the batch experiments which were conducted in a syringe-like adsorption chamber was observed to proceed in accordance with the pseudo-second order kinetic model. The combined presence of micropores and mesopores in the material is thought to be the key to the high kinetic performance, which was outstanding in a comparison with other porous materials reported in the literature.
Enhanced SO 2 adsorption of activated carbon fibers is obtained by tailoring a specific micro-mes... more Enhanced SO 2 adsorption of activated carbon fibers is obtained by tailoring a specific micro-mesoporous structure in the fibers. This architecture is obtained via metal catalytic activation of the fibers with a novel precursor, cobalt naphthenate, which contrary to other precursors, also enhances spinnability and carbon fiber yield. In the SO 2 oxidation, it is demonstrated that the combination of micropores and large mesopores is the main factor for an enhanced catalytic activity which is superior to that observed in other similar microporous activated carbon fibers. This provides an alternative way for the development of a new generation of catalytic material.
This work describes the chemical activation of a coke using two different activating agents in or... more This work describes the chemical activation of a coke using two different activating agents in order to investigate their behaviour as electrodes in supercapacitors. A coke was chemically activated with two hydroxides (KOH and NaOH) under nitrogen flow, at a constant mass hydroxide/coke ratio of 2 and temperatures of 600, 650 and 700 ºC. All the samples were characterized in terms of porosity by N 2 sorption at 77 K, surface chemistry by temperature programmed desorption (TPD) and electrical conductivity. Their electrochemical behaviour as electric double layer capacitors was determined using galvanostatic, voltammetric and impedance spectroscopy techniques, in an aqueous medium with 1M H 2 SO 4 as electrolyte. Large differences in capacitive behaviour with the increase in current density were found between the two series of activated samples. The different trends were correlated with the results obtained from the TPD analysis of the CO-type oxygen groups. It was found that these oxygen groups make a positive contribution to capacitance finding a good correlation between the specific capacitance values and the amount of these oxygen groups was found for both series.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
This work describes a novel route for the preparation of pitches by oxidative polymerization of a... more This work describes a novel route for the preparation of pitches by oxidative polymerization of an industrial anthracene oil (AO) in a microwave semi-pilot equipment consisting in a multimode applicator having a 2.45 GHz magnetron with variable microwave power. The experimental five variables of microwave heating of AO air-blowing range between 320-380 ˚C (temperature), 0.2-3.9 ˚C min-1 (heating rate), 1.5-5 h (soaking time), 16-20.5 % (air/AO ratio) and 200-1500 g (initial weight). Their effect on the overall microwave air-blowing process is evaluated by means of a statistical analysis. A detailed characterization of the pitches has been carried out in terms of ultimate analysis, softening point, solubility parameters (toluene insolubles (TI) and quinoline insolubles (QI)) and thermogravimetric analysis. The experiments were also carried out by using conventional heating for comparative purposes. The detailed study of the electric energy consumption of the overall microwave treatment allows estimating a significant electric energy saving of about 20 % when compared to conventional heating thus representing an excellent result in the production of carbon precursors.
Index 1.-NMR and IR spectra of 1 and 2 S-2 2.-1 H-PRESAT NMR of CNT-1 and CNT-2 S-4 3.-NMR and IR... more Index 1.-NMR and IR spectra of 1 and 2 S-2 2.-1 H-PRESAT NMR of CNT-1 and CNT-2 S-4 3.-NMR and IR spectra of 1-Ir and 3-Ir S-5 4.-XPS characterization of CNT-2, and Elemental analysis and XPS data of parent and functionalized CNT samples S-9 5.-TGA characterization of CNT-1, CNT-2, and CNT-2-Ir S-10 6.-TEM characterization of CNT, CNT-1-Ir, CNT-2-Ir and EDX of CNT-2-Ir S-10 7.-XPS characterization of CNT-1-Ir and CNT-2-Ir S-12 8.-CAN-driven water oxidation by the homogeneous catalysts 1-Ir and 3-Ir. S-12 9.-Electrocatalytic water oxidation experiments S-13
The development of more efficient electrode materials is essential to obtain vanadium redox flow ... more The development of more efficient electrode materials is essential to obtain vanadium redox flow batteries (VRFBs) with enhanced energy densities and to make these electrochemical energy storage devices more competitive. A graphene-modified graphite felt synthesized from a raw graphite felt and a graphene oxide water suspension by means of electrophoretic deposition (EPD) is investigated as a suitable electrode material in the positive side of a VRFB cell by means of cyclic voltammetry, impedance spectroscopy and charge/discharge experiments. The remarkably enhanced performance of the resultant hybrid material, in terms of electrochemical activity and kinetic reversibility towards the VO 2+ /VO 2 + , and mainly the markedly high energy efficiency of the VRFB cell (c.a. 95.8 % at 25 mA cm-2) can be ascribed to the exceptional morphological and chemical characteristics of this tailored material. The 3D architecture consisting of fibers interconnected by graphene-like sheets positively contributes to the proper development of the vanadium redox reactions and so represents a significant advance in the design of effective electrode materials.
Brief C4F8plasma exposure on platelet carbon nanofibers can lead to fabrication of novel LIB anod... more Brief C4F8plasma exposure on platelet carbon nanofibers can lead to fabrication of novel LIB anodes with enhanced rate performances.
This paper reports on the development of novel Ti-doped 3D carbon fibre composites (CFCs) and the... more This paper reports on the development of novel Ti-doped 3D carbon fibre composites (CFCs) and their performance when exposed to transient thermal loads (disruptions) in the electron beam facility JUDITH at different conditions. Depending on the applied load, the CFCs showed three steps of erosion: 1) breaking of PAN fibres with pull out from the surface; 2) cracking and ablation of pitch fibres close to the interface of PAN/pitch fibre-bundles; 3) finally, erosion of pitch fibres in the centre of the bundle. The addition of titanium carbide resulted in a significant improvement in thermal shock behaviour of these materials compared to their undoped counterparts.
Biological membranes are currently used in Ophthalmology in order to treat different ocular disor... more Biological membranes are currently used in Ophthalmology in order to treat different ocular disorders. These membranes have different properties such as cellular biocompatibility and promoting wound healing. Moreover, intrinsic antimicrobial properties could also be desirable because it would allow their use reducing the risk of infections. Graphene and its derivatives are promising biomaterials that already proved their bactericidal effect. However, their clinical use is limited due to the controversial results regarding their toxicity. In this work, we have developed and characterized a reduced graphene oxide membrane (rGOM) for its use in ocular Regenerative Medicine, and studied its in vitro and in vivo biocompatibility and genotoxicity with different types of human ocular cells. We proved that rGOM allowed the growth of different ocular cells without inducing in vitro or in vivo cytotoxicity or genotoxicity in the short-term. These results indicate that rGOM may be a promising candidate in Regenerative Medicine for the treatment of different ocular pathologies.
A commercial impregnating coal-tar pitch was thermally treated at 4308C for 2-5 h in nitrogen. Re... more A commercial impregnating coal-tar pitch was thermally treated at 4308C for 2-5 h in nitrogen. Resultant pitches, which contained mesophase ranging from 10 to 46 vol.%, were filtered to separate the isotropic phases, in order to study their contribution to the rheology of the whole pitches. The parent pitch, thermally treated pitches and the individual isotropic phases were characterized by measuring their elemental composition, softening point, carbon yield, solubility in toluene and in N-methyl-2-pyrrolidone, mesophase content (by optical microscopy) and X-ray diffraction parameters. The rheological behavior of the pitches and the isotropic phases was studied using steady shear rheometry. Results showed that not only had the whole pitches, which were partially anisotropic, a non-Newtonian behavior, but also the single isotropic phases.
The phase-mineral and chemical composition of magnetic (MCs) and char (CCs) concentrates recovere... more The phase-mineral and chemical composition of magnetic (MCs) and char (CCs) concentrates recovered from five fly ashes (FAs) produced in four large Spanish thermo-electric power stations was characterized. The MCs and CCs were isolated by magnetic ...
The current work investigates the performance of petroleum coke (PC) as a blended fuel under pulv... more The current work investigates the performance of petroleum coke (PC) as a blended fuel under pulverized-fuel combustion conditions. Three full-scale combustion experiments were carried out: a pure Carboniferous, high volatile bituminous coal and two blends of this coal with different proportions of PC. The samples studied included feed fuels and blends, fly ashes, chars taken at different positions of the combustion chamber, and chars prepared in a drop tube reactor to test the performance of the individual fuels. The addition of PC led to a substantial increase in the unburned carbon of the fly ashes. The petrographic analysis of the granulometric fractions of the fuels revealed that this increase cannot be attributed to an enrichment in coke of the coarser fractions, as reported in the literature. On the contrary, the finer fraction contained slightly more coke than the raw blend. The petrographic analysis of the chars collected with the suction probe and the fly ashes showed that the two blended fuels were strongly enriched in PC-derived material, indicating a poorer combustibility compared to the high volatile bituminous coal. It is concluded that the reactivity of the blends in the later stages of combustion is related with the contents of PC-derived chars and the burnout itself.
A comparative study of several screen-printed electrodes modified with electrochemically reduced ... more A comparative study of several screen-printed electrodes modified with electrochemically reduced graphene oxides (ERGO) by means of a constant current has been carried out. The ERGOs were produced from graphene oxides (GO) with different controlled functional groups contents and locations. The experimental reduction conditions were optimized for each particular GO to generate ERGO-modified electrodes with the aim of improving the performance of the dopamine redox process. The ERGO-modified electrodes exhibited a larger electroactive area, a higher reversibility of the redox process, faster kinetics, and greater double-layer capacitance. Analysis of the reduction degree and residual functional groups by means of X-ray photoelectron spectroscopy (XPS) after and before reduction enabled us to determine the relation between the electrochemical behavior and morphology of the electrodes. A hydrazine-reduced graphene oxide showed the best analytical performance with a higher sensitivity (0.259 μA/μM vs. 0.090 μA/μM in the case of a bare electrode), and a linear range from 1-100 μM. It was found that both the experimental reduction conditions and starting graphene material are critical for obtaining a modified electrode with a suitable electrochemical behavior and properties and that a constant current is a suitable technique for the reduction of graphene oxides, especially for screen-printed electrodes. Graphene, a two-dimensional carbon material with highly useful properties including a large surface area and high mechanical, thermal and chemical stabilities, has emerged as a very interesting material for electrochemical applications, especially in (bio)sensors due to its excellent properties such as high electron conductivity, fast heterogeneous electron-transfer rate at the graphene sheet edges and basalplane defect sites, large surface area and good biocompability. 1-4 The most suitable graphene material for modifying electrochemical sensors is graphene oxide (GO) due to its high capacity to be dispersed in aqueous solvents that allows a more efficient electrode modification. GO is usually produced by the oxidation of graphite, a methodology based on the Hummers 5 or Brodie method, 6 which is considered to be the best alternative for the preparation of graphene on a large scale. 7 Additionally, the preparation of GO can be modified by using graphites with different crystalline structures or by different preparation methods 8 giving rise to graphene materials of different sheet size, structure and properties, variables that can also be tuned to improve the electrochemical performance of electrodes. Although several studies on GO improving electrode properties have been reported, 9,10 in most cases a previous GO reduction is carried out in order to decrease the number of oxygen-based functional groups to obtain better electrochemical properties. 13 Several authors have reported that the electrocatalysis is influenced by the orientation of the graphene sheets with respect to the electrode surface, the C/O atomic ratio, or the synthesis route of the material. 14 For instance, graphene nanoribbons with different oxidation degrees were employed for the optimization of the detection of several analytes, showing how the graphene structure had a significant effect on the electrochemical detection. For the development of sensors and biosensors, screen-printed electrodes (SPEs) are among the most widely used platforms due to the low cost of their fabrication, high sensitivity, and their easily modified surfaces with compounds such as proteins or nanomaterials, that increase their active area and electrocatalytical properties. 22 These nanostructured SPEs have been used for several (bio)sensing applications. The aim of this work was to study the electrochemical performace of ERGO-modified screen-printed electrodes and, particularly, the effect of different graphenes on the electrochemical behavior of dopamine using the modified electrodes. Dopamine was selected because it is one of the most widely used model analytes for the characterization of electrodes and would facilitate a comparison between our results and the results obtained with other graphene or electrode materials. Screen-printed carbon electrodes (SPCEs) were modified using three GOs with different content and location of defects and functional groups. Electrochemically reduced graphene oxides were obtained by in situ electrochemical reduction using a constant current and the effect on the electrochemical process of dopamine was studied under several experimental conditions (reduction current, reduction time, pH, GO amount) by a multifactorial design. The main
Graphene materials have recently attracted increasing interest due to the excellent physico-chemi... more Graphene materials have recently attracted increasing interest due to the excellent physico-chemical properties that they can exhibit.[1] One interesting application is as electrodes in vanadium redox flow batteries (VRFBs). These are promising large-scale energy storage devices in which the electrodes must be carefully selected since they support the chemical reactions necessary for the operation of the battery. In this regard, graphenes obtained by thermal treatment of graphite oxide exhibited an excellent performance due to their high electrical conductivity and a high mechanical stability.[2]
Ana M. Pérez-Mas, Laura Fernández-García, Patricia Álvarez, Patricia Blanco, Ricardo Santamaría, ... more Ana M. Pérez-Mas, Laura Fernández-García, Patricia Álvarez, Patricia Blanco, Ricardo Santamaría, Marcos Granda, Clara Blanco, Rosa Menéndez Instituto Nacional del Carbón, CSIC, P.O.: 73, 33080 Oviedo, Spain [email protected] Abstract The morphology, size and height of graphene sheets are currently analysed by AFM without much difficulty. However, when dealing with graphenes obtained by thermal reduction of graphene oxides, the sheets cannot be easily visualized by this technique, mainly because of their shape, roughness and typical wrinkles, which difficult their AFM monitorization at the different temperatures. The aim of this work is to evaluate the effect of the thermal treatment on the graphene oxide (GO) sheet morfology in different substrates by means of AFM. For that, a GO obtained by a modified Hummer’s method [1] and subsequently sonicated (exfoliated) for 8h [2], was initially drop casted into silicon and HOPG substrates. After that, the whole systems were heated in a...
Multifunctional elastomer nanocomposites have been applied in several high-tech fields. The desig... more Multifunctional elastomer nanocomposites have been applied in several high-tech fields. The design of materials with tailored properties capable of tuning their performance is a topical challenge. Here, we demonstrate that it is possible to modulate the mechanical and transport properties of silicone rubber nanocomposites by controlling the structure, chemical composition and morphology of the graphene material. Intrinsic graphene properties, such as remaining oxygen groups, specific surface area, and aspect ratio, among others, have a profound effect on the final properties of the nanocomposite. Thus, the thermal conductivity benefits from larger filler size and high aromatic restoration. Whereas mechanical properties and electrical conductivity require a proper balance between filler/polymer matrix interaction and a partial aromatic restoration.
A proper design of heterogeneous molecular catalysts supported on carbon materials requires a sys... more A proper design of heterogeneous molecular catalysts supported on carbon materials requires a systematic study of "metal−carbon support interactions" and their influence on catalytic activity. In this study, hybrid materials containing covalently anchored iridium N-heterocyclic carbene (NHC) organometallic complexes have been successfully prepared from oxidized and partially reduced carbon nanotubes (CNTs). The preparation method for these supported materials relies on the selective functionalization of the superficial hydroxylic groups using the imidazolium salt, 1-(3hydroxypropyl)-3-methyl-1H-imidazol-3-ium chloride. The hydrogen transfer catalysis activity of these nanotube-based hybrid catalysts was tested by the reduction of cyclohexanone to cyclohexanol with 2-propanol, and the results of the tests were compared with those obtained using similar hybrid graphene-based catalysts. While EXAFS analysis revealed a common first coordination shell of the iridium atom for all the hybrid materials examined, independently of whether they were either supported on carbon nanotubes or graphene materials, catalytic activity in all the reduced materials was significantly superior. Moreover, catalytic systems based on reduced
A coal-tar-derived mesophase was chemically activated to produce a high surface area (3,200 m 2 ... more A coal-tar-derived mesophase was chemically activated to produce a high surface area (3,200 m 2 /g) carbon with a porosity made up of both micropores and mesopores. Its adsorption capacities were found to be among the highest ever reported in literature, reaching values of 860 mg/g and 1,200 mg/g for the adsorption of benzene and toluene, respectively, and 1,200 mg/g for the combined adsorption of benzene and toluene from an industrial wastewater. Such high values imply that the entire pore system, including the mesopore fraction, is involved in the adsorption process. The almost complete pore filling is thought to be due to the high relative concentrations of the tested solutions, resulting from the low saturation concentration values for benzene and toluene, which were obtained by fitting the adsorption data to the BET equation in liquid phase. The kinetics of adsorption in the batch experiments which were conducted in a syringe-like adsorption chamber was observed to proceed in accordance with the pseudo-second order kinetic model. The combined presence of micropores and mesopores in the material is thought to be the key to the high kinetic performance, which was outstanding in a comparison with other porous materials reported in the literature.
Enhanced SO 2 adsorption of activated carbon fibers is obtained by tailoring a specific micro-mes... more Enhanced SO 2 adsorption of activated carbon fibers is obtained by tailoring a specific micro-mesoporous structure in the fibers. This architecture is obtained via metal catalytic activation of the fibers with a novel precursor, cobalt naphthenate, which contrary to other precursors, also enhances spinnability and carbon fiber yield. In the SO 2 oxidation, it is demonstrated that the combination of micropores and large mesopores is the main factor for an enhanced catalytic activity which is superior to that observed in other similar microporous activated carbon fibers. This provides an alternative way for the development of a new generation of catalytic material.
This work describes the chemical activation of a coke using two different activating agents in or... more This work describes the chemical activation of a coke using two different activating agents in order to investigate their behaviour as electrodes in supercapacitors. A coke was chemically activated with two hydroxides (KOH and NaOH) under nitrogen flow, at a constant mass hydroxide/coke ratio of 2 and temperatures of 600, 650 and 700 ºC. All the samples were characterized in terms of porosity by N 2 sorption at 77 K, surface chemistry by temperature programmed desorption (TPD) and electrical conductivity. Their electrochemical behaviour as electric double layer capacitors was determined using galvanostatic, voltammetric and impedance spectroscopy techniques, in an aqueous medium with 1M H 2 SO 4 as electrolyte. Large differences in capacitive behaviour with the increase in current density were found between the two series of activated samples. The different trends were correlated with the results obtained from the TPD analysis of the CO-type oxygen groups. It was found that these oxygen groups make a positive contribution to capacitance finding a good correlation between the specific capacitance values and the amount of these oxygen groups was found for both series.
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Papers by Rosa Menéndez