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Volume 6, June

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C, Volume 6, Issue 3 (September 2020) – 9 articles

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Open AccessArticle
Catalysts for Methane Steam Reforming Reaction: Evaluation of CeO2 Addition to Alumina-Based Washcoat Slurry Formulation
C 2020, 6(3), 52; https://doi.org/10.3390/c6030052 - 03 Aug 2020
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Abstract
The effect of the addition of CeO2 to alumina-based washcoat slurry formulation on the methane steam reforming (MSR) reaction was investigated. Five Al2O3-CeO2-based washcoat slurries, differing from each other in the Al2O3/CeO [...] Read more.
The effect of the addition of CeO2 to alumina-based washcoat slurry formulation on the methane steam reforming (MSR) reaction was investigated. Five Al2O3-CeO2-based washcoat slurries, differing from each other in the Al2O3/CeO2 ratio (nominal ratio equal to ∞, 0.042, 0.087, 0.250, 0.667) were prepared, dried and calcined; the resulting powders were loaded with nickel as an active metal and the obtained catalysts were tested in MSR reaction. Five cylindrical silicon carbide (SiC) monoliths were washcoated with the prepared slurries and their mechanical resistance was evaluated through the ultrasound adherence test. The activity tests results highlighted the best performance in terms of methane conversion and hydrogen selectivity of the powder catalyst, with the Al2O3/CeO2 percentage nominal ratio equal to 0.042. A structured catalyst was finally prepared by loading a SiC monolith with the most active catalytic formulation and tested in MSR reaction. The performance of the structured catalyst was evaluated in terms of methane conversion and its stability was verified in a time-on-stream test, which allowed for the evaluation of the carbon formation rate; furthermore, its activity was characterized by the estimation of the kinetic parameters. The results highlighted the beneficial effect of ceria addition on the catalytic activity; moreover, compared with data of the literature, the calculated carbon formation rate demonstrated a good resistance of the catalyst to coke formation. Full article
(This article belongs to the Special Issue Carbide Derived Carbons)
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Open AccessFeature PaperArticle
Effect of Cellulose Nanocrystals on the Coating of Chitosan Nanocomposite Film Using Plasma-Mediated Deposition of Amorphous Hydrogenated Carbon (a–C:H) Layers
C 2020, 6(3), 51; https://doi.org/10.3390/c6030051 - 30 Jul 2020
Viewed by 167
Abstract
The substitution of petroleum-based polymers with naturally derived biopolymers may be a good alternative for the conservation of natural fossil resources and the alleviation of pollution and waste disposal problems. However, in order to be used in a wide range of applications, some [...] Read more.
The substitution of petroleum-based polymers with naturally derived biopolymers may be a good alternative for the conservation of natural fossil resources and the alleviation of pollution and waste disposal problems. However, in order to be used in a wide range of applications, some biopolymers’ properties should be enhanced. In this study, biocompatible, non-toxic, and biodegradable chitosan (CS) film and CS reinforced with 10 wt% of cellulose nanocrystals (CN–CS) were coated with amorphous hydrogenated carbon layers (a–C:H) of different thickness. To investigate the effect of the nano-reinforcement on the a–C:H layer applied, mild radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) was used to coat the CS and its CN–CS bio-nanocomposite film. Both the surface characteristics and the chemical composition were analyzed. The surface morphology and wettability were examined by ex-situ atomic force microscopy (AFM) and contact angle measurements (CA), respectively. Hereby, the relationship between sp2/sp3 ratios on a macroscopic scale was also evaluated. For the investigation of the chemical composition, the surface sensitive synchrotron X-ray radiation techniques near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) as well as diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) were used. Full article
(This article belongs to the Special Issue Characterization of Disorder in Carbons)
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Open AccessFeature PaperArticle
Evidence for Glass Behavior in Amorphous Carbon
C 2020, 6(3), 50; https://doi.org/10.3390/c6030050 - 30 Jul 2020
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Abstract
Amorphous carbons are disordered carbons with densities of circa 1.9–3.1 g/cc and a mixture of sp2 and sp3 hybridization. Using molecular dynamics simulations, we simulate diffusion in amorphous carbons at different densities and temperatures to investigate the transition between [...] Read more.
Amorphous carbons are disordered carbons with densities of circa 1.9–3.1 g/cc and a mixture of sp2 and sp3 hybridization. Using molecular dynamics simulations, we simulate diffusion in amorphous carbons at different densities and temperatures to investigate the transition between amorphous carbon and the liquid state. Arrhenius plots of the self-diffusion coefficient clearly demonstrate that there is a glass transition rather than a melting point. We consider five common carbon potentials (Tersoff, REBO-II, AIREBO, ReaxFF and EDIP) and all exhibit a glass transition. Although the glass-transition temperature (Tg) is not significantly affected by density, the choice of potential can vary Tg by up to 40%. Our results suggest that amorphous carbon should be interpreted as a glass rather than a solid. Full article
(This article belongs to the Special Issue Characterization of Disorder in Carbons)
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Open AccessArticle
Effects of the Stacking Faults on the Electrical Resistance of Highly Ordered Graphite Bulk Samples
C 2020, 6(3), 49; https://doi.org/10.3390/c6030049 - 25 Jul 2020
Viewed by 241
Abstract
High anisotropy and the existence of two-dimensional highly conducting interfaces at stacking faults parallel to the graphene planes of the graphite structure influence, in a non-simple way, the transport properties of highly oriented graphite. We report two related effects on the electrical resistance [...] Read more.
High anisotropy and the existence of two-dimensional highly conducting interfaces at stacking faults parallel to the graphene planes of the graphite structure influence, in a non-simple way, the transport properties of highly oriented graphite. We report two related effects on the electrical resistance of highly oriented pyrolytic as well as of natural graphite bulk samples, measured with the four points method in the temperature range 300 K T 410 K. A qualitative and quantitative change in the temperature dependence of the resistance was obtained by simply enlarging the electrodes and contacting the edges of the internal interfaces on the same sample. Additionally, at temperatures T350 K the resistance can change with time. We show that this temperature-dependent annealing effect is related to the stacking faults and can irreversibly change the absolute value of the resistance and its temperature dependence. A partial recovery is obtained after leaving the sample at normal conditions for several days. The overall results stress the importance of the electrodes location on a bulk graphite sample, the contribution of the stacking faults in the interpretation of the measured transport properties and the need of systematic studies on the influence of high temperature annealing on the interfaces properties. Full article
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Open AccessArticle
Improving the Performance of Printable Carbon Electrodes by Femtosecond Laser Treatment
C 2020, 6(3), 48; https://doi.org/10.3390/c6030048 - 16 Jul 2020
Viewed by 186
Abstract
Low-cost carbon-conductive films were screen-printed on a Plexiglas® substrate, and then, after a standard annealing procedure, subjected to femtosecond (fs) laser treatments at different values of total accumulated laser fluence ΦA. Four-point probe measurements showed that, if ΦA > [...] Read more.
Low-cost carbon-conductive films were screen-printed on a Plexiglas® substrate, and then, after a standard annealing procedure, subjected to femtosecond (fs) laser treatments at different values of total accumulated laser fluence ΦA. Four-point probe measurements showed that, if ΦA > 0.3 kJ/cm2, the sheet resistance of laser-treated films can be reduced down to about 15 Ω/sq, which is a value more than 20% lower than that measured on as-annealed untreated films. Furthermore, as pointed out by a comprehensive Raman spectroscopy analysis, it was found that sheet resistance decreases linearly with ΦA, due to a progressively higher degree of crystallinity and stacking order of the graphitic phase. Results therefore highlight that fs-laser treatment can be profitably used as an additional process for improving the performance of printable carbon electrodes, which have been recently proposed as a valid alternative to metal electrodes for stable and up-scalable perovskite solar cells. Full article
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Open AccessArticle
BMIM-BF4 RTIL: Synthesis, Characterization and Performance Evaluation for Electrochemical CO2 Reduction to CO over Sn and MoSi2 Cathodes
C 2020, 6(3), 47; https://doi.org/10.3390/c6030047 - 15 Jul 2020
Viewed by 270
Abstract
Development of a practicable artificial photosynthesis process has been considered today as one of the top-most research priorities to address the problems related to the global warming and the associated social cost of carbon, and to develop the renewable fuels employable in place [...] Read more.
Development of a practicable artificial photosynthesis process has been considered today as one of the top-most research priorities to address the problems related to the global warming and the associated social cost of carbon, and to develop the renewable fuels employable in place of fossil fuels. For this purpose, a simple and inexpensive route has been devised to synthesize a high-purity bmim[BF4] to employ as a helper catalyst to promote the electrochemical CO2 reduction (ECR) to CO formation over Sn and MoSi2 cathodes. The rates of CO2 reduction over Sn and MoSi2 cathodes have been determined to be >110 mA/cm2 during cyclic voltammetry. The CO formation at a current density of >100 mA/cm2 in the ECR reaction is very essential to consider this reaction for industrial practice when the required electricity derived from sunlight is available at an affordable price. The bmim[BF4] mediated ECR reaction over Sn and MoSi2 cathodes has been identified to be a revere reaction of CO oxidation in air. The experiments with isotopic 13CO2 confirmed that CO2 is the only source of CO formation in the ECR reaction. The underlying reaction mechanism in bmim[BF4] mediated ECR reaction over Sn has been presented and discussed in this article. Full article
(This article belongs to the Special Issue Ionic liquids for CO2 Capture and Reduction)
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Open AccessFeature PaperReview
Characterization of Carbon Materials for Hydrogen Storage and Compression
C 2020, 6(3), 46; https://doi.org/10.3390/c6030046 - 09 Jul 2020
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Abstract
Carbon materials have proven to be a suitable choice for hydrogen storage and, recently, for hydrogen compression. Their developed textural properties, such as large surface area and high microporosity, are essential features for hydrogen adsorption. In this work, we first review recent advances [...] Read more.
Carbon materials have proven to be a suitable choice for hydrogen storage and, recently, for hydrogen compression. Their developed textural properties, such as large surface area and high microporosity, are essential features for hydrogen adsorption. In this work, we first review recent advances in the physisorption characterization of nanoporous carbon materials. Among them, approaches based on the density functional theory are considered now standard methods for obtaining a reliable assessment of the pore size distribution (PSD) over the whole range from narrow micropores to mesopores. Both a high surface area and ultramicropores (pore width < 0.7 nm) are needed to achieve significant hydrogen adsorption at pressures below 1 MPa and 77 K. However, due to the wide PSD typical of activated carbons, it follows from an extensive literature review that pressures above 3 MP are needed to reach maximum excess uptakes in the range of ca. 7 wt.%. Finally, we present the adsorption–desorption compression technology, allowing hydrogen to be compressed at 70 MPa by cooling/heating cycles between 77 and 298 K, and being an alternative to mechanical compressors. The cyclic, thermally driven hydrogen compression might open a new scenario within the vast field of hydrogen applications. Full article
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Open AccessArticle
Synthesis and Characterization of Activated Carbon Foam from Polymerization of Furfuryl Alcohol Activated by Zinc and Copper Chlorides
C 2020, 6(3), 45; https://doi.org/10.3390/c6030045 - 07 Jul 2020
Viewed by 241
Abstract
Polymerization of furfuryl alcohol carried out using ZnCl2 or CuCl2 as Lewis acid activators was investigated by exploring various synthesis parameters in order to produce activated carbons with different porosity and metal load. The temperature of polymerization was changed according to [...] Read more.
Polymerization of furfuryl alcohol carried out using ZnCl2 or CuCl2 as Lewis acid activators was investigated by exploring various synthesis parameters in order to produce activated carbons with different porosity and metal load. The temperature of polymerization was changed according to Lewis acidity strength of the two metal chlorides: 0 °C for CuCl2 and 80 °C for ZnCl2. The polymer obtained was pyrolyzed under pure He flow or under 1000 ppm O2/He flow at 600 or 850 °C in order to produce activated carbons with specific textural features. The load and nature of the residual metal after pyrolysis were determined by ICP and XRD analyses, respectively. Copper was mostly preserved even at high pyrolysis temperature in contrast to zinc, which was almost totally lost at 850 °C. A foamy structure was detected by SEM analysis for all samples. Textural properties were determined by both N2 and CO2 physisorption; surface areas and pore size distributions were evaluated according to BET, DFT and DR models. The polymerization activated by ZnCl2 produced carbons with larger surface areas were also related to the presence of some mesopores, whereas CuCl2 promoted the prevailing formation of narrow micropores, making these materials particularly suited to H2 storage applications. Full article
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Open AccessArticle
Graphene Oxide/Fe-Based Composite Pre-Polymerized Coagulants: Synthesis, Characterization, and Potential Application in Water Treatment
C 2020, 6(3), 44; https://doi.org/10.3390/c6030044 - 30 Jun 2020
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Abstract
This study presents for the first time the synthesis and characterization of GO (graphene oxide), PFSiC (polyferric silicate chloride), and hybrid GO-PFSiC derivatives, aiming to enhance synergistically the performance of coagulation, when applied for the treatment of water. The structure and the morphology [...] Read more.
This study presents for the first time the synthesis and characterization of GO (graphene oxide), PFSiC (polyferric silicate chloride), and hybrid GO-PFSiC derivatives, aiming to enhance synergistically the performance of coagulation, when applied for the treatment of water. The structure and the morphology of composite GO-PFSiC coagulants were studied in detail by the application of FTIR, XRD, and SEM characterization techniques. Furthermore, the proposed coagulants were applied for the treatment of simulated turbid surface water. The effects of the reagent’s dosage, pH value, and experimental/operational conditions on the coagulation efficiency, applied mainly for the removal of turbidity, were examined. The results, obtained from the FTIR and XRD measurements, showed the presence of a bond between the PFSiC and the GO surface, indicating that the PFSiC particles are distributed uniformly on the surface of graphene, which was also confirmed by the SEM images. Especially, the composite compound GO-PFSiC1.5-15-0.5 presents the most uniform distribution of iron on the surface of graphene oxide and exhibits the optimum coagulation efficiency, while it significantly reduces the turbidity for doses above 3–5 mg/L, i.e., achieving the respective legislation limit as proposed by WHO. Specifically, at the alkaline pH values (>7.9), the removal of turbidity reaches 96%. Consequently, the results of this study render these materials as potential coagulant agents for further research and applications, aiming to also achieve the co-removal of other water components. Full article
(This article belongs to the Special Issue Characterization and Standardization of Graphene Materials)
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