2022

Jump to: 2021, 2020

23 pages, 5569 KiB

Open AccessReview

Fabrication of Metal/Graphene Composites via Cold Spray Process: State-of-the-Art and the Way Forward

by Krishnamurthy Prasad, Rizwan Abdul Rahman Rashid, Novana Hutasoit, Suresh Palanisamy and Nishar Hameed

C 2022, 8(4), 65; https://doi.org/10.3390/c8040065 - 15 Nov 2022

Viewed by 2348

Abstract

Cold spray (CS)-fabricated metal–graphene composites have applications in several fields ranging from tribology and corrosion protection to antibacterial applications. However, it is critical from a process perspective to create a viable feedstock, and to this end, there are two widely reported techniques: ball [...] Read more.

Cold spray (CS)-fabricated metal–graphene composites have applications in several fields ranging from tribology and corrosion protection to antibacterial applications. However, it is critical from a process perspective to create a viable feedstock, and to this end, there are two widely reported techniques: ball milling and in situ reduction. In this paper, the CS feedstocks prepared via these two methods are compared and contrasted with other miscellaneous techniques in the literature based on their efficacies and the end properties of the fabricated coatings. CS metal–graphene composite coatings are found to display self-healing behaviour and excellent corrosion/wear resistance and mechanical properties, but at this juncture, there is a gap in the literature as far as the CS fabrication of self-standing metal–graphene composite parts is concerned. Several future research avenues are discussed to fully comprehend the printability and functionality of metal/GNP composite cold-sprayed structures. Full article

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17 pages, 9097 KiB

Open AccessArticle

Asymmetrical Cross-Sectional Buckling in Arc-Prepared Multiwall Carbon Nanotubes Revealed by Iodine Filling

by Abraao Cefas Torres-Dias, Anthony Impellizzeri, Emmanuel Picheau, Laure Noé, Alain Pénicaud, Christopher Ewels and Marc Monthioux

C 2022, 8(1), 10; https://doi.org/10.3390/c8010010 - 27 Jan 2022

Viewed by 2763

Abstract

We report the intercalation of iodine chains in highly crystalline arc-discharge multiwalled carbon nanotubes (MWCNTs), not in the central cavity but instead between the concentric graphene shells. High-resolution transmission electron microscopy demonstrated that the intercalation was asymmetric with respect to the longitudinal axis [...] Read more.

We report the intercalation of iodine chains in highly crystalline arc-discharge multiwalled carbon nanotubes (MWCNTs), not in the central cavity but instead between the concentric graphene shells. High-resolution transmission electron microscopy demonstrated that the intercalation was asymmetric with respect to the longitudinal axis of the nanotubes. This filling is explained through the existence of asymmetric intershell channels which formed as the tubes shrank upon cooling after growth. Shrinkage occurred because the geometrically constrained equilibrium intershell spacing was higher at growth than room temperature, due to the highly anisotropic coefficient of thermal expansion of graphite (or graphene stacks). Computational modelling supported the formation of such cavities and explained why they all formed on the same side of the tubes. The graphene shells were forced to bend outward, thereby opening aligned intergraphene nanocavities, and subsequently allowing the intercalation with iodine once the tube ends were opened by oxidative treatment. These observations are specific to catalyst-free processes because catalytic processes use too low temperatures, but they are generally applicable in geometrically closed carbon structures grown at high temperatures and so should be present in all arc-grown MWCNTs. They are likely to explain multiple observations in the literature of asymmetric interlayer spacings in multiple-shell graphenic carbon structures. Full article

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2021

Jump to: 2022, 2020

17 pages, 2768 KiB

Open AccessArticle

High Surface Area Nanoporous Activated Carbons Materials from Areca catechu Nut with Excellent Iodine and Methylene Blue Adsorption

by Sahira Joshi, Rekha Goswami Shrestha, Raja Ram Pradhananga, Katsuhiko Ariga and Lok Kumar Shrestha

C 2022, 8(1), 2; https://doi.org/10.3390/c8010002 - 27 Dec 2021

Cited by 11 | Viewed by 4073

Abstract

Nanoporous carbon materials from biomass exhibit a high surface area due to well-defined pore structures. Therefore, they have been extensively used in separation and purification technologies as efficient adsorbents. Here, we report the iodine and methylene blue adsorption properties of the hierarchically porous [...] Read more.

Nanoporous carbon materials from biomass exhibit a high surface area due to well-defined pore structures. Therefore, they have been extensively used in separation and purification technologies as efficient adsorbents. Here, we report the iodine and methylene blue adsorption properties of the hierarchically porous carbon materials prepared from Areca catechu nut. The preparation method involves the phosphoric acid (H₃PO₄) activation of the Areca catechu nut powder. The effects of carbonization conditions (mixing ratio with H₃PO₄, carbonization time, and carbonization temperature) on the textural properties and surface functional groups were studied. The optimum textural properties were obtained at a mixing ratio of 1:1, carbonized for 3 h at 400 °C, and the sample achieved a high specific surface area of 2132.1 m² g⁻¹ and a large pore volume of 3.426 cm³ g⁻¹, respectively. The prepared materials have amorphous carbon structures and contain oxygenated surface functional groups. Due to the well-defined micro-and mesopore structures with the high surface area and large pore volume, the optimal sample showed excellent iodine and methylene blue adsorption. The iodine number and methylene blue values were ca. 888 mg g⁻¹ and 369 mg g⁻¹, respectively. The batch adsorption studies of methylene dye were affected by pH, adsorbent dose, contact time, and initial concentration. The optimum parameters for the methylene blue adsorption were in alkaline pH, adsorbent dose of 2.8 g L⁻¹, and contact time of 180 min. Equilibrium data could be best represented by the Langmuir isotherm model with a monolayer adsorption capacity of 333.3 mg g⁻¹. Thus, our results demonstrate that the Areca catechu nut has considerable potential as the novel precursor material for the scalable production of high surface area hierarchically porous carbon materials that are essential in removing organic dyes from water. Full article

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26 pages, 2122 KiB

Open AccessReview

Removal of Hydrophobic Contaminants from the Soil by Adsorption onto Carbon Materials and Microbial Degradation

by Shippi Dewangan, Amarpreet K. Bhatia, Ajaya Kumar Singh and Sónia A. C. Carabineiro

C 2021, 7(4), 83; https://doi.org/10.3390/c7040083 - 03 Dec 2021

Cited by 8 | Viewed by 3647

Abstract

The pollution of soil is a worldwide concern as it has harmful consequences on the environment and human health. With the continuous expansion of industry and agriculture, the content of hydrophobic organic pollutants in the soil has been increasing, which has caused serious [...] Read more.

The pollution of soil is a worldwide concern as it has harmful consequences on the environment and human health. With the continuous expansion of industry and agriculture, the content of hydrophobic organic pollutants in the soil has been increasing, which has caused serious pollution to the soil. The removal of hydrophobic organic contaminants from soil, aiming to recover environmental safety, is an urgent matter to guarantee sufficient food and water for populations. Adsorption has proven to be an effective and economically practicable method for removing organic contaminants. This paper summarizes the use of low-cost adsorbents, such as biochar and activated carbon, for removing hydrophobic organic contaminants from soil. Biochar is usually appropriate for the adsorption of organic contaminants via the adsorption mechanisms of electrostatic interaction, precipitation, and ion exchange. Biochar also has numerous benefits, such as being obtained from several kinds of raw materials, having low costs, recyclability, and potential for environmental treatment. This paper illustrates biochar’s adsorption mechanism for organic contaminants and discusses the microbial degradation of hydrophobic organic contaminants. Full article

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21 pages, 51157 KiB

Open AccessReview

Carbon Nanoarchitectonics for Energy and Related Applications

by Rekha Goswami Shrestha, Lok Kumar Shrestha and Katsuhiko Ariga

C 2021, 7(4), 73; https://doi.org/10.3390/c7040073 - 19 Oct 2021

Cited by 12 | Viewed by 3104

Abstract

Nanoarchitectonics has been recently proposed as a post-nanotechnology concept. It is the methodology to produce functional materials from nanoscale units. Carbon-based materials are actively used in nanoarchitectonics approaches. This review explains several recent examples of energy and related applications of carbon materials from [...] Read more.

Nanoarchitectonics has been recently proposed as a post-nanotechnology concept. It is the methodology to produce functional materials from nanoscale units. Carbon-based materials are actively used in nanoarchitectonics approaches. This review explains several recent examples of energy and related applications of carbon materials from the viewpoint of the nanoarchitectonics concept. Explanations and discussions are described according to the classification of carbon sources for nanostructured materials: (i) carbon nanoarchitectonics from molecules and supramolecular assemblies; (ii) carbon nanoarchitectonics from fullerenes; (iii) carbon nanoarchitectonics from biomass; and (iv) carbon nanoarchitectonics with composites and hybrids. Functional carbon materials can be nanoarchitected through various processes, including well-skilled organic synthesis with designed molecular sources; self-assembly of fullerenes under various conditions; practical, low-cost synthesis from biomass; and hybrid/composite formation with various carbon sources. These examples strikingly demonstrate the enormous potential of nanoarchitectonics approaches to produce functional carbon materials from various components such as small molecules, fullerene, other nanocarbons, and naturally abundant biomasses. While this review article only shows limited application aspects in energy-related usages such as supercapacitors, applications for more advanced cells and batteries, environmental monitoring and remediation, bio-medical usages, and advanced devices are also expected. Full article

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14 pages, 4105 KiB

Open AccessArticle

Monitoring of Curing and Cyclic Thermoresistive Response Using Monofilament Carbon Nanotube Yarn Silicone Composites

by Tannaz Tayyarian, Omar Rodríguez-Uicab and Jandro L. Abot

C 2021, 7(3), 60; https://doi.org/10.3390/c7030060 - 04 Aug 2021

Cited by 2 | Viewed by 1985

Abstract

The curing process and thermoresistive response of a single carbon nanotube yarn (CNTY) embedded in a room temperature vulcanizing (RTV) silicone forming a CNTY monofilament composite were investigated toward potential applications in integrated curing monitoring and temperature sensing. Two RTV silicones of different [...] Read more.

The curing process and thermoresistive response of a single carbon nanotube yarn (CNTY) embedded in a room temperature vulcanizing (RTV) silicone forming a CNTY monofilament composite were investigated toward potential applications in integrated curing monitoring and temperature sensing. Two RTV silicones of different crosslinking mechanisms, SR₁ and SR₂ (tin- and platinum-cured, respectively), were used to investigate their curing kinetics using the electrical response of the CNTY. It is shown that the relative electrical resistance change of CNTY/SR₁ and CNTY/SR₂ monofilament composites increased by 3.8% and 3.3%, respectively, after completion of the curing process. The thermoresistive characterization of the CNTY monofilament composites was conducted during heating–cooling ramps ranging from room temperature (RT~25 °C) to 100 °C. The thermoresistive response was nearly linear with a negative temperature coefficient of resistance (TCR) at heating and cooling sections for both CNTY/SR₁ and CNTY/SR₂ monofilament composites. The average TCR value was −8.36 × 10⁻⁴ °C⁻¹ for CNTY/SR₁ and −7.26 × 10⁻⁴ °C⁻¹ for CNTY/SR₂. Both monofilament composites showed a negligible negative residual relative electrical resistance change with average values of ~−0.11% for CNTY/SR₁ and ~−0.16% for CNTY/SR₂ after each cycle. The hysteresis amounted to ~21.85% in CNTY/SR₁ and ~29.80% in CNTY/SR₂ after each cycle. In addition, the effect of heating rate on the thermoresistive sensitivity of CNTY monofilament composites was investigated and it was shown that it reduces as the heating rate increases. Full article

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14 pages, 4891 KiB

Open AccessArticle

Preparation and Carbonization of Glucose and Pyromellitic Dianhydride Crosslinked Polymers

by Fabrizio Caldera, Antonella Moramarco, Federico Cesano, Anastasia Anceschi, Alessandro Damin and Marco Zanetti

C 2021, 7(3), 56; https://doi.org/10.3390/c7030056 - 26 Jul 2021

Viewed by 2853

Abstract

In this work, four types of nanosponges were prepared from pyromellitic dianhydride (PMDA) and D-glucose (GLU) with different molar ratios (1.5:1, 2:1, 2.5:1 and 3:1). The obtained PMDA/GLU nanosponges were then pyrolyzed at 800 °C for 30 min under N₂ gas flow. [...] Read more.

In this work, four types of nanosponges were prepared from pyromellitic dianhydride (PMDA) and D-glucose (GLU) with different molar ratios (1.5:1, 2:1, 2.5:1 and 3:1). The obtained PMDA/GLU nanosponges were then pyrolyzed at 800 °C for 30 min under N₂ gas flow. The prepared polymeric nanosponges were investigated by FTIR spectroscopy, elemental and thermogravimetric analyses to unravel the role played by the different molar ratio of the precursors in the formation of the polymer. The pyrolyzed nanosponges were investigated by means of porosity measurements, X-ray diffraction analysis, Raman spectroscopy and high-resolution transmission electron microscopy. Notably, no significant correlation of the amounts of used precursors with the porous texture and structure was evidenced. The results corroborate that PMDA and GLU can be easily combined to prepare nanosponges and that the carbon materials produced by their pyrolysis can be associated with glassy carbons with a microporous texture and relatively high surface area. Such hard carbons can be easily obtained and shrewdly used to segregate relatively small molecules and organic contaminants; in this study methylene blue adsorption was investigated. Full article

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7 pages, 1645 KiB

Open AccessArticle

Raman Spectroscopy Investigation of Graphene Oxide Reduction by Laser Scribing

by Vittorio Scardaci and Giuseppe Compagnini

C 2021, 7(2), 48; https://doi.org/10.3390/c7020048 - 17 Jun 2021

Cited by 50 | Viewed by 9887

Abstract

Laser scribing has been proposed as a fast and easy tool to reduce graphene oxide (GO) for a wide range of applications. Here, we investigate laser reduction of GO under a range of processing and material parameters, such as laser scan speed, number [...] Read more.

Laser scribing has been proposed as a fast and easy tool to reduce graphene oxide (GO) for a wide range of applications. Here, we investigate laser reduction of GO under a range of processing and material parameters, such as laser scan speed, number of laser passes, and material coverage. We use Raman spectroscopy for the characterization of the obtained materials. We demonstrate that laser scan speed is the most influential parameter, as a slower scan speed yields poor GO reduction. The number of laser passes is influential where the material coverage is higher, producing a significant improvement of GO reduction on a second pass. Material coverage is the least influential parameter, as it affects GO reduction only under restricted conditions. Full article

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11 pages, 2378 KiB

Open AccessArticle

Variable Temperature Synthesis of Tunable Flame-Generated Carbon Nanoparticles

by Francesca Picca, Angela Di Pietro, Mario Commodo, Patrizia Minutolo and Andrea D’Anna

C 2021, 7(2), 44; https://doi.org/10.3390/c7020044 - 06 May 2021

Cited by 3 | Viewed by 2349

Abstract

In this study, flame-formed carbon nanoparticles of different nanostructures have been produced by changing the flame temperature. Raman spectroscopy has been used for the characterization of the carbon nanoparticles, while the particle size has been obtained by online measurements made by electrical mobility [...] Read more.

In this study, flame-formed carbon nanoparticles of different nanostructures have been produced by changing the flame temperature. Raman spectroscopy has been used for the characterization of the carbon nanoparticles, while the particle size has been obtained by online measurements made by electrical mobility analysis. The results show that, in agreement with recent literature data, a large variety of carbon nanoparticles, with a different degree of graphitization, can be produced by changing the flame temperature. This methodology allows for the synthesis of very small carbon nanoparticles with a size of about 3–4 nm and with different graphitic orders. Under the perspective of the material synthesis process, the variable-temperature flame-synthesis of carbon nanoparticles appears as an attractive procedure for a cost-effective and easily scalable production of highly tunable carbon nanoparticles. Full article

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20 pages, 6030 KiB

Open AccessArticle

Nanocomposite of Ellagic Acid with Multi-Walled Carbon Nanotubes for the Simultaneous Voltammetric Detection of Six Biomolecules

by Najmeh Sabbaghi, Meissam Noroozifar and Kagan Kerman

C 2021, 7(2), 43; https://doi.org/10.3390/c7020043 - 03 May 2021

Cited by 4 | Viewed by 2612

Abstract

In this proof-of-concept study, a highly sensitive electrochemical sensor using a graphite paste electrode modified with ellagic acid and multi-walled carbon nanotubes (MGPE/MWCNTs-EA) was developed for the simultaneous determination of six biomolecules: ascorbic acid (AA), dopamine (DA), uric acid (UA), tryptophan (Trp), xanthine [...] Read more.

In this proof-of-concept study, a highly sensitive electrochemical sensor using a graphite paste electrode modified with ellagic acid and multi-walled carbon nanotubes (MGPE/MWCNTs-EA) was developed for the simultaneous determination of six biomolecules: ascorbic acid (AA), dopamine (DA), uric acid (UA), tryptophan (Trp), xanthine (XA), and caffeine (CA). Differential pulse voltammetry (DPV) was performed at a potential range from 0.1–1.2 V vs. Ag/AgCl in phosphate electrolyte (pH 2.0). The modified GPE enabled the simultaneous determination of biomolecules under investigation in human urine and blood serum samples with detection limits ranging from 11–91 nM with recoveries of 94.0–106.0%. The electrochemical performance of the modified GPE for the analytes was stable and reproducible and checked with standard high performance liquid chromatography technique. The data suggested that the modified GPE provided a promising platform for routine quantitative determination of the biomolecules under investigation in quality control studies of real samples collected from food and pharmaceutical products. Full article

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21 pages, 11991 KiB

Open AccessArticle

Polyamide 12/Multiwalled Carbon Nanotube and Carbon Black Nanocomposites Manufactured by 3D Printing Fused Filament Fabrication: A Comparison of the Electrical, Thermoelectric, and Mechanical Properties

by Nectarios Vidakis, Markos Petousis, Lazaros Tzounis, Emmanuel Velidakis, Nikolaos Mountakis and Sotirios A. Grammatikos

C 2021, 7(2), 38; https://doi.org/10.3390/c7020038 - 23 Apr 2021

Cited by 33 | Viewed by 4345

Abstract

In this study, nanocomposites with polyamide 12 (PA12) as the polymer matrix and multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) at different loadings (2.5, 5.0, and 10.0 wt.%) as fillers, were produced in 3D printing filament form by melt mixing extrusion process. [...] Read more.

In this study, nanocomposites with polyamide 12 (PA12) as the polymer matrix and multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) at different loadings (2.5, 5.0, and 10.0 wt.%) as fillers, were produced in 3D printing filament form by melt mixing extrusion process. The filament was then used to build specimens with the fused filament fabrication (FFF) three-dimensional (3D) printing process. The aim was to produce by FFF 3D printing, electrically conductive and thermoelectric functional specimens with enhanced mechanical properties. All nanocomposites’ samples were electrically conductive at filler loadings above the electrical percolation threshold. The highest thermoelectric performance was obtained for the PA12/CNT nanocomposite at 10.0 wt.%. The static tensile and flexural mechanical properties, as well as the Charpy’s impact and Vickers microhardness, were determined. The highest improvement in mechanical properties was observed for the PA12/CNT nanocomposites at 5.0 wt.% filler loading. The fracture mechanisms were identified by fractographic analyses of scanning electron microscopy (SEM) images acquired from fractured surfaces of tensile tested specimens. The nanocomposites produced could find a variety of applications such as; 3D-printed organic thermoelectric materials for plausible large-scale thermal energy harvesting applications, resistors for flexible circuitry, and piezoresistive sensors for strain sensing. Full article

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19 pages, 5291 KiB

Open AccessReview

Impact of Graphene or Reduced Graphene Oxide on Performance of Thermoelectric Composites

by Olena Okhay and Alexander Tkach

C 2021, 7(2), 37; https://doi.org/10.3390/c7020037 - 21 Apr 2021

Cited by 7 | Viewed by 4239

Abstract

In recent years, worldwide research has been focused on clean and sustainable energy sources that can respond to the exponentially rising energy demands of humankind. The harvesting of unused heat in relation to automotive exhaustion, industrial processes, and home heating is one possible [...] Read more.

In recent years, worldwide research has been focused on clean and sustainable energy sources that can respond to the exponentially rising energy demands of humankind. The harvesting of unused heat in relation to automotive exhaustion, industrial processes, and home heating is one possible way of enabling the transformation from a fossil fuel-based society to a low-carbon socioeconomic epoch. Thermoelectric (TE) generators can convert heat to electrical energy thanks to high-performance TE materials that work via Seebeck effects when electricity appears between the cold part and the hot part of these materials. High figure of merit (ZT) TE material is characterized by high electrical conductivity and Seebeck coefficient, together with low thermal conductivity. This article aims to summarize ZT values reported for chalcogenides, skutterudites, and metal oxides with graphene (G) or reduced graphene oxide (rGO), and intends to understand the relationship between the addition of G-rGO to composites and ZT variation. In a majority of the publications, ZT value increases with the addition of G/rGO, although the relative growth of ZT varies for different material families, as well as inside the same group of materials, with it often being related not to a G/rGO amount but with the quality of the composite. Full article

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16 pages, 6462 KiB

Open AccessArticle

Preparation of Pt/CNT Thin-Film Electrodes by Electrochemical Potential Pulse Deposition for Methanol Oxidation

by Jose Quintero-Ruiz, Ramiro Ruiz-Rosas, Javier Quílez-Bermejo, David Salinas-Torres, Diego Cazorla-Amorós and Emilia Morallón

C 2021, 7(2), 32; https://doi.org/10.3390/c7020032 - 26 Mar 2021

Cited by 7 | Viewed by 2933

Abstract

High-quality performance of catalysts is increasingly required to meet industry exigencies. However, chemical synthesis is often insufficient to maximize the potential properties of the catalysts. On the other hand, electrochemical synthesis has arisen as a promising alternative to overcome these limitations and provide [...] Read more.

High-quality performance of catalysts is increasingly required to meet industry exigencies. However, chemical synthesis is often insufficient to maximize the potential properties of the catalysts. On the other hand, electrochemical synthesis has arisen as a promising alternative to overcome these limitations and provide precise control in the preparation of catalysts. In this sense, this work involved the well-controlled electrochemical synthesis of a catalyst based on platinum nanoparticle deposition on carbon nanotubes using only electrochemical treatments. Thin films of functionalized carbon nanotubes were cast onto the surface of a glassy carbon electrode using potential pulsed electrodeposition, resulting in a better distribution of the carbon nanotubes on the electrode when comparing with traditional methods. Then, platinum nanoparticles were electrodeposited on the carbon nanotube-modified electrode. To check the performance of the catalyst and the relevance of the electrochemical synthesis treatments, the samples were analyzed as electrocatalysts towards methanol electrooxidation, showing an important improvement in the catalytic activity in comparison with electrodes that were prepared by traditional methodologies. Full article

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28 pages, 4895 KiB

Open AccessFeature PaperReview

sp² Carbon Stable Radicals

by Elena F. Sheka

C 2021, 7(2), 31; https://doi.org/10.3390/c7020031 - 26 Mar 2021

Cited by 7 | Viewed by 3842

Abstract

sp² Nanocarbons such as fullerenes, carbon nanotubes, and graphene molecules are not only open-shell species, but spatially extended, due to which their chemistry is quite specific. Cogently revealed dependence of the final products composition on size and shape of the carbons in [...] Read more.

sp² Nanocarbons such as fullerenes, carbon nanotubes, and graphene molecules are not only open-shell species, but spatially extended, due to which their chemistry is quite specific. Cogently revealed dependence of the final products composition on size and shape of the carbons in use as well as on the chemical prehistory is accumulated in a particular property—the stabilization of the species’ radical efficiency, thus providing the matter of stable radicals. If the feature is highly restricted and rarely available in ordinary chemistry, in the case of sp² nanocarbons it is just an ordinary event providing, say, tons-in-mass stable radicals when either producing such widely used technological products as carbon black or dealing with deposits of natural sp² carbons such as anthracite, shungite carbon, and other. Suggested in the paper is the consideration of stable radicals of sp² nanocarbons from the standpoint of spin-delocalized topochemistry. Characterized in terms of the total and atomically partitioned number of effectively unpaired electrons as well as of the distribution of the latter over carbon atoms and described by selectively determined barriers of different reactions exhibiting topological essence of intermolecular interaction, sp² nanocarbons reveal a peculiar topokinetics that lays the foundation of the stability of their radical properties. Full article

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10 pages, 7496 KiB

Open AccessArticle

Impact of Nitrogen, Boron and Phosphorus Impurities on the Electronic Structure of Diamond Probed by X-ray Spectroscopies

by Sneha Choudhury, Ronny Golnak, Christian Schulz, Klaus Lieutenant, Nicolas Tranchant, Jean-Charles Arnault, Marie-Amandine Pinault-Thaury, François Jomard, Peter Knittel and Tristan Petit

C 2021, 7(1), 28; https://doi.org/10.3390/c7010028 - 09 Mar 2021

Cited by 3 | Viewed by 3701

Abstract

Doping diamond with boron, nitrogen or phosphorus enables a fine tuning of its electronic properties, which is particularly relevant for applications involving electron emission. However, the chemical nature of the doping sites and its correlation with electron emission properties remain to be clarified. [...] Read more.

Doping diamond with boron, nitrogen or phosphorus enables a fine tuning of its electronic properties, which is particularly relevant for applications involving electron emission. However, the chemical nature of the doping sites and its correlation with electron emission properties remain to be clarified. In this work, we applied soft X-ray spectroscopy techniques to probe occupied and unoccupied electronic states in undoped, boron-, phosphorus- and nitrogen-containing single crystal diamonds. X-ray absorption, X-ray emission and X-ray photoemission spectroscopies, performed at the carbon K-edge, provide a full picture of new electronic states created by impurities in diamond. The different probing depths of fluorescence- and electron-based detection techniques enable a comparison between surface and bulk contributions. Full article

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21 pages, 23265 KiB

Open AccessArticle

Stabilization and Carbonization of PAN Nanofiber Mats Electrospun on Metal Substrates

by Jan Lukas Storck, Bennet Brockhagen, Timo Grothe, Lilia Sabantina, Bernhard Kaltschmidt, Khorolsuren Tuvshinbayar, Laura Braun, Ewin Tanzli, Andreas Hütten and Andrea Ehrmann

C 2021, 7(1), 12; https://doi.org/10.3390/c7010012 - 27 Jan 2021

Cited by 11 | Viewed by 4262

Abstract

Polyacrylonitrile (PAN) nanofiber mats are typical precursors for carbon nanofibers. They can be fixed or even elongated during stabilization and subsequent carbonization to gain straight, mechanically robust carbon nanofibers. These processes necessitate additional equipment or are—if the nanofiber mats are just fixed at [...] Read more.

Polyacrylonitrile (PAN) nanofiber mats are typical precursors for carbon nanofibers. They can be fixed or even elongated during stabilization and subsequent carbonization to gain straight, mechanically robust carbon nanofibers. These processes necessitate additional equipment or are—if the nanofiber mats are just fixed at the edges—prone to resulting in the specimens breaking, due to an uneven force distribution. Hence, we showed in a previous study that electrospinning PAN on aluminum foils and stabilizing them fixed on these substrates, is a suitable solution to keep the desired morphology after stabilization and incipient carbonization. Here, we report on the influence of different metallic and semiconductor substrates on the physical and chemical properties of the nanofiber mats after stabilization and carbonization at temperatures up to 1200 °C. For stabilization on a metal substrate, an optimum stabilization temperature of slightly above 240 °C was found, approached with a heating rate of 0.25 K/min. Independent from the substrate material, SEM images revealed less defect fibers in the nanofiber mats stabilized and incipiently carbonized on a metal foil. Finally, high-temperature carbonization on different substrates is shown to allow for producing metal/carbon nano-composites. Full article

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8 pages, 1614 KiB

Open AccessArticle

Surface Charge Effects on Adsorption of Solutes by Poplar and Elm Biochars

by Steven C. Peterson, Sanghoon Kim and Jason Adkins

C 2021, 7(1), 11; https://doi.org/10.3390/c7010011 - 26 Jan 2021

Cited by 4 | Viewed by 2143

Abstract

Elm and poplar are two tree species that can provide a large amount of low-value feedstock for biochar production due to their rapid growth rate (poplar), and susceptibility to disease and/or infestation (both elm and poplar). Biochar has been studied recently as filtration [...] Read more.

Elm and poplar are two tree species that can provide a large amount of low-value feedstock for biochar production due to their rapid growth rate (poplar), and susceptibility to disease and/or infestation (both elm and poplar). Biochar has been studied recently as filtration medium for water purification, as it provides a renewable alternative to activated carbon. In this work, the adsorption efficiency of biochars made from elm and poplar as a function of pyrolysis temperature were studied by ultraviolet (UV) adsorption of dyes with positive, neutral, and negative charges to determine what factors had the greatest effect on adsorption of these dyes. It was found that conductivity of the biochars increased with pyrolysis temperature, and that this factor was more important than surface area in terms of adsorbing charged dyes. Both elm and poplar biochars were not effective in adsorbing neutral dyes. This research demonstrates that elm and poplar biochars adsorb charged (either positively or negatively) solutes more efficiently than uncharged ones because they carry both charges themselves. Therefore, these biochars would make excellent candidates as renewable filtration media for charged contaminants. Full article

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12 pages, 2734 KiB

Open AccessArticle

Asymmetric Supercapacitors: Optical and Thermal Effects When Active Carbon Electrodes Are Embedded with Nano-Scale Semiconductor Dots

by Haim Grebel

C 2021, 7(1), 7; https://doi.org/10.3390/c7010007 - 15 Jan 2021

Cited by 5 | Viewed by 2124

Abstract

Optical and thermal effects in asymmetric supercapacitors, whose active-carbon (AC) electrodes were embedded with nano-Si (n-Si) quantum dots (QD), are reported. We describe two structures: (1) p-n-like, obtained by using a polyethylimine (PEI) binder for the “n” electrode and a polyvinylpyrrolidone (PVP) binder [...] Read more.

Optical and thermal effects in asymmetric supercapacitors, whose active-carbon (AC) electrodes were embedded with nano-Si (n-Si) quantum dots (QD), are reported. We describe two structures: (1) p-n-like, obtained by using a polyethylimine (PEI) binder for the “n” electrode and a polyvinylpyrrolidone (PVP) binder for the “p” electrode; (2) a single component binder—poly(methyl methacrylate) (PMMA). In general, AC appears black to the naked eye and one may assume that it indiscriminately absorbs all light spectra. However, on top of a flat lossy spectrum, AC (from two manufacturers) exhibited two distinct absorption bands: one in the blue (~400 nm) and the other one in the near IR (~840 nm). The n-Si material accentuated the absorption in the blue and bleached the IR absorption. Both bands contributed to capacitance increase: (a) when using aqueous solution and a PMMA binder, the optical-related increased capacitance was 20% for low n-Si concentration and more than 100% for a high-concentration dose; (b) when using ion liquid (IL) electrolyte, the large, thermal capacitance increase (of ca. 40%) was comparable to the optical effect (of ca. 42%) and hence was assigned as an optically induced thermal effect. The experimental data point to an optically induced capacitance increase even in the absence of the n-Si dots. Overall, the experimental data suggest intriguing possibilities for optically controlled supercapacitors. Full article

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13 pages, 3041 KiB

Open AccessArticle

First-Principles Study of the Electronic Properties and Thermal Expansivity of a Hybrid 2D Carbon and Boron Nitride Material

by Okikiola Olaniyan and Lyudmila V. Moskaleva

C 2021, 7(1), 5; https://doi.org/10.3390/c7010005 - 12 Jan 2021

Viewed by 2583

Abstract

In an attempt to push the boundary of miniaturization, there has been a rising interest in two-dimensional (2D) semiconductors with superior electronic, mechanical, and thermal properties as alternatives for silicon-based devices. Due to their fascinating properties resulting from lowering dimensionality, hexagonal boron nitride [...] Read more.

In an attempt to push the boundary of miniaturization, there has been a rising interest in two-dimensional (2D) semiconductors with superior electronic, mechanical, and thermal properties as alternatives for silicon-based devices. Due to their fascinating properties resulting from lowering dimensionality, hexagonal boron nitride (h-BN) and graphene are considered promising candidates to be used in the next generation of high-performance devices. However, neither h-BN nor graphene is a semiconductor due to a zero bandgap in the one case and a too large bandgap in the other case. Here, we demonstrate from first-principles calculations that a hybrid 2D material formed by cross-linking alternating chains of carbon and boron nitride (HCBN) shows promising characteristics combining the thermal merits of graphene and h-BN while possessing the electronic structure characteristic of a semiconductor. Our calculations demonstrate that the thermal properties of HCBN are comparable to those of h-BN and graphene (parent systems). HCBN is dynamically stable and has a bandgap of 2.43 eV. At low temperatures, it exhibits smaller thermal contraction than the parent systems. However, beyond room temperature, in contrast to the parent systems, it has a positive but finitely small linear-thermal expansion coefficient. The calculated isothermal bulk modulus indicates that at high temperatures, HCBN is less compressible, whereas at low temperatures it is more compressible relative to the parent systems. The results of our study are important for the rational design of a 2D semiconductor with good thermal properties. Full article

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2020

Jump to: 2022, 2021

83 pages, 8766 KiB

Open AccessReview

Nanostructured Graphene Oxide-Based Hybrids as Anodes for Lithium-Ion Batteries

by Poonam Sehrawat, Abid Abid, Saikh S. Islam, Alain Mauger and Christian M. Julien

C 2020, 6(4), 81; https://doi.org/10.3390/c6040081 - 16 Dec 2020

Cited by 12 | Viewed by 5518

Abstract

Presently, the negative electrodes of lithium-ion batteries (LIBs) are constituted by carbon-based materials, which exhibit a limited specific capacity 372 mAh g⁻¹ associated with the cycle in the composition between C and LiC₆. Therefore, many efforts are currently made towards [...] Read more.

Presently, the negative electrodes of lithium-ion batteries (LIBs) are constituted by carbon-based materials, which exhibit a limited specific capacity 372 mAh g⁻¹ associated with the cycle in the composition between C and LiC₆. Therefore, many efforts are currently made towards the technological development of nanostructured graphene materials because of their extraordinary mechanical, electrical, and electrochemical properties. Recent progress on advanced hybrids based on graphene oxide (GO) and reduced graphene oxide (rGO) has demonstrated the synergistic effects between graphene and an electroactive material (silicon, germanium, metal oxides (MO_x)) as electrode for electrochemical devices. In this review, attention is focused on advanced materials based on GO and rGO and their composites used as anode materials for lithium-ion batteries. Full article

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32 pages, 8356 KiB

Open AccessFeature PaperArticle

A Study on the Effect of Carbon Nanotubes’ Distribution and Agglomeration in the Free Vibration of Nanocomposite Plates

by D. S. Craveiro and M. A. R. Loja

C 2020, 6(4), 79; https://doi.org/10.3390/c6040079 - 30 Nov 2020

Cited by 7 | Viewed by 3060

Abstract

The present work aimed to characterize the free vibrations’ behaviour of nanocomposite plates obtained by incorporating graded distributions of carbon nanotubes (CNTs) in a polymeric matrix, considering the carbon nanotubes’ agglomeration effect. This effect is known to degrade material properties, therefore being important [...] Read more.

The present work aimed to characterize the free vibrations’ behaviour of nanocomposite plates obtained by incorporating graded distributions of carbon nanotubes (CNTs) in a polymeric matrix, considering the carbon nanotubes’ agglomeration effect. This effect is known to degrade material properties, therefore being important to predict the consequences it may bring to structures’ mechanical performance. To this purpose, the elastic properties’ estimation is performed according to the two-parameter agglomeration model based on the Eshelby–Mori–Tanaka approach for randomly dispersed nano-inclusions. This approach is implemented in association with the finite element method to determine the natural frequencies and corresponding mode shapes. Three main agglomeration cases were considered, namely, agglomeration absence, complete agglomeration, and partial agglomeration. The results show that the agglomeration effect has a negative impact on the natural frequencies of the plates, regardless the CNTs’ distribution considered. For the corresponding vibrations’ mode shapes, the agglomeration effect was shown in most cases not to have a significant impact, except for two of the cases studied: for a square plate and a rectangular plate with symmetrical and unsymmetrical CNTs’ distribution, respectively. Globally, the results confirm that not accounting for the nanotubes’ agglomeration effect may lead to less accurate elastic properties and less structures’ performance predictions. Full article

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18 pages, 3246 KiB

Open AccessArticle

Nitrate Catalytic Reduction over Bimetallic Catalysts: Catalyst Optimization

by A. Sofia G. G. Santos, João Restivo, Carla A. Orge, M. Fernando R. Pereira and O. Salomé G. P. Soares

C 2020, 6(4), 78; https://doi.org/10.3390/c6040078 - 28 Nov 2020

Cited by 14 | Viewed by 3540

Abstract

The catalytic removal of nitrate (NO₃⁻) in water using hydrogen as a reducing agent was studied using palladium-copper bimetallic catalysts in different supports. Commercial carbon nanotubes (CNTs), used as received and with different mechanical (CNT (BM 2h)) and chemical modifications [...] Read more.

The catalytic removal of nitrate (NO₃⁻) in water using hydrogen as a reducing agent was studied using palladium-copper bimetallic catalysts in different supports. Commercial carbon nanotubes (CNTs), used as received and with different mechanical (CNT (BM 2h)) and chemical modifications (CNT (BM 4h)-N), titanium dioxide (TiO₂) and composite materials (TiO₂-CNT) were considered as main supports for the metallic phase. Different metal loadings were studied to synthesize an optimized catalyst with high NO₃⁻ conversion rate and considerable selectivity for N₂ formation. Among all the studied support materials, the milled carbon nanotubes (sample CNT (BM 2h) was the support that showed the most promising results using 1%Pd-1%Cu as metallic phases. The most active catalysts were 2.5%Pd-2.5%Cu and 5%Pd-2.5%Cu supported on CNT (BM 2h), achieving total conversion after a 120 min reaction with N₂ selectivity values of 62% and 60%, respectively. Reutilization experiments allowed us to conclude that these catalysts were stable during several reactions, in terms of NO₃⁻ conversion rate. However, the consecutive reuse of the catalyst leads to major changes concerning NH₄⁺ selectivity values. Full article

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6 pages, 1550 KiB

Open AccessCommunication

Bacteria Supported on Carbon-Coated Monoliths for Water Denitrification

by David Espinosa-Iglesias, Esther Bailón-García, Mª Isidora Bautista-Toledo, Francisco Carrasco-Marín and Agustín F. Pérez-Cadenas

C 2020, 6(4), 77; https://doi.org/10.3390/c6040077 - 24 Nov 2020

Viewed by 2379

Abstract

Escherichia coli bacteria were grown inside the channels of cordierite monoliths previously coated with a very good adhered carbon layer. These monolithic structures were tested at room temperature for the nitrate elimination of water solutions working as a batch monolithic bioreactor and showed [...] Read more.

Escherichia coli bacteria were grown inside the channels of cordierite monoliths previously coated with a very good adhered carbon layer. These monolithic structures were tested at room temperature for the nitrate elimination of water solutions working as a batch monolithic bioreactor and showed very good results, as 100% of the nitrates and nitrites were completely removed in the used experimental conditions. Different rate flows of bacteria growth and nitrate elimination were studied, showing that the higher the flow velocity, the faster the nitrate elimination. Finally, the reproducibility tests confirmed the good performance of the proposed bioreactor. Full article

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14 pages, 3027 KiB

Open AccessArticle

New Insights into H₂S Adsorption on Graphene and Graphene-Like Structures: A Comparative DFT Study

by Azam Salmankhani, Zohre Karami, Amin Hamed Mashhadzadeh, Mohammad Reza Ganjali, Vahid Vatanpour, Amin Esmaeili, Sajjad Habibzadeh, Mohammad Reza Saeb, Vanessa Fierro and Alain Celzard

C 2020, 6(4), 74; https://doi.org/10.3390/c6040074 - 09 Nov 2020

Cited by 14 | Viewed by 4084

Abstract

The efficient removal of pollutants from different environments has been one of the great challenges for scientists in recent years. However, the understanding of the mechanisms underlying this phenomenon is still the subject of passionate debates, mainly due to the lack of experimental [...] Read more.

The efficient removal of pollutants from different environments has been one of the great challenges for scientists in recent years. However, the understanding of the mechanisms underlying this phenomenon is still the subject of passionate debates, mainly due to the lack of experimental tools capable of detecting events at the atomic scale. Herein, a comparative theoretical study was carried out to capture the adsorption of H₂S on metal oxide surfaces such as zinc oxide (ZnO) and beryllium oxide (BeO), as well as graphene and Ni-decorated graphene. A simulation based on density-functional theory (DFT) was carried out by adopting General Gradient Approximation (GGA) under the Perdew–Burke–Ernzerhof (PBE) function. The calculations quantified H₂S adsorption on the considered metal oxide sheets as well as on the non-decorated graphene having a physical nature. In contrast, H₂S adsorbed on Ni-decorated graphene sheet gave an adsorption energy of −1.64 eV due to the interaction of S and Ni atoms through the formation of a covalent bond, proof of chemisorption. It seems that the graphene sheet decorated with Ni atoms is a more suitable adsorbent for H₂S molecules than BeO, ZnO, or non-decorated graphene, providing a theoretical basis for future studies. Full article

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12 pages, 3127 KiB

Open AccessArticle

Carbon Nanodots Synthesized from Dunaliella salina as Sun Protection Filters

by Theodoros G. Chatzimitakos, Athanasia Kasouni, Anastassios Troganis, Ioannis Leonardos, Ioannis Tzovenis, Alexandros Ntzouvaras and Constantine Stalikas

C 2020, 6(4), 69; https://doi.org/10.3390/c6040069 - 30 Oct 2020

Cited by 5 | Viewed by 3292

Abstract

Carbon nanodots (CNDs) are more and more being exploited for various applications including biological ones. To this end, they have been thoroughly studied for their potential as antibacterial, wound healing, and bioimaging agents. In this study, we examined the sun protection properties of [...] Read more.

Carbon nanodots (CNDs) are more and more being exploited for various applications including biological ones. To this end, they have been thoroughly studied for their potential as antibacterial, wound healing, and bioimaging agents. In this study, we examined the sun protection properties of CNDs. Dunaliella salina was selected as a promising precursor for the synthesis of CNDs which were compared with those produced by citric acid, a widely used precursor for such materials. The CNDs were examined spectrophotometrically, and the sun protection factors were calculated. Additionally, in vitro experiments were carried out to evaluate their UV protection properties and to obtain better insight into whether CNDs are suitable to be used as filters for the development of new sunscreens. The results were conclusive that both CNDs possess favorable properties that potentiate their use for the development of sunscreens. However, the CNDs from Dunaliella salina were found to be superior to those derived from citric acid. Therefore, they can further be exploited as sun protection filters. Full article

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14 pages, 2737 KiB

Open AccessFeature PaperArticle

Electrochemical Aspects of a Nitrogen-Doped Pseudo-Graphitic Carbon Material: Resistance to Electrode Fouling by Air-Aging and Dopamine Electro-Oxidation

by Kailash Hamal, Jeremy May, Haoyu Zhu, Forrest Dalbec, Elena Echeverria, David N. McIlroy, Eric Aston and I. Francis Cheng

C 2020, 6(4), 68; https://doi.org/10.3390/c6040068 - 27 Oct 2020

Cited by 5 | Viewed by 2902

Abstract

The nitrogen-doped form of GUITAR (pseudo-Graphite from the University of Idaho Thermalized Asphalt Reaction) was examined by X-ray photoelectron, Raman, and X-ray diffraction spectroscopies and cyclic voltammetry (CV). Electrochemical studies indicate that N-GUITAR exhibits significant resistance to fouling by adsorption and by passivation. [...] Read more.

The nitrogen-doped form of GUITAR (pseudo-Graphite from the University of Idaho Thermalized Asphalt Reaction) was examined by X-ray photoelectron, Raman, and X-ray diffraction spectroscopies and cyclic voltammetry (CV). Electrochemical studies indicate that N-GUITAR exhibits significant resistance to fouling by adsorption and by passivation. Unlike other carbon materials, it maintains fast heterogenous electron transfer (HET) kinetics with Fe(CN)₆^3−/4− with exposure to air. The CV peak potential separation (ΔEp) of 66 mV increased to 69 mV in 3 h vs. 67 to 221 mV for a highly oriented pyrolytic graphite (HOPG) electrode. Water contact angle measurements indicate that N-GUITAR was able to better maintain a hydrophilic state during the 3-h exposure, going from 55.8 to 70.4° while HOPG increased from 63.8 to 80.1°. This indicates that N-GUITAR better resisted adsorption of volatile organic compounds. CV studies of dopamine also indicate N-GUITAR is resistant to passivation. The ΔEp for the dopamine/o-dopaminoquinone couple is 83 mV indicating fast HET rates. This is reflected in the peak current ratios for the oxidation and reduction processes of 1.3 indicating that o-dopaminoquinone is not lost to passivation processes. This ratio along with the minimal signal attenuation is the best reported in literature. Full article

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11 pages, 1718 KiB

Open AccessReview

Mechanisms of Carbon Nanotubes and Graphene Growth: Kinetics versus Thermodynamics

by Luís Sousa Lobo and Sónia A. C. Carabineiro

C 2020, 6(4), 67; https://doi.org/10.3390/c6040067 - 27 Oct 2020

Cited by 3 | Viewed by 2764

Abstract

Thermodynamics must be favorable for the growth of carbon nanotubes (CNTs) and graphene to take place, but a kinetic study is required to find the operating mechanism. In fact, thermodynamics indicates whether a reaction is possible; however, the route prevailing is not necessarily [...] Read more.

Thermodynamics must be favorable for the growth of carbon nanotubes (CNTs) and graphene to take place, but a kinetic study is required to find the operating mechanism. In fact, thermodynamics indicates whether a reaction is possible; however, the route prevailing is not necessarily the most thermodynamically favorable, but the fastest one. Detailed kinetic studies state that there are three alternative routes operating under different temperature and pressure rates. The modes and rates of diffusion of carbon (C) atoms and noble metals have been known since the 1930s, but proof of C bulk diffusion operating in CNT growth came from detailed kinetic studies performed in the early 1970s, when reversible versus irreversible C formation was discussed with examples. The reason for interstitial C bulk diffusion in transition metals is evidenced based on the values of covalent radius. The reason for operating under steady-state conditions (linearity of the weight versus time) when searching for the operating mechanism is discussed herein. The steady-state C formation process operates sometimes with two different solid phases at each side of the catalyst particle (e.g., Ni and Ni₃C), with thicknesses proportional to 1/D of the respective C bulk diffusivities when the carbon bulk diffusion step is the rate-determining one. Full article

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20 pages, 7686 KiB

Open AccessArticle

Characterization of Molecular Spacer-Functionalized Nanostructured Carbons for Electrical Energy Storage Supercapacitor Materials

by Justin Zuczek, Matthew Bonfield, Nesreen Elathram, William R. Hixson, Terawit Kongruengkit, James B. Mitchell, Nickolas Zelenka, Leonid D. Popov, Andrey Morozov, Igor N. Shcherbakov and Jordan C. Poler

C 2020, 6(4), 66; https://doi.org/10.3390/c6040066 - 23 Oct 2020

Viewed by 2701

Abstract

The use of molecular spacers between Carbon Nanotubes (CNTs) has been shown to increase the ion-accessible surface area for use in supercapacitor materials. Maintaining porosity and electrical conductivity is important for maximizing capacitance, energy storage, and power. Two reported novel coordination complexes have [...] Read more.

The use of molecular spacers between Carbon Nanotubes (CNTs) has been shown to increase the ion-accessible surface area for use in supercapacitor materials. Maintaining porosity and electrical conductivity is important for maximizing capacitance, energy storage, and power. Two reported novel coordination complexes have shown exceptional Faradaic charge transfer and binding capabilities to prevent CNT aggregation. Dispersion stability measurements show less aggregation of HiPco Single Walled CNTs (SWCNTs) compared to other chirality and multilayered nanotubes. Cu2FcOH binds weakly to CNTs compared +2Zn2 and +2Ru2 due to Columbic electrostatic interactions, which is favorable because it does not collapse the electrical double layer as strongly as +2Zn2 or +2Ru2. Adsorption isotherms and a full characterization (¹H NMR, ATR FT-IR, UV-Vis, CV) of these novel complexes are presented. Electrical characterization using CV, charge discharge, and electrochemical impedance spectroscopy and the supercapacitor performance of functionalized thin film electrodes are presented as a function of spacer properties and nanostructured carbon tube diameter. This study uses rigid, earth-abundant coordination complexes that bind to and intercalate between SWCNTs. These functionalized nanostructured carbons are then used to make electrodes for electrical double layer supercapacitors. A complete description of the synthesis, characterization, and processing of these materials is described. Full article

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19 pages, 3504 KiB

Open AccessArticle

Improving the Activity of Fe/C/N ORR Electrocatalyst Using Double Ammonia Promoted CO₂ Laser Pyrolysis

by Henri Perez, Mathieu Frégnaux, Emeline Charon, Arnaud Etcheberry and Olivier Sublemontier

C 2020, 6(4), 63; https://doi.org/10.3390/c6040063 - 14 Oct 2020

Viewed by 2655

Abstract

Recently, we reported the use of CO₂ laser pyrolysis for the synthesis of promising Fe/C/N electrocatalysts for Oxygen Reduction Reaction (ORR) in fuel cells. The set-up used single laser pyrolysis of an aerosolized solution of iron acetylacetonate in toluene with ammonia, both [...] Read more.

Recently, we reported the use of CO₂ laser pyrolysis for the synthesis of promising Fe/C/N electrocatalysts for Oxygen Reduction Reaction (ORR) in fuel cells. The set-up used single laser pyrolysis of an aerosolized solution of iron acetylacetonate in toluene with ammonia, both as laser energy transfer agent and nitrogen source. In the present paper, we investigate the effect of a second ammonia promoted CO₂ laser pyrolysis on the feature and ORR activity of Fe/C/N electrocatalysts. Indeed, compared to single pyrolysis, the second ammonia promoted CO₂ laser pyrolysis could be an interesting way to synthesize in one-step performing ORR electrocatalysts on a large scale. For this comparison, a two-stage reactor was built, allowing both single ammonia-induced CO₂ laser pyrolysis as reported previously or double ammonia-induced CO₂ laser pyrolysis. In the latter configuration, the catalyst nanopowder flow is formed at the first stage of the reactor, then mixed with a second ammonia flow and allowed to cross a second CO₂ laser beam, thus undergoing a second ammonia-induced CO₂ laser pyrolysis before being collected on filters. It is found that the second ammonia-induced CO₂ laser pyrolysis significantly improves the ORR performances of the materials prepared by single CO₂ laser pyrolysis. The effect is demonstrated for three different catalysts for which the onset potentials for the ORR from single-stage to double-stage configuration increase from 625 mV to 845 mV, 790 mV to 860 mV, and 800 mV to 885 mV, respectively. The selectivity of the ORR was determined at 600 mV/SHE and lie between 3.41 and 3.72. These promising performances suggesting potentialities for the one-step formation of highly active Fe/C/N ORR electrocatalysts are discussed, based on results of surface analysis by XPS, specific surface area measurements, and Raman spectroscopy. Full article

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18 pages, 3613 KiB

Open AccessArticle

Facile Method to Prepare pH-Sensitive PEI-Functionalized Carbon Nanotubes as Rationally Designed Vehicles for Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) Delivery

by Vassilis Tangoulis, Nikolia Lalioti, John Parthenios, Nathan Langford, Eugenia Valsami-Jones, Chrisoula Kakoulidou, George Psomas and Vlasoula Bekiari

C 2020, 6(4), 62; https://doi.org/10.3390/c6040062 - 07 Oct 2020

Cited by 4 | Viewed by 2483

Abstract

A new pH-sensitive system designed for drug-delivery purposes and based on functionalized multiwall magnetic carbon nanotubes (Mag-CNTs) was synthesized for the effective incorporation of non-steroidal anti-inflammatory drugs (NSAIDs), aiming at drug release in characteristic acidic conditions close to the actual conditions of inflamed [...] Read more.

A new pH-sensitive system designed for drug-delivery purposes and based on functionalized multiwall magnetic carbon nanotubes (Mag-CNTs) was synthesized for the effective incorporation of non-steroidal anti-inflammatory drugs (NSAIDs), aiming at drug release in characteristic acidic conditions close to the actual conditions of inflamed tissues. Cationic hyperbranched polyethyleneimine (PEI) was immobilized on the surface of Mag-CNTs via electrostatic interactions between the positively charged protonated amines within the polymer and the carboxyl groups on the chemically oxidized Mag-CNT surface. The addition of the NSAID with a carboxylate donor, Naproxen (NAP), was achieved by indirect coupling through the amino groups of the intermediate linker PEI. FT-IR, Raman, and UV–vis spectroscopy were employed to fully characterize the synthesized nanocarrier and its functionalization procedure. The interaction of the designed nanocarrier with bovine serum albumin (BSA) was studied in vitro by fluorescence emission spectroscopy while its in vitro interaction with calf-thymus (CT) DNA was monitored by UV–vis spectroscopy and viscosity measurements and via competitive studies with ethidium bromide. The calculated binding constants were compared to those of free NAP revealing a higher binding affinity for BSA and CT DNA. Finally, drug-release studies were performed, revealing that the electrostatic linkage ensures an effective release of the drug in the acidic pH typical of inflamed cells, while maintaining the multiwall nanotubes (MWNTs)–drug conjugates stable at the typical bloodstream. Full article

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12 pages, 3672 KiB

Open AccessArticle

Hypergolic Materials Synthesis through Reaction of Fuming Nitric Acid with Certain Cyclopentadienyl Compounds

by Nikolaos Chalmpes, Athanasios B. Bourlinos, Veronika Šedajová, Vojtěch Kupka, Dimitrios Moschovas, Apostolos Avgeropoulos, Michael A. Karakassides and Dimitrios Gournis

C 2020, 6(4), 61; https://doi.org/10.3390/c6040061 - 05 Oct 2020

Cited by 9 | Viewed by 3429

Abstract

Recently we have shown the importance of hypergolic reactions in carbon materials synthesis. However, hypergolic reactions could be certainly expanded beyond carbon synthesis, offering a general preparative pathway towards a larger variety of materials. Cyclopentadienyls are one of the most common ligands in [...] Read more.

Recently we have shown the importance of hypergolic reactions in carbon materials synthesis. However, hypergolic reactions could be certainly expanded beyond carbon synthesis, offering a general preparative pathway towards a larger variety of materials. Cyclopentadienyls are one of the most common ligands in organometallic chemistry that react hypergolicly on contact with strong oxidizers. By also considering the plethora of cyclopentadienyl compounds existing today, herein we demonstrate the potential of such compounds in hypergolic materials synthesis in general (carbon or inorganic). In a first example, we show that cyclopentadienyllithium reacts hypergolicly with fuming nitric acid to produce carbon. In a second one, we show that ferrocene and cobaltocene also react hypergolicly with the concentrated acid to afford magnetic inorganic materials, such as γ-Fe₂O₃ and metallic Co, respectively. The present results further emphasize the importance and universal character of hypergolic reactions in materials science synthesis, as an interesting new alternative to other existing and well-established preparative methods. Full article

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14 pages, 6191 KiB

Open AccessReview

Tetrel Bonding Interactions Involving Carbon at Work: Recent Advances in Crystal Engineering and Catalysis

by Antonio Frontera

C 2020, 6(4), 60; https://doi.org/10.3390/c6040060 - 25 Sep 2020

Cited by 24 | Viewed by 3577

Abstract

The σ- and π-hole interactions are used to define attractive forces involving elements of groups 12–18 of the periodic table acting as Lewis acids and any electron rich site (Lewis base, anion, and π-system). When the electrophilic atom belongs to group 14, the [...] Read more.

The σ- and π-hole interactions are used to define attractive forces involving elements of groups 12–18 of the periodic table acting as Lewis acids and any electron rich site (Lewis base, anion, and π-system). When the electrophilic atom belongs to group 14, the resulting interaction is termed a tetrel bond. In the first part of this feature paper, tetrel bonds formed in crystalline solids involving sp³-hybridized carbon atom are described and discussed by using selected structures retrieved from the Cambridge Structural Database. The interaction is characterized by a strong directionality (close to linearity) due to the small size of the σ-hole in the C-atom opposite the covalently bonded electron withdrawing group. The second part describes the utilization of two allotropic forms of carbon (C₆₀ and carbon nanotubes) as supramolecular catalysts based on anion–π interactions (π-hole tetrel bonding). This part emphasizes that the π-hole, which is considerably more accessible by nucleophiles than the σ-hole, can be conveniently used in supramolecular catalysis. Full article

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13 pages, 2137 KiB

Open AccessArticle

Heterogeneous Organo- and Metal Catalysis Using Phosphine Oxide Derivatives Anchored on Multiwalled Carbon Nanotubes

by Maria Cristina Ligi, Anna Flis, Giacomo Biagiotti, Giulia Serrano, K. Michał Pietrusiewicz and Stefano Cicchi

C 2020, 6(3), 57; https://doi.org/10.3390/c6030057 - 21 Sep 2020

Cited by 1 | Viewed by 2682

Abstract

Oxidized multiwalled carbon nanotubes were modified anchoring phosphine oxides and used as heterogeneous catalysts. A proper substitution of the phosphine oxides allowed the use of the Tour reaction and the nitrene cycloaddition to obtain functionalized carbon nanotubes (CNT) with a loading up to [...] Read more.

Oxidized multiwalled carbon nanotubes were modified anchoring phosphine oxides and used as heterogeneous catalysts. A proper substitution of the phosphine oxides allowed the use of the Tour reaction and the nitrene cycloaddition to obtain functionalized carbon nanotubes (CNT) with a loading up to 0.73 mmol/g of material. The catalysts proved efficient in Wittig reactions, Mitsunobu reactions, and Staudinger ligations. Furthermore, the phosphorus decorated CNT were used to produce nanocomposite with Pd nanoparticles able to catalyze Heck reactions. Full article

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18 pages, 2507 KiB

Open AccessArticle

Nitrogen Doped Superactivated Carbons Prepared at Mild Conditions as Electrodes for Supercapacitors in Organic Electrolyte

by María José Mostazo-López, Ramiro Ruiz-Rosas, Tomomi Tagaya, Yoshikiyo Hatakeyama, Soshi Shiraishi, Emilia Morallón and Diego Cazorla-Amorós

C 2020, 6(3), 56; https://doi.org/10.3390/c6030056 - 20 Sep 2020

Cited by 6 | Viewed by 2622

Abstract

Nitrogen functionalization of a highly microporous activated carbon (S_BET > 3000 m²/g), to be used as electrode of electric double layer capacitor (EDLC), was carried out by different methods based on organic chemistry protocols at low temperature and selective thermal [...] Read more.

Nitrogen functionalization of a highly microporous activated carbon (S_BET > 3000 m²/g), to be used as electrode of electric double layer capacitor (EDLC), was carried out by different methods based on organic chemistry protocols at low temperature and selective thermal post-treatments under inert atmosphere. The combination of both methods allowed the production of carbon materials with very similar surface area (2400–3000 m²/g) and different surface chemistry. The nitrogen functionalization by chemical methods produce the attachment of 4 at. % N (XPS) by consumption of oxygen functional groups. The thermal treatments rearrange the surface chemistry by decreasing and converting both nitrogen and oxygen moieties. The effect of surface chemistry on the performance of these materials as electrodes for symmetric supercapacitors was analyzed in organic electrolyte (1M TEMABF₄/propylene carbonate). The devices showed high gravimetric capacitance (37–40 F/g) and gravimetric energy density (31–37 Wh/kg). The electrochemical stability of the EDLC was evaluated by a floating test under severe conditions of voltage and temperature. The results evidence an improvement of the durability of nitrogen-doped activated carbons modified by chemical treatments due to the decrease of detrimental oxygen functionalities and the generation of nitrogen groups with higher electrochemical stability. Full article

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