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C, Volume 2, Issue 3 (September 2016) – 6 articles

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8446 KiB

Open AccessArticle

Flexible Carbon Aerogels

by Marina Schwan and Lorenz Ratke

C 2016, 2(3), 22; https://doi.org/10.3390/c2030022 - 6 Sep 2016

Cited by 9 | Viewed by 7573

Abstract

Carbon aerogels are highly porous materials with a large inner surface area. Due to their high electrical conductivity they are excellent electrode materials in supercapacitors. Their brittleness, however, imposes certain limitations in terms of applicability. In that context, novel carbon aerogels with varying degree of flexibility have been developed. These highly porous, light aerogels are characterized by a high surface area and possess pore structures in the micrometer range, allowing for a reversible deformation of the aerogel network. A high ratio of pore size to particle size was found to be crucial for high flexibility. For dynamic microstructural analysis, compression tests were performed in-situ within a scanning electron microscope allowing us to directly visualize the microstructural flexibility of an aerogel. The flexible carbon aerogels were found to withstand between 15% and 30% of uniaxial compression in a reversible fashion. These findings might stimulate further research and new application fields directed towards flexible supercapacitors and batteries. Full article

(This article belongs to the Special Issue Graphene Aerogels)

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2072 KiB

Open AccessArticle

Synergetic Hybrid Aerogels of Vanadia and Graphene as Electrode Materials of Supercapacitors

by Xuewei Fu, Yuming Chen, Yu Zhu and Sadhan C. Jana

C 2016, 2(3), 21; https://doi.org/10.3390/c2030021 - 4 Aug 2016

Cited by 2 | Viewed by 5949

Abstract

The performance of synergetic hybrid aerogel materials of vanadia and graphene as electrode materials in supercapacitors was evaluated. The hybrid materials were synthesized by two methods. In Method I, premade graphene oxide (GO) hydrogel was first chemically reduced by L-ascorbic acid and then soaked in vanadium triisopropoxide solution to obtain V₂O₅ gel in the pores of the reduced graphene oxide (rGO) hydrogel. The gel was supercritically dried to obtain the hybrid aerogel. In Method II, vanadium triisopropoxide was hydrolyzed from a solution in water with GO particles uniformly dispersed to obtain the hybrid gel. The hybrid aerogel was obtained by supercritical drying of the gel followed by thermal reduction of GO. The electrode materials were prepared by mixing 80 wt % hybrid aerogel with 10 wt % carbon black and 10 wt % polyvinylidene fluoride. The hybrid materials in Method II showed higher capacitance due to better interactions between vanadia and graphene oxide particles and more uniform vanadia particle distribution. Full article

(This article belongs to the Special Issue Graphene Aerogels)

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3343 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Simple Process for Sidewall Modification of Multi-Walled Carbon Nanotubes with Polymer Side Chain Radicals Generated by Ultraviolet-Induced C–Cl Bond Dissociation of Polystyrene Derivatives

by Tomoya Takada, Takuma Baba and Shigeaki Abe

C 2016, 2(3), 20; https://doi.org/10.3390/c2030020 - 26 Jul 2016

Cited by 3 | Viewed by 7263

Abstract

In this work, we investigated a simple one-step process for the formation of chemical bonds between multi-walled carbon nanotubes (MWCNTs) and benzyl-type side chain radicals generated by UV photolysis of polystyrene derivatives containing the chloromethyl (–CH₂Cl) group. Poly(4-chloromethyl)styrene, or styrene/4-(chloromethyl)styrene random copolymer, was mixed with MWCNTs in 1-methyl-2-pyrrolidone and irradiated with ultraviolet (UV) light. Films of polymer/MWCNT mixtures before and after UV irradiation were fabricated, and then examined by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. According to the XPS analysis, the amount of Cl atoms in the mixture was found to decrease upon UV irradiation, indicating that the Cl atoms generated by photolysis of chloromethyl groups escaped from the reaction system in the form of gaseous Cl₂. The structural change of CNTs after UV irradiation was also observed by comparing the G/D ratios (the intensity ratio of the G to D bands) of the Raman spectra obtained before and after UV irradiation. Similar phenomena were also confirmed in the case of the polymer/MWCNT mixture containing hydroxylammonium chloride as a dispersant of MWCNTs. These results confirmed the UV-induced covalent bond formation between polymer side chains and MWCNTs. Full article

(This article belongs to the Special Issue Surface Modification of Carbon Nanotubes)

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8832 KiB

Open AccessArticle

Carbon Nanofibers Grown on Large Woven Cloths: Morphology and Properties of Growth

by Vitaly Koissin, Ton Bor, Željko Kotanjac, Leon Lefferts, Laurent Warnet and Remko Akkerman

C 2016, 2(3), 19; https://doi.org/10.3390/c2030019 - 4 Jul 2016

Cited by 6 | Viewed by 5625

Abstract

The morphology and chemical composition of carbon nanofibers in situ grown on a large carbon-fiber woven fabric are studied using SEM measurements, X-ray Diffraction, X-ray Flourescence, and X-ray Photoelectron Spectroscopy. Results show that nanofibers can have a density and a morphology potentially advantageous for application in polymer-matrix composites. The fiber surface functional groups significantly change after the growth and this also potentially provides a better interfacial adhesion. These advantages can be controlled, e.g., by the catalyst loading and the type of solvent used for its deposition. Full article

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2931 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermochemistry of a Biomimetic and Rubisco-Inspired CO₂ Capture System from Air

by Andrew Muelleman, Joseph Schell, Spencer Glazer and Rainer Glaser

C 2016, 2(3), 18; https://doi.org/10.3390/c2030018 - 1 Jul 2016

Cited by 6 | Viewed by 8463

Abstract

In theoretical studies of chemical reactions the reaction thermochemistry is usually reported for the stoichiometric reaction at standard conditions (ΔG°, ΔH°, ΔS°). We describe the computation of the equilibrium concentrations of the CO₂-adducts for the general capture reaction CO₂ + Capture System ⇆ CO₂-adduct (GCR) and the rubisco-type capture reaction CO₂ + Capture System ⇆ CO₂-adduct + H₂O (RCR) with consideration of the reaction CO₂(g) ⇆ CO₂(aq) via Henry’s law. The resulting equations are evaluated and graphically illustrated as a function of atmospheric CO₂ concentration and as a function of temperature. The equations were applied to the thermochemistry of small molecule rubisco-model reactions and series of additional model reactions to illustrate the range of the Gibbs free enthalpy for the effective reversible capture and of the reaction entropy for economic CO₂ release at elevated temperature. A favorable capture of free enthalpy is of course a design necessity, but not all exergonic reactions are suitable CO₂ capture systems. Successful CO₂ capture systems must allow for effective release as well, and this feature is controlled by the reaction entropy. The principle of using a two-pronged capture system to ensure a large negative capture entropy is explained and highlighted in the graphical abstract. It is hoped that the presentation of the numerical examples provides useful guidelines for the design of more efficient capture systems. Full article

(This article belongs to the Special Issue Materials and Processes for Carbon Dioxide Capture and Utilisation)

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2681 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Tuning CNT Properties for Metal-Free Environmental Catalytic Applications

by Raquel P. Rocha, Olívia S.G.P. Soares, José L. Figueiredo and Manuel Fernando R. Pereira

C 2016, 2(3), 17; https://doi.org/10.3390/c2030017 - 29 Jun 2016

Cited by 29 | Viewed by 8486

Abstract

The application of carbon nanotubes (CNTs) as metal-free catalysts is a novel approach for heterogeneous liquid phase catalytic systems. Textural and chemical modifications by liquid/gas phase or mechanical treatments, as well as solid state reactions, were successfully applied to obtain carbon nanotubes with different surface functionalities. Oxygen, nitrogen, and sulfur are the most common heteroatoms introduced on the carbon surface. This short-review highlights different routes used to develop metal-free carbon nanotube catalysts with enhanced properties for Advanced Oxidation Processes. Full article

(This article belongs to the Special Issue Surface Modification of Carbon Nanotubes)

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