C — Journal of Carbon Research — Open Access Journal

This work reviews the latest developments of cathodes for electrochemical CO₂ reduction, with carbon black, mesoporous carbons, carbon nanofibers, graphene, its derivatives and/or carbon nanotubes as constituents. Electrochemical CO₂ reduction into fuels and chemicals powered by renewable energy is a technology that can contribute to climate change mitigation. Strategies used in this fast-evolving field are discussed, having in mind a commercial application. Electrochemical performance of several materials is analyzed, using in some cases the findings of theoretical computational studies, which show the enormous potential of these materials. Considerable challenges still lie ahead to bring this technology into industrial deployment. However, the significant progress achieved so far shows that further R&D efforts might pay off. Full article

Lignin is a significant by-product of the paper pulping and biofuel industries. Upgrading lignin to a high-value product is essential for the economic viability of biorefineries for bioethanol production and environmentally benign pulping processes. In this work, the feasibility of lignin-derived activated carbons for hydrogen storage was studied using a Design of Experiments methodology, for a time and cost-efficient exploration of the synthesis process. Four factors (carbonisation temperature, activation temperature, carbonisation time, and activation time) were investigated simultaneously. Development of a mathematical model allowed the factors with the greatest impact to be identified using regression analysis for three responses: surface area, average pore size, and hydrogen uptake at 77 K and 1 bar. Maximising the surface area required activation conditions using the highest settings, however, a low carbonisation temperature was also revealed to be integral to prevent detrimental and excessive pore widening. A small pore size, vital for efficient hydrogen uptake, could be achieved by using low carbonisation temperature but also low activation temperatures. An optimum was achieved using the lowest carbonisation conditions (350 °C for 30 min) to retain a smaller pore size, followed by activation under the severest conditions (1000 °C for 60 min) to maximise surface area and hydrogen uptake. These conditions yielded a material with a high surface area of 1400 m² g⁻¹ and hydrogen uptake of 1.9 wt.% at 77 K and 1 bar. Full article

A new mesoporous carbon (MC) is obtained from pyrolysis of resorcinol/formaldehyde resin, polymerized in the presence of tetraethoxysilane and Pluronic F108, followed by pyrolysis at 800 °C and silica removal. The reaction mixture in a molar ratio of 1F108/60resorcinol/292 formaldehyde/16900 H₂O/50 tetraethoxysilane heated at 67 °C produces MC nanoparticles (200 nm average size) exhibiting 3D bimodal mesopores (3.9 and 8.2 nm), 1198 m²/g surface area, 1.8 cm³/g pore volume, and important graphitic character for use as a conductive material. Composites LiFePO₄/carbon prepared with MC or commercial Super P, by the slurry method, were tested as coin Li-ion battery (LiB) cathodes. Super P (40 nm average particle size) exhibits better graphitic character, but lower porosity than MC. LiFePO₄/MC shows better specific capacity (161 mAhg⁻¹) than LiFePO₄/Super P (126 mAhg⁻¹), with a retention capacity (RC) after cycling at C/10 of 81%. Both composites with MC and Super P show well-distributed particles. According to impedance analysis, MC mesoporosity improves the charge transfer kinetics (CTK) more than Super P, producing a cathode with higher efficiency, although lithium ions’ diffusion decreases because larger MC particles form longer diffusion paths. Owing to the good specific capacity of the LiB cathode prepared with MC, research looking into improving its retention capacity should be a focus. Full article

In the ranking of cosmic abundance of the elements, carbon is the second element, after oxygen, able to form multiple bonds propagating the formation of a network, thus playing an essential role in the formation of nanometer- to micrometer-sized interstellar dust grains. Astrophysical spectroscopic observations give us remote access to the composition of carbonaceous and organic interstellar grains. Their presence and abundances from spectroscopic observations and the phases of importance for the Galactic carbon budget are considered in this article. Full article

Multiwavelength Raman spectroscopy (325, 514, 633 nm) was used to analyze three different kinds of samples containing sp² and sp³ carbons: chemical vapor deposited diamond films of varying microstructure, a plasma-enhanced chemical vapor deposited hydrogenated amorphous carbon film heated at 500 °C and highly oriented pyrolytic graphite exposed to a radio-frequent deuterium plasma. We found evidence that the lower part of the phonon density of states (PDOS) spectral region (300–900 cm⁻¹) that rises when defects are introduced in crystals can give more information on the structure than expected. For example, the height of the PDOS, taken at 400 cm⁻¹ and compared to the height of the G band, depends on the sp² content, estimated by electron energy-loss spectroscopy. This ratio measured with 633 nm laser is more intense than with 514 nm laser. It is also correlated for diamond to the relative intensity ratio between the diamond band at 1332 cm⁻¹ and the G band at ≈1500–1600 cm⁻¹ when using 325 nm laser. Moreover, it is found that the shape of the PDOS of the exposed graphite samples is different when changing the wavelength of the laser used, giving evidence of a double resonance mechanism origin with the rise of the associated D₃, D₄ and D₅ bands, which is not the case for a-C:H samples. Full article

Cyclodextrins (CDs) are oligosaccharides composed of six (α), seven (β) or eight (γ) glucose units. Their inner hydrophobic cavity and hydrophilic external surface enable the formation of the “host-guest inclusion complex” with different organic or inorganic molecules showing high molecular selectivity. For these characteristics, CDs have many potential applications in electrochemical sensing. To enable CDs immobilization on the electrode surfaces, different chemical modifications are needed depending of the electrode material, while nanomaterials have been exploited to enhance the sensing signal. The CDs binding onto gold nanoparticles or carbon nanotubes, as an electron-transfer mediator to the electrode surface, is a typical example of it, while also graphene is largely used. The aim of the present review is to give an overview of CDs properties and their applications to electrochemical sensors for medical diagnostics. Different kinds for the functionalization of CDs onto electrode surfaces will be reviewed as well as their performance in presence of nanomaterials. Finally, CDs-based devices for sensing biomedical molecules of biomedical interest will be briefly presented and discussed. Full article

In this work, we report a simple, one-step, green procedure to fabricate strong blue and yellow photoluminescent graphene quantum dots (GQDs) as by-product of the synthesis of mesoporous graphene hydrogel (GHs). The graphene hydrogel was obtained by chemical reduction of graphene oxide using ascorbic acid at mild temperature. As a consequence of the network formation, small fluorescent GQDs can be isolated from the residual solvent, purified from the by-products and finally concentrated to produce GQDs. The GQDs chemistry and morphology were characterized by X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The GQDs mean diameter was about 5–10 nm and they exhibited an intense luminescence in the visible range with an excitation wavelength-dependent fluorescence. Our experiments showed that GQDs were easily internalized in living cells and furthermore, such internalization did not adversely affect cell viability. Full article

A char produced from spent tire rubber showed very promising results as an adsorbent of Remazol Yellow (RY) from aqueous solutions. Spent tire rubber was submitted to a pyrolysis process optimized for char production. The obtained char was submitted to chemical, physical, and textural characterizations and, subsequently, applied as a low-cost adsorbent for dye (RY) removal in batch adsorption assays. The obtained char was characterized by relatively high ash content (12.9% wt), high fixed-carbon content (69.7% wt), a surface area of 69 m²/g, and total pore volume of 0.14 cm³/g. Remazol Yellow kinetic assays and modelling of the experimental data using the pseudo-first and pseudo-second order kinetic models demonstrated a better adjustment to the pseudo-first order model with a calculated uptake capacity of 14.2 mg RY/g char. From the equilibrium assays, the adsorption isotherm was fitted to both Langmuir and Freundlich models; it was found a better fit for the Langmuir model to the experimental data, indicating a monolayer adsorption process with a monolayer uptake capacity of 11.9 mg RY/g char. Under the experimental conditions of the adsorption assays, the char presented positive charges at its surface, able to attract the deprotonated sulfonate groups (SO₃⁻) of RY; therefore, electrostatic attraction was considered the most plausible mechanism for dye removal. Full article

In this work, zinc oxide-decorated graphene oxide (ZnO–rGO) was successfully synthesized with a fast reflux chemical procedure at 100 °C. An equal mass ratio of graphene oxide (GO) and zinc acetate was used as starting materials dissolved, respectively, in ultrapure distilled water and dimethylformamide (DMF). Particularly, pure GO was synthesized using Hummers modified protocol by varying the mass ratio of (graphite:potassium permanganate) as follows: 1:2, 1:3, and 1:4, which allow us to obtain six types of pure and decorated samples, named, respectively, GO1:2, GO1:3, GO1:4, ZnO–rGO1:2, ZnO–rGO1:3, and ZnO–rGO1:4 using reflux at 100 °C. X-ray diffraction, FTIR, and Raman spectroscopy spectra confirm the formation of wurzite ZnO in all ZnO-decorated samples with better reduction of GO in ZnO–rGO1:4, confirming that a higher degree of graphene oxidation allows better reduction during the decoration process with ZnO metal oxide. Antioxidant activity of pure and zinc oxide-decorated graphene oxide samples were compared using two different in vitro assays (DPPH radical and H₂O₂ scavenging activities). Considerable in vitro antioxidant activities in a concentration-dependent manner were recorded. Interestingly, pristine GO showed more elevated scavenging efficiency in DPPH tests while ZnO-decorated GO was relatively more efficient in H₂O₂ antioxidant assays. Full article

The present survey reports on the colloidal stability of aqueous dispersions of nitrogen-rich carbon nanodots (N-CDs). The N-CDs were synthesized by thermally induced decomposition of organic precursors and present an inner core constituted of a $\beta {-\mathrm{C}}_3{\mathrm{N}}_4$ crystalline structure surrounded by a surface shell containing a variety of polar functional groups. N-CDs size and structure were checked by combined analysis of XRD (X-ray Diffraction) and TEM (Transmission Electron Microscopy) measurements. FTIR (Fourier-Transform Infrared Spectroscopy) experiments revealed the presence of carboxyl and amide groups on N-CDs surface. Towards a better understanding of the relation between colloidal stability and surface charge development, zetametry experiments were applied in N-CDs dispersions at different pHs and constant ionic strength. The increase of the absolute values of zeta potential with the alkalinization of the dispersion medium is consistent with the deprotonation of carboxyl groups on N-CDs surface, which agrees with the macroscopic visual observations of long-term colloidal stability at pH 12. The saturation value of N-CDs surface charge density was evaluated by means of potentiometric-conductometric titrations. The difference between carboxyl-related surface charge and the one determined by zeta potential measurements point to the presence of oxidized nitrogen functionalities onto the N-CDs surface in addition to carboxyl groups. These novel results shed light on the electrostatic repulsion mechanism that allows for the remarkable colloidal stability of N-CDs dispersions. Full article

Defects in diamond-like carbon coatings deposited on corrosion sensitive 100Cr6 steel have been studied. Diamond-like carbon (DLC) thin films are promising for corrosion protection due to chemical inertness and low electrical conductivity. Nevertheless, the performance of these coating is highly sensitive to the presence of uncoated areas. These defects represent the primary way of substrate degradation in aggressive environments. An in situ optical microscopy coupled to an electrochemical activation was developed to reveal micrometric growth defects and observe that they were at the origin of corrosion. A square wave voltammetry was applied to increase the sensitivity of electrochemical techniques based on the detection of the dissolution of the bare metal surface triggered by the presence of uncoated spots. This method can be utilized to quantify defect density arising from vapor deposition processes. Full article

Over the past decade, carbon nanostructures (CNSs) have been widely used in a variety of biomedical applications. Examples are the use of CNSs for drug and protein delivery or in tools to locally dispense nucleic acids to fight tumor affections. CNSs were successfully utilized in diagnostics and in noninvasive and highly sensitive imaging devices thanks to their optical properties in the near infrared region. However, biomedical applications require a complete biocompatibility to avoid adverse reactions of the immune system and CNSs potentials for biodegradability. Water is one of the main constituents of the living matter. Unfortunately, one of the disadvantages of CNSs is their poor solubility. Surface functionalization of CNSs is commonly utilized as an efficient solution to both tune the surface wettability of CNSs and impart biocompatible properties. Grafting functional groups onto the CNSs surface consists in bonding the desired chemical species on the carbon nanoparticles via wet or dry processes leading to the formation of a stable interaction. This latter may be of different nature as the van Der Waals, the electrostatic or the covalent, the π-π interaction, the hydrogen bond etc. depending on the process and on the functional molecule at play. Grafting is utilized for multiple purposes including bonding mimetic agents such as polyethylene glycol, drug/protein adsorption, attaching nanostructures to increase the CNSs opacity to selected wavelengths or provide magnetic properties. This makes the CNSs a very versatile tool for a broad selection of applications as medicinal biochips, new high-performance platforms for magnetic resonance (MR), photothermal therapy, molecular imaging, tissue engineering, and neuroscience. The scope of this work is to highlight up-to-date using of the functionalized carbon materials such as graphene, carbon fibers, carbon nanotubes, fullerene and nanodiamonds in biomedical applications. Full article

Unexpectedly bright photoluminescence emission can be observed in materials incorporating inorganic carbon when their size is reduced from macro–micro to nano. At present, there is no consensus in its understanding, and many suggested explanations are not consistent with the broad range of experimental data. In this Review, I discuss the possible role of collective excitations (excitons) generated by resonance electronic interactions among the chromophore elements within these nanoparticles. The Förster-type resonance energy transfer (FRET) mechanism of energy migration within nanoparticles operates when the composing fluorophores are the localized electronic systems interacting at a distance. Meanwhile, the resonance interactions among closely located fluorophores may lead to delocalization of the excited states over many molecules resulting in Frenkel excitons. The H-aggregate-type quantum coherence originating from strong coupling among the transition dipoles of adjacent chromophores in a co-facial stacking arrangement and exciton transport to emissive traps are the basis of the presented model. It can explain most of the hitherto known experimental observations and must stimulate the progress towards their versatile applications. Full article

The commercially acquired aqueous solution of “carbon quantum dots” sample was evaluated by optical absorption and fluorescence emission methods; in reference to aqueous dispersed small carbon nanoparticles and representative carbon dots prepared from chemical functionalization of the carbon nanoparticles. The results suggest a very low content of carbon that is associated with nanoscale carbon particles/domains in the as-supplied sample; and likely significant contamination by dye-like species/mixtures. In the absence of any information on the synthesis and history of the commercial sample, the possible cause of the contamination was illustrated by an example on similar dye formation in the one-pot carbonization synthesis of “red carbon dots” from citric acid–formamide precursor mixtures under too mild processing conditions that were insufficient for the intended carbonization. The negative impacts to the carbon dots research field by the apparent proliferation and now commercial availability of carbon-deficient or even largely carbon-less “carbon quantum dots”, which are more susceptible to dye contamination or dominance, are discussed. Full article

Considering typical spectra of a broad range of carbonaceous materials from gas-shale to nanotubes, various ways by which defects show up in Raman spectra are exampled and discussed. The position, resonance behavior, and linewidth of both the D and G bands are compared, even if in some cases obtaining accurate information on the materials from the fitting parameters is a difficult task. As a matter of fact, even if a full picture is unreachable, defining parameter trends is one acceptable option. Two ways to determine the linewidth, either graphically and or by fitting are proposed in order to be able to compare literature data. The relationship between the crystallite size obtained from the linewidth and from X-ray diffraction, which is complementary to the Tuinstra and Koenig law, is examined. We show that a single approach is not possible unless modeling is performed and therefore that analysis of Raman spectra should be adapted to the specificities of each sample series, i.e., a minimum of knowledge about the materials is always required. Full article

Of great concern are the residual antibiotics from dirt that can be found in farm soil and wastewater. This kind of emerging pollutant into engineered nanomaterials is riveting. This work proposes the elimination and transformation of a beta-lactam antibiotic, oxacillin, from environmental waste to graphene quantum dots (GQDs). Two protocols were followed in which the use of ethylenediamine (EDA) in the transformation leads to GQDs with excellent optical properties. Therefore, two types of GQDs were synthesized in a Teflon-lined stainless autoclave by a thermal procedure using oxacillin in the absence and presence of EDA. The ensuing e-GQDs from oxacillin and EDA display a stronger fluorescence emission in comparison to those synthesized without EDA (o-GQDs). The combination of Kaiser test analyses, infrared (IR) and Raman measurements revealed the presence of oxygen-containing groups and primary amines at the edges of the graphitic nanolayer for e-GQDs. This straightforward strategy brings hope and opens a new interest in waste recycling by means of extracting residual contaminants from the environment for their further transformation into adequate non-toxic graphitic nanomaterials with potential applications. Full article

Graphite has been widely used by humans for a large part of their history. Nevertheless, it has only recently been possible to isolate its basic unit: carbon atoms arranged in a honeycomb structure on a single plane, namely graphene. Since its discovery, many techniques have been developed and improved to properly synthesize graphene and its derivatives which are part of the novel class of two-dimensional materials. These advanced materials have imposed themselves in nanotechnology thanks to some outstanding physical properties due to their reduced dimensions. In the case of graphene, its reduced dimension gives rise to a high electrical mobility, a large thermal conductivity, a high mechanical resistance, and a large optical transparency. Therefore, such aspect is of great scientific interest for both basic and applied research, ranging from theoretical physics to surface chemistry and applied solid state physics. The connection between all these fields is guaranteed by spectroscopy and especially by Raman spectroscopy which provides a lot of information about structural and electronic features of graphene. In this review, the authors present a systematized collection of the most important physical insights on the fundamental electronic and vibrational properties of graphene, their connection with basic optical and Raman spectroscopy, and a brief overview of main synthesis methods. Full article

Herein, we report the successful use of newspaper as a substrate for the growth of single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition (CVD) with intriguing results demonstrating that (a) the large surface area of newspaper stock allows for SWCNT growth and (b) only newspaper produced with kaolin clay sizing allowed for SWCNT growth. Kaolin newsprint was impregnated with Al₂O₃ and Fe(NO₃)₃·9H₂O (as precursors to Fe_xO_y nanoparticles), and calcined (30 min at 400 °C). The subsequent char residue was loaded into a CVD chamber and used as a substrate for SWCNT growth at 750 °C, using H₂, C₂H₂, and water vapor as the growth gas. Samples of raw carbon soot exhibiting fluorescence spectra, indicative of SWCNTs, were further evaluated by resonant Raman spectroscopy, and by transmission electron microscopy (TEM). The calcinated substrate remnants were evaluated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Experiments utilizing paper substrates produced with kaolin filler resulted in hybridized sp²–sp³ bonded carbon species. The soot was found to consist primarily of carbon nanotubes and bi-layer graphene in the form of collapsed nanotubes, also known as graphene nanoribbons (GNR). Full article

High-pressure carbon monoxide (HiPco)-synthesized single-walled carbon nanotubes (SWCNTs) have been a widely studied carbon nanomaterial for nearly two decades. It has been the de facto standard for SWCNT research, be it functionalization, separation and purification, or composites, as a result of the consistent, high-quality material that was made available at an affordable price to researchers worldwide. The recent shutdown of the HiPco reactor at Rice University has resulted in a scarcity of HiPco material available to the research community, and a new source of similar SWCNTs is desperately needed. Continued research and development on the design, materials used, and the overall process have led to a new HiPco material, referred to as NoPo HiPCO^®, as an alternative to the erstwhile Rice HiPco SWCNTs. In this work, we have compared the two HiPco materials, and aim to provide more clarity for researchers globally on the state of HiPco SWCNTs for research and applications alike in 2019. Full article