C, Volume 7, Issue 2 (June 2021) – 20 articles

In this work, we present a relevant upgrade to the technique of pulsed laser ablation of fluorescent nanodiamonds (NDs), relying on an automatized graphite-target movement maintaining a constant level of liquid nitrogen over its surface during hours of deposition. Around 60 mg of NDs nanopowder was synthesized and optomagnetically characterized to assess its optical quality. Chemical purification of the ablated nanopowders, which removes the graphitic byproducts, permits to obtain pure fluorescent NDs with an efficiency of 7 ± 1% with respect to the total nanopowder mass. This value compares positively with the efficiency of other commercial NDs synthesis techniques such as detonation, cavitation, and high pressure–high temperature. Full article

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

Metal–organic frameworks (MOFs) are crystalline materials with permanent porosity, composed of metal nodes and organic linkers whose well-ordered arrangement enables them to act as ideal templates to produce materials with a uniform distribution of heteroatom and metal elements. The hybrid nature of MOFs, well-defined pore structure, large surface area and tunable chemical composition of their precursors, led to the preparation of various MOF-derived porous carbons with controlled structures and compositions bearing some of the unique structural properties of the parent networks. In this regard, an important class of MOFs constructed with porphyrin ligands were described, playing significant roles in the metal distribution within the porous carbon material. The most striking early achievements using porphyrin-based MOF porous carbons are here summarized, including preparation methods and their transformation into materials for electrochemical reactions. Full article

The aim of this study was to investigate the electrochemical behaviour of aqueous electrolytes on thin-layer (20 µm) nanoporous carbide-derived carbon (CDC) composite fibrous directly electrospun electrodes without further carbonisation. There have been previously investigated fibrous electrodes, which are produced by applying different post-treatment processes, however this makes the production of fibrous electrodes more expensive, complex and time consuming. Furthermore, in the present study high specific capacitance was achieved with directly electrospun nanoporous CDC-based fibrous electrodes in different neutral aqueous electrolytes. The benefit of fibrous electrodes is the advanced mechanical properties compared to the existing commercial electrode technologies based on pressure-rolled or slurry-cast powder mix electrodes. Such improved mechanical properties are preferred in more demanding applications, such as in the space industry. Electrospinning technology also allows for larger electrode production capacities without increased production costs. In addition to the influence of aqueous electrolyte chemical composition, the salt concentration effects and cycle stability with respect to organic electrolytes are investigated. Cyclic voltammetry (CV) measurements on electrospun electrodes showed the highest capacitance for asymmetrical cells with an aqueous 1 M NaNO₃-H₂O electrolyte. High CV capacitance was correlated with constant current charge–discharge (CC) data, for which a specific capacitance of 191 F g⁻¹ for the positively charged electrode and 311 F g⁻¹ for the negatively charged electrode was achieved. The investigation of electrolyte salt concentration on fibrous electrodes revealed the typical capacitance dependence on ionic conductivity with a peak capacitance at medium concentration levels. The cycle-life measurements of selected two-electrode test cells with aqueous and non-aqueous electrolytes revealed good stability of the electrospun electrodes. Full article

Molybdenum disulfide quantum dots (MoS₂ QDs) are a unique class of zero-dimensional (0D) van der Waals nanostructures. MoS₂ QDs have attracted significant attention due to their unique optical, electronic, chemical, and biological properties due to the presence of edge states of these van der Waals QDs for various chemical functionalization. Their novel properties have enabled applications in many fields, including advanced electronics, electrocatalysis, and biomedicine. In this review, the various synthesis techniques, the novel properties, and the wide applications of MoS₂ quantum dots are discussed in detail. Full article

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

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

Environmental issues urge for the substitution of petrochemical-based raw materials with more environmentally friendly sources. The biggest advantages of PLA over non-biodegradable plastics are that it can be produced from natural sources (e.g., corn or sugarcane), and at the end of its lifetime it can be returned to the soil by being composted with microorganisms. PLA can easily substitute petroleum-based plastics in a wide range of applications in many commodity products, such as disposable tableware, packaging, films, and agricultural twines, partially contributing to limiting plastic waste accumulation. Unfortunately, the complete replacement of fossil fuel-based plastics such as polyethylene (PE) or poly(ethylene terephthalate) (PET) by PLA is hindered by its higher cost, and, more importantly, slower degradation as compared to other degradable polymers. Thus, to make PLA more commercially attractive, ways to accelerate its degradation are actively sought. Many good reviews deal with PLA production, applications, and degradation but only in the medical or pharmaceutical field. In this respect, the present review will focus on controlled PLA degradation and biodegradation in technical applications. The work will include the main degradation mechanisms of PLA, such as its biodegradation in water, soil, and compost, in addition to thermal- and photo-degradation. The topic is of particular interest to academia and industry, mainly because the wider application of PLA is mostly dependent on discovering effective ways of accelerating its biodegradation rate at the end of its service life without compromising its properties. Full article

Thermogravimetric analysis (TGA) has been recognized as a simple and reliable analytical tool for characterization of industrially manufactured graphene powders. Thermal properties of graphene are dependent on many parameters such as particle size, number of layers, defects and presence of oxygen groups to improve the reliability of this method for quality control of graphene materials, therefore it is important to explore the influence of these parameters. This paper presents a comprehensive TGA study to determine the influence of different particle size of the three key materials including graphene, graphene oxide and graphite on their thermal parameters such as carbon decomposition range and its temperature of maximum mass change rate (T_max). Results showed that T_max values derived from the TGA-DTG carbon combustion peaks of these materials increasing from GO (558–616 °C), to graphene (659–713 °C) and followed by graphite (841–949 °C) The T_max values derived from their respective DTG carbon combustion peaks increased as their particle size increased (28.6–120.2 µm for GO, 7.6–73.4 for graphene and 24.2–148.8 µm for graphite). The linear relationship between the T_max values and the particle size of graphene and their key impurities (graphite and GO) confirmed in this study endows the use of TGA technique with more confidence to evaluate bulk graphene-related materials (GRMs) at low-cost, rapid, reliable and simple diagnostic tool for improved quality control of industrially manufactured GRMs including detection of “fake” graphene. Full article

Nitrogen-doped carbon dots (N-doped C-dots) was synthesized by using poly(vinyl amine) (PVAm) as a nitrogen source and citric acid (CA) as a carbon source via the hydrothermal method. Various weight ratios of CA and PVAm (CA:PVAm) were used to synthesize N-doped C-dots. The N-doped C-dots revealed emission at 440 nm with excitation at 360 nm and were found to increase the fluorescence intensity with an increase in the amount of PVAm. The blood compatibility studies revealed no significant hemolysis for N-doped C-dots that were prepared at different ratios of CA:PVAm for up to 500 μg/mL concentration with the hemolysis ratio of 1.96% and the minimum blood clotting index of 88.9%. N-doped C-dots were found to be more effective against Gram-positive bacteria than Gram-negative bacteria, with the highest potency on Bacillus subtilis (B. subtilis). The increase in the weight ratio of PVAm in feed during C-dots preparation from 1 to 3 leads to a decrease of the minimum bactericidal concentration (MBC) value from 6.25 to 0.75 mg/mL for B. subtilis. Antibiofilm ability of N-doped C-dots prepared by 1:3 ratio of CA:PVAm was found to reduce %biofilm inhibition and eradication- by more than half, at 0.78 mg/mL for E. coli and B. subtilis generated biofilms and almost destroyed at 25 mg/mL concentrations. Full article

Biomass wastes are abundant around us. They are renewable and inexpensive. Product manufacturing from renewable resources has caught increasing interest recently. Activated carbon preparation from biomass resources, including various trees, leaves, plant roots, fruit peels, and grasses, is a good example. In this paper, an overview of activated carbon production from biomass resources will be given. The first part will be on the processing technologies. The second part will focus on the carbon activation methods. The third part will introduce the biomass resources. The fourth part will be on surface modification of activated carbon through the addition of various components. Finally, the development of product applications will be discussed with an emphasis on adsorption, filtration, water purification, energy conversions, and energy storage. Full article

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

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

Carbon based materials exhibit interesting mechanical, thermal and electrical properties which make them excellent contenders for use as fillers in composites as film. Graphene has been vastly used among the carbon-based materials. More recently eco-friendly carbon-based materials like biochar have emerged. The deployment of carbon-based materials in films needs to be studied since films are more versatile and permit the exploitation of electrical properties of such materials over circuits and systems. Typical circuits and systems exploiting electrical properties of novel materials perform a number of applications including sensing, detection, tunable devices and energy harvesting. In this paper, films composed of 9:1 graphene or biochar are deployed on a microstrip line. The morphological properties of graphene and biochar and their respective films are studied with Raman spectra and Field Emission Scanning Electron Microscope (FESEM). The electrical properties (four-point probe measurements and scattering parameter measurements) of the films. Low frequency measurements are used as starting point for circuit models estimating the lumped impedance of the films. From the morphological characterization it is shown that biochar films appear as granulates carbonaceous materials whereas graphene films contains several flakes forming a network. From the low frequency measurements and microwave characterization it is seen that graphene films are more conductive as compared to biochar films. In many applications, it is useful to know the surface impedance of the film since it varies on interaction with any external stimulus (variation of pressure, humidity, gas, etc.). Full article

Boron nitride quantum dots (BNQDs) have gained increasing attention for their versatile fluorescent, optoelectronic, chemical, and biochemical properties. During the past few years, significant progress has been demonstrated, started from theoretical modeling to actual application. Many interesting properties and applications have been reported, such as excitation-dependent emission (and, in some cases, non-excitation dependent), chemical functionalization, bioimaging, phototherapy, photocatalysis, chemical, and biological sensing. An overview of this early-stage research development of BNQDs is presented in this article. We have prepared un-bias assessments on various synthesis methods, property analysis, and applications of BNQDs here, and provided our perspective on the development of these emerging nanomaterials for years to come. Full article

Carbon capture and storage (CCS) is an established and verified technology that can implement zero emissions on a large enough scale to limit temperature rise to below 2 °C, as stipulated in the Paris Agreement. However, leakage from CCS sites must be monitored to ensure containment performance. Surface monitoring of carbon dioxide (CO₂) concentrations at onshore CCS sites is one method to locate and quantify CCS site leakage. Employing soil accumulation chambers, we have established baseline data for the natural flux of CO₂ as a threshold alert to detect CO₂ leakage flux to ensure the safety of onshore CCS sites. Within this context, we conducted on-site CO₂ measurements at three different locations (A, B, and C) on the INAS test field at the Ito campus, Kyushu University (Japan). Furthermore, we developed a specific measurement system based on the closed-chamber method to continuously measure CO₂ flux from soil and to investigate the correlation between CO₂ flux from the soil surface and various parameters, including environmental factors and soil sample characteristics. In addition, gas permeability and the effect of different locations on soil CO₂ flux are discussed in this study. Finally, we present an equation for estimating the soil CO₂ flux used in the INAS field site that includes environmental factors and soil characteristics. This equation assists in defining the threshold line for an alert condition related to CO₂ leakage at onshore CCS sites. Full article

The effects of two types of carbon nanotubes, namely multiwall (MWCNT) and single-wall (SWCNT) carbon nanotube, on the thermal and mechanical properties of acrylonitrile-butadiene-styrene (ABS) nanocomposites, have been investigated. ABS filled-CNT nanocomposites with various filler loadings of 5–10 wt% were properly produced by a solvent-free process in blend compounding at 190 °C. Compression moulded plates and extruded filaments were obtained at 190 °C and 230 °C, respectively. Melt flow index (MFI), shore hardness, Vicat temperature, differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) were performed to characterize and compared the different CNT nanocomposites. ABS/SWCNT composite filaments showed higher tensile properties (i.e., stiffness and strength), than ABS/MWCNT. The electrical resistivity of ABS/SWCNT and ABS/MWCNT filaments decreased to 0.19 Ω.cm and 0.65 Ω.cm for nanocomposites with 10 wt% of nanofillers; a power law was presented to describe the electrical resistivity of composites as a function of the CNTs content. A final comparative parameter regarding melt flow, stiffness and conductivity was also evaluated for understanding the combined effects of the nanofillers. SWCNT nanocomposites exhibited better overall cumulative results than MWCNT nanocomposites. Full article

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

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

We warmly thank all the colleagues who have enthusiastically participated in the project of this Special Issue on “2D Ultra-Thin Carbon Films”, considering a globally unfavorable context characterized by (i) a myriad of publication options; (ii) strong pressure, by the highly competitive research (and researcher) funding and evaluation system, to publish in high impact factor journals, specifically for topics of worldwide interest; and (iii) all sorts of restrictions imposed by the sanitary crisis [...] Full article