Carbon Trends最新文献

Rising carbon dioxide emissions due to fossil fuel combustion has led to the urgent need to investigate and adopt different energy solutions that can mitigate this problem. Hydrogen has surfaced as a promising alternative in the pursuit for CO₂-neutral energy systems. Microwave pyrolysis of methane has recently emerged as an innovative method to accomplish this goal. To enhance our understanding of this technique and its scalability, it is essential to explore the microwave characteristics of the carbon used and generated during this process. This work investigates the microwave properties of two carbon samples (seed carbon; SC and product carbon; PC) from microwave-driven pyrolysis of methane. The cavity perturbation technique was employed from room temperature to 1250 °C for frequencies of 397, 912, 1429, 1948 and 2467 MHz. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis were also performed to elucidate the permittivity results. It was found that SC initially showed a decline in permittivity values up to 200 °C which is attributed to the release of moisture from the sample. These results were correlated to TGA/DSC which showed 5 % mass loss from 100 to 155 °C. The permittivity gradually reached a peak after which it started to fall due to high conductivity. In the case of the PC, the permittivities exhibited undulations but the values remained consistent. Since this form of carbon is formed at elevated temperature, no loss in moisture was seen in TGA/DSC. These findings indicate that the microwaves can penetrate and heat both the samples uniformly across their entire volume, resulting in efficient heating. SC demonstrated higher permittivity magnitudes compared to PC, suggesting its better responsiveness to microwave fields. Nonetheless, the possibility of thermal runaway in SC renders it less favorable for applications involving microwave-driven pyrolysis. XRD analysis showed that the samples SC and PC demonstrated amorphous carbon structures, with PC showing indications of graphitization to some extent. Both SC and PC have the potential to serve as microwave heat carriers in the methane pyrolysis process. This suggests that utilizing the carbon produced can enable a self-sufficient process, eliminating the necessity for costly catalysts.

Carbon materials are unique materials for their diversity, owing to three possible hybridisation states (sp, sp², sp³), their ability to switch from one phase to another upon various external stresses (thermal, mechanical, pressure…), and the tolerance of graphene (sp²C) to defects of many kinds. This makes their description difficult, due to the lack of standardised vocabulary and misuses or ignorance of the existing ones. A common language is needed so that every word has the same meaning to everyone and that carbon scientists understand each other as accurately as possible. This paper aims to clarify the basic terminology to be used on this matter, by reminding some important definitions or terms, e.g. allotrope, polymorphism, molecular form, crystallite, graphitic, graphene, graphene layer, graphenic, graphitisation, graphitisation treatment..., based on authoritative publications when available. In addition, as sp²C-based carbon materials exhibit the largest variability, a four-term description scheme (namely: morphology, texture, nanotexture, structure) is proposed and argued, which is believed to be sufficient (and necessary) to describe any kind of carbons, but molecular forms. Applying the recommendations proposed is expected to bring more consistency, clarity, and understandability to the forthcoming literature dealing with carbon materials.

The race and the discovery of novel two-dimensional (2D) carbon-based materials have been intensified because many are suitable for energy storage systems, thermoelectric devices, and catalysis applications. Therefore, this study introduces to the scientific community a novel 2D nanosheet named graphenyldiene (GPD), which is formed by arranging cyclobutadiene and bi-phenyl groups to create a monolayer with octadecagonal, hexagonal and tetragonal rings. The cohesive energy of GPD is only 1.37 and 0.65 eV/atom higher than graphene and biphenylene, respectively. Molecular dynamics simulations confirmed its structural and thermal stability. The GPD monolayer remains stable, with no significant deformations at around 1000 K, and the disintegration of the geometry occurs only at a temperature of 1500 K, which is characterized by the formation of an amorphous graphdiyne. The GPD electronic structure shows a direct band gap transition, 1.26 eV, at the Γ point. GPD is a promising alternative to electronic devices due to its carrier mobility of around 10³.cm²/V.s. Also, the GPD satisfies the Born-Huang criterion for mechanical stability with elastic constants C₁₁ = 157.62 N/m, C₁₂ = 53.66 N/m and C₆₆ = 51.98 N/m. The Bader's topological analysis indicated that all bonds have strong shared shell characteristics. Finally, the vibrational analysis identified 54 modes, where 21 are Raman active, with A_1g and E_2g modes dominating the spectrum at 1347, 1685 and 1697 cm⁻¹.

Ammonia (NH₃) is one of the compounds found in water, and when it exceeds the threshold, it can become toxic, posing a problem for fish farmers. This research aims to reduce the ammonia (NH₃) levels using activated carbon adsorbents based on nutmeg shell. The activated carbon was produced using a 1 M HCl solution as an activator with temperature variations of 600 °C, 650 °C, and 700 °C. The activated carbon obtained complies with the SNI No.06–3730–1995 standard, with characteristics of 9.23 % moisture content, 8.45 % volatile matter content, 9.71 % ash content, and 81.84 % bound carbon content. The best sample was obtained with an adsorbent mass of 6 g at 700 °C, reducing Ammonia (NH₃) by 90 % with an adsorption capacity of 0.03 mg/g. Subsequently, the sample was subjected to Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), and Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) analysis. Functional carbon groups were identified, especially at wavenumbers 3745.22 cm⁻¹ and 3621.27 cm⁻¹, facilitating adsorption. The sample had an amorphous structure but contained crystalline carbon structures. The highest peak observed was at 29.57° with a miller index (201). The surface of the sample exhibited pores, predominantly composed of carbon and oxygen. The adsorption mechanism of ammonia (NH₃) on activated carbon occurs through intermolecular interactions. This research demonstrates the potential of a newly developed material for reducing NH₃.

Oxidation of graphite and subsequent exfoliation leads to single layer graphene oxide (GO). One of the key structural features of GO is the presence of different kinds of defects that dictates their various physical and chemical properties. Molecular dynamics simulations with ReaxFF force fields have been widely used to generate realistic models of GO. In these simulations, the extent and distribution of the defects are varied by changing the initial oxygen (O)/carbon (C) ratio while the defect density is often measured by the total number of non-graphitic carbon (non-gC) atoms. Our calculations suggest that this parameter overestimates the defect densities at low O/C ratio. Herein, we employ the relative area of the defects as an alternative metric to gauge the defect density. Being exclusive to the defects and sensitive to the structural irregularities, this metric works well at both low and high defect densities. In another example, we consider the reduction of GO to reduced graphene oxide (rGO) for different O/C ratios, where the decrease in the number of non-gC atoms is associated with the formation of comparatively larger defects. Hence, it is unclear whether the extent of reduction in the defect density (if at all) should vary monotonically with the O/C ratio. The defect area, unlike the count of the non-gC atoms, mirrors this ambiguity and the change with respect to O/C ratio is not strictly monotonic. Additionally, we also investigate the dependence of the defect distribution and defect area on the size of the simulation cell.

Using PVC as raw material and KOH as activator, the carbon adsorption material with ultra-high specific surface area up to 5677.2 m²/g was prepared by chemical activation method, and its structure was characterized to study its adsorption performance on methylene blue solution; the activated mixture was analyzed for chlorine element and the recovery of chlorine element was calculated. The results show that the surface of the obtained activated carbon material is in the shape of smooth lotus root flakes with well-developed pore structure; the adsorption value of methylene blue adsorption can reach 765.0 mg/g, which can adsorb methylene blue solution quickly and efficiently; the elemental chlorine can be recovered efficiently with a recovery rate of 95.33 %, which can effectively reduce the toxic hydrogen chloride gas produced in the process of PVC pyrolysis. Excellent adsorption capacity of H₂, CO₂ and CH₄. This experiment can provide an effective method for the harmless treatment of PVC.

In this work, we use a novel methodology to analyse how the critical compositional variables of MgOC bricks affect their chemical degradation by oxygen attack; the study focuses on the effect of the graphite content, the presence of aluminium, and the binder type. Oxidation tests are performed at 1000 °C, a typical preheating condition for steelmaking ladles, under two atmospheric conditions: one simulated the oxygen concentration in air, and the other, with a lower amount of oxygen, reproduces the conditions of the inner part of the brick when liquid steel is present. It was found that: a) the addition of Al reduces the carbon oxidation kinetic, mainly at a low O₂ partial pressure, b) increasing the graphite content led to a smaller decarburized area with higher O₂ consumption, and c) mixing CarboRes® with phenolic resin resulted in a higher O₂ consumption but at a slower oxidation rate.

Search for one dimensional (1D) van der Waals materials has become an urgent need to meet the demand as building blocks for high performance, miniaturized, lightweight device applications. Polyyne, a 1D atomic chain of carbon is the thinnest and strongest allotrope of carbon, showing promising applications in new generation low dimensional devices due to the presence of a band gap. A system of two carbon chains held together by van der Waals interaction has been theoretically postulated and shows band gap tunability under structural changes which finds applications in the realms of resistive switching and spintronics. In this study, we use first principles Density Functional Theory (DFT) to show a sharp semiconductor to metal transition along with the emergence of an asymmetry in the spin polarized density of states for single and two polyyne chains under a transverse electric field. The thermodynamic stability of the system has been substantiated through the utilization of Ab Initio Molecular Dynamics (AIMD) simulations, phonon dispersion curve analyses, and formation energy calculations. Furthermore, in addition to its dynamic stability assessment, phonon calculations have served to identify Raman-active vibrational modes which offers an invaluable non-destructive experimental avenue for discerning electronic phase transitions in response to an applied electric field. Our study presents a predictive framework for the prospective utilization of one and two polyyne chains in forthcoming flexible nano-electronic and spintronic devices. The future prospects of the system are contingent upon advancements in nano-electronics fabrication techniques and the precise construction of circuitry for harnessing spin-related applications.

We present a facile one-step hydrothermal method for the fabrication of free-standing graphene paper using aqueous graphene oxide (GO) dispersion as the starting material. Notably, the method does not require the use of any additives for the reduction and preparation of the graphene paper. The resulting graphene paper exhibits a high degree of reduction, as confirmed by X-ray photoelectron spectroscopy (XPS) analysis, revealing a carbon-to-oxygen (C/O) ratio of ∼7. The fabricated graphene paper also demonstrates excellent conductivity, with a measured value of ∼1900 S/m, and sheet resistance of around 100 Ω/sq. Furthermore, the energy storage capability of the graphene paper based electrode is evaluated, which shows a promising specific capacity of 249 F/g at a current density of 1 A/g in 1M H₂SO₄ as the ionic medium. Additionally, the electrode has also demonstrated remarkable energy density and power density values of 28.68 Wh/Kg and 455 W/Kg, respectively. Overall, the resulting graphene paper exhibits high conductivity and excellent electrochemical performance, making it a promising candidate for various energy storage applications.

Activated biochars were obtained from pyrolysis and CO₂-physical activation of four different biomasses including tannery shaving waste (T), vine wood waste (W), barley waste (B) and Sargassum, brown macroalgae of Venice lagoon (A). The potential of obtained carbonaceous materials as the supports of Ni,Al catalysts was investigated in levulinic acid (LA) conversion to γ-valerolactone (GVL) as a model hydrogenation reaction. Al-containing species as the Lewis acid sites for the dehydration step were incorporated to the supports using wet impregnation or precipitation. Ni as a hydrogenation active phase was added to the supports via wet impregnation. Biochar-based supports and catalysts were characterized by AAS, elemental analysis, FTIR, N₂ physisorption, XRD, SEM, EDS, TEM, He-TPD, NH₃-TPD and TPR techniques. The catalysts were tested for LA hydrogenation to GVL in a batch system and aqueous medium. The results showed that Ni supported on activated biochar was not active due to a lack of Lewis acid sites for dehydration. Precipitated Al-containing species on the biochar-based supports demonstrated a better catalytic performance in the reaction compared to impregnated one because of different interactions with the support and Ni species. Among different supports, the activated biochars obtained from T and W acted as the best ones. A higher catalytic efficiency was strongly influenced by the chemical (aromaticity and stability, presence of N,O-doped and functional groups), textural (the porous texture and surface area), and morphological (higher dispersion of active phases) properties of activated biochars obtained from different biomasses with different natures.