Formation Of Carbon Materials Research Articles

Sugar derived hydrochar catalysts for enhanced biodiesel production via esterification

Sugars and sugar alcohols are renewable raw materials which can be used for char production. Their acid-catalyzed hydro-carbonization results in the formation of carbon materials with acidic functional groups on the surface, which makes them suitable to be used as heterogeneous catalysts in esterification reactions. Hydrochars materials were prepared by low-temperature slow carbonization of glycerol, xylitol, sucrose, and glucose in the presence of different amounts of H2SO4 (mass ratios from 1 to 4). The hydrochars were extensively characterized and tested in the methanolysis reaction of oleic acid. All the carbon materials were amorphous with features of polyaromatic sheets with hydroxyl (–OH), carboxylic acid (–COOH), and sulfonic (−SO3H) functional groups. The effect of the oleic acid water content on catalytic performance was studied, showing a strong inhibition effect due to the hygroscopic character of catalysts induced by sulfonic groups and other surface groups with oxygen. Under the conditions evaluated (5 % wt. of catalyst, methanol/oleic acid = 9 M ratio, methanol reflux temperature) the sucrose-derived catalyst prepared with the highest H2SO4 content showed the best performance, leading to methyl oleate yield > 90 % after 2 h of reaction, which is only achieved by the majority of analogous catalysts reported in the literature after 4 to 8 h of reaction. The data showed that there is a correlation between the methyl ester yield and the graphitization of the catalyst, as this makes the catalyst more hydrophobic, which is an advantage in esterification catalysts.

Predicting decomposition temperatures and carbonization feasibility of heterocycles with their decomposition mechanism

Pyrolysis of heterocyclic compounds such as Meldrum’s acid (MA) derivatives has been studied with focus on two key mechanisms analysing their energy barrier diagrams using the hybrid density functional theory method M06-2X. The feasibility of these decomposition reactions was calculated specifically for MA, monomethyl Meldrum’s acid (MMA), dimethyl Meldrum’s acid (DMMA), methylene Meldrum’s acid (MeMA) and (dimethylamino)methylene Meldrum’s acid (DMAMeMA), based on previous experimental analysis. The barrier to initial decomposition products (ketene or substituted ketenes with CO2 and acetone) were found to be endothermic requiring activation energies (∼180 – 230 kJ/mol) at decomposition temperatures of 280, 299, 301, 503 and 414 K respectively. Transition state theory calculations show MeMA and DMAMeMA are thermally more stable than other derivatives with low values for the rate constants and high energy barriers to produce initial decomposition products, suggesting they can produce fine carbon materials during carbonization. DMMA is found the best option for obtaining heteroatoms-doped carbon material formation.

Investigation on the influence of reaction temperature on the structural and magnetic properties of morphologically diverse carbon nanotubes synthesized using LaNi5Pt0.5 alloy catalyst

The decisive aim of this work relies on studying the impact of catalytic reaction temperature on the physiognomies of the carbon nanotubes (CNTs) synthesized through the catalytic chemical vapor deposition (CCVD) technique. LaNi5Pt0.5 alloy catalyst was employed to mediate the nucleation and growth of CNTs under three different reaction temperatures. Preliminarily, X-ray diffraction analysis and Raman spectroscopical investigation confirm the successful formation of carbon material under the reported reaction parameters. Further, the morphological diversity of CNTs produced through the influence of reaction temperature is verified through Field emission scanning electron microscopy and transmission electron microscopy. The CNTs were observed as helically coiled, Ni encapsulated, and hollow with a narrow cavity at 600 °C, 700 °C, and 800 °C respectively. Moreover, selected area electron diffraction analysis and energy dispersive X-ray analysis authenticated the aforementioned inferences. A detailed study of the growth mechanism based on the reaction temperature and its influences on the catalyst bed and decomposition of the carbon source is proposed. Finally, the prepared CNTs were distinguished through the magnetic coercivity values and the magnetic properties were studied.

Carbon Fibers Prepared via Solution Plasma-Generated Seeds.

Carbon fibers are materials with potential applications for CO2 capture due to their porous structure and high surface areas. Nevertheless, controlling their porosity at a microscale remains challenging. The solution plasma (SP) process provides a fast synthesis route for carbon materials when organic precursors are used. During the discharge and formation of carbon materials in solution, a soot product-denominated solution plasma-generated seeds (SPGS) is simultaneously produced at room temperature and atmospheric pressure. Here, we propose a preparation method for carbon fibers with different and distinctive morphologies. The control over the morphology is also demonstrated by the use of different formulations.

Plasma–Solution Junction for the Formation of Carbon Material

The solution plasma process (SPP) can provide a low-temperature reaction field, leading to an effective synthesis of N-doped graphene with a high N content and well-structured planar structure. However, the interactions at the plasma–solution interface have not been well understood; therefore, it needs to be urgently explored to achieve the modulation of the SPP. Here, to address the knowledge gap, we experimentally determined the physical parameters of the spital distribution in the plasma phase, plasma–gas phase, and gas–liquid phase of the SPP by the Langmuir probe system with modification. Based on the assumption that plasma can act similarly to semiconductors with the Fermi level above the vacuum level, an energy band diagram of the plasma–solution junction could be proposed for the first time. It was observed that the Fermi level of the organic molecule could determine the magnitude of electron temperature in plasma, i.e., benzene produced the highest electron temperature, followed by phenol, toluene, and aniline. Finally, we found that the electron temperature at the interface could induce quenching, leading to the formation of multilayer large-size-domain carbon products. It provided significant evidence for achieving nonequilibrium plasma modulation of carbon nanomaterial synthesis.

Formation of Carbon Materials by the Oxidative Pyrolysis of Methane on Resistive Catalysts

Formation of Carbon Materials by the Oxidative Pyrolysis of Methane on Resistive Catalysts

Insights into the Reaction Routes for H2 Formation in the Ethanol Steam Reforming on a Catalyst Derived from NiAl2O4 Spinel

This work describes the satisfactory performance of a Ni/Al2O3 catalyst derived from NiAl2O4 spinel in ethanol steam reforming and focuses on studying the prevailing reaction routes for H2 formation in this system. NiAl2O4 spinel was synthesized using a coprecipitation method and reduced at 850 °C to obtain a Ni/Al2O3 catalyst. The spinel structure and catalyst were characterized using XRD, TPR, N2 physisorption, NH3 adsorption and TPD, TPO, SEM, and TEM. The experiments were carried out in a fluidized-bed reactor at 500 or 600 °C and different space-time values, using pure ethanol, ethanol–water, pure ethylene, or ethylene–water feeds. The reaction takes place through two paired routes activated by each catalyst function (metal and acid sites) whose extent is limited by the selective catalyst deactivation. The results evidence that at the beginning of the reaction the main route for the formation of H2 and carbon (nanotubes) is the dehydration of ethanol on acid sites followed by decomposition of ethylene on the Ni–Al2O3 interface. This route is favored at 500 °C. After the rapid deactivation of the catalyst for ethylene decomposition, the route of H2 formation by steam reforming of ethanol and water gas shift reactions over Ni sites is favored. The morphology of the carbon deposits (nanotubes) allows the catalyst to maintain a notable activity for the latter pathways, with stable formation of H2 (during 48 h in the experiments carried out). At 600 °C, the extent of the gasification reaction of carbon species lowers the carbon material formation. The high formation of carbon material is interesting for the coproduction of H2 and carbon nanotubes with low CO2 emissions.

Self‐Assembly/Sacrificial Synthesis of Highly Capacitive Hierarchical Porous Carbon from Longan Pulp Biomass

AbstractExploration of efficient strategies for highly capacitive electrodes is of great significance for the development of advanced energy devices. Herein, we propose a novel method for the preparation of a hierarchical porous carbon material derived from longan pulp biomass for application in supercapacitors. First, a precursor of the two‐dimensional graphitized carbon with uniform carbon spheres is self‐assembled via a hydrothermal method with a post‐calcination process. After that, the longan pulp hierarchical porous carbon with inner pores is achieved through an embedding method with a mixture of precursor, KOH and KCl at high‐pressure and appropriate annealing temperature by self‐sacrificial means. The rich mesopores inside the sheet of LHPC‐3 demonstrate a more conducive strategy to create holes inside the materials, which is beneficial for electrical double‐layer capacitance. As a result, the LHPC‐3 is characterized with a high specific surface area of 1678 m2 g−1 and an abundance of meso‐/micropores, which facilitate the electrolyte penetration and mass transfer rates. Accordingly, LHPC‐3 exhibits an excellent specific capacitance of 380 and 153 F g−1 at 0.5 A g−1 in three‐electrode and symmetric supercapacitor systems, respectively. The new synthesis strategy is more conducive to the internal pore formation of carbon materials and has the potential to be widely applied to the synthesis of other electrochemical materials.

The effects of anions on the structure and the electrochemical performance of carbon materials for supercapacitors

A simple method by using Ni-based salts as the catalysts has been successfully developed to prepare porous carbons. The results show that Ni-based salts significantly affect the morphology, porous structure and graphitization degree of carbon materials. More importantly, it is found that the anions in the Ni-based salts also play important roles sor have synergistic effects for the formation of carbon materials. The obtained porous carbons can be used as electrode materials for supercapacitors and present excellent electrochemical behaviors. It is found that mesopores can accelerate the ion diffusion, ensuring full utilization of micropores and increasing gravimetric capacitance. Furthermore, a rational proportion between mesopores and micropores is also important for improving the electrochemical performance of porous carbons. In addition, the better electron conductivity arising from higher graphitization degree is also beneficial for the improvement of electrochemical behaviors.

Improving the Micropore Capacity of Activated Carbon by Preparation under a High Magnetic Field of 10\u2009T

The influence of an applied magnetic field on the formation of carbon materials from coal tar pitch is investigated. Under an applied magnetic field, crystallites in a mesophase resembling liquid crystals are magnetically oriented during the carbonization process. Compared with that under a nonmagnetic field, carbonized coal tar pitch under a strong magnetic field of 10 T, generated by a superconducting magnet, has a highly oriented structure of carbon crystallites. The orientation of samples prepared under 2 T, which can easily be supplied by an electromagnet, was insufficient. Activation by potassium hydroxide is effective for affording a precursor for activated carbon. The activated carbon obtained under a strong magnetic field has a unique adsorption ability, which arises from its increase in relative surface area and total pore volume compared with those of an activated carbon sample prepared from a precursor produced under zero magnetic field. The precursor carbonized under a magnetic field of 10 T contains a larger number of crystallites than that carbonized under a 0-T magnetic field, which leads to high-performance activated carbon.

Hierarchical nanostructured carbons as CO2 adsorbents

Synthesis and characterization of hierarchical carbon materials, CMK-5 type, with high specific surface areas and large pore volumes is reported and tested in CO2 adsorption. These materials were successfully synthesized by the nanocasting process using a hard silica template SBA-15, furfuryl alcohol (FA) as carbon precursor, and 1,3,5-trimethylbenzene (TMB) as solvent. The percentage of FA, and the FA:TMB volume ratio were the synthesis parameters evaluated to determine the accurate amounts to impregnate the pore walls of the template. Both parameters influence the formation of carbon materials with a 2D porous structure and hexagonal tube array. CMK-5 materials achieved specific surface areas up to 2200 m2/g and total pore volumes ca. 2 cm3/g. The characterization techniques allowed us to establish a correlation between the different textural, structural and morphological properties and the carbon dioxide adsorption capacity. The CO2 adsorption capacity at 308 K up to 1 bar has a strong relationship only with the micropore volume, but at higher pressure (up to 10 bar) the CO2 adsorption capacity depends not simply on the amount of micropores but also of the small mesopores present in these carbons, reaching a maximum value of 7 mmol/g, at 308 K and up to 10 bar.

Structural Properties of Porous Carbon Material Formation Activated with Potassium Hydroxide

Structural Properties of Porous Carbon Material Formation Activated with Potassium Hydroxide

Carbon material formation and residue characteristics of SBA-15 and nickel impregnated SBA-15 as exemplified by acetone decomposition

Abstract In this research, SBA-15 (Santa Barbara Amorphous-15) is used as the template and nickel serves as the impregnating catalyst for conversion to Ni-SBA-15. In the present test, the BET surface area of SBA-15 is 652 m2/g and Ni-SBA-15 477 m2/g. The average pore size for SBA-15 is 41 A and for the Ni-SBA-15 is 56 A. The carbon material synthesized between 650 and 850 °C using scarping acetone solvent on the templates. Analysis reveals that the bigger the average pore diameter, the smaller the BET surface area and pore volume of the carbon materials which form on SBA-15 and Ni-SBA-15. The exterior of the SBA-15 becomes coated with soot particles; acetone and Ni-SBA-15 combine to form carbon nanotubes at 650, 750, and 850 °C. Less than 10% of the acetone forms carbon materials on the templates, with the majority decomposing to form tar or be discharged as exhaust gas. During the gas phase, BETX (benzene, ethyltoluene, toluene, and xylene), propene and isopentane are the main VOC compositions during solvent pyrolysis. PAHs are mainly composed of naphthalene and pyrene during the acetone breakdown on the SBA-15 and Ni-SBA-15. These results reveal that Ni catalyst can enhance PAH formation to form carbon materials and decrease VOC concentration.

Fundamental Study of Carbon Materials Derived from Empty Fruit Bunch via Hydrothermal Carbonization

The utilization of biomass has recently gained great attention in recent years owing to growth of global environmental concerns. The aim of this work is to study the morphology of carbon materials derived from biomass oil palm empty fruit bunch (EFB) via hydrothermal carbonization (HTC) at different temperatures (160 - 200 °C) and times (4 - 12 h) followed by carbonization at 300 - 900 °C under nitrogen atmosphere for 2 h. The physiochemical properties of carbon sample were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and surface area analysis. The results demonstrated that the increase of hydrothermal temperature, hydrothermal time, and carbonization temperature resulted in the formation of carbon materials with higher surface area, porosity and carbon content. Our results revealed that carbon derived from EFB via HTC at optimal condition exhibited porous structure with high surface area, which can be further applied for absorbent applications.

Preparation of phenol-formaldehyde resin-coupled TiO2 and study of photocatalytic activity during phenol degradation under sunlight

In this study, phenol-formaldehyde resin-coupled TiO2 (PF/TiO2) photocatalysts were synthesized via the sol–gel method using tetrabutyl titanate as a precursor and they were tested to determine their activities during the photocatalytic degradation of phenol. The as-synthesized products were characterized using Fourier transform-infrared spectroscopy, X-ray diffraction, UV–visible diffuse reflectance spectroscopy, and transmission electron microscopy. The results showed that TiO2 was in the anatase phase in the as-synthesized PF/TiO2 product and the crystallite size was smaller than that for TiO2. The coupling of PF increased the light absorption capacity of TiO2. Under irradiation with natural sunlight, TiO2 (500 °C, 2 h) obtained a phenol degradation rate of 28.9% after 7.5 h whereas 4% PF/TiO2 (200 °C, 2 h) degraded phenol more efficiently (62.8%) in the same time according to high performance liquid chromatography. The higher photocatalytic activity of 4% PF/TiO2 (200 °C, 2 h) can be attributed to a combination of factors, including graphite carbon material formation, a smaller crystallite size, and stronger optical absorption in the visible region. The graphite carbon material facilitated better electron transport and helped to minimize electron–hole recombination in the photocatalyst, thereby enhancing the degradation efficiency.

Nitrile chain reactions for cyano-based ionic liquid derived mesoporous carbon as efficient bifunctional electrocatalyst

Different from the intermediate nitrile cyclotrimerization reactions, a new nitrile chain reaction is proposed to interpret the condensation and carbonization process of cyano-based ionic liquids [MCNIm][TFSI] which is used as a model precursor. The nitrile chain reaction forms several oligomers including dimers, trimers and tetramers during the condensation process at low temperature. The results show the oligomers are pyrolyzed to small fragments at high temperature undergoing a variety of cross-linking and recombination to produce more stable benzene and pyridine based polycyclic aromatic groups prior to the final mesoporous carbon material formation. The cyano-based ionic liquids and nitrile chain reaction mechanism readily yields mesoporous carbon with a specific surface area of 1050 m2 g−1 and a high co-doping with N and S and a content of graphitized material. In terms of potential applications, the N, S-codoped mesoporous carbon material facilitates excellent bifunctional electrocatalytic activity toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) comparable to the benchmark of those commercial 20 wt% Pt/C and RuO2 catalysts, respectively. Remarkably, our analyses show bis(trifluoromethanesulphonyl)-imide (TFSI) anions display much better thermal stability than imidazolium cations, which suggests future potential for other functional cations with more thermally stable intermediate polymeric structures.

Toluene decomposition on mesoporous templates to form carbon materials and residue characteristics

Santa Barbara Amorphous-15 (SBA-15) was selected as the template and Ni as the catalyst. The BET surface areas of SBA-15 and Ni-SBA-15 were 626 ± 55 and 458 ± 65 m2/g, respectively, and the pore sizes were 45 ± 5 and 48 ± 5 Å, respectively. These materials were identified as mesoporous and were composed of a series of small rods into organized bundles and an orderly hexagonal structure. Carbon material was synthesized at 750–950 °C using toluene as the carbon source on the templates. Results showed that the average pore diameter increased with a decrease in BET surface area and pore volume for the formation of carbon materials on SBA-15 and Ni-SBA-15. Only soot particles remained on the surface of SBA-15, but toluene accompanied by Ni-SBA-15 formed carbon nanotubes at 850 and 950 °C. There was less than 15% toluene to form carbon materials on the templates, and most of the toluene decomposed to form tar and exhaust gas. During toluene pyrolysis, benzene, ethyl toluene, toluene, and xylene were the main VOCs in the gas phase. Naphthalene and pyrene were the primary PAHs during toluene breakdown on SBA-15 and Ni-SBA-15. The work indicates that the Ni catalyst could decrease VOC concentration and enhance the formation of carbon materials.

Characteristics of Carbon Material Formation on SBA-15 and Ni-SBA-15 Templates by Acetylene Decomposition and Their Bioactivity Effects.

Carbon spheres and tubes were formed from acetylene decomposition on SBA-15 and Ni-SBA-15 at 650–850 °C. At 650 °C, the decomposed carbons covered the surface of the support, and no carbon spheres and filament materials were formed. Carbon sphere formation occurred at 750 °C–850 °C; with diameters ranging from 0.8 μm–1.1 μm. For Ni-SBA-15, the diameters of the spheres and filaments were 0.8 μm and 62 nm, respectively, at 650 °C. At 750 °C, the diameter of the ball carbon materials ranged from 0.7 μm–0.8 μm, the diameter of the carbon tubes formed was 120–130 nm, and their pore diameter was 8.0 nm–11 nm. At 850 °C, the diameters of ball carbon materials and carbon tubes were similar to those of the materials at the formation temperature, 750 °C. Si, O and C were the main constituents of SBA-15; Ni-SBA-15 and carbon material formation supports. High-ring PAHs (such as BaP (five rings); IND (six rings); DBA (five rings) and B[ghi]P (six rings)) exist in carbon materials. SBA-15 revealed insignificant cytotoxicity, but Ni-SBA-15 inhibited the proliferation of human lung cancer cells (A549). Less inhibition on cell viability and reactive oxidative species (ROS) generation on A549 were determined for carbon material formation on the Ni-SBA-15 compared to the Ni-SBA-15.

Carbon material formation on SBA-15 and Ni-SBA-15 and residue constituents during acetylene decomposition

Carbon materials including carbon spheres and nanotubes were formed from acetylene decomposition on hydrogen-reduced SBA-15 and Ni-SBA-15 at 650–850°C. The physicochemical characteristics of SBA-15, Ni-SBA-15 and carbon materials were analyzed by field emission scanning electronic microscopy (FE-SEM), Raman spectrometry, and energy dispersive spectrometry (EDS). In addition, the contents of polyaromatic hydrocarbons (PAHs) in the tar and residue and volatile organic compounds (VOCs) in the exhaust were determined during acetylene decomposition on SBA-15 and Ni-SBA-15. Spherical carbon materials were observed on SBA-15 during acetylene decomposition at 750 and 850°C. Carbon filaments and ball spheres were formed on Ni-SBA-15 at 650–850°C. Raman spectroscopy revealed peaks at 1290 (D-band, disorder mode, amorphous carbon) and 1590 (G-band, graphite sp2 structure)cm−1. Naphthalene (2 rings), pyrene (4 rings), phenanthrene (3 rings), and fluoranthene (4 rings) were major PAHs in tar and residues. Exhaust constituents of hydrocarbon (as propane), H2, and C2H2 were 3.9–2.6/2.7–1.5, 1.4–2.8/2.6–4.3, 4.2–2.4/3.2–1.7% when acetylene was decomposed on SBA-15/Ni-SBA-15, respectively, corresponding to temperatures ranging from 650 to 850°C. The concentrations of 52 VOCs ranged from 9359 to 5658 and 2488 to 1104ppm for SBA-15 and Ni-SBA-15 respectively, at acetylene decomposition temperatures from 650 to 850°C, and the aromatics contributed more than 87% fraction of VOC concentrations.

Nitrogen-containing mesoporous carbons prepared from melamine formaldehyde resins with CaCl 2 as a template

Melamine formaldehyde resins were synthesized with encapsulated CaCl 2 as a template. Carbonization at high temperatures led to the formation of carbon materials containing N atoms. Washing with de-ionized water removed encapsulated CaCl 2, resulting in the formation of mesopores (3–30 nm) with the high surface areas (770–1300 m 2/g). The template can be recycled and the method is simple and cost effective as compared to the hard template techniques. The mesoporous carbons containing nitrogen (NMC) thus prepared exhibited the amphipathic surfaces (both hydrophilic and lipophilic) and adsorbed great amount of water and benzene. In addition, the incorporated N atoms exhibited quite strong basicity for the adsorption of great amount of SO 2.