High yield one-step synthesis of carbon spheres produced by dissociating individual hydrocarbons at their autogenic pressure at low temperatures

Hydrocarbons containing 5–14 carbon atoms (pentane, cyclohexane, camphorquinone, xylene, mesitylene, camphene, decahydronaphthalene, diphenylmethane, and anthracene) are individually dissociated under their autogenic pressure developed at 700 °C to produce pure carbon moieties from the respective hydrocarbon precursor. From all of the hydrocarbons, more than 99% pure carbon is obtained in spherical, filament- or egg-like microstructures. One of the key peculiarities in the thermal dissociation of various hydrocarbons, followed by solidification under autogenic pressure, is the formation of products in micrometer dimensions. It is in contrast to previous work with organometallic precursors, which yield nanometric products via a similar method. These results are compared with those obtained for the thermal dissociation of the same hydrocarbons under flow conditions. Specific systematic morphological, structural, and compositional analysis is presented for the products obtained from the thermal dissociation of diphenylmethane. A possible formation mechanism for the obtained products is provided.     

Transesterification kinetics of palm olein oil using supercritical methanol

Continuous transesterification of palm olein oil using supercritical methanol was investigated in the absence of a catalyst. The variables studied were reaction temperature (270–350 °C), pressure (20–40 MPa), and residence time (5–25 min), with a methanol-to-oil molar ratio of 40. Preheating at 245 °C was used to form a homogeneous phase in the absence of thermal decomposition of palm olein oil. The activation energies and reaction activation volumes of the fatty acid methyl ester (FAME), and those of the individual components (C16:0, C18:0, C18:1, and C18:2 methyl esters), were calculated. The entropies of activation (ΔS^‡) of the transesterification reactions were also obtained. As the transesterification of vegetable oil in supercritical methanol included a strongly negative (−175 J/mol K) entropy of activation, transesterification required harsh conditions.     

XPS and NMR studies of phosphoric acid activated carbons

Chemical structure of phosphorus species in two series of polymer-based and fruit-stone-based carbons obtained by phosphoric acid activation at 400–1000 °C were investigated by XPS and solid state ³¹P-NMR and ¹³C-NMR. It has been shown that the most abundant and thus thermally stable phosphorus species in all investigated carbons is phosphate-like structure bound to carbon lattice via C-O-P bonding. Small contribution of phosphonates (C-P-O linkage) was observed by ³¹P NMR in carbons obtained at temperature range of 500–700 °C, phosphorus oxide was evidenced by XPS in carbon prepared at 900 °C and elemental phosphorus in carbon activated at 1000 °C.     

Synthesis of monodispersed prolate spheroid shaped paramagnetic carbon

We demonstrate a single step, efficient, catalyst-and-solvent-free and scalable process for the synthesis of monodisperse, prolate spheroid shaped carbon (PSC) with 3 μm polar and 1.5 μm equatorial diameters by thermolysis of refined corn oil in a closed SS reactor at 700 °C. The autogenic pressure and in situ mass spectra during the thermolysis of corn oil were measured to gain insight on the reaction products as a function of temperature. We have characterized the morphology, structure, composition and magnetic property of PSC by using SEM, EDX, XRD, pair distribution function (PDF), solid state ¹³C NMR, Raman spectroscopy and EPR. We propose a putative mechanism for their formation by using all the complementary data.     

Carbon spherules: synthesis, properties and mechanistic elucidation

Perfect spherical morphology of non-graphitic carbon is prepared by heating mesitylene at 700 °C in a closed cell. It produced mono-dispersed, 2.5 ± 0.05 μm size carbon spherules with a smooth surface, and which have a surface area of 8 m²/g. Morphological and structural analysis of the product is carried out with TEM, HR-SEM, BET surface area, EDAX, C, H, N, S analysis, XRD, HR-TEM, ESR and Raman spectroscopy. The formation of the spherical shape of the carbon bodies is discussed on the basis of the arrangement of the disordered carbon layers.     

The electronic behavior of calcined material obtained from a manganese-O-phenylene-S-rhenium-S-phenylene hybrid copolymer

The calcinations of a manganese-O-phenylene-S-rhenium-S-phenylene hybrid copolymer under an argon atmosphere at 600–900 °C were carried out. Calcined materials were found to be composed of MnS particles and metallic Re in a matrix of carbon clusters. ESR spectra reveal the calcined materials to have a photoresponsive oxidation–reduction function via the electron transfer process MnS → Re and/or carbon clusters. The surface of the calcined materials was modified with Pt particles and the reduction ability of the resulting materials was examined. It has been found that the material calcined at 800 °C loaded with Pt particles could decompose water under visible-light irradiation.     

Synthesis of carbon nanobelts using a colloidal suspension of Co–Al layered double hydroxide nanosheets

A solvothermal method was developed to synthesize carbon nanobelts using a colloidal suspension of Co–Al layered double hydroxide nanosheets. The product is composed of abundant belt-like bundles with a width of 30–100 nm and a length of up to 1 μm. X-ray diffraction patterns show only one sharp reflection at the 2θ value of 26.9°. A control experiment shows that the dodecylsulfate anion is helpful for the formation of well-defined carbon nanobelts.     

Controlling the diameter distribution of carbon nanotubes grown from camphor on a zeolite support

Single-wall and multi-wall carbon nanotubes (SWNTs and MWNTs, respectively) of controlled diameter distribution were selectively grown by thermal decomposition of a botanical hydrocarbon, camphor, on a high-silica zeolite support impregnated with Fe-Co catalyst. Effects of catalyst concentration, growth temperature and camphor vapor pressure were investigated in wide ranges, and diameter distribution statistics of as-grown nanotubes was analyzed. High yields of metal-free MWNTs of fairly uniform diameter (∼10 nm) were grown at 600-700 °C, whereas significant amounts (∼30%) of SWNTs were formed at 850-900 °C within a narrow diameter range of 0.86-1.23 nm. Transmission electron microscopy and micro-Raman spectroscopy reveal that camphor-grown nanotubes are highly graphitized as compared to those grown from conventional CNT precursors used in chemical vapor deposition.     

Surface characteristics and electrochemical capacitances of carbon aerogels obtained from resorcinol and pyrocatechol using boric and oxalic acids as polymerization catalysts

Carbon aerogels were prepared by carbonizing (at 500–1500 °C) organic aerogels obtained from the polymerization reaction of resorcinol and/or pyrocatechol with formaldehyde using boric and oxalic acids as polymerization catalysts. Prepared samples were characterized by different techniques to ascertain their composition, surface chemistry, morphology, and surface physics, determining their electrochemical capacitances in acidic medium. The use of pyrocatechol yielded carbon aerogels that were micro–mesoporous, showing Type IV N₂ adsorption isotherms with Type H2 hysteresis cycles. The volume and size of mesopores depended on the acid catalyst used and the temperature at which the carbon aerogel was obtained. Conversely, the sample prepared with resorcinol and boric acid as catalyst was micro–macroporous and that obtained with a resorcinol–pyrocatechol mixture was micro–mesoporous but with large mesopores. Most of the boric acid used was lost during the exchange of water with acetone in the organic hydrogels before their supercritical CO₂ drying. Carbon aerogels obtained at 900 °C and using boric acid as polymerization catalyst showed a capacitance between 17 and 24 μF/cm². Boron influenced the capacitance because it increased the oxygen content. Sample synthesized using pyrocatechol, formaldehyde, and oxalic acid and heat-treated at 900 °C had the highest capacitance, 34 μF/cm².     

Thermal treatment of pyrolytic lignin and polyethylene terephthalate toward carbon fiber production

In this work, pyrolytic lignin (PL) was thermally co-treated with polyethylene terephthalate (PET) to produce carbon fiber precursor. The produced PL-PET precursors were thoroughly characterized and analyzed, and then being processed into carbon fiber. It was found that a novel precursor, rather than their physical blending, was formed by the thermal co-treatment, indicating there were strong interactions between PL and PET. The novel PL-PET precursors had enhanced thermal properties and rheological characteristics, therefore are more suitable for processing into better carbon fibers based on melt-spinning method. In this study, the precursor fibers derived from the co-treatment of PL and 5% PET were also stretched under tension during stabilization step to reduce the fiber diameter and improve molecular orientation. The resulting carbon fibers with an average diameter of 12.6 μm had the tensile strength of up to 1220 MPa. This work demonstrated that PET could be used to improve the processability and quality of lignin-based carbon fiber when it is chemically bonded with lignin-based precursor. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48843.     

Facile synthesis of polypyrrole nanospheres and their carbonized products for potential application in high-performance supercapacitors

A facile method to prepare uniform polypyrrole (PPy) nanospheres is developed by using 3-chloroperbenzoic acid as oxidant, structure-induced reagent and dopant for polymerization of pyrrole without introducing extra acid, template and surfactant. The as-synthesized PPy nanospheres with an average diameter of 100–200 nm and conductivity about 10⁻² S cm⁻¹ are characterized by SEM, FTIR, UV–vis spectroscopy, XRD and elemental analysis in an effort to determine the identity of the nanospheres and the mechanism relevant to their formation and stabilization. Influences of experimental conditions on the morphology of the PPy nanospheres have been investigated. Via the high temperature pyrolyzation at 900 °C, the nitrogen-doped carbon nanospheres have been obtained from the PPy nanospheres precursors, which have a high conductivity of 10–100 S cm⁻¹, showing a good potential as the electrode materials for high-performance supercapacitors due to their excellent electrochemical performance.     

Synthesis of biodiesel from soybean oil using supercritical methanol in a one-step catalyst-free process in batch reactor

The transesterification of soybean oil with supercritical methanol in a batch reactor with no added catalyst was investigated, studying the evolution of intermediate products (monoglycerides and diglycerides) as well as the conversion of triglycerides and the yield of fatty acid methyl esters and glycerol. Experiments were carried out in a temperature range of 250–350 °C (12–43 MPa) at reaction times of between 15 and 90 min for a methanol-to-oil molar ratio of 43:1. The best reaction conditions in this one-step supercritical process (325 °C/35 MPa and 60 min), in which triglyceride conversion was practically total, led to a maximum yield of fatty acid methyl esters of 84%. In these conditions an 8.1 wt% of monoglycerides and diglycerides remained in the medium. Although the use of more severe reaction conditions (longer reaction times and higher temperatures) reduced the content of these glycerides, the yield of methyl esters decreased due to their thermal decomposition.     

Blends of ethylene–octene copolymers with different chain architectures – Morphology,thermal and mechanical behavior

Blends of two elastomeric ethylene–octene copolymers with similar octene contents having a random (ORC) and a blocky architecture (OBC) are prepared by melt mixing. The thermal and mechanical properties of ORC, OBC and their blends are investigated by DSC, dynamic mechanical analysis and tensile tests. The morphology of the semi-crystalline samples is studied by AFM and WAXS. Two types of crystals have been observed: (i) Orthorhombic crystals forming lamellae with an estimated thickness of about 13 nm composed mainly of long polyethylene-like sequences of OBC that melt a temperature of about 120 °C and (ii) fringed micellar crystals with a thickness of 2–4 nm formed basically by short polyethylene-like sequences of ORC that have melting temperatures between 30 and 80 °C. The amorphous phase contains a relatively homogeneous mixture of segments of both components indicated by the relatively uniform shape of the loss modulus peaks from dymamic-mechanical measurements for all investigated copolymers and blends. ORC crystallization is hindered in blends as indicated by lower melting enthalpies. This might be related to the high octene content of the amorphous phase at the relevant crystallization temperature as well as geometrical constraints since ORC crystallization occurs in an already semi-crystalline polymer. The results of tensile tests show that the mechanical behavior can be tailored via blend composition and morphology of the semi-crystalline material. The findings clearly indicate that blending is a powerful strategy to optimize the properties of polyolefin-based copolymers.     

Effect of sodium addition on the preparation of hydroxyapatites and biphasic ceramics

HAP and biphasic ceramics of two different HAP and β-TCP proportions with substituted sodium were prepared through an aqueous precipitation method. The prepared powders were characterized by XRD, thermal analysis, FT-IR and elemental analysis. Sodium was found to incorporate into the apatite structure without showing any significant change in the phase behaviour of the resultant apatites. The substitution of sodium in the calcium deficient apatites tends to form a biphasic mixture of HAP and β-TCP, while the effect of calcination beyond 700 °C and the resultant mixtures were dependent on the initial Ca/P ratios of the precursors. The calculated lattice parameter values for sodium substituted apatites have shown a marginal increase in c-axis values thereby leading to the enlargement of the hexagonal cell volume with respect to the pure HAP prepared under the same experimental conditions. Powders obtained from the present results were stable up to 1200 °C.     

The synthesis of vertically-aligned carbon nanotubes on an aluminum foil laminated on stainless steel

Aligned carbon nanotubes (CNTs) were grown on an aluminum foil laminated on a flexible stainless steel (SS) substrate. Lamination was carried out under a pressure of 10 MPa with simultaneously heating at 400 °C. The laminated Al foil was spray-coated with an iron chloride catalyst precursor solution and the CNTs were grown using water-assisted chemical vapor deposition at 810 °C. The CNTs grew as vertically aligned forests, approximately 600 μm in height, within 600 s without crumpling of the Al foil. The Al foil acts as a sacrificial barrier layer to grow the CNTs. The CNTs had 2–30 walls with an inner diameter of 3–8 nm. Thermogravimetric and field emission analysis of the CNTs revealed a degradation temperature and turn-on field of 643.5 °C and 0.46 V/μm, respectively. Transmission electron microscopy and X-ray photoelectron spectroscopy were used to analyze the Al–SS interface and chemical states. After removing the CNTs, the flexible SS substrate could be cleaned, recoated with Al and reused for CNT growth. Overall, this process is a repeatable and continuous roll-to-roll processable method that can be scaled up for industrial production.     

The effect of particle size on the formation and structure of carbide-derived carbon on β-SiC nanoparticles by reaction with chlorine

Carbide-derived carbon (CDC) coatings were produced by reaction with pure chlorine gas on the surface of β-SiC nanoparticles. Various CDC thicknesses were obtained using moderate temperatures (565–635 °C) associated with a short time (30 min) of chlorination under atmospheric pressure. Such conditions enable controlled layer-by-layer silicon extraction from SiC material. Kinetics of CDC formation were assessed using three SiC laser pyrolysis-produced nanopowders of different average size. Under the same conditions, the smallest particle size material is more prone to chlorination and exhibits a thicker carbon coating. Effect of particle size distribution on reactivity with chlorine is also discussed. After achieving carbide to carbon partial conversion, tem observations show good covering and adherent carbon coatings on remaining SiC material, N₂ adsorption analysis show that CDC coating is microporous and has a specific surface area exceeding 1000 m² g⁻¹. Thermogravimetric analysis coupled with mass spectroscopy under He gas flow, is used to determine the thermal stability and the nature of volatile species trapped in the microporosity. Under an O₂ gas flow, the amount of CDC formed is measured by burning it off at temperatures of 400–750 °C, before the onset of oxidation of the remaining SiC.     

Functional polymer–polymer/carbon nanotube bi-component fibers

Bi-component fibers typically combine multiple functions that arise from at least two distinct components. As a result, these fibers can incorporate carbon nanotubes, which impart specific and controllable mechanical, electrical, and thermal transport properties to the fibers. Using gel spinning, sheath-core polyacrylonitrile–polyacrylonitrile/carbon nanotube bi-component fibers with a diameter of less than 20 μm and carbon nanotube concentrations of up to 10 wt% were produced. In these fibers, the carbon nanotubes were well dispersed and aligned along the fiber axis. The fibers exhibited a tensile strength as high as 700 MPa, and a tensile modulus as high as 20 GPa, as well as enhanced electrical and thermal conductivities when compared to the fibers without carbon nanotubes.     

Effect of film formation process on residual stress of poly(p-phenylene biphenyltetracarboximide) in thin films

Soluble poly(p-phenylene biphenyltetracarboxamine acid) (BPDA-PDA PAA) precursor, which was synthesized from biphenyltetracarboxylic dianhydride and p-phenylene diamine in N-methyl-2-pyrrolidone (NMP), was spin-cast on silicon substrates, followed by softbake at various conditions over 80–185°C. Softbaked films were converted in nitrogen atmosphere to be the polyimide films of ca. 10 μm thickness through various imidizations over 120–400°C. Residual stress, which is generated at the polymer/substrate interface by volume shrinkage, polymer chain ordering, thermal history, and differences between properties of the polymer film and the substrate, was measured in situ during softbake and subsequent imidization processes. Polymer films imidized were further characterized in the aspect of polymer chain orientation by prism coupling and X-ray diffraction. Residual stress in the polyimide film was very sensitive to all the film formation process parameters, such as softbake temperature and time, imidization temperature, imidization step, heating rate, and film thickness, but insensitive to the cooling process. Softbaked precursor films revealed 9–42 MPa at room temperature, depending on the softbake temperature and time. That is, residual stress in the precursor film was affected by the amount of residual solvent and by partial imidization possibly occurring during softbake above the onset of imidization temperature, ca. 130°C. A lower amount of residual solvent caused higher stress in the precursor film, whereas a higher degree of imidization led to lower stress. Partially imidized precursor films were converted to polyimide films revealing relatively high stresses. After imidization, polyimide films exhibited a wide range of residual stress, 4–43 MPa at room temperature, depending on the histories of softbake and imidization. Relatively high stresses were observed in the polyimide films which were prepared from softbaked films partially imidized and by rapid imidization process with a high heating rate. The residual stress in films is an in-plane characteristic so that it is sensitive to the degree of in-plane chain orientation in addition to the thermal history term. Low stress films exhibited higher degree of in-plane chain orientation. Thus, residual stress in the film would be controlled by the alignment of polyimide chains via the film formation process with varying process parameters. Conclusively, in order to minimize residual stress and to maximize in-plane chain orientation, precursor films should be softbaked for 30 min-2 h below the onset imidization temperature, ca. 130°C, and subsequently imidized over the range of 300–400°C for 1–4 h by a two-step or multi-step process with a heating rate of ? 5.0 K min⁻¹, including a step to cover the boiling point, 202°C, of NMP. In addition, the final thickness of the imidized films should be <20 μm. © 1997 Elsevier Science Ltd.     

The influence of different carbon sources in the carbothermal reduction and nitridation (CRN) synthesis of SiAlON from nanocomposite precursors based on Al–SBA-15

Nanocomposites of Al–SBA-15 with the organic polymers poly-4-vinyl pyridine (P4VP) and polyacrylamide (PAM) were synthesized to produce SiAlON precursors containing various carbon contents. These CRN precursors, and their products after firing under N₂ at 1450 °C for 3 h were investigated by XRD, SEM/EDS and surface area analysis (BET) to compare the influence of the organic polymer carbon source. The results were also compared with those from precursors containing carbon black as the carbon source. XRD and SEM/EDS analysis of the Al–SBA-15 confirmed the formation of mesoporous structures, while BET and pore size distribution measurements indicated that the entry of P4VP into the Al–SBA-15 nanocomposite precursor is significantly more efficient than that of PAM. Firing these precursors in nitrogen produced β-SiAlON and β-cristobalite. At all carbon concentrations the P4VP nanocomposite precursors formed significantly more SiAlON than those of the PAM and carbon black precursors, due to the proximity of a greater amount of the organic carbon source to the silica template in the P4VP composite, and possibly also to the lack of oxygen in the P4VP monomer, in contrast with PAM. At least twice the stoichiometric amount of carbon was required in all cases, with optimal SiAlON formation occurring in the P4VP precursor containing 6 times the stoichiometric amount of carbon. Increasing the carbon content further suppresses SiAlON formation, possibly due to the build-up of back pressure of CO by-products in the pores of the nanocomposite.     

Ultralight conducting polymer/carbon nanotube composite aerogels

By embedding carbon nanotubes into poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT–PSS) supermolecular hydrogels in the presence of a very small amount of polyvinyl alcohol (PVA), we have presented the fabrication of ultralight conducting polymer/carbon nanotube composite aerogels with the apparent density of 0.04–0.07 g/cm³ made by supercritical CO₂ drying of as-made composite hydrogel precursors. The carbon nanotubes employed here are directly applicable to pristine (MWCNTs) or acid treated (c-MWCNTs) multi-wall nanotubes. Infra-red spectroscopy is used to confirm that PVA used for stabilizing nanotubes during the synthesis of hydrogel precursors has been completely removed by solvent exchange before supercritical CO₂ drying. The morphology and textural properties of the resultant composite aerogels are investigated by scanning electron microscopy, nitrogen adsorption/desorption, and X-ray powder diffraction tests. The thermal stability, together with electrical conductivities, of the resulting composite aerogels is revealed by the thermal gravitational analysis as well as conductivity tests. The results show that embedding of either MWCNTs or c-MWCNTs into PEDOT–PSS aerogel matrix can significantly enhance the specific surface areas (280–400 m²/g), the thermal stability and electrical conductivities (1.2–6.9 × 10⁻² S/cm) of the resulting composite aerogels.