High Degree Of Graphitization Research Articles

Facile Synthesis of Zinc‐Containing Mesoporous Silicate from Iron Tailings and Enhanced Fire Retardancy of Rigid Polyurethane Foam

AbstractIron tailings (ITS), as solid decay absolved afterward beneficiation, are adverse to the environment. ITS to prepare zinc‐containing mesoporous silicate (MAO‐Zn) by a calcination‐crystallization method are used. An admixture of ammonium polyphosphate (APP) and MAO‐Zn can solve the problem of poor flame retardancy in rigid polyurethane foam (RPUF), giving them higher thermal stability and lower heat release. The total heat release rate and smoke factor values exhibited by RPUF‐3 are 24.52 MJ m−2 and 234.29 MW m−2 respectively, a decrease of 38.45% and 29.60% respectively compared to pure RPUF. Lower combustible and toxic gas release intensities are in RPUF‐3. Meanwhile, RPUF‐3 possesses enhanced compactness char residue with higher graphitization degree, endowing RPUF‐3 with excellent fire observed performance. This work demonstrates the potential of ITS in the fire retardancy field.

A comprehensive evaluation on thermo-chemical potential of longan waste for the production of chemicals and carbon materials

Longan waste (shell and seed) is a by-product of longan processing industry and accounts for near 90 % of the total fruit weight, which is a most promising renewable energy and can be converted into value-added chemicals and carbon materials by pyrolysis. However, detailed pyrolysis characteristics, kinetics, product formation mechanism, and char properties of longan waste were never studied. This work provided the first comprehensive investigations on the thermal decomposition of longan waste based on the combined pyrolysis method. The results showed that longan shell and seed were different in chemical compositions, pyrolysis characteristics, and product distributions. Longan seed was easy to decompose at a low temperature and showed a smaller Ea of about 160 kJ/mol. However, longan shell could produce more H2, CH4, HCHO, phenols, and aldehydes compared with longan seed. The formation mechanisms of 6 gases and 33 condensable compounds were deeply discussed. In addition, longan shell char was rich in Ca/Mg-containing minerals, whereas longan seed char had a higher graphitization degree and a larger surface area of 236.4 m2/g. On the whole, the longan waste is a very potential feedstock for the productions of energy, value-added chemicals, and carbon materials in an efficient and environmentally sustainable way.

Relevance of soot formation characteristics to equivalence ratio and CO2 addition of acetylene flame

Soot is a common byproduct of fuel combustion that not only blocks machine operation but damages the environment and human health. A premixed acetylene flame was used to investigate the effects of equivalence ratio (2.30–2.66) and CO 2 addition (10% ∼ 50%) on soot formation characteristics evaluated by TG, SEM, TEM, Raman, FT-IR, and XPS. In the flame at φ = 2.47, the produced soot exhibits a higher activation energy with a larger particle size, less disordered structure, lower level of aliphatic carbon and higher degree of graphitization. The addition of 25% CO 2 results in the formation of soot with low activation energy, large particles, more disordered carbons, low sp 2 /sp 3 ratio and low surface oxygen content. Furthermore, it is found that the soot oxidation reactivity is correlated to the disorder structure, graphitized degree and oxygen-containing groups. Rate of production (ROP) analysis was conducted by kinetic simulation to better understand the characteristics of acetylene soot formation. • Characteristics of acetylene soot at various equivalent ratios and CO 2 are studied. • Natures of soot show volcano curves with flame equivalence ratio and CO 2 addition. • Soot reactivity is related to disorder carbon, graphitization and oxygen content. • Effects of equivalent ratio and CO 2 on rate of production of benzene are exhibited.

Biosynthesis of conductive and paramagnetic value-added rare earth graphitic materials

Sustainable circularity of rare earth elements (REEs) can be achieved by phytoextraction of REEs from waste and remanufacturing them as value-added products. We have demonstrated erbium, europium, gadolinium, neodymium, and yttrium uptake using Eleocharis acicularis. The highest accumulation was observed for neodymium and gadolinium (56 and 55 mg/g dry weight), whereas yttrium (39 mg/g dw) had the lowest bioaccumulation from a feed solution of 300 mg/L over 10 days. The REE-accumulated biomass was used as raw material for graphitization at 1200°C. A higher degree of graphitization was observed in REE-graphitic material (GM) (0.91–0.97) and the lowest was observed in the non-exposed control biomass-GM (0.81), indicating the catalytic action of the REEs. XRD and SAED diffractograms showed the multilayer polycrystalline nature of the GMs, and Raman spectra demonstrated the presence of sp2 hybridization. Furthermore, Gd-GM had higher conductivity (1.09 × 104 S/m) than the commercial graphite (8.21 × 103 S/m) at 30 MPa applied pressure. The REE-GMs showed high capacitance (measured at 20–300 kHz) and an optical band gap of less than 1.11 eV. Additionally, Gd-GM showed significant paramagnetic properties, making it a potential precursor for sustainable MRI contrast agent synthesis.

Thermal conductivity enhancement of carbon fiber/epoxy composites via constructing three-dimensionally aligned hybrid thermal conductive structures on fiber surfaces

Owing to high graphitization degree, polyacrylonitrile (PAN)-based high modulus carbon fiber (HMCF) can not only be used as the general structural reinforcement for advanced composites, but also be applied to improve the thermal conductivities (TC) of polymer composites. However, the enhancement of through-thickness TC of composites remains extremely challenging due to fiber anisotropy and the lack of continuous thermal conductive path among CFs. In the present work, three-dimensional (3D) hybrid thermal conductive structures were constructed onto PAN-CF surfaces to prepare HMCF/epoxy composites with high through-thickness TC. In details, crosslinked high thermal conductive Ni/CNT hybrid network was firstly electrodeposited onto HMCF surfaces, which also provided abundant channels for the impregnation of easily graphitized poly-p-phenylene benzobisoxazole (PBO)/graphene oxide (GO). The freeze-drying assisted grafting of 3D-oriented PBO/GO and high-temperature heat treatments were further conducted to create the 3D graphite structures onto CFs. The interconnected Ni/CNT networks with 500 nm thickness and 3D aligned PBO-graphite bridging structures with an average thickness of 1 μm contributed to the formation of efficient heat conduction pathways along the through-thickness direction. Additionally, high-temperature treatment had been proven critical to effective heat conductions. Especially, PAN-CF with the 3D hybrid thermal conductive structures treated at 2100 °C (named CNC@PG-2100) exhibited superior TC, and the maximum TC value of CNC@PG-2100 reinforced composites reached 5.39 W/(m‧K) at the CF loading of 55%, which improved by 573% compared to that of composites reinforced by untreated PAN-CFs (0.94 W/(m‧K)).

Fe/N co-doped hierarchically porous carbon on N-doped carbon nanotubes towards oxygen reduction reaction

Rational design of efficient and durable non-noble transition metal doped carbon-based oxygen reduction electrocatalysts is the key to reduce catalyst cost and optimize fuel cell performance. Herein, hierarchically porous Fe/N co-doped porous carbon on N doped carbon nanotubes (Fe/N-C@NCNTs) are prepared via the pyrolysis of Fe-doped ZIF-8 embedded on polypyrrole nanotubes (PNTs). The as-prepared Fe/N-C@NCNTs electrocatalyst exhibits the limit current density of 5.7 mA cm−2 and the half-wave potential of 0.84 V (vs. RHE), indicating the excellent oxygen reduction performance. Furthermore, the electrocatalytic activity of Fe/N-C@NCNTs is only reduced by 7% after 650 min of the stability test. The remarkable oxygen reduction performance is attributed to the synergistic effects of abundant Fe-Nx-C active sites, high graphitization degree and hierarchically porous structure of electrocatalyst.

Unburned Carbon from Fly Ash as a Source of Graphite Materials

ABSTRACT Unburned carbon from fly ash and its graphitization products (at temperatures of 2400 and 3000°C) were tested using scanning electron microscope (SEM), X-ray diffraction (×RD) and micro-Raman spectroscopy. The same tests were also carried out for synthetic and natural graphite. Various morphological forms of products with a high degree of graphitization, such as spheroidal graphite, hexagonal plates, column plates, and jagged-edge films were identified in the sample of unburned carbon annealed at 3000°C. The product of thermal treatment at the temperature of 3000°C has the interlayer spacing d002 value characteristic for semigraphite. With increasing temperature the number of crystallites in stack N, their height Lc002 and aromaticity fa increases. The degree of G graphitization of annealed samples increases more than twice with increasing temperature. With the increase of the temperature the aliphatic chains are decomposed and the aromatic systems are reconstructed, so the degree of internal structure order increases. The Raman examinations showed that the structural parameters determined for the graphite and carbonizate samples after thermal treatment at the temperature of 3000°C are equal in the standard deviation range.

Regulating Oxygen Configuration in Hierarchically Porous Carbon Nanosheets for High-Rate and Durable Na+ Storage.

Surface oxygen functionalities (particularly C-O configuration) in carbon materials have negative influence on their electrical conductivity and Na+ storage performance. Herein, we propose a concept from surface chemistry to regulate the oxygen configuration in hierarchically porous carbon nanosheets (HPCNS). It is demonstrated that the C-O/C=O ratio in HPCNS reduces from 1.49 to 0.43 and its graphitization degree increases by increasing the carbonization temperature under a reduction atmosphere. Remarkably, such high graphitization degree and low C-O content of the HPCNS-800 are favorable for promoting its electron/ion transfer kinetics, thus endowing it with high-rate (323.6 mAh g-1 at 0.05 A g-1 and 138.5 mAh g-1 at 20.0 A g-1 ) and durable (96 % capacity retention over 5700 cycles at 10.0 A g-1 ) Na+ storage performance. This work permits the optimization of heteroatom configurations in carbon for superior Na+ storage.

Improving the flame retardancy of sustainable lignin-based epoxy resins using phosphorus/nitrogen treated cobalt metal-organic frameworks

Lignin and glyoxal are potential sustainable substitutes for preparing lignin-based epoxy resins but exhibit poor flammability; although lignin incorporation enhances the charring capacity of thermosetting materials, intense burning occurs on ignition. A metal-organic framework (P-MOF) comprising cobalt and phosphorus/nitrogen components was therefore synthesized to improve fire safety. Limiting oxygen index (LOI) and vertical burning tests (UL-94) indicate excellent flame retardancy, with a higher LOI value and V-0 rating level achieved after P-MOF addition. Cone calorimeter tests investigating gaseous inhibition of epoxy matrixes reveal that heat release and smoke production dramatically decrease on addition of P-MOF because of fire quenching (phosphorus organic component) and smoke suppression (cobalt component). Synergy between lignin and P-MOF components suppressed combustion of condensed phases, producing more char residues with a higher degree of graphitization. A mechanism for the flame retardancy of the epoxy composite is proposed, which highlights the promise of P-MOF additives for reducing fire hazards due to cobalt-catalyzed CO oxidation during epoxy burning.

Role of the Potential Range during Stress Testing of Platinum-Containing Electrocatalysts at Elevated Temperature

The durability of low temperature proton exchange membrane fuel cell (PEMFC) catalysts crucially affects their lifetime. The choice of carbon support is important in terms of increasing the stability of catalysts. In this research, Pt/C samples were obtained using the polyol synthesis method on two types of carbon supports: the standard support, Vulcan XC-72, and carbon support with a high degree of graphitization, ECS-002402. One method for assessing structural characteristics is through transmission electron microscopy (TEM), according to which materials G1 and G2 showed an average nanoparticle size of 3.7 and 4.2 nm, respectively. On all catalysts, the oxygen reduction reaction proceeded according to the four electron mechanism. Durability was assessed by changes in ESA and activity in the ORR after 1000 cycles, with changes in the upper potential values: 0.7; 1.0; 1.2; and 1.4 V. After accelerated stress testing, the G1 material showed the greatest residual activity at a potential of 1.4 V (165 A/g (Pt). Based on the results of comparing various ADT protocols, the optimal mode of 0.4 and 1.4 V was chosen, and should be used for further studies comparing the durability of Pt/C catalysts.

High performance bio-supercapacitor electrodes composed of graphitized hemicellulose porous carbon spheres.

A template-free and one-step carbonization process was developed for fabricating graphitic porous carbon spheres (GPCSs) on hemicelluloses as the electrode material for supercapacitors. This method is green, low-energy, and less time consuming compared to the conventional two-step process (pore-forming and graphitizing). It uses K2FeO4, a mild activating agent that fulfills synchronous activation and graphitization. The GPCSs is regular spherical shape, have high nanoporosity, a large specific surface area (1,250 m2 g−1), and have a high graphitization degree. A unique structural advantage includes a rich interconnected conductive network for electron transfer that shortens the ion transport distance of the electrolyte. Remarkably, the GPCSs electrode displays outstanding electrochemical performance including high specific capacitance (262 F g−1 at 1.0 A g−1), rate capability energy (80%, 20 A g−1), and excellent cycling stability (95%, 10,000 cycles). This work represents a powerful methodology to develop sustainable and low-cost energy storage devices from hemicellulose.

ZIF-8 derived bimetallic Fe–Ni-Nanoporous carbon for enhanced oxygen reduction reaction

The development of highly efficient nοn-nοble metaӏ catalysts for (ОRR) in PEMFCs is at the heart of the research, yet their performance is not satisfactory. The Fe–N active sites enclosed in carbon matrix are generally agreed to be the most promising active sites for ORR. In view of this, further effort is made to increase the Fe–N active sites. Here we present the fabrication of novel FeNi bimetallic electrоcatalyst obtained from ZIF, which consists of FeNi nanоallоys incorporated in N-doped carbon (FeNi-NC) featuring carbon nanotubes and porous carbon demonstrates outstanding results for ОRR. The Fe–N and Ni–N active sites synergistically enhance the ORR activity of FeNi-NC catalyst. The FeNi-NC showed remarkable performance in KОH with the half-wave and onset potential of 0.89 V and 0.99 V vs RHE, respectively. This catalyst shows exceptional stability in methanol equivalent to Pt/C commercial. The FeNi-NC retained 71%, while Pt/C commercial retained only 59% of its original current density. The exceptional stability and activity might be associated with the interplay among FeNi active sites and N-doped carbon, the distinct nanо-structure made up of porous carbon and carbon nanotubes with a high graphitization degree.

Controllable construction of gradient modulus intermediate layer on high strength and high modulus carbon fibers to enhance interfacial properties of epoxy composites by efficient electrochemical grafting

The interface is a fundamental and crucial research topic throughout the development of carbon fiber reinforced polymer composites. However, it is a huge challenge to solve the problem of fiber surface inertness thoroughly to enhance the interfacial bonding with the resin, especially for high modulus carbon fibers with higher degree of graphitization and fewer microcrystalline active points for commercial production. This manuscript reports that different monomers were selected to in situ electrografting on the fiber surface to design and control the physical/chemical structure and rigidity/flexibility of the interface. The interfacial bonding performance of the composites was greatly improved, interlaminar shear strength (ILSS), interfacial shear strength (IFSS) and transverse fiber bundle tensile strength (TFBT) were increased by 15.9%, 46.8% and 39.6%, respectively, and the tensile strength of the single fiber was also increased by 12.7%. This simple, efficient (1–3min), environmental (water as solvent) and economical method shows great application prospects of fiber surface treatment technology in the next generation.

Influence of active alkali and alkaline earth metals on physicochemical structures of co-pyrolysis-gasification coupling char

ABSTRACT The influences of active alkali and alkaline earth metals (Ac-AAEMs) on the physicochemical properties of chars during co-pyrolysis-gasification coupling were studied in this paper. The mixed samples were obtained according to four mixing ways: original coal and original corn stovers (OSM+OCS), pickling coal and original corn stovers (PSM+OCS), original coal and pickling corn stovers (OSM+PCS), and pickling coal and pickling corn stovers (PSM+PCS). The influences of Ac-AAEMs in OSM (Ac-AAEMs-OSM), Ac-AAEMs in OCS (Ac-AAEMs-OCS), and Ac-AAEMs in OSM+OCS (Ac-AAEMs-blends) on the pore structures of gasification chars were characterized by IOSM, IOCS, and IOSM+OCS, respectively. The results showed that Ac-AAEMs-OCS and Ac-AAEMs-blends, especially Ac-AAEMs-OCS, significantly promoted the development of mesopores. Furthermore, Ac-AAEMs-OCS and Ac-AAEMs-blends have good catalytic effects on the specific surface area of chars, especially at 20 minutes of gasification. Compared with PSM+PCS char, the specific surface areas of PSM+OCS char, OSM+OCS char, and OSM+PCS char obtained at 20 minutes of gasification increased by 203%, 157%, and 7%, respectively. Besides, the Ac-AAEMs are conducive to destroying the carbon structure with a high graphitization degree and promoting the formation of disordered amorphous carbon. The magnitude of their catalytic ability is Ac-AAEMs-blends >Ac-AAEMs-OCS>Ac-AAEMs-OSM.

Ternary (N, B, F)-Doped Biocarbon Derived from Bean Residues as Efficient Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions

Development of efficient metal-free carbon-based electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are of great significance for Zn-air batteries. Herein, a porous biocarbon bifunctional catalyst (C-NBF-G) was directly synthesized via simple alkali activation and carbonization from bean residues. C-NBF-G exhibited hierarchical porous structures, ternary heteroatom (N, B, and F) doping, a large specific surface area, and a relatively high degree of graphitization. The synergistic action of these characteristics contributed to the outstanding catalytic properties of C-NBF-G for ORR and OER. The catalyst demonstrated an onset potential of 0.94 V, half-wave potential of 0.824 V, and a limiting current density of 5.92 mA cm−2, comparable to those of the commercial 20 wt% Pt/C catalysts. C-NBF-G also exhibited an OER overpotential of 333 mV at 10 mA cm−2 and a Tafel slope of 114 mV dec−1, lower than those of the commercial Pt/C and RuO2 catalysts. These results proved the promising performance of C-NBF-G as a bifunctional catalyst for the ORR and OER.

Highly graphitized lignin-derived porous carbon with hierarchical N/O co-doping “core-shell” superstructure supported by metal-organic frameworks for advanced supercapacitor performance

Porous carbon nanoparticles have been widely utilized as electrode materials for electric double-layer capacitors (EDLCs) owing to their rich microporous and mesoporous structures. Herein, we successfully prepared lignin@ZIF-8 based carbon with hierarchical porous “core-shell” graphitized superstructure (KGC-EHL@ZIF-8) fabricated by carbonized ZIF-8 NPs as “core” and lignin derived graphitized porous carbon layer as “shell” via a two-stage carbonization-graphitization process for advanced supercapacitor performance. The prepared KGC-EHL@ZIF-8 NPs possess a high graphitization degree, high porosity with micro/meso porous hierarchical structure and high content of N/O co-dopants induced by the synergistic effects of ZIF-8 NPs coupling potassium hydroxide (KOH) activation treatment, thus guaranteeing excellent electrochemical performance. As a result, the graphitization degree of lignin-derived porous carbon “shell” structure increased with KOH ratio, and the maximum specific surface area of 2307.3 m2·g−1 was successfully obtained at a mass ratio (KOH/C-EHL@ZIF-8 NPs) of 1:1. The maximum specific capacitance within three-electrode system was 462.6 F·g−1 at 0.5 A·g−1 with a porous carbon “shell” thickness of around 75.25 nm. Moreover, the areal energy density of assembled supercapacitor can reach to 1.95 mWh·cm−2 at a power density of 27.44 mW·cm−2. This study put forward a novel strategy to efficiently harness lignin combined with a metal–organic framework for the construction of porous electrodes with hierarchical nanostructure for high-performance supercapacitors.

Construction of high-performance LiMn0.8Fe0.2PO4/C cathode by using quinoline soluble substance from coal pitch as carbon source for lithium ion batteries

LiMn0.8Fe0.2PO4 nanocrystal composite cathode material for lithium ion batteries was prepared via a simple solvothermal method. The quinoline soluble substance from coal pitch (QS) was used as the coated carbon source to prepare LiMn0.8Fe0.2PO4/C. The structural performance of QS and QS-C, and the effects of QS-C on the physical, chemical and electrochemical properties of LiMn0.8Fe0.2PO4/C were investigated. The research shows that QS is an aromatic compound containing C–N and C–S bonds, and the structure of QS-C is a streamlined structure with high graphitization degree. Hence, the N, S-dual doped carbon conductive network can be effectively established to enhance charge transfer and the diffusion and migration rate of lithium ion. The prepared LiMn0.8Fe0.2PO4/C delivery excellent specific discharge capacity of 159.2, 145.7, and 117.3 mAh·g-1 at 0.1, 1, and 5 C, respectively. After 150 cycles at 1 C, the specific discharge capacity was still 133.5 mAh·g-1, and the capacity retention is 93%. This work provides a new insight into the search for coated carbon sources.

Bitumen-Derived Onion-Like Soft Carbon as High-Performance Potassium-Ion Battery Anode.

Potassium-ion batteries (PIBs) have been regarded as a competitive alternative for lithium-ion batteries, owing to the natural abundance, low cost, and similar rocking-chair working mechanism of potassium element. However, it is challenging to simultaneously prepare suitable potassium ion anode materials of low voltage plateau, high capacity, and long cycle life. In this work, onion-like soft carbon (OLSC) of high heteroatom content is prepared by using solvent-sensitive self-assembly properties of asphaltene molecules. The OLSC electrode exhibits a low voltage plateau because of a high degree of graphitization. Meanwhile, it possesses excellent cycling stability and rate capability due to the high stability of the onion-like structure and fast transport of potassium ions, the latter of which is caused by heteroatom-induced expanded interlayers as found by first-principle calculations. Compared with existing carbon materials, the OLSC synthesized in this study exhibits a high reversible capacity of 466mAhg-1 at 20mAg-1 , a reversible capacity of 222mAhg-1 and capacity retention of 95% after 1600 cycles at 1Ag-1 . This work connects the nanostructure of carbon materials and electrochemical performance and provides new insights in improving carbon-based anodes for PIBs.

Lightweight Flexible Polyimide-Derived Laser-Induced Graphenes for High-Performance Thermal Management Applications

Laser pyrolysis of polyimide (PI) is a promising approach for preparing porous graphenes with hierarchical structures. In this study, we used a dual-focusing lens with a collimator to generate a highly concentrated CO2 laser beam with a high focal energy density. The resulting PI-derived graphene (PIDG) obtained under high-intensity laser irradiation possessed a high degree of graphitization, a low sheet resistance (27.4 Ω/sq.), and a large surface area (240.4 m2/g). Through optimization of the high-intensity laser parameters, we obtained a hierarchical PIDG possessing a fiber-like structure. We used this PIDG as a flexible heater and efficient heat sink for Si photovoltaic (PV) and light-emitting diode (LED) modules. The developed heater could reach a temperature of 202.6 °C under an applied voltage of 16 V, with rapid responses and remarkable flexibility. As a result of improved convective and radiative heat dissipation, the PIDG-based heat sink lowered the operating temperatures of the Si PV and LED modules efficiently. Accordingly, the power conversion efficiency of the Si PV and the lifetime of the LED module both increased dramatically.

Lotus pollen-derived hierarchically porous carbons with exceptional adsorption performance toward Reactive Black 5: Isotherms, kinetics and thermodynamics investigations

The removal of azo dye from wastewater is urgent due to its massive discharge from various industries and high toxicity. Adsorption is an efficient removal method, but it is limited by the low adsorption capacity of the present adsorbents. Herein, a high-efficiency and sustainable adsorbent for Reactive Black 5 (RB5) was developed, which was obtained using lotus pollen as carbon precursors followed by carbonization and activation with KOH. The as-prepared lotus pollen-derived hierarchically porous carbons (LPHPCs) showed exceptional adsorption performance for RB5, the maximal equilibrium adsorption capacity can reach 615.6 mg/g on LPHPC-2.5, and 269.6 mg/g on LPHPC-1.0, which were far superior to that of commercial activated carbon (CAC) (94.7 mg/g). Their adsorption performance for RB5 under different conditions was examined, such as different initial concentration, adsorbent dosage, inorganic salt concentration, temperature and pH. The adsorption isotherms, kinetics, thermodynamic properties and mechanisms were systematically investigated in depth. The results demonstrated that the adsorption process of RB5 onto LPHPCs involved dominant physical adsorption together with necessary chemical adsorption. The comparative advantages of LPHPCs over CAC for RB5 adsorption were ascribed to the higher specific surface area and larger appropriate pore volume, higher degree of graphitization and better affinity. The findings revealed that LPHPCs are promising adsorbents for the adsorption removal of anionic dyes from wastewater.