Structure Of Carbon Layers Research Articles

Physicochemical structure, combustion characteristics and SiO2 properties of entrained flow gasification ash

During the gasification process of coal, fine ash (FA) and coarse slag (CS) solid waste are produced, which contain a large amount of residual carbon and ash (mainly SiO2), resulting in energy waste and environmental pollution. Therefore the main goal of this research is to recover the wasted energy from FA and CS. The investigation of the physicochemical structure, combustion characteristics and SiO2 properties of entrained flow gasification ash (EFGA) is an important basis for the valorization of EFGA. The physicochemical, combustion characteristics and SiO2 properties of EFGA in a entrained flow bed of 112,000 Nm3/h gas-forming capacity were investigated, showing that FA and CS undergo different gasification processes, with FA having a more developed pore structure and high specific surface area. FA and CS have different degrees of graphitization, with defects or heteroatoms in FA causing a scattered carbon layer structure with an irregular graphitic carbon crystal structure, and organic molecular functional group fragments forming an indeterminate structure and active sites. The organic molecule functional group fragments constitute an indeterminate structure and active sites. Kinetic analysis shows that the influence of chemical structure on the combustion characteristics of EFGA is higher than that of physical structure. Compared to CS, FA has fewer active sites and a small number of oxygen-containing functional groups, resulting in a weaker combustion reactivity of FA. The combustion activity of EFGA is lower than that of circulating fluidized bed gasification ash and anthracite, making it difficult to be eliminated by direct combustion, although co-combustion is feasible. The specific surface area of SiO2 prepared by EFGA after acid treatment and calcination is small (<39.7086 m2/g), SiO2 exists as crystals and the elemental silicon exists mainly in the form of Si–O, O–Si–O and hydrated silicon dioxide Si–O2-nH2O, which can be used as a raw material for the preparation of silica.

Fabrication of Si@mesocarbon microbead (MCMB) anode based on carbon texture for lithium-ion batteries

Efficient management of the carbon structure is challenging for silicon/carbon anodes for lithium-ion batteries. Here, a uniquely structured composite (Si@MCMB), with silicon nanoparticles (Si NPs) embedded in the turbostratic carbon layer texture of mesocarbon microbeads (MCMB), has been designed. Mesophase pitch was used as the carbon precursor because of its unique carbon layer structure and porosity after carbonization. As a result, the Si@MCMB composite anode showed good cycle life and rate capability compared to materials obtained by the conventional carbon coating method. This arrangement of the turbostratic carbon layer texture should provide silicon volume expansion space, ion/electron diffusion channels, and mechanical strength.

Synergistic flame retardancy of linear low-density polyethylene with surface modified intumescent flame retardant and zinc borate

Aluminum diethylphosphinate (ADP) was surface modified with the silane coupling agent KH-560, and mixed intumescent flame retardants (IFRs) were prepared with neopentyl glycol (NPG) and melamine (MEL). Then mixed IFRs and zinc borate (ZB) were compounded and added into linear low-density polyethylene (LLDPE) material. The morphology, composition, and structure of LLDPE/IFRs/ZB composites were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The maximum limiting oxygen index of LLDPE/IFRs/ZB composites is 28.7%, and the combustion grade is V0. The thermogravimetric analysis results showed that the thermal degradation rate of LLDPE/IFRs/ZB composites decreased, and the carbon residue reached 15.3 wt% at 700 ℃. The cone calorimeter test showed that peak heat release rate (PHRR), total heat release rate (THR), peak smoke release rate (PSPR), and total flue gas output (TSP) of LLDPE/IFRs/ZB composites decreased by 52.5%, 24.7%, 30%, and 15.5%, respectively, compared with pure LLDPE, significantly improving the flame retardant and smoke suppression performances of LLDPE. The residual carbon analysis shows that the CC and POC bonds in the modified mixed IFR strengthen the carbon layer structure and form a denser intumescent carbon layer, effectively hindering flame propagation. The experimental results show that the new intumescent flame retardant is a remarkable breakthrough in both flame retardancy and smoke suppression compared with ordinary intumescent flame retardants, and is more suitable for flame retardant polymer materials than traditional intumescent flame retardants.

Efficient oxygen evolution reaction on RuO2 nanoparticles decorated onion-like carbon (OLC)

Oxygen evolution reaction (OER) is an important half-cell reaction of the electrical water splitting, for its high overpotential associated with sluggish OER kinetics. Therefore, it is critical to develop highly active and durable electrocatalysts to reduce the overpotential. Herein, ultra-small RuO2 nanoparticles (NPs) supported on onion-like carbon (OLC) and carbon nanotube (CNT) are successfully synthesized by means of wet impregnation combined with annealing treatment, respectively. The microstructure characterization results showed OLC perfect graphitic carbon layer structure, and the RuO2 NPs supported on the OLC possess larger particle size compared with the RuO2 NPs supported on the CNT. Moreover, the electronic structure of Ru in RuO2/OLC was also optimized by the OLC support to be beneficial for the OER. The OER performance of the catalysts were investigated in 1 M KOH solution. The results show RuO2/OLC has a comparable OER activity to the commercial RuO2, but a significantly higher mass activity than the commercial RuO2. When compared with the RuO2/CNT, RuO2/OLC not only exhibits lower overpotential and Tafel slop, but also owns more active sites and higher TOF value, indicating the OLC support improved the OER activity of RuO2/OLC. Moreover, RuO2/OLC showed a superior stability compared with RuO2/CNT, which can be attributed to the excellent electrochemical oxidation-resistance of the OLC.

Highly dispersed and stable nano zero-valent iron doped electrospun carbon nanofiber composite for aqueous hexavalent chromium removal.

In this work, a nZVI doped electrospun carbon nanofiber (nZVI-CNF) composite was prepared and applied for aqueous hexavalent chromium (Cr(vi)) removal. Firstly, FeCl3/PAN nanofibers were prepared by a simple electrospinning method; Then, nZVI-CNFs were obtained by carbonization of FeCl3/PAN nanofibers at 800 °C. The surface morphology and internal structure of nZVI-CNFs were characterized by SEM and TEM, showing that the uniformly dispersed nZVI particles were well integrated into the carbon layer structure. The Cr(vi) removal efficiency of nZVI-CNFs was 91.5% with a Cr(vi) concentration of 10 mg L−1 and the mechanism was further studied by XRD and XPS. Meanwhile, the nZVI-CNFs exhibited good stability over a wide range of pH values from 4–8 and a long time placement stability. Furthermore, nZVI-CNFs can be used as a filter membrane for continuous treatment of wastewater, suggesting great potential for practical application.

The behavior of the different catalysts for model carbon hydrogasification

The catalytic hydrogasification of activated carbon/bituminous char/anthracite char with the different catalysts were performed in a pressurized thermogravimetry analysis (PTGA). The GC, BET were used to characterize the physical structure and chemical reaction process ofcarbon. The function principle of Co to the carbon-hydrogen reaction was preliminarily obtained. The results showed that the catalytic activity of transition metals (Fe, Co, Ni) was significantly better than that of alkali metals and alkaline earth metals during the process of activated carbon hydrogasification. There were two catalytic zones of low temperature (600–750°C) and high temperature (> 800°C) in the catalytic process. The emergence of the low temperature catalytic zone could be attributed to the interaction between the transition metal oxides and carbon. The transition metal was embedded in carbon layer structure during the activated carbon hydrogasification, then parts of carbon structure was activated, resulting in the cleavage of carbon-carbon bonds. The adequate active hydrogen could be supplied by Co at 850°C when the pressure was beyond 1 MPa. Briefly, the reaction temperature was the crucial factor for the cleavage of carbon-carbon bonds. The model carbon with higher specific surface area and weaker carbon structure could be converted efficiently even with lower loading amount of catalyst.

Effect of aluminum hydroxide (ATH) on flame retardancy and smoke suppression properties of SBS-modified asphalt

In this study, ATH-modified asphalt of different compositions (0wt%, 5wt%, 10wt%, 15wt%, and 20wt%) were prepared for testing. Its flame-retardant performance and dynamic smoke release characteristics were investigated by using the limiting oxygen index (LOI) test and TG-FTIR technology. After pyrolysis, the carbon layer's structure, morphology, and element distribution were analyzed by scanning electron microscopy-energy disperse spectroscopy (SEM-EDS). Adding ATH increased the LOI value of the base asphalt by up to 23.1%. The TG-FTIR results showed that ATH significantly improved the flame-retardant performance of asphalt through three physical effects: cooling, dilution, and heat insulation. Adding ATH to asphalt affected adsorption and blocking, thus reducing smoke, promoting carbon formation, and improving its smoke suppression. Observations of the microscopic carbon layer showed that incorporating ATH improved the integrity and strength of its structure. Based on these results, a mechanistic model of the flame retardancy and smoke suppression of ATH-modified asphalt was established.

Anti-aggregation growth and hierarchical porous carbon encapsulation enables the C@VO2 cathode with superior storage capability for aqueous zinc-ion batteries

Self-aggregation and sluggish transport kinetics of cathode materials would usually lead to the poor electrochemical performance for aqueous zinc-ion batteries (AZIBs). In this work, we report the construction of C@VO2 composite via anti-aggregation growth and hierarchical porous carbon encapsulation. Both of the morphology of composite and pore structure of carbon layer can be regulated by tuning the adding amount of glucose. When acting as cathode applied for AZIBs, the C@VO2-3:3 composite can deliver a high capacity of 281 mAh g−1 at 0.2 A g−1. Moreover, such cathode also exhibits a remarkably rate capability and cyclic stability, which can release a specific capacity of 195 mAh g−1 at 5 A g−1 with the capacity retention of 95.4% after 1000 cycles. Besides that, the evolution including the crystal structure, valence state and transport kinetics upon cycling were also deeply investigated. In conclusion, benefited from the synergistic effect of anti-aggregation morphology and hierarchical porous carbon encapsulation, the building of such C@VO2 composite can be highly expected to enhance the ion accessible site, boost the transport kinetics and thus performing a superior storage performance. Such design concept can be applied for other kinds of electrode materials and accelerating the development of high-performance AZIBs.

Modified New Microporous Carbon Layer Structure for Improved PEM Fuel Cell Performance with Low-Pt Catalyst Loadings

Three types of commercial carbon black with different porosity and hydrophilicity were investigated at various conditions in a new architecture of microporous carbon layers where they are deposited directly on the low loading cathode catalyst layers (0.1 mgPt cm−2) of membrane electrode assemblies (MEAs) used in H2/O2 fuel cells. The benefits of this modified microporous layer (MPL) include reduced interfacial gaps present between the catalyst layer and the conventional MPL-coated gas diffusion layer of the MEAs, reduced water accumulation, and therefore, higher power densities. Acetylene Black and Vulcan XC72R based modified MPLs with mass loadings in the range of 0–1.0 mg cm−2 show improved fuel cell performance in the higher current density regions due to their lower porosity and higher hydrophobicity. The MPL optimum loading under wet and dry conditions is found to be around 0.8 mg cm−2 (∼20 μm), at which a power gain of up to ∼37% is possible as a result of the improved interlayer contact and mass transport under wet conditions as well as enhanced membrane and cathode catalyst layer hydration under dry conditions. Detailed performance characteristics and longer-term studies performed under different humidification levels were also examined and are discussed in this paper.

Acicular or octahedral Fe3O4/rice husk-based activated carbon composites through graphitization synthesis as superior electromagnetic wave absorbers

We designed unique acicular or octahedral Fe3O4/rice husk-based activated carbon (AC) composites in electromagnetic wave (EMW) absorption. The key factors included the carbon layer structure and the regular metal oxide (Fe3O4) morphology. Particularly, the experiments involved a thorough ball milling method on biological substrates, which would significantly improve the absorber performance than conventional treated steps. The microstructures were controlled flexibly by adjusting the ratio of activator and magnetizing agent. The formed pores and the regular structures enhanced multiple interface polarizations. The minimum reflectance (RLmin) values of sample H4 reached –52.137, –41.918, –51.733, and –47.614 dB at 1.669, 2.002, 2.393, and 3.000 mm, respectively. The RLmin values were mainly concentrated in C, X and Kμ bands, and the reflectance (RL ≤ –10 dB) values covered a wide frequency range of approximately 13 GHz. In summary, the composites had the characteristics of interface engineering, high specific surface area, strong dielectric, and magnetic loss.

Thermal-insulating, flame-retardant and mechanically resistant aerogel based on bio-inspired tubular cellulose

Inspired by the tubular structures found in naturally occurring thermal-insulating materials, tubular cellulose aerogels with improved mechanical resistant, thermal-insulating and flame-retardant properties were prepared from kapok fibers via a facile process. In contrast to fragileness of traditional organic-inorganic composites, an optimized sample exhibited an ultra-high compressive strength of 32 MPa. The tubular structure of this material resulted in a 37.4 °C increase in heat preservation compared with that obtained from a pulp aerogel without this morphology. The H3PO4 decomposed from (NH4)2HPO4 in the formulation crosslinked the outermost cellulose fibers to generate a clay-reinforced dense carbon layer in conjunction with montmorillonite, which restricted the movement of flames and the outflow of volatile compounds. The gaseous voids of internal tubular fibers interrupted the heat transport pathways to inhibit thermal transmission and trapped combustible volatiles to reduce the penetration pressure experienced by the dense carbon layer greatly. The combined effects of the carbon layer and tubular structure effectively limited the transfer of heat, oxygen and volatiles, leading to non-combustion of the optimal sample. This study provided a cost-effective and facile approach to prepare of thermal-insulating, fire-safe and high-strength aerogel showing promising applications in exterior wall insulation and vehicle interior.

Preparation of the organic–inorganic double‐shell microencapsulated aluminum hypophosphite and its improved flame retardancy and mechanical properties of epoxy resin composites

AbstractTo develop the functional particles with better flame‐retardant and compatibility with epoxy resin (EP) matrix, organic–inorganic double‐shell microencapsulated aluminum hypophosphite (MSiAHP) was prepared by situ polymerization. The water contact angles of MSiAHP (62.4°) is significantly larger than that of aluminum hypophosphite (34.4°), which shows that the organic shell material of MSiAHP endows excellent hydrophobicity and water resistance. With the incorporation of MSiAHP, EP/30%MSiAHP composite exhibits limiting oxygen index value of 27.3% and V‐0 rating. Furthermore, the cone calorimetry test reveals that MSiAHP reduces the peak heat release rate, total heat release and total smoke release of EP matrix by 33.3%, 24.4% and 56.6%, respectively. Besides, due to the unique organic–inorganic double‐shell structure of MSiAHP particles, EP/30%MSiAHP composite achieves greater thermal stability and higher char yields than pure EP. The investigation of the products in the gas and condensed phase demonstrates that MSiAHP is beneficial to the generation of a high‐density and compact carbon layer structure with a high graphitization degree, and delay the generation time of pyrolysis products in the gas phase, which can improve the fire safety of EP composites effectively. Furthermore, preeminent dispersion and compatibility of MSiAHP lead to EP/MSiAHP composites with excellent mechanical properties.

The heat insulation and smoke suppression effect of M-Si-phosphocarbonaceous catalyzed by metal salt-doped APP silicon gel in situ build in wood

Wood is favored by furniture and decorative materials due to its beautiful color and texture, lightweight and high strength, but the thermal stability and flame retardants of wood have not been well solved. In this paper, metal salt-doped ammonium polyphosphate silicon gel (Cu, Mn/APP/Gel) was trapped in the wood cell wall and cell cavity by vacuum-pressure infusion method and vacuum drying method. Compared with unmodified wood, Cu, Mn/APP/Gel impregnated wood can rapidly enhance the flame retardant and smoke suppression capability of wood due to the catalysis of Cu2+ and Mn2+, and the total heat release rate, heat release rate peak value, mean heat release rate, smoke produce rate, total smoke release, CO and CO2 yield (YCO, YCO2) are obviously reduced. The electronic microscope picture of the burned carbon layer shows that the Cu, Mn/APP/Gel doped wood no longer has a clear and beautiful carbon layer formed by cell structure, but completely forms a whole. It is this dense and firm carbon layer structure that effectively inhibits the thermal decomposition of wood and has a role in flame retardant and smoke suppression. This study proposed an environment-friendly and green scheme for flame retardant modification of wood.

Screen-printed conductive carbon layers for dye-sensitized solar cells and electrochemical detection of dopamine

In the field of printed electronics, carbon and its allotropes are today among the most studied materials due to their unique physical and chemical properties. In this work, carbon dispersions were used for the preparation of screen-printed carbon electrodes applied as counter electrodes (CEs) for the dye-sensitized solar cells and as working electrodes for electrochemical sensing. Following the simple and quick homogenization process, carbon dispersions were subjected to thermogravimetric analysis to closely examine drying, eventually sintering processes after printing. The influence of the graphite:carbon black ratio was investigated. The structure of composite carbon layers was analyzed by scanning electron microscopy and optical microscopy. The DSSC CEs printed from the dispersion containing 100 wt% of CB exhibited the highest catalytic activity for the effective reduction of oxidized triiodide I3− back to iodide I− within the solar cell. The highest conversion efficiency achieved for the high-temperature processed CE was 3.05% with the fill factor of 0.65. The same composition of the carbon WE was used for the quantitative analysis of neurotransmitter dopamine. Based on the cyclic voltammetry measurements, the sensor showed a limit of detection of 13.3 nM for dopamine.

Coral-like porous composite material of silicon and carbon synthesized by using diatomite as self-template and precursor with a good performance as anode of lithium-ions battery

Developing silicon based anode of lithium-ion battery (LIB) is seriously blocked by the huge volume change of lithiation and delithiation and the corresponded high cost paying to solve it, although Si with the theoretical capacity of 4200 mAh g−1 for Li+ storage. In this study, natural diatomite with low cost was using as precursor and self-template to produce Si and construct porous structure, a coral-like porous Si/C (CLP-Si/C) material has been successfully synthesized through the NaCl added magnesiothermic reduction reaction (MRR) technology and acetylene CVD method. The hierarchical structure of macro-/mesopores in CLP-Si/C are inherited from diatomite itself and produced by removing the unreacted SiO2 in diatomite and the byproduct of MgO of MRR. Acetylene CVD further constructs a shell-core structure of carbon layers and Si particles. The hierarchical pores and core-shell structure make CLP-Si/C exhibit a stable cycling performance as LIB anode that the capacity of 990.6 mAh g−1 can be kept after 100 cycles at a rate of 250 mA g−1. This work provides a simple, low-cost and scalable strategy for producing porous Si/C anode materials with high-performance by using diatomite as both precursor and template, and is promising in the development of practical application of Si based anode materials of lithium-ion battery.

Facile Synthesis of Hierarchical Hollow CoP@C Composites with Superior Performance for Sodium and Potassium Storage

AbstractHierarchical hollow CoP and carbon composites were obtained through a facile synthetic method, where carbonization and phosphorization of the precursor were completed within one single step. The composites are composed of hollow CoP@C spheres, which are further made up of CoP nanoparticles with a thin outer carbon layer. Electrochemical performances of the prepared CoP@C composites as anodes for sodium and potassium storage were evaluated and compared. In situ TEM, in situ synchrotron XRD, and DFT calculations were conducted to study the structural evolution and the interaction between Na/K and CoP during cycling processes. Benefiting from the synergistic effect of conductive carbon layer and hierarchical hollow structure, the as‐prepared CoP@C composites demonstrate superior sodium and potassium storage capability as anode materials for rechargeable batteries.

Facile Synthesis of Hierarchical Hollow CoP@C Composites with Superior Performance for Sodium and Potassium Storage.

Hierarchical hollow CoP and carbon composites were obtained through a facile synthetic method, where carbonization and phosphorization of the precursor were completed within one single step. The composites are composed of hollow CoP@C spheres, which are further made up of CoP nanoparticles with a thin outer carbon layer. Electrochemical performances of the prepared CoP@C composites as anodes for sodium and potassium storage were evaluated and compared. In situ TEM, in situ synchrotron XRD, and DFT calculations were conducted to study the structural evolution and the interaction between Na/K and CoP during cycling processes. Benefiting from the synergistic effect of conductive carbon layer and hierarchical hollow structure, the as-prepared CoP@C composites demonstrate superior sodium and potassium storage capability as anode materials for rechargeable batteries.

Assembly of MOFs/polymer hydrogel derived Fe3O4-CuO@hollow carbon spheres for photochemical oxidation: Freezing replacement for structural adjustment

We report a new strategy for fabrication of magnetic core–shell Fe3O4-CuO@carbon hollow sphere derived from MOFs/sodium alginate (SA) hydrogel through one-pot synthesis of ferrocene CVD and pyrolysis. Development of freezing-replacement by n-hexane overcame SA capsule shrink induced by heat-treatment and created highly-stable coconut shell-like superstructures, which allowed active sites homogeneously distributed on no-defect surface and improved magnetic and photocatalytic activity of composites. The turn over frequency (TOF) of Fe3O4-CuO@C for organic pollutants degradation was 2.3 h−1 under visible light irradiation, much higher than most of reported catalysts. The synergistic effect of bimetallic clusters and carbon matrix facilitated the charge separation and accelerated H2O2 activation to yield high active radicals. Layer structure and good interfacial contact of metallic sites and porous carbon was beneficial for enhancing photocatalytic activity. The progresses offer a feasible route to rational design of MOF-derived hybrid hollow materials with tailored structure and properties for various applications.

Fabrication of hierarchical MnxOy@SiO2@C-Ni nanowires for enhanced catalytic performance

A novel structure of hierarchical SiO2@C-Ni nanoflakes on MnxOy nanowires is designed, in which Ni nanoparticles (NPs) are highly-density embedded in the carbon layer derived from polydopamine(PDA). MnO2 nanowires are started as carriers and SiO2 layer is used as scarifying template coating on the nanowires, which is further chemically reacted with nickel source to forming nickel silicate (NS) nanoflakes on MnO2 nanowires (MnO2@NS). The formed hierarchical nanoflakes of MnO2@NS are further coated by PDA, serving as a reductive agent to form Ni particles in the following N2 carbonization process. The calcination temperature has a great impact on the sizes of reduced Ni NPs, and 500℃ yields samples with ultrafine magnetic Ni NPs, while higher temperatures destroy the layer structure of graphene-like carbon and cause agglomerations of Ni NPs. MnxOy@SiO2@C-Ni/500 shows the best catalytic performance on the reduction of 4-nitrophenol due to the ultrafine and highly dispersed Ni NPs.

Optimizing nanocarbon shell in zero-valent iron nanoparticles for improved electron utilization in Cr(VI) reduction

A core-shell structured zero-valent iron@carbon (ZVI@C) nanocompoiste was designed to improve the electron utilization of ZVI in the Cr(VI) reduction. The porosity of carbon layer in ZVI@C was optimized for improving the efficiency of electron utilization of ZVI in the Cr(VI) reduction process. The porous structure of carbon layer was controllably synthesized by adjusting the carbon source and the ratio of C/Fe in the precursor. The glucose was suggested as the optimal carbon source, and a high specific surface area (37.067 m2/g) was reached for the prepared ZVI@C when the ratio of C/Fe was controlled at 20. These ZVI@C performed well on Cr(VI) reduction, e.g. a complete reduction of Cr(VI) (2 mg/L) to Cr(III) within 10 min. The removal capacity (800 mg/g) exceeded previously recorded ZVI based adsorbents. The pH and initial Cr(VI) concentration were demonstrated as the key factors for the efficient electron utilization of ZVI. Furthermore, the efficiency of electron utilization of the ZVI increased up to 80% when the concentration of Cr(VI) was 2000 mg/L and the pH was controlled at 3, which was much higher than 8% of the naked ZVI.