Nanoporous carbon/MnO2 (C–MnO2) composites with foam-like structure based on modified nitrile butadiene rubber were achieved by thermal treatment, followed by alkaline solution etching and dipping method. The XRD, nitrogen adsorption and desorption, and SEM and TEM were used to characterize the microstructure of the obtained C–SiO2, C and C–MnO2. Finally, all the obtained samples have been used in three-electrode system to study the electrochemical properties including cyclic voltammetry, galvanostatic charge/discharge and AC impedance for supercapacitor. The study found that the specific capacity of C–MnO2 electrode material for supercapacitor could reach as high as 109 F/g under the current density of 0.5 A/g, which is much higher than those of the other two. These superior electrochemical properties are attributed to the synergistic effect MnO2 particles with the C matrix which functions as a conductive support.
Microtextural and surface chemical heterogeneities of activated carbons (AC) have been studied to see their distinctive role for the adsorption of CO2, CO and N2 at 25 °C and up to 850 Torr. Not only the microtextural properties influence the adsorption of the gases, particularly CO2, but the chemical surface heterogeneity also plays a significant role for CO2 adsorption. The volume of ultramicropores < 7 Å is of predominantly importance in high CO2 adsorption at pressures above 30 Torr. However, the average size of micropores and their size distribution, and the chemical surface heterogeneity are much more critical at the Henry’s law region (< 30 Torr). The latter could be well characterized by the amount and Henry constant of CO2 adsorption at the low pressures, the Toth model parameters, the change in CO2/ CO and CO2/ N2 selectivities with respect to pressure, the amount of CO from the thermal decomposition, and the direct probing of very strong basicity sites using a technique that is the temperature-programmed desorption of CO2 adsorbed. All of them are consistent with the difference in the energetic nonuniformity between ACs studied, except for the last measure whose results could be reasonably explained when combining with the microtextural heterogeneity.
In this paper, an analytical model is developed for electrical conductivity of nanocomposites, particularly polymer/carbon nanotubes nanocomposites. This model considers the effects of aspect ratio, concentration, waviness, conductivity and percolation threshold of nanoparticles, interphase thickness, wettability between polymer and filler, tunneling distance between nanoparticles and network fraction on the conductivity. The developed model is confirmed by experimental results and parametric studies. The calculations show good agreement with the experimental data of different samples. The concentration and aspect ratio of nanoparticles directly control the conductivity. Moreover, a smaller distance between nanoparticles increases the conductivity based on the tunneling mechanism. A thick interphase also causes an increased conductivity, because the interphase regions participate in the networks and enhance the effectiveness of nanoparticles.
Various semi-cokes were obtained from medium–low-temperature pyrolysis of Shenmu long flame coal. The combustion characteristic index and CO2 gasification reactivity of semi-cokes were measured and analyzed using thermogravimetry analysis. The influence of particle size on CO2 gasification reactivities of these semi-cokes was studied. In addition, the Brunauer–Emmett–Teller surface area (SBET), carbon material structure order and carbon crystalline structure were examined by N2 adsorption, Raman spectroscopy and powder X-ray diffraction. All of these properties were used to evaluate the CO2 gasification reactivity of these semi-cokes. The results show that the gasification reactivity of semi-cokes decreases with an increasing crystallinity and structure order. Surface area of the pores is proportional to the reactivity of the semi-coke; the greater the surface area, the faster the gasification reaction rate.
Energy and environmental are always two major challenges for the sustainable development of the modern human being. For avoiding the serious environmental pollution caused in the fabrication process of porous carbon, a popular energy storage material, we reported a facile, green and activating agent free route hereby directly carbonizing a special biomass, Glebionis coronaria. A nitrogen doped hierarchical porous carbon with a specific surface area of up to 1007 m2 g−1 and a N doping content of up to 2.65 at.% was facilely fabricated by employing the above route. Benefiting from the peculiarly hierarchical porous morphology, enhanced wettability and improved conductivity, the obtained material exhibits superior capacitance performance, which capacitance reaches up to 205 F g−1 under two-electrode configuration, and no capacitance loss is observed after 5000 cycles. Meanwhile, the capacitance retention of the obtained material arrives up to 95.0% even under a high current density of 20 A g−1, illuminating its excellent rate capability. The fabricated nitrogen-doped hierarchical porous carbon with larger capacitance than commercial activated carbon, excellent rate capability and cycle stability is an ideal cost-efficient substitution of commercial activated carbon for supercapacitor application.
A new discrete bis-dithiolene complex, [ PPh4]2[Zn(DMED)2] (1; DMED = 1,2-dicarbomethoxy-1,2-dithiolate) with sulfurbased radical character was synthesized and structurally characterized. Complex 1 is stable and exhibits a square planar geometry around the zinc metal. 1 forms nanospheres through a one-pot water-induced self-assembly in a mixture of solvents (acetonitrile–water). These nanospheres were further decorated with water-soluble carbon nanotubes (wsCNTs) through hydrogen bonding between the peripheral –COOCH3 groups of 1 and surfacial carboxyl groups of wsCNTs to assemble into a spherical nanocomposite. The as-prepared nanocomposite showed fluorescence emissions in visible region due to the separation of energy states of the nanospheres assisted by wsCNTs, suggesting the future possibilities of these new materials for use in biomedical application.
Carbon fibers (CF) are predominantly being manufactured from polyacrylonitrile (PAN) based precursors which require solution spinning utilizing health hazardous organic solvent. This also adds to the cost of production due to the investment for the solvent recovery. Study of melt processable precursors has long been sought as a solution for health and environmental problems associated with the use of hazardous solvent. No use of solvent for spinning will also reduce the cost of manufacturing. Our coworker Deng et al. reported the possibility of using acrylonitrile-co-1-vinylimidazole (AN/VIM) copolymer as melt processable CF precursor. Here we report a successful preparation of carbon fiber from the co-polymer. We successfully demonstrated the preparation of thinner precursor fibers and carbon fibers through our optimization study of melt spinning, annealing, stabilization and carbonization.
The present study examined changes in surface shape and pore size observed in carbon black particles isothermally oxidized in an air atmosphere according to their burn-off ratio. Carbon black materials were fed into a horizontal tubular furnace in an air atmosphere when the inside temperature reached 600 °C. Subsequently, while changing the isothermal oxidation time, carbon black samples with different burn-off ratios were obtained, i.e., 10.5, 20.0, 30.4, 41.0, 49.9, 59.8, 71.1, and 81.0%. The scanning electron microscope analysis revealed that the observed carbon black particles were in the form of aggregated primary particles, and that there was no change in the particle size of these primary particles as the burn-off process proceeded. The latter observation supported the observation that pores were formed in the carbon black samples during the burn-off process. Notably, the Brunauer–Emmett–Teller analysis exhibited hysteresis curves, indicating that the corresponding adsorption isotherms were of IV-type. It was also found that the area of the hysteresis curves increased as the burn-off process proceeded. The specific surface area of the raw carbon black sample was 58.00 m2/g, while that of the 81.0% sample was about 4.1 times the figure at 240.27 m2/g. The total pore volume VT was 0.17 cm3/g for the raw sample, and it was much higher for the 81.0% sample at 0.58 cm3/g. The transmission electron microscope analysis showed that the raw carbon black particles had a spherical shape with a smooth surface, but inner pores were not observed. In the 49.9% sample, pores with a size of about 5 nm were observed inside carbon black particles. Notably, the size of the pores observed in the 81.0% sample was about 20 nm and the large pores were created by the collapsing and merging of the smaller pores by oxidation.
Single C-vacancy and pyridine-like N3 defect are usually formed on the single-walled carbon nanotube (SWCNT) and they have unique properties for potential applications. In this paper, we use density functional theory to investigate the discrepancies of such two structures from the geometric and electronic aspects. Our results indicate that the existed single vacancy in the SWCNT can lead to somewhat electron localization because of the lone pair electrons; while the N3 embedded SWCNT ( N3-SWCNT) has stronger chemical reactivity and electron localization than the single vacancy SWCNT (SV-SWCNT) due to the great charge transfer between N3 group and C atom on the tube sidewall. Through the investigation of Ag-doping on the above two nano-structures, we found that the single Ag atom is much more stably adsorbed on the N3- SWCNT sidewall compared with SV-SWCNT, forming higher binding energy and higher electron transfer. Our calculation would shed light on the physicochemical property of SWCNT-based material and thus extend their potential applications in many fields.
Fibrous adsorbents, such as activated carbon fibers (ACF) have acknowledged advantages of rapid adsorption rate and ease of modification compared with granular and powdered adsorbents. Based on the surface modification of lyocell-based ACF, we observed different surface characteristics of ACF samples with variation in the mixing ratio and impregnation time of H3PO4, NaCl, and KMnO4 solution. For an engineering application, we also explored the adsorption characteristics of thusproduced ACF samples onto volatile organic compounds (VOCs). Isothermal adsorption experiments were performed using toluene and benzene as adsorbates. Results indicate that both physical and chemical surface properties have an effect on the adsorption of volatile organic compounds (VOCs).
To enhance mechanical properties through improvement of dispersion stability of carbon black (CB) in epoxy resins, fluorine functional groups were introduced on the CB surface by fluorination. The changes in the chemical properties and dispersion stabilities after fluorination were evaluated with different partial pressures of fluorine gas. The mechanical properties of the fluorinated CB/epoxy composites were evaluated by the test of tensile, impact strengths and creep behavior. The fluorinated CB/epoxy composites showed approximately 1.6 and 1.1 times enhancement in the tensile and impact strengths compared to that of neat epoxy, respectively. Moreover, when a constant load was applied at 323 K, the fluorinated CB/epoxy composites lasted longer and had smaller strain changes than those of the raw CB/epoxy composites. Thus, well-dispersed CB by fluorination in epoxy resins effectively transfers mechanical stress.
In this study, we prepared ACFs with a high specific surface area from various precursors (rayon, pitch, and oxidized polyacrylonitrile-based fibers) by a steam-activation technique and investigated the effects of the micropore and mesopore fraction on 2-CEES adsorption behaviors. The activation time was precisely controlled so that the activation yield was in the range of 35–40% to ensure the mechanical properties of the ACFs. The N2 adsorption isotherm characteristics at 77K were confirmed by Brunauer–Emmett–Teller, Barrett–Joyner–Halenda and non-local density functional theory equations. The adsorption capacities of the ACF were measured by breakthrough experiments in the gas phase (750 μg/mL of 2-CEES in N2 flow). The removal efficiency of the ACFs was evaluated and compared with that of AC. From the results, specific surface areas and total pore volume of the ACF were determined to be 1380–1670 m2/g and 0.61–0.82 cm3/g, respectively. It was also observed that various pore characteristics of ACF were found to be dependent on crystallite structure of each precursor. The break through time (C/C0 = 0.10) was in the order of Oxi-Pan-H-9-2 < Saratoga AC < Rayon-H-9-3 < Pitch-H-9-4. This indicates that 2-CEES adsorption capacity could be a function not only of specific surface area or total pore volume, but also of sub-mesopore volume fraction in the range of 1.5–2.5 nm of adsorbents.