Abstract: Tea waste (TW) was crushed into powder and mixed with graphene oxide (GO) in water, followed by adjusting the pH value of the resulting suspension with ammonia, adding FeCl2·4H2O under magnetic stirring, filtration and drying to prepare a rGO/Fe3O4/TW composite. The microstructure and crystal phase of the composite were characterized by FTIR and XRD. The effects of the pH value, adsorption time and initial uranium concentration on the uranium removal rate were investigated. Results indicate that rGO/Fe3O4/TW has excellent adsorption performance with an uranium removal rate up to nearly 100% in a short time at an initial uranium concentration of 10 mg. L-1. The maximum adsorption capacity of rGO/Fe3O4/TW is 103.84 mg. g-1 while that of TW is 97.70 mg. g-1. The rGO/Fe3O4/TW adsorbed with uranium is easily separated from the solution by appying magnetic field. The isotherm and kinetics of uranium adsorption on rGO/Fe3O4/TW are best fitted by the Langmuir isotherm model and the pseudo-second-order model. The rGO/Fe3O4/TW and TW have a good reusability with an uranium removal rate of about 85% after five cycles.
Abstract: A reduced graphene oxide (H-rGO)/TiO2–composite (H-TiO2@rGO) as a catalyst for photocatalytic degradation of rhodamine B (Rh B) and methyl orange (MO) was prepared by hydrothermal treating a dispersant of TiO2 nanoparticles with sizes of 5-10 nm and GO obtained by the Hummers method from coal-based graphite in water. Compared with the M-TiO2@GO and M-TiO2@rGO composites by a wet mixing method, results indicated that the TiO2 nanoparticles in H-TiO2@rGO were uniformly decorated on both sides of rGO sheet, forming a stacked-sheet structure while apparent aggregation of TiO2 nanoparticles was found in both M-TiO2@GO and M-TiO2@rGO. Therefore, H-rGO@TiO2 had the highest catalytic activity towards degradation of Rh B and MO under visible light irradiation among the three, where the incorporation of rGO into TiO2 helps to narrow the band gap of TiO2, inhibit the recombination rate of electron–hole pairs and provide conductive networks for electron transfer.
Abstract: In order to improve the interfacial bonding between carbon fiber (CF) and polycarbonate(PC), sizing agents of water-borne polycarbonate (WPC) and water-borne polyurethane (WPU) containing carbon nanotubes (CNTs) were used to treat CFs. CNTs were introduced onto the surfaces of CF by sizing process. The effects of sizing agents and CNTs content on the interfacial properties of composites were investigated by two methods, single fiber fragmentation test (SFFT) for monofilament reinforced composite and transvers tensile for directional bundle composite, respectively. The results show that WPU is more conducive to improving the interfacial bonding properties of CF/PC composites because of its film-forming property, and the addition of CNTs has a beneficial effect on the interfacial properties of composites. CNTs can effectively prevent interfacial slip, thus significantly improve the interfacial properties in SFFT, while the improvement is not obvious in transvers tensile besause the adhesion of sizing agents plays an important role.
Abstract: Transforming waste resources into energy storage materials is a new way to turn waste into treasure and solve the problem of energy shortage and environmental pollution in current society. In this paper, nitrogen/phosphorus co-doped activated carbon material was synthesized from the waste cotton fabric by one-step carbonization and activation in molten salt system combined with ammonium polyphosphate co-doping technology. The morphology, structure and composition of the materials were characterized by scanning electron microscopy (SEM), nitrogen adsorption desorption (BET), Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS). The cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) were used to test the supercapacitor performance of the prepared materials. The results show that the waste cotton fabric, which is mixed with ammonium polyphosphate in the ZnCl2/KCl molten salt medium, then treated by carbonization and activation under high temperature, generates the nitrogen/phosphorus co-doped activated carbon with the specific surface area of 751 m2·g−1. In the three-electrode system, the specific capacitance is as high as 423 F·g−1 (at a current density of 0.25 A·g−1), and its capacitance retention is as high as 88.9% of the initial capacitance after 5000 cycles at a current density of 5 A·g−1. Meanwhile, when the material was assembled into a symmetrical supercapacitor, its best energy density can achieve 28.67 Wh·kg−1 at a power density of 200 W·kg−1. According to these results, converting waste cotton fabric resources into energy storage materials has succeeded in achieving high value-added reuse of waste textiles.
Abstract: Three-dimensional (3D) of nitrogen-doped carbon nanofibers (NCFs) derived from polyacrylonitrile (PAN) polymer were successfully synthesized by a combined electrospinning/carbonization technique. NCFs can be obtained under appropriate pyrolysis temperature and were employed as positive current collector containing Li2S6 catholyte solution for lithium sulfur (Li-S) batteries. The physical and electrochemical behaviors of the NCFs were investigated and found that the electrochemical performances of the NCFs are dependent on the pyrolysis temperatures. Results show that NCFs carbonized at 900 ℃ delivered a reversible capacity of 875 mAh·g−1 at a high sulfur loading of 4.19 mg·cm−2 and retained at 707 mAh·g−1 after 250 cycles at 0.2 C. The coulombic efficiency of NCFs-900@Li2S6 electrode is almost 98.55% over the entire cycling. Additionally, the capacity retention of electrode reaches 81.53% even at a high current density of 1C for over 150 cycles.
Abstract: Nanostructured phenolic resin-based carbon aerogels with abundant network structure are regarded as ideal energy storage materials for supercapacitors. However, the initial bulk form and low capacity of previously reported porous carbon aerogels are unacceptable for practical application. Herein, phenolic resin-based porous carbon spheres were synthesized by a facile hydrothermal synthetic approach. The porous carbon spheres were investigated by various characterizations, such as SEM, BET and XPS, ect. Interestingly, it was found that the number of ammonium groups, length of the alkyl chain and hydrothermal temperature played a vital rule in porous structure, size and uniformity of carbon spherical. Besides, NH+ 4 was necessary to obtain the carbon sphere and no obvious effect on the crystal structure of porous carbon spheres by varying in parameters. The samples CN-80 exhibited the highest specific capacitance of 233.8 F g−1 at the current density of 1.0 A g−1. This result showed that the higher specific surface area, porosity and defect are probably the crucial factors to improve electrode capacitance. CN-80 own excellent capacitance retention of 98% after 10000 charge/discharge cycles at 7 A g−1, indicating its good cycle stability.
Abstract: The radial structure of pre-oxidized fibers and its distribution directly affect the performance of the resulting carbon fibers. Optimizing the radial distribution of pre-oxidized structure and establishing the relationship between the pre-oxidized structure of polyacrylonitrile fibers and the mechanical properties of the final carbon fibers will help to optimize the pre-oxidation conditions in the preparation of high-performance carbon fibers. Herein, solid-state nuclear magnetic resonance spectroscopy, optical microscopy, thermogravimetric analysis, and mechanical tests were used to investigate the effect of the pre-oxidation reaction rate on the radial structural distribution of pre-oxidized fibers and the mechanical properties of the resulting carbon fibers. The pre-oxidation reaction rates were controlled by regulating the pre-oxidation temperature gradient. The results showed that the pre-oxidation degree of pre-oxidized fibers increased with both the overall and initial rates of pre-oxidation. With increasing the overall pre-oxidation reaction rate, the pre-oxidized structure was deepened into the core region of the fibers, the content of oxygen-containing functional groups increased, the thermal stability of the fibers decreased, the graphitization degree of the corresponding carbon fibers increased, but the density of the carbon fibers decreased and the mechanical properties of the carbon fibers were degraded. With increasing the initial reaction rate of pre-oxidation, the radial distribution of the pre-oxidation structure was effectively improved, the content of oxygen-containing functional groups of the pre-oxidized fibers increased slightly, their thermal stability was improved, the degree of graphitization and density of the final carbon fibers increased, and the tensile strength and tensile modulus of the final carbon fibers were markedly increased. A new type of carbon fibers with high strength, medium modulus and a relatively large diameter was obtained under the optimized pre-oxidation conditions.
Abstract: Micro/mesopore carbon spheres as electrode materials of supercapacitors were prepared by hydrothermal carbonization followed by KOH/NaOH activation using sucrose as the carbon precursor. The effects of KOH and NaOH activation parameters on the specific surface area, pore size distribution and electrochemical performance of the carbon spheres were investigated. Results indicate that the use of NaOH leads to the development of mesopores while the use of KOH is favorable to increase specific surface area and micropore volume. The pore size distribution of carbon spheres could be adjusted by varying the fraction of NaOH in the activation agent. A balanced capacitance and rate performance of the supercapacitor electrode in both 6 mol L−1 KOH aqueous electrolyte and 1 mol L−1 MeEt3NBF4/PC electrolyte is achieved when the carbonized product is activated at a mass ratio of NaOH+KOH/ carbonized product of 3∶1 with a NaOH/KOH mass ratio of 2∶1. As-prepared porous carbon delivers a capacitance of 235 F g-1 at 0.1 A g-1 and capacitance retention rate of 81.5% at 20 A g-1 in the 6 mol L−1 KOH aqueous electrolyte. In 1 mol L−1 MeEt3NBF4/PC, the cell based on the porous carbon delivers the highest energy and power output of 30.4 Wh kg−1 and 18.5 kW kg−1, respectively.
Abstract: Hydroxyl- and amino- functionalized carbon fibers (CF-OH and CF-NH2) were prepared by surface oxidation with mixed acid and grafting with ethylenediamine, respectively. The functionalized CFs were sized with a sulfonated poly (ether ether ketone) (SPEEK) sizing agent to prepare CF-OH-SPEEK and CF-NH2-SPEEK. The effect of surface functionalization on the surface properties of CFs and the interfacial properties in PEEK maxtrix composites were investigated. Results show that the numbers of surface functional groups and wettability of CFs increase significantly after surface functionalization. There are chemical reactions between CFs and the sizing agent, which improve the interfacial adhesion between CFs and the sizing agent. The interfacial shear strengths of CF-OH-SPEEK and CF-NH2-SPEEK reinforced PEEK matrix composites are increased by 6.2 and 14.0%, respectively, as compared with that with CFs desized and sized with SPEEK. The surface functionalization is beneficial to improve the interfacial adhesion of thermoplastic-coated CF/PEEK composites.
Abstract: In this work, carboxyl-functionalized carbonaceous material doped with N, P and O (denoted as CS-COOH) was fabricated by calcining a precursor, polyphosphazene, for adsorption applications. Employing TEM, SEM, XPS and FTIR techniques, the structure of CS-COOH was determined. The CS-COOH was also investigated for the adsorption of U(VI) from an aqueous solution. The results show that the adsorption kinetics was fitted well by the pseudo-second-order model and the maximum adsorption capacity determined by the Langmuir model at 298 K was 402.9 mg/g. In addition, the CS-COOH exhibited good adsorption results after five adsorption-desorption cycles. According to the XPS analysis, the enhanced U(VI) adsorption capacity was mainly attributed to the carboxyl groups and strong covalent bonds between heteroatoms with uranyl ions.
Abstract: The microstructural characteristics of the high thermal conductive (500−1127 W·m−1·K−1) mesophase pitch-based carbon fibers were compared based on characterization by XRD, Raman spectroscopy, SEM and TEM. The relationship between microstructural characteristics and thermal conductivity was obtained. The results show that a radial structure is always accompanied by a split structure and high thermal conductivity. La has a more significant impact on the thermal conductivity than Lc, and ID/IG value on the cross section obtained from Raman spectra can be used as an essential index to evaluate the thermal conductivity of the carbon fibers. The microstructural characteristics including large graphite crystallite size, high preferred orientation degree along the axis direction, and few crystallite defects contribute to the high thermal conductivity of the carbon fibers.
Abstract: A novel hybrid aerogel which can be magnetically extracted from water so filtration is unnecessary was developed. The hybrid (3DmGT-PVA) consists of 3D magnetic graphene-carbon nanotubes, which attracts dye, chained to polyvinyl alcohol, can be extracted from the water. Results indicated that a mass ratio of 12∶1 iron (III) chloride hexahydrate (FeCl3·6H2O) to graphene oxide (GO) and oxidized carbon nanotubes (O-CNT) mixture maximized adsorption capacity (qe=71.03 mg g−1 on methylene blue (MB)) and had a magnetic strength of MS=3.519 emu g−1. 3DmGT-PVA was shown to adsorb the most common dyes, crystal violet (CV, η=8.9%), methyl orange (MO, η=4.2%) and the mixture of MB, MO and CV (cocktail, η=11.1%). It was found that 3DmGT-PVA can be reused for three regeneration cycles, with a regeneration efficiency of over 82%. Finally, this aerogel was proved to be not toxic to the living organism, strongly proposing that this 3DmGT-PVA shows great promise as a means of treating industrial wastewater.
Abstract: Supercapacitors have gradually become an important energy storage device. Based on mechanisms of energy storage, supercapacitors are generally categorized into pseudocapacitors and electric double-layer capacitors (EDLCs). Nowadays, the electrodes are mainly carbon materials in commercial EDLCs. Hollow carbon spheres (HCSs) have attracted extensive attention in the electrode materials of EDLCs owing to their large specific surface area, high electrical conductivity, excellent electrochemical stability and high mechanical strength. Progress in the preparation of HCSs including the hard templating method, soft templating method, template-free methods and modified Stöber method, along with the electrochemical performance of the corresponding HCSs in EDLCs is reviewed. The correlation of the specific surface area, pore size and doped foreign atoms to the electrochemical performance of HCSs is summarized, which will shed some light on the preparation of HCSs with low-cost and high-performance for uses in supercapacitors and other fields.
Abstract: Matrix graphite (MG) was purified by high temperature purification (HTP), and their properties and microstructures were measured and analyzed to investigate the effect of HTP temperature on the property improvement of A3-3 MG as a pebble fuel element, and to optimize the purification temperature. Results showed that all the properties of MG specimens purified at temperatures from 1600 to 1900 ℃ met the technical requirements. X-ray diffraction analysis results showed that the microstructures of MG after HTP were significantly improved. With increasing the purification temperature from 1600 to 1900 ℃, MG gradually became ordered, the microstructures became better gradually for improving the comprehensive performance. The ash content decreased abruptly after HTP at 1600 ℃, but changed little when the purification temperature rose from 1600 to 1900 ℃. The microstructure improvement at high temperatures played a decisive role in increasing the oxidative corrosion resistance of MG. Therefore, HTP is very important and necessary, and cannot be canceled in the production of pebble fuel elements. This study provides an important reference to determine an optimal HTP temperature of pebble fuel elements for improving the production efficiency and reducing production cost in the commercial production of pebble fuel elements in the future.
Abstract: The phosphorus-doped carbon materials as one of novel carbon catalysts towards the hydrogen evolution reaction (HER) have attracted considerable attention over the past years, however, the role of C-P species in them in the HER activity is still not revealed up to now. To explore the effect of C-P species in carbon-based catalysts on their HER performance, we prepared four phosphorus-doped carbon nanotubes (PDCNTs) with different distributions of graphite-, pyridine- and pyrrole-like three P species and explored the correlations between their HER activity and three C-P contents. Results show that one prepared PDCNTs with an overpotential of 0.266 V at the current density of 10 mA/cm−2 exhibit much high HER activity in acid medium. Meanwhile, density functional theory calculations reveal that the pentagon- and nine-membered ring defects from the destruction of graphite-P mainly bring the HER performance, providing a deep insight into the HER on the surface of phosphorus-containing carbon catalysts.
Abstract: Graphite is the most widely used anode material for lithium ion batteries (LIBs), and increasing the sphericity and density of graphite is the main way to further improve energy density of LIBs. Herein, we report a simple preparation of high tap-density graphite granules by the high-shear wet granulation. In this way, we densified two kinds of graphite into granule, namely wet-granulation graphitic onion-like carbon (WG-GOC) and wet-granulation artificial graphite (WG-AG). It is found that, compared with the original graphite before granulation, the tap density of WG-GOC increases by ca.34%, and WG-AG increases by ca.44%. Therefore, when as the anode of LIBs,, the volumetric capacities of WG-GOC and WG-AG have increased by ca.35% and ca.55%, respectively, at the current density of 50 mA g−1. In addition, the rate performance of WG-GOC also has been significantly improved. The volumetric capacity of WG-GOC increased by 169.1% at the current density of 2000 mA g−1. The significant improvement of electrochemical performance benefits from the higher tap density of the prepared graphite granules. Hence, we developed a facile wet-granulation to prepare high tap-density graphite anodes, which conducive to the development of high volumetric capacity.
Abstract: Highly efficient synthesis of nitrogen-doped carbons with different porous structures is reported using shrimp shell as the carbon and nitrogen source, and its CaCO3 component as the hard template and the activator. The content of CaCO3 in shrimp shell can be tuned easily in the range of 0-100% by leaching with an acetic acid solution for different times. CaO derived from decomposition of CaCO3 acts as the activator and template to tailor the pore sizes of the carbons. CO2 derived from decomposition of CaCO3 also plays an activating role. Their specific surface areas, pore volumes, ratios of micropore volumes to total pore volumes can be adjusted in the range of 117.6-1137 m2 g-1, 0.14-0.64 cm3 g-1, and 0-73.4%, respectively. When used as the electrodes of supercapacitor, the porous carbon obtained with a leaching time of 92 min exhibits the highest capacitances of 328 F g-1 at 0.05 A g-1 in a 6 M KOH electrolyte and 619.2 F g-1 at 0.05 A g-1 in a 1 M H2SO4 electrolyte. Its corresponding energy density at a power density of 1470.9 W kg-1 is 26.0 Wh kg-1. This work provides a low cost method for fabricating porous carbons to fulfill the high-value-added use of biomass.