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2018, 33(4): .

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A review of the control of pore texture of phosphoric acid-activated carbons

ZUO Song-lin

2018, 33(4): 289-302.

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Phosphoric acid activation is a chemical activation process that has been widely used to produce activated carbons from lignocellulose. The author systemically reviews the process from the role of the acid, and the pore structure, chemical properties and uses of these activated carbons. This review provides comprehensive information on the control of the pore structure and proposes that the interaction of the phosphoric acid and the lignocellulose results in the formation of phosphoric acid/biopolymer composites so that the activation can be simply regarded as two successive steps, which are formation and thermal decomposition of such composites. Based on this idea, the paper comprehensively analyzes the effect of many factors including the composition and texture of the raw materials and the impregnation parameters on the constituents and structures of the H₃PO₄/biopolymer composite and thus on the pore structure of the activated carbon. These complex factors include (1) the composition of the lignocellulose and pretreatment of the raw materials, (2) cellular structure and crystallinity, (3) impregnation parameters such as impregnation ratio, method, temperature and time. During the subsequent heat treatment of the H₃PO₄/biopolymer composite, the significant effect of the heating program on the formation and development of pore structure, including such parameters as temperature, heating rate and any intermediate isothermal treatment, and carbonization atmosphere including inert gases, oxidative gases and steam are reviewed. Finally, the roles of the oxidative atmosphere and other oxidants during activation are outlined, and two types of carbonization and their effect on pore development are also proposed and discussed.

Fabrication of magnetic activated carbons from corn cobs using the pickle liquor from the surface treatment of iron and steel

WANG Fang, DANG Yan-qiu, TIAN Xun, Steven Harrington, MA Lei, MA Yan-qing

2018, 33(4): 303-309. doi: 10.1016/S1872-5805(18)60340-3

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Corn cobs were impregnated with the pickle liquor from the surface treatment of iron and steel at ambient temperature for 24 h, dried at 393 K for 12 h and carbonized at 573, 773 and 973 K for 1 h to obtain magnetic activated carbons (MACs). The adsorption of methyl orange (MO) onto the MACs was investigated under different conditions. Results show that the surface area of the MACs increases with carbonization temperature from 423.5 to 784.76 m² g^-1. The MACs consist of hematite (Fe₂O₃) and magnetite (Fe₃O₄). The MAC obtained at 973 K has the highest MO monolayer adsorption capacity of 555.56 mg g^-1 at 298 K in a water sample containing MO dye. The adsorption is endothermic and obeys pseudo-first-order kinetics. The MACs can be easily separated from the dye water by an external magnet.

A dramatic improvement in the tensile strength of fullerene needle-like crystals

Toshio Konno, Takatsugu Wakahara, Kun'ichi Miyazawa, Kazuhiro Marumoto

2018, 33(4): 310-315. doi: 10.1016/S1872-5805(18)60341-5

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Needle-like crystals consisting of a solid solution of C₆₀-C₇₀ fullerene were synthesized by a liquid-liquid interfacial precipitation method using toluene and 2-propanol as solvents. A machined crystal with a V-notch was placed in a focused ion beam scanning electron microscope where it was bent until fracture by pushing it with a molybdenum probe to measure its mechanical properties and its fracture surface was examined. The crystals had a tensile strength of 58-71 MPa, which is much higher than C₆₀ fullerene needle-like crystals and slightly larger than alumina, and a fracture toughness of 1.1-1.3 MPa m^1/2. Moreover, it is possible to change the plasticity and fracture toughness of the C₆₀-C₇₀ crystals by solvation of different numbers of fullerene molecules. The C₆₀-C₇₀ fullerene crystals have the potential for use as electrodes, anchors for brittle materials, and ductile wires to carry electricity.

Synthesis of porous graphene-like carbon materials for high-performance supercapacitors from petroleum pitch using nano-CaCO₃ as a template

LIU Ming-jie, WEI Feng, YANG Xue-mei, DONG Shi-an, LI Ying-jie, HE Xiao-jun

2018, 33(4): 316-323. doi: 10.1016/S1872-5805(18)60342-7

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Porous graphene-like carbon materials (PGCMs) for supercapacitors were synthesized from petroleum pitch by a nano-CaCO₃ template strategy combined with KOH activation. The PGCMs were characterized by TEM, XPS, Raman spectroscopy and N₂ adsorption. Results show that their specific surface areas are 1 542-2 305 m² g^-1, depending on the template/pitch ratio, KOH/pitch ratio and activation temperature. The PGCMs feature interconnected graphene-like carbon layers with abundant small pores. The optimum supercapacitor electrode is produced when the PGCM is synthesized with a template/pitch ratio of 1.5, a KOH/pitch ratio of 1.5 at 850℃ for 1h. It has a specific capacitance of 293 F g^-1 at a current density of 0.05 A g^-1, an excellent rate capability with a capacitance of 231 F g^-1 at a current density of 20 A g^-1 and an outstanding cycling stability with a 97.4% capacitance retention after 7 000 cycles in a 6 M KOH aqueous electrolyte. It also exhibits a high specific capacitance of 267 F g^-1 at a current density of 0.05 A g^-1, and a high energy density of 148.3 Wh kg^-1 at a power density of 204.2 W kg^-1 in a BMIMPF₆ ionic liquid electrolyte. This is a possible method for the synthesis of PGCMs for high-performance supercapacitors.

Fluorinated multiwall carbon nanotubes for high rate lithium ion primary batteries

CHEN Long, SUN Xiao-gang, QIU Zhi-wen, CAI Man-yuan

2018, 33(4): 324-332.

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Fluorinated graphite (F-graphite) and multiwall carbon nanotubes (F-MWCNTs) were synthesized by direct fluorination with fluorine gas and used as the cathode materials of lithium primary batteries. Their microstructures were characterized by SEM, TEM, XRD and XPS. Results show that the F-MWCNTs have a core-shell structure with the outer layers fluorinated while the inner ones retain their pristine graphitized structure. A F-MWCNT electrode exhibited a higher discharge capacity and a higher discharge plateau than a F-graphite electrode at the same C rates. The discharge capacities of the F-MWCNT and F-graphite electrodes reached 822 and 786.1 mAh/g at 0.05 C, respectively. The corresponding values reached 375.4 and 283.7 mAh/g at 2 C, indicating an excellent rate performance for the former.

One-pot synthesis of N, S co-doped photoluminescent carbon quantum dots for Hg²⁺ ion detection

WEI Ju-meng, LIU Bi-tao, ZHANG Xin, SONG Chang-chun

2018, 33(4): 333-340. doi: 10.1016/S1872-5805(18)60343-9

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N and S co-doped carbon quantum dots (N, S-CQDs) with a high fluorescence quantum yield (12.6%) were synthesized by a one-pot hydrothermal method. Results indicate that the N, S-CQDs have a small particle size and an amorphous structure, exhibiting unique surface states and excitation wavelength-independent fluorescent properties. Co-doping of N and S increases the electron-transfer rate and improves the coordination interaction between the N, S-CQDs and Hg²⁺ ions. The N, S-CQDs show a high sensitivity and selectivity in detecting Hg²⁺ ions even for a lake water sample. They are promising fluorescence probes for environmental monitoring.

Synthesis and electrochemical performance of flexible cellulose nanofiber-carbon nanotube/natural rubber composite elastomers as supercapacitor electrodes

HAN Jing-quan, LU Kai-yue, YUE Yi-ying, MEI Chang-tong, WANG Hui-xiang, YAN Peng-bin, XU Xin-wu

2018, 33(4): 341-350.

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High strength, flexible and conductive composite elastomers for use as supercapacitor electrodes were synthesized using cellulose nanofibers (CNFs) and carbon nanotubes (CNTs) as the fillers, and natural rubber (NR) as the elastomer. An aqueous suspension of CNFs and CNTs was added to a natural rubber aqueous emulsion containing sulfur and a vulcanization accelerator, and the mixture was homogenized at a high-pressure, coprecipitated with a 1 M H₂SO₄ solution and vulcanized to obtain the composite elastomer. The microstructure, mechanical properties, electrical conductivity and electrochemical performance of the CNF-CNT/NR elastomers were investigated. Results showed that CNFs significantly improved the dispersion of CNTs in the aqueous suspension, leading to homogenous composite elastomers. The tensile strength and elastic modulus were significantly improved by adding CNFs. When the contents of CNFs and CNTs were 3 and 10 parts per 100 NR by weight, the tensile strength and elastic modulus of the composite reached maximum values of 6.44±0.32 and 8.77±0.48 MPa, respectively, and it was highly stretchable and flexible with a stable electrical conductivity of 1.78±0.86 S/m after stretching, bending and folding. It had a specific capacitance of 107 F/g at a current density of 0.3 A/g and retained 83% of the initial value at 1.0 A/g after cycling for 1200 times. This novel flexible, stretchable and conductive soft elastomer is useful in flexible electronic devices.

Microstructure and thermophysical properties of graphite foam/Sn-Bi alloy composites for use as a thermal sink for electronics

LIAN Peng-fei, SONG Jin-liang, LEI Shi-wen, TAO Ze-chao, ZHAO Hong-chao, ZHANG Jun-peng, LIU Zhan-jun

2018, 33(4): 351-356. doi: 10.1016/S1872-5805(18)60344-0

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Two mesophase pitch-based graphite foams with densities of 0.62±0.01 (GF1) and 0.84±0.01 g/cm³ (GF2) were prepared by foaming the pitch in an autoclave at 723 K, 6.0 MPa and 763 K, 13.4 MPa, respectively, followed by carbonization at 1273 K for 2 h and graphitization at 2973 K for 0.5 h. The GFs were infiltrated by a Sn-Bi liquid to prepare GF/Sn-Bi alloy composites for use as thermal sinks for electronics. The microstructures and thermophysical properties of the composites were investigated. Results indicated that GF1 had a larger cells and thinner cell walls than GF2. The Sn-Bi liquid was well infiltrated into cells of the GFs, resulting in composites with densities of 5.60±0.01 and 3.83±0.01 g/cm³ for GF1 and GF2, respectively. The thermal diffusivity and coefficient of thermal expansion (CTE) of the GF1/Sn-Bi composite were 51.6±2 mm²/s and 16.6±0.02 ppm/K, respectively. The corresponding values for the GF2/Sn-Bi were 163.1±3 mm²/s and 8.08±0.02 ppm/K. The GF2/Sn-Bi composite had a high thermal diffusivity and a low CTE value matching that of semiconductor chips and packaging materials.

Numerical simulation of carrier gas effects on flow field, species concentration and deposition rate in the chemical vapor deposition of carbon

YIN Teng, JIANG Bing-yan, SU Zhe-an, FAN Zhe-qiong, HUANG Qi-zhong

2018, 33(4): 357-363. doi: 10.1016/S1872-5805(18)60345-2

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A 2D numerical model was established for simulating the chemical vapor deposition (CVD) of carbon in a vertical reactor. A full multi-component diffusion model was proposed to describe the diffusion of the gas species. The effects of Ar, N₂ or H₂ carrier gases on the flow field, species concentration and deposition rate of pyrocarbon were investigated using C₃H₆ as the carbon source. Results show that H₂ improves the stability of the gas flow. The concentration distributions of CH₄, C₂H₂, C₂H₄ and C₆H₆ are uniform in H₂. The pyrocarbon deposition rate is lowered, but the uniformity of deposition is improved when H₂ is used as the carrier gas compared with N₂ or Ar. The simulation results agree well with the experimental ones.

Electroless Ag deposition on the cell walls of carbon foam by a displacement method

GUO Cong-cong, LIU Xiu-jun, LI Tong-qi, LEI Yan, ZHAI Li-li

2018, 33(4): 364-369. doi: 10.1016/S1872-5805(18)60346-4

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To obtain efficient metalization of the surface and cell walls of carbon foam, an electroless silver displacement deposition method was investigated, in which a copper layer was first electroless-deposited and then displaced by silver. The purity of the silver coating, and the morphology, microstructure, mechanical strength and electrical conductivity of the resulting carbon foams were characterized by SEM, EDS, XRD, mechanical and conductivity tests. Results indicate that a uniform and continuous silver film is formed on the cell walls of the carbon foam with a better adhesion to the carbon compared to that obtained using the traditional one-step silver plating method. The coating is crystalline silver without copper or silver oxide. The conductivity and mechanical strength of these carbon foams increase from 700 to 2 055 S/cm and 0.54 to 1.05 MPa, respectively when the silver content is increased from 0 to 15.5 wt%.

The microstructure and ablation behavior of carbon fiber/phenolic aerogel composites

ZHU Zhao-xian, Dong Jin-xin, JIA Xian-feng, LONG Dong-hui, LING Li-cheng

2018, 33(4): 370-376.

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Carbon fiber/phenolic aerogel composites (C/PA) were prepared through sol-gel polymerization of a phenolic resin followed by ambient pressure drying using carbon fiber mats as the reinforcements. The composites have low densities (0.27-0.40 g/cm³) and low room-temperature thermal conductivities (0.056-0.068 W·(m·K)^-1). The bend strength of the composite prepared from the pierced carbon fiber mat (P-C/PA) is twice that of the laminated carbon fiber mat (L-C/PA). The highest bend strength obtained was 35.9 MPa for the P-C/PA with a density of 0.40 g/cm³. Under ablation at 2000℃ for 60 s, the mass and linear ablation rates of the P-C/PA were 0.0043 g/s and 0.0147 mm/s, respectively. The phenolic nanoparticles in the aerogel were easily decomposed, evaporated and sublimed to remove superficial heat while the porous network of the aerogels effectively prevented heat transfer from the surface to the interior of the composite. C/PA composites are excellent candidates for bifunctional ablation/insulation applications.

A comparative study of the fuzz produced by friction and tension in China T800 and Toray T800H carbon fiber tows

LI Long, PAN Yue-xiu, ZHU Shi-peng, FENG Zhi-hai, YANG Yun-hua, SONG Yi-jun, SONG Huan-yu

2018, 33(4): 377-384.

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The fuzzes weights in Toray T800H and China T800 carbon fiber tows were investigated under friction by rubbing the fiber tows between a pair of sponges and tension along the fiber tows by stretching. Results show that the fuzzes weights of China T800 are much higher than in Toray T800H. The effect of a compressive load on the sponges and a tensile force on the fiber tows on the fuzzes weights is noticeably different for the two tows. SEM images show that the fuzzes weights of China T800 are more than that in Toray T800H. AFM indicates that the sizing of China T800 is less uniform than that of Toray T800H. Moreover, interweaving of the filaments in China T800 is more apparent than in Toray T800H. These three factors contribute jointly to the larger fuzzes weights and its more obvious increase under both friction and tension for the China T800 than the Toray T800H tows.

“Carbon”-Continuing story——A review of 2018 World Conference on Carbon

LIU Xu-guang

2018, 33(4): 385-389.

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The annual World Conference on Carbon, Carbon 2018, was held in Madrid, Spain and was hosted by the Spain Carbon Group during July 1-6, 2018. About 703 attendees from 53 countries participated in the conference, and 794 papers were accepted for discussion, including 5 plenary lectures, 49 keynote talks, 337 oral presentation and 403 posters involved in 10 topics,namely, graphene and graphite; advanced carbon materials:nanotubes, fullerenes, carbon fibres and carbon based composites; coal, coke and carbon black; thermo-chemical conversion processes; preparation, characterization, simulation and modelling of carbon; electrochemical applications; catalysis application; environmental applications; gas separation and storage; carbons for health, medical and biological applications. Graphene, carbon dots, carbon aerogels and other new carbon materials feature more intensive and extensive fundamental researches and diversified applications. Doping heteroatoms or loading metal oxides during preparation of carbon matrix composites have been important means to tune their properties and applications. Energy storage carbon, environment-friendly carbon and healthy carbon will be the hot applications of carbon materials.

2018 Vol. 33, No. 4

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