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2018, 33(1): .

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Carbon-supported metal single atom catalysts

LI Hai, ZHANG Hai-xia, YAN Xiao-li, XU Bing-she, GUO Jun-jie

2018, 33(1): 1-11. doi: 10.1016/S1872-5805(18)60322-1

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Metal single atom catalysts (SACs) have been attracting increasing attention in recent years owing to their incredible performance in several key catalytic reactions such as the oxygen reduction reaction and CO oxidation. The construction of well dispersed stable SACs can not only make it possible to understand the catalytic reactions on the atomic scale, but is also important for developing novel industrial catalysts. Recent efforts have been focused on dispersing metal SACs on carbon substrates rather than on metals or metal oxides for improved catalytic behavior. Especially, graphene-based materials have proven to be excellent candidates for supporting SACs due to their unique structural and electronic properties. Nevertheless, the anchoring mechanism between metal SACs and carbon substrates is not well understood. Here we review the many roles of carbon materials as the support of SACs and highlight the anchoring mechanism. We also propose some suggestions to improve the experimental and theoretical research methods to expand the number of applications and realize industrial applications.

Progress in research on the preparation of carbon dots and their use in tumor theranostics

LU Chun-xiang, LI li-ping

2018, 33(1): 12-18.

Abstract(424)

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Carbon dots (CDs), as a novel class of carbon-based nanomaterials, have attracted tremendous attention in biomedicine owing to their excellent optical properties, low toxicity, good water solubility and easy surface modification. In this review, we introduce various methods for their synthesis based on technology and recent research progress on red-emission and near-infrared emission CDs, and address the use of CDs in the diagnosis and therapy treatment of tumors. The review also summarizes the limiting factors that affect the development of CDs and possible new advances.

Stabilizing graphene layers by intercalating laponite between them

LI Jing, CUI Jin-can, YANG Zhen-zhen, QIU Han-xun, TANG Zhi-hong, YANG Jun-he

2018, 33(1): 19-25. doi: 10.1016/S1872-5805(18)60323-3

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The reduction of graphene oxide (GO) leads to the re-stacking/agglomeration of graphene layers, which results in their precipitation from an aqueous dispersion. A laponite colloid was used to prevent re-stacking and stabilize an aqueous dispersion of reduced graphene oxide (RGO) by dispersing GO in the colloid, followed by reduction with hydrazine hydrate under microwave radiation. Results indicate that re-stacking is prevented as proven by the disappearance of the RGO (002) peaks in the XRD pattern. A laponite/RGO (w/w:1:1) dispersion shows the highest stability under centrifugation at 10 000 rpm and the largest Brunauer-Emmett-Teller surface area, which is 17.6% higher than that of RGO and 34.4% higher than laponite. Electrostatic interaction between negatively-charged RGO layers and positively-charged laponite edges lead to an intercalation structure, which is responsible for the non-stacking RGO and its stable dispersion in water. This intercalation method offers an alternative way for the dispersion of graphene layers.

Synthesis of copper sulfide/reduced graphene oxide nanocomposites for use as the counter electrodes of high-performance CdS-sensitized solar cells

Amr Hessein, Ahmed Abd El-Moneim

2018, 33(1): 26-35. doi: 10.1016/S1872-5805(18)60324-5

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Copper sulfide (Cu_xS)/reduced graphene oxide (RGO) nanocomposites were prepared by a one-pot hydrothermal method with various contents of GO in the initial precursor. The nanocomposites were first blended with a polyvinylidene fluoride binder, then coated onto SnO_x^2-F_x substrates,which were used as the counter electrodes (CEs) of quantum dot solar cells (QDSCs) using a CdS-sensitized TiO₂ as a photoanode. The microstructure and performance of the CEs were characterized by FE-SEM, XRD, Raman spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Results show that the Cu_xS/RGO CEs are superior to the conventional Cu₂S/brass CE. The stoichiometry and morphology of the Cu_xS nanocrystals are significantly influenced by the initial GO content in the precursor. A Cu_xS/RGO nanocomposite with more active sites for effective S_x^2- ion reduction in a polysulfide electrolyte (S^2-/S_x^2-) is optimally obtained at a medium GO content in the precursor. The QDSC assembled with the optimized Cu_xS/RGO CE exhibits a reproducible high and stable power conversion efficiency of 2.36% under an illumination intensity of 100 mW/cm², which is higher than the value (1.57%) of the cell with the Cu₂S/brass CE. The improved performance is attributed to the synergistic effect between the Cu_xS nanocrystals and conductive RGO in the Cu_xS/RGO CE, where RGO acts as both a co-catalyst to accelerate the polysulfide reduction and a conductivity promoter to decrease the series resistance of the CE.

The cytotoxicity of water-soluble carbon nanotubes on human embryonic kidney and liver cancer cells

YU Shi-ping, SU Xu-dong, DU Jing-lei, WANG Jun-li, GAO Yu-duan, ZHANG Li, CHEN Lin, YANG Yong-zhen, LIU Xu-guang

2018, 33(1): 36-46. doi: 10.1016/S1872-5805(18)60325-7

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The cytotoxicity of polyethylene glycol-modified carbon nanotubes (PEG-CNTs) on human embryonic kidney cells (293T) and hepatoma cells (HepG₂) was studied in vitro. The effect of the concentration of PEG-CNTs on the cell activity and survival rate was detected by a colorimetric assay method after exposure for 24, 48 and 72 h. The dead HepG₂ cells obtained by incubation in solutions with different concentrations of PEG-CNTs for 24 h can be stained by a dye, propidium iodide, and the cell mortality was determined by flow cytometry. Results show that the toxicity of PEG-CNTs with a good water solubility towards 293T and HepG₂ cells increases with increasing PEG-CNT concentration. When the concentration of the PEG-CNTs is less than 100 μg/mL, the toxicity of the PEG-CNTs is Grade Ⅰ(non-toxic) and when it is greater than 100 μg/mL but less than 200 μg/mL it is Grade Ⅱ(mildly toxic), according to the ISO2109932-5 cytotoxicity standard. The toxicity grade does not change with increased time.

Specific heat capacities and flow resistance of an activated carbon with adsorbed helium as a regenerator material in refrigerators

CHEN Liu-biao, KONG Chun-hui, WU Xian-lin, ZHOU Yuan, WANG Jun-jie

2018, 33(1): 47-52. doi: 10.1016/S1872-5805(18)60326-9

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An ideal regenerator material is characterized by a high specific heat capacity and a low flow resistance, and the specific heat capacity of the working gas must be low. However, the specific heat capacity of a helium working gas is much higher than that of the general regenerator materials in the temperature range 4-30 K, which severely limits the improvement of the refrigerator performance. The helium adsorption capacity of the activated carbon was first evaluated. The heat capacity and flow resistance of the activated carbon with adsorbed helium were measured and compared with the commonly-used regenerator materials such as stainless steel wire mesh, lead, and magnetic Er₃Ni and HoCu₂. Results show that the specific heat capacity of the activated carbon with adsorbed helium are higher than those of the other materials investigated at 3.0 MPa and 16-25 K, and its flow resistance is close to that of Er₃Ni, a little bit higher than that of HoCu₂, and much less than that of the stainless steel wire mesh. These results confirm that it is feasible to use activated carbon with adsorbed helium as a regenerator material.

Electrochemical performance of a porous graphitic carbon-based supercapacitor in three different electrolytes

YE Ling, HUANG Zheng-hong, SHEN Wan-ci, LU Rui-tao, KANG Fei-yu, YANG Quan-hong

2018, 33(1): 53-60.

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A porous graphitic carbon (PGC) was prepared by the one-step activation and graphitization of mesocarbon microbeads using NaOH and FeCl₃ as the activation reagent and graphitization catalyst, respectively. All supercapacitors constructed from the PGC using 1 M LiPF₆/EC:DEC (v/v=1), 1 M Et₄NBF₄/PC and 1 M[BMIM]BF₄/AN as the electrolytes show good electrochemical properties, with the optimum electrolyte being Et₄NBF₄/PC.

H₃PO₄ activated carbons as the electrode materials of supercapacitors using an ionic liquid electrolyte

ZHANG Qiu-hong, ZUO Song-lin, WEI Xin-yu, WANG Yong-fang

2018, 33(1): 61-70.

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H₃PO₄-activated carbons were prepared from Chinese fir sawdust, and their pore structure, surface chemistry and morphology were characterized by nitrogen adsorption, SEM and XPS. Their electrochemical performance as electrode materials for supercapacitors using[BMIM] [PF6] as the electrolyte was investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. Results indicate that H₃PO₄ activation at 800 to 950℃ produces highly developed mesopores with a volume percentage as high as 66% of the total porosity. The carbon prepared at a H₃PO₄ to sawdust mass ratio of 3:1 has a specific capacitance of 162 F/g and delivers an energy density of 22.5 Wh/kg at 0.5 A/g. The specific capacitance remains at 86% after 5 000 cycles at 5 A/g, suggesting good cycling stability and rate capability. H₃PO₄ activation is an effective method to prepare activated carbons for use in ionic liquid-based supercapacitors.

Preparation and characterization of high softening point and homogeneous isotropic pitches produced from distilled ethylene tar by a novel bromination method

GE Chuan-zhang, SUN Zhen-long, YANG Hai-xiao, LONG Dong-hui, QIAO Wen-ming, LING Li-cheng

2018, 33(1): 71-81. doi: 10.1016/S1872-5805(18)60327-0

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Homogeneous isotropic pitches with high softening points were prepared from vacuum-distilled heavy residue ethylene tar (ET-HR) by a two-step method of bromination and subsequent dehydrobromination/polycondensation. The ET-HR was first brominated at 30 or 200℃, and then heat-treated at 350℃ to enable the dehydrobromination/polycondensation reactions. GC/MS and LDI TOF/MS spectra indicated that the ET-HR was mainly composed of compounds containing 3-to 6-ring aromatic species with a considerable aliphatic chain content. Compared with thermal condensation alone, such a two-step method increased the softening point of the pitches from 152 to 264℃ with a yield in the range of 62 wt.%-67 wt.% and a coking value in the range of 57 wt.%-77 wt.%, depending on the bromination temperature and the bromine content. Structural characterization of the as-prepared pitches by elemental analysis, 1H NMR, FT-IR and LDI-TOF/MS showed increased aromatization and polymerization of the precursor during the dehydrobromination/polycondensation. All the homogeneous isotropic pitches showed an ability to transform into an anisotropic texture after coking at 800℃.

Preparation and antioxidation property of a SiC-MoSi₂-Si multilayer coating on a C/C composite

LI Shuai-peng, ZHANG Ming-yu, HUANG Dong, LI Lie-wu, LI Jun, HUANG Qi-zhong

2018, 33(1): 82-87.

Abstract(328)

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A multilayer SiC-MoSi₂-Si coating was prepared on the surface of a C/C composite by a two-step pack cementation method, in which the sample was first buried in a powder mixture containing Si, C(graphite), Al₂O₃ and SiC followed by heat treatment at 2023 K for 2 h in Ar and then treated for a second time in another powder mixture containing MoSi₂, Si, SiC and C(graphite). The microstructure of the resulting coating was characterized by XRD, SEM equipped with EDS and backscattered SEM. The isothermal oxidation of the coating was investigated in an electric furnace. Results indicated that the multilayer coating was composed of a SiC inner layer, a SiC-Si gradient middle layer and a MoSi₂-Si-SiC outer layer. The mass loss of the coating obtained after only the first step is 0.8% after oxidation at 177 3 K for 10 h in air while the two-step coating shows no mass loss but a mass gain of 0.65%, indicating that the mass gain due to the formation of SiO₂ from Si or SiC is higher than the mass loss from carbon oxidation.

The influence of seed crystals on the quality of single-crystal diamond produced by a microwave plasma CVD method

WU Gai, CHEN Mei-hua

2018, 33(1): 88-96.

Abstract(722)

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Natural diamonds from Liaoning and Shandong provinces, a HPHT diamond from Russia and a CVD diamond from the Element Six Company in America were selected as seed crystals for the growth of diamonds using the microwave plasma CVD method. The seeds and grown diamonds were characterized by FTIR, Raman spectroscopy, photoluminescence spectroscopy, XRD and AFM. Results indicate that the natural diamonds are type IaAB with a unique orientation and great differences in internal stress and crystalline quality. The HPHT and CVD diamonds are type Ib and type Ⅱa, respectively, with an angular deviation of 1-2.5 degrees and better crystal structure, and are more suitable for the CVD growth of single-crystal diamonds with little variation in internal stress and crystalline quality. The diamond layers grown on the natural IaAB seed crystals from Liaoning and Shandong provinces are polycrystalline with a serious lattice mismatch and impurities of microcrystalline graphite and amorphous carbon while the diamond layers grown on the HPHT type Ib seed crystal from Russia and the CVD type Ⅱa seed crystal from the Element Six Company are both of high quality. Moreover, the diamond layer grown on the CVD seed crystal has a narrower FWHM of the Raman peaks and a lower amount of non-diamond carbon impurity, indicating that it has a better crystalline quality than the diamond layer grown on the HPHT seed crystal.

2018 Vol. 33, No. 1

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