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2017, 32(5): .

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The use of carbon quantum dots as fluorescent materials in white LEDs

CUI Bo, FENG Xiao-ting, ZHANG Feng, WANG Ya-ling, LIU Xu-guang, YANG Yong-zhen, JIA Hu-sheng

2017, 32(5): 385-401. doi: 10.1016/S1872-5805(17)60130-6

Abstract(417)

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Carbon quantum dots (CQDs) have attracted a lot of attention for their potential applications in light-emitting diodes (LEDs), ion detection, bioimaging, solar technology and photocatalysis. Among these, LEDs, mainly white LEDs, have become a research focus and have developed rapidly. Recent advances in white LEDs constructed from different fluorescent materials, including the CQD-containing composites and single CQDs, are described. Research on white LEDs based on single CQDs are highlighted. Finally, some problems and prospects relating to the use of single CQDs in white LEDs are given to point out the improvements required in the fluorescent properties of CQDs, which play a key role in white LEDs.

Barium (Ⅱ)-doped zinc ferrite-reduced graphene oxide nanohybrids for superior adsorption and magnetic properties

FEI Peng, QIAO Jun, HUO Jin-xian, LIU Jian-hong, ZHONG Ming, SU Bi-tao

2017, 32(5): 402-410. doi: 10.1016/S1872-5805(17)60131-8

Abstract(291)

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A one-step solvothermal method was used to prepare barium (Ⅱ)-doped zinc ferrite/reduced graphene oxide (Ba²⁺-ZF/rGO) magnetic nanohybrid adsorbents. During the solvothermal treatment, Ba²⁺-ZF nanoparticles were formed from Ba²⁺, Fe³⁺ and Zn²⁺ chlorides, which were anchored on the surface of rGO obtained from the reduction of GO with ethylene glycol. TEM and SEM results show that the Ba²⁺-ZF nanoparticles are uniformly distributed on the rGO sheets without any agglomeration. When used as adsorbents, the Ba²⁺-ZF/rGO nanohybrid with an rGO content of 35% possesses excellent adsorption capacities for methylene blue at different initial concentrations and the adsorption kinetics can be well-described by the pseudo-second-order kinetic model. The formation of Fe²⁺ from FeCl₃·6H₂O and the doping of Ba²⁺ into the spinel structure dramatically improve the magnetism of the zinc ferrite, which makes the magnetic separability of the nanohybrid outstanding. The Ba²⁺-ZF/rGO nanohybrid could be used as an efficient, magnetically separable adsorbent for removing organic dyes.

An arm-like electrothermal actuator based on superaligned carbon nanotube/polymer composites

ZHOU Zhi-wei, YAN Qin-hua, LIU Chang-hong, FAN Shou-shan

2017, 32(5): 411-418. doi: 10.1016/S1872-5805(17)60132-X

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A superaligned carbon nanotube film embedded in polymers shows promising applications in the fields of electrothermal actuation because of their homogenous conductivity, good biocompatibility and mechanical properties. We fabricated a simple U-shaped gadget from the composite to investigate the electrothermal actuation mechanism. The gadget can curl to 730°, which is several times larger than existing actuators. A helix-shaped arm-like actuator (artificial arm) was also made from the composite, which exhibited a large twisting deformation (more than 700° twisting, 49.2% length constriction and 26.4% diameter constriction) when driven with low electrical fields (less than 500 V/m or 41 V). The actuation of the U-shaped gadget and the artificial arm can be precisely controlled by the applied voltage or electrical power. The gripping force of the clenched arm is about 4 g, 26 times its own weight. This points to a new way for manipulating objects and its potential application in the biomimetic field.

Nitrogen-doped carbon coatings on carbon nanotubes as efficient oxygen reduction catalysts

LI Li-xiang, ZHAO Hong-wei, XING Tian-yu, GENG Xin, SONG Ren-feng, AN Bai-gang

2017, 32(5): 419-426.

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Polypyrrole-coated carbon nanotubes (PPy-CNTs) synthesized by an in-situ chemical polymerization approach were heat-treated at 600, 800 and 1 000℃ in N₂ to prepare N-doped carbon coatings on CNTs (NC-CNTs). The specific surface area (SSA) and pore volume of the NC-CNTs increase significantly with heat treatment temperature and the nitrogen content decreases. Also, as the temperature increases the content of pyrrolic-N decreases while that of the graphitic-N increases. The SSA and pore volume of the NC-CNT1000 are 3 and 1.7 times higher than those of the NC-CNT600. As metal free electrocatalysts, the NC-CNTs show significant ORR activity in a basic electrolyte, but it is not proportional to their total nitrogen content. The ORR mechanism of the NC-CNT600 and NC-CNT800 belongs to a two-electron transfer reaction while that of the NC-CNT1000 to a mixture of the two-electron and four-electron transfer reactions. The NC-CNT1000 exhibits the best ORR activity and durability among the samples owing to its highest SSA and pore volume as well as having the largest amount of graphitic-N.

C-S hybrids prepared by electrodeposition and thermal diffusion methods from kapok-based amorphous carbon flakes as the cathode materials of Li-S batteries

HUANG Hui, SHEN Yong, XIA Yang, LIANG Chu, GAN Yong-ping, TAO Xin-yong, ZHANG Jun, ZHANG Wen-kui

2017, 32(5): 427-433.

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Kapok-based carbon nanoflakes (KCNs) were prepared by high-temperature calcination of kapok fibers as the carbon source. Electrodeposition or thermal diffusion were used to load sulfur onto the KCNs to obtain S-C hybrids for use as the cathode materials of Li-S batteries. The effect of the preparation method on the microstructure and electrochemical properties of the hybrid was investigated. It was found that small sulfur particles are evenly distributed on the surface of KCNs by electrodeposition while a sulfur layer is formed by thermal diffusion. The electrodeposited and thermally loaded C-S hybrids respectively deliver initial discharge capacities of 1 199.7 and 714.7 mAh·g^-1 at a current density of 100 mA·g^-1, which drop to 623.0 and 367.7 mAh·g^-1 after 200 cycles. The sulfur particles formed by electrodeposition have a higher utilization rate and stronger chemical bonding to the carbon than the sulfur formed by thermal diffusion, and this decreases the loss of sulfur during cycling.

Chemical vapor infiltration of pyrocarbon from propene into model capillaries

TANG Zhe-peng, LI Ai-jun, LI Zhao-qian, PENG Yu-qing

2017, 32(5): 434-441.

Abstract(412)

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7 dead-end parallel capillaries 1.0 mm in diameter, 31.0 mm in length and 10 mm separation were aligned perpendicular to the axis of a gas conducting tube and infiltrated at 1 223 K and 40 kPa (N₂:C₃H₆=9:1) for 75 h with a gas residence time of 0.56 s within the tube. The thickness of the pyrocarbon layers produced was determined along each capillary at 15h intervals. Results indicate that the pyrocarbon deposition rate decreases from the mouth to the end of the capillaries and the rate gradients are lower in the capillaries nearer to the gas inlet. Pyrocarbon deposition in the capillaries was simulated by a deposition model using the lumped reaction mechanism. The gas composition in the capillary mouths was obtained from computation by assuming that gas-phase reactions are homogeneous and the tube is a plug flow reactor. The calculated deposition rate profiles agree well with the experimental ones. Both the experimental and theoretical results indicate that pore blockage is relieved by reducing the gas residence time within the conducting tube.

The effect of nitrogen and/or boron doping on the electrochemical performance of non-caking coal-derived activated carbons for use as supercapacitor electrodes

LU Qian, XU Yuan-yuan, MU Sha-jiang, LI Wen-cui

2017, 32(5): 442-450. doi: 10.1016/S1872-5805(17)60133-1

Abstract(620)

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Coal-based activated carbons doped with either N or B or a combination of the two were prepared for use as the electrode materials of supercapacitors by ball milling and subsequent activation using Xinjiang non-caking coal, melamine and boric acid as the respective carbon, nitrogen and boron sources. FTIR spectroscopy and XPS reveal that the B and N atoms are substitutionally incorporated into the carbon skeleton. These doped activated carbons contain a large number of mesopores. Cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy show that N-and B-doped activated carbons have a superior capacitance and rate performance to the non-doped one. The B-N co-doped material has the highest specific capacitance of 176 F·g^-1 at 0.5 A·g^-1, which is attributed to a synergistic effect of B-N co-doping. The capacitance of the co-doped sample remains at 96% of the original value after 20 000 cycles.

Microporous activated carbons from coconut shells produced by self-activation using the pyrolysis gases produced from them, that have an excellent electric double layer performance

SUN Kang, LENG Chang-yu, JIANG Jian-chun, BU Quan, LIN Guan-feng, LU Xin-cheng, ZHU Guang-zhen

2017, 32(5): 451-459. doi: 10.1016/S1872-5805(17)60134-3

Abstract(589)

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Coconut shell-based activated carbons were prepared by self-activation using the pyrolysis gases generated from them. The process was carried out at high temperatures in a closed reactor filled with coconut shell under a high pressure that was generated by pyrolysis gases. Results indicate that the activated carbon prepared at 900℃ for 6 h has a specific surface area, total pore volume, micropore percentage, iodine adsorption capacity and methylene blue adsorption capacity of 1 194.4 m²/g, 0.528 cm³/g, 87.8%, 1 280 mg/g and 315 mg/g, respectively. When used as the electrode material of electrochemical capacitors this activated carbon exhibits a specific capacitance of 258 F/g, a high capacitance retention rate of 97.2% after 3 000 charge/discharge cycles and a small impedance. The water vapor and carbon dioxide generated by the pyrolysis of the coconut shell in the closed reactor act as activating agents and also increase the pressure of the reaction system. This is favorable for the activation of the formed char. This self-activation method was also used to prepare activated carbons with high adsorption capacities for iodine and methylene blue from almond stones, pecan shells and slash pine sawdust, indicating that it is a very simple, efficient, environmentally friendly and economical method for the preparation of biomass-based activated carbons for supercapacitor electrode materials and adsorption.

Effects of surface oxygen functional groups on activated carbon on the adsorption and photocatalytic degradation activities of a TiO₂-AC hybrid for methylene blue and methylene orange

ZHONG Yong-ke, ZHOU Bin, ZHANG Cheng-jiang, WU Di

2017, 32(5): 460-466.

Abstract(485)

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A series of activated carbons (AC) with different amounts of surface oxygen functional groups was obtained by nitric acid oxidation and heat treatment at different temperatures, and these were used as supports for a TiO₂ photocatalyst. The nature and number of the surface oxygen functional groups were determined by Boehm titration. The pore texture and morphology of the ACs and the TiO₂-AC hybrid were characterized by nitrogen adsorption and scanning electron microscopy. The adsorption and photocatalytic activity of the material under ultraviolet light irradiation were investigated using methylene blue (MB, cation dye) and methylene orange (MO, anion dye) as the model compounds. Results show that the oxidation and heat treatment change the surface oxygen functional groups much more than they do the pore texture. The surface oxygen functional groups, especially the surface carboxylic acid, control the adsorption and photocatalytic activities for MB and MO over the TiO₂-AC hybrid. The surface oxygen functional groups have a much greater influence on MB degradation than that on MO. The photocatalytic degradation activity for MB decreases at all heat treatment temperatures while that for MO is increased by heat treatment at 250℃.

The effect of mechanical vibration on the structure of needle coke prepared from a modified coal tar pitch

WANG Ying, DONG Ya-wei, ZHONG Cun-gui, CAO qing

2017, 32(5): 467-473.

Abstract(509)

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A medium coal-tar pitch was refined to remove the quinoline insoluble fraction and then modified with triacetate glycerol at 230℃ for 5 h. The modified pitch was carbonized at 550℃ under mechanical vibration. The effect of the mechanical vibration on microstructure of the coke was investigated by TG, FT-IR, XRD, SEM and polarized microscopy. Results indicate that the thermal stability and carbonization yield of the pitch increase and its aromatic/aliphatic hydrogen ratio is decreased by the modification. The mechanical vibration facilitates the coalescence of mesophase microbeads and the formation of a linear fiber structure during carbonization. The Lc of the semi-coke increases, d₀₀₂ decreases and the fiber structure remains after calcination at 1 300℃. A needle coke with high performance can be prepared by a combination of the modification and mechanical vibration.

The structure of an in-situ formed titanium-boron-carbon coating on a graphite substrate

YANG Jin-hua, GUO Quan-gui, LIU Zhan-jun, QIU Hai-peng, JIAO Jian

2017, 32(5): 474-480. doi: 10.1016/S1872-5805(17)60135-5

Abstract(294)

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A titanium-boron-carbon coating was fabricated on a graphite substrate by heating TiB₂ powder on a graphite surface above the eutectic temperature. The coating consisted of a pure graphite layer on the outer surface and a TiB₂-C alloy layer inside. The graphite layer had many wrinkles due to the difference in the thermal expansion coefficients of TiB₂ and graphite. The TiB₂-C alloy layer had a continuous three-dimensional interpenetrating network microstructure. The d₀₀₂ value of the graphite in the alloy layer was 0.335 6 nm, which was quite close to that of single crystal graphite (0.335 4 nm). Raman and X-ray photoelectron spectroscopy indicated that the graphite in both layers was doped substitutionally with boron atoms. A water quench thermal shock test verified a high adhesion strength between the coating and the substrate. This method is promising for the fabrication of thermal barrier coatings on carbon materials.

2017 Vol. 32, No. 5

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