A combined hydrothermal/hydrogen reduction method has been developed for the mass production of helical carbon nanotubes (HCNTs) by the pyrolysis of acetylene at 475 °C in the presence of Fe(3)O(4) nanoparticles. The synthesized HCNTs have been characterized by high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, vibrating sample magnetometry, and contact-angle measurements. The as-prepared helical-structured carbon nanotubes have a large specific surface area and high peroxidase-like activity. Catalysis was found to follow Michaelis-Menten kinetics and the HCNTs showed strong affinity for both H(2)O(2) and 3,3',5,5',-tetramethylbenzidine (TMB). Based on the high activity, the HCNTs were firstly used to develop a biocatalyst and amperometric sensor. At pH 7.0, the constructed amperometric sensor showed a linear range for the detection of H(2)O(2) from 0.5 to 115 μM with a correlation coefficient of 0.999 without the need for an electron-transfer mediator. Because of their low cost and high stability, these novel metallic HCNTs represent a promising candidate as mimetic enzymes and may find a wide range of new applications, such as in biocatalysis, immunoassay, and environmental monitoring.

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Recently, many approaches were applied for assembling graphene sheets into a three-dimensional structure. However, it is still a great challenge to obtain a three-dimensional macroporous graphene network with high mechanical strength after drying. Herein, an ammonia strengthened three-dimensional graphene aerogel was prepared. Based on graphene chemistry and ice physics, the mechanical strength of graphene aerogel was improved greatly when the graphene hydrogel was treated by ammonia solution at an ambient temperature. The results demonstrated that the three-dimensional structure of graphene aerogels was destroyed thoroughly without ammonia solution treatment; conversely, the three-dimensional structure was maintained and the compressive strength was improved to 152 kPa at the static load after it was treated by ammonia solution at 90 °C for only 1 h. This phenomenon is due to two reasons: (1) the low freezing point of ammonia solution, which effectively retarded its freezing and then kept the porous structure undestroyed; (2) the reaction between ammonia and graphene hydrogel, which brought some covalent bonds among graphene sheets. We believe our efforts may pave the way for the development and application of three-dimensional graphene based materials.

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principle, the corrosive issues of the sodium polysulfi des still exist at this modest temperature. Therefore, a desirable solution of safety problems is to develop a room temperature (RT) Na-S batteries.Due to low ion conductivity of the solid electrolyte and contact problems between electrodes and current collectors, the confi guration design of HT Na-S batteries may not be for RT Na-S batteries. Consequently, several attempts have been made to use polymer electrolytes in RT Na-S batteries. [6][7][8] Unfortunately, poor cycle life and low capacity were displayed. Liquid electrolytes, which have been demonstrated with good ion conductivity and widely used in lithium-ion batteries and even in Li-S batteries, [9][10][11][12] are probably suitable for RT Na-S batteries. However, as is well known, metal Na has similar chemical characteristics to Li, the S cathode in RT Na-S batteries will face the same issues observed in Li-S batteries as: i) low active material utilization, ii) poor cycle life, and iii) low Coulumbic effi ciency. [13][14][15] These drawbacks arise mainly from insulating nature of S, dissolution of polysulfi de intermediates in liquid electrolytes and large volume change during charge/ discharge. [16][17][18][19] Signifi cant advances have been achieved for Li-S batteries in decade years. The strategies include coating S with conductive polymers or carbon materials, infusing S into porous carbon, and employing different organic electrolytes. [20][21][22][23][24][25] Among these, one of the most attractive strategies is to encapsulate S with a self-supporting and void-containing carbon matrix. [20][21][22]26,27 ] Although the approach of carbon matrix supporting S can signifi cantly improve the S utilization and restrain the solubility of lithium polysulfi des, especially by infusing S into the micropores of carbon materials, the C/S composite cathodes showed outstanding cycling life even using carbonate electrolytes, but the S loading is limited to around 30% in the C−S composite due to the insulating nature of S 2 , Li 2 S 2 and Li 2 S and the side reaction between high-order polysolfi des and electrolyte, which leads to low overall capacity. [ 21 ] In order to increase the S loading of the S-based cathode, a high-cost electrolyte with linear and cyclic ethers, such as bis-(trifl uoromethane) sulfonimide lithium (LiTFSI) in dimethoxyethane and dioxolane and tetra(ethylene glycol) dimethyl ether, is generally adopted in the Li-S cells. [28][29][30] Although the use of high-cost ether-based electrolyte in Li-S batteries can increase S loading, it also generates shuttle reaction, reducing the cycle life and Coulumbic effi ciency. Recently, transition metal (Co, Ni and Cu etc.) sulfi des have been investigated as cathode materials for Li-S batteries and shown fairly stable cycle life, which are attributed to chemical stabilization of S. [31][32][33][34][35][36] The similar features between Na and Li bring us to consider whether it is possible