Solubilization of single-wall carbon nanotubes in Organic solvents without sidewall functionalization

Single walled carbon nanotubes (SWNTs) may be made soluble in a range of organic solvents without sidewall functionalization via their reduction by Na/Hg amalgam in the presence of dibenzo-18-crown-6. The [Na(dibenzo-18-crown-6)]n[SWNT] complex has been characterized by UV-Visible, Raman, and AFM and is consistent with no additional sidewall functionalization as compared with raw SWNTs, while MALDI-MS shows the presence of the [Na(dibenzo-18-crown-6)]+ ion. Solubility is greatest in CH2Cl2 and DMF being comparable to surfactant dispersed SWNTs, however, measurable solubilities are also observed in hexane, toluene, and alcohols. Reaction with alkyl halides (bromohexane, 1-iodododecane) yields alkyl functionalized SWNTs (i.e., C6H11-SWNTs and C12H25-SWNTs) with an C(SWNT):alkyl ratio (ca. 40:1) significantly lower than that observed by the analogous reaction of alkyl halides with reduced SWNTs formed by the Billups method in liquid ammonia.     

A new method of comprehensive utilization of rice husk

Rice husk is an abundant agricultural byproduct. The research on comprehensive utilization of rice husk to prepare xylose, activated carbon and silica was carried out. The hydrolysis conditions of xylan in rice husk to produce xylose were as follows: the concentration of H(2)SO(4) was 3.6% (wt.%), the temperature was 100°C, the ratio of rice husk mass (g) to H(2)SO(4) solution (ml) was 1:5 and the time was 3 h. The hydrolysis degree of xylan reached 95.6%. The resulting residues were used to prepare activated carbons with the BET surface area of 1763 m(2)/g when 50% H(3)PO(4) was impregnated with rice husk with the ratio of 5:1 at 500°C for 0.5 h. The produced carbons had effective adsorption capability to purify the xylose solution. Furthermore, they exhibited good electrochemical performance. After adsorption, activated carbons were calcined to produce silica with the diameter of 30 nm.     

Catalytic chemical vapor deposition of single-wall carbon nanotubes at low temperatures

We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350 degrees C by catalytic chemical vapor deposition from undiluted C2H2. NH3 or H2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.     

CVD金刚石薄膜(111)与(100)取向生长的热力学分析

用非平衡热力学耦合模型计算了CVD金刚石薄膜生长过程中C2H2与CH3浓度之比[C2H2]/[CH3]随衬底温度和CH4浓度的变化关系,从理论上探讨了金刚石薄膜（111）面和（100）面取向生长与淀积条件的关系。在衬底温度和CH4浓度由低到高的变化过程中,[C2H2]/[CH3]逐渐升高,导致金刚石薄膜的形貌从（111）晶面转为（100）晶面。添加氧后C2H2与CH3浓度都将下降,但C2H2下降得更多,因而添加氧也使[C2H2]/[CH3]下降,从而有利于生长（111）晶面的金刚石薄膜。     

Importance of fundamental sp, sp2, and sp3 hydrocarbon radicals in the growth of polycyclic aromatic hydrocarbons

The most basic chemistry of products formation in hydrocarbons pyrolysis has been explored via a comparative experimental study on the roles of fundamental sp, sp(2), and sp(3) hydrocarbon radicals/intermediates such as ethyne/ethynyl (C(2)H(2)/C(2)H), ethene/ethenyl (C(2)H(4)/C(2)H(3)), and methane/methyl (CH(4)/CH(3)) in products formations. By using an in situ time-of-flight mass spectrometry technique, gas-phase products of pyrolysis of acetylene (ethyne, C(2)H(2)), ethylene (ethene, C(2)H(4)), and acetone (propanone, CH(3)COCH(3)) were detected and found to include small aliphatic products to large polycyclic aromatic hydrocarbons (PAHs) of mass 324 amu. Observed products mass spectra showed a remarkable sequence of mass peaks at regular mass number intervals of 24, 26, or 14 indicating the role of the particular corresponding radicals, ethynyl (C(2)H), ethenyl (C(2)H(3)), or methyl (CH(3)), in products formation. The analysis of results revealed the following: (a) product formation in hydrocarbon pyrolysis is dominated by hydrogen abstraction and a vinyl (ethenyl, C(2)H(3)) radical addition (HAVA) mechanism, (b) contrary to the existing concept of termination of products mass growth at cyclopenta fused species like acenaphthylene, novel pathways forming large PAHs were found succeeding beyond such cyclopenta fused species by the further addition of C(2)H(x) or CH(3) radicals, (c) production of cyclopenta ring-fused PAHs (CP-PAHs) such as fluoranthene/corannulene appeared as a preferred route over benzenoid species like pyrene/coronene, (d) because of the high reactivity of the CH(3) radical, it readily converts unbranched products into products with aliphatic chains (branched product), and (e) some interesting novel products such as dicarbon monoxide (C(2)O), tricarbon monoxide (C(3)O), and cyclic ketones were detected especially in acetone pyrolysis. These results finally suggest that existing kinetic models of product formation should be modified to include the reported novel species and their formation pathways. It is expected that outcomes of this study will be useful to understand the products formation from reactors to interstellar atmospheres as well as the growth mechanism of carbon nanomaterials.     

Synthesis of ultrasmooth nanostructured diamond films by microwave plasma chemical vapor deposition using a He/H(2)/CH(4)/N(2) gas mixture

Ultrasmooth nanostructured diamond (USND) films were synthesized on Ti-6Al-4V medical grade substrates by adding helium in H(2)/CH(4)/N(2) plasma and changing the N(2)/CH(4) gas flow from 0 to 0.6. We were able to deposit diamond films as smooth as 6 nm (root-mean-square), as measured by an atomic force microscopy (AFM) scan area of 2 μm(2). Grain size was 4-5 nm at 71% He in (H(2) + He) and N(2)/CH(4) gas flow ratio of 0.4 without deteriorating the hardness (~50-60 GPa). The characterization of the films was performed with AFM, scanning electron microscopy, x-ray diffraction (XRD), Raman spectroscopy, and nanoindentation techniques. XRD and Raman results showed the nanocrystalline nature of the diamond films. The plasma species during deposition were monitored by optical emission spectroscopy. With increasing N(2)/CH(4) feedgas ratio (CH(4) was fixed) in He/H(2)/CH(4)/N(2) plasma, a substantial increase of CN radical (normalized by Balmer H(α) line) was observed along with a drop in surface roughness up to a critical N(2)/CH(4) ratio of 0.4. The CN radical concentration in the plasma was thus correlated to the formation of ultrasmooth nanostructured diamond films.     

Effect of the on/off cyclic modulation time ratio of C2H2/H2 flow on the low temperature deposition of carbon nanofilaments

Low temperature (less than 600 degrees C) deposition of carbon nanofilaments (CNFs) could be achieved on the silicon oxide substrate by thermal chemical vapor deposition system. We used Fe(CO)5 as the catalyst precursor for CNFs formation. For the enhancement of CNFs formation density, the source gas flow was intentionally manipulated as the cyclic on/off modulation of C2H2/H2 flow during the initial deposition stage. The CNFs formation density on silicon oxide substrate could be much enhanced by the cyclic modulation process having the higher growing/etching time ratio (180/30 s). Furthermore, the lattice structures of CNFs developed into carbon nanotubes at the higher growing/etching time ratio (180/30 s) case. The solely hydrogen gas feeding (C2H2 flow off) time during the initial deposition stage seems to play an important role for the variation in the CNFs formation characteristics by the cyclic modulation process.     

Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition

Silicon carbide films with different carbon concentrations x(C) have been synthesized by inductively coupled plasma chemical vapor deposition from a SiH(4)/CH(4)/H(2) gas mixture at a low substrate temperature of 500?°C. The characteristics of the films were studied by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy, and Raman spectroscopy. Our experimental results show that, at x(C) = 49?at.%, the film is made up of homogeneous nanocrystalline cubic silicon carbide without any phase of silicon, graphite, or diamond crystallites/clusters. The average size of SiC crystallites is approximately 6?nm. At a lower value of x(C), polycrystalline silicon and amorphous silicon carbide coexist in the films. At a higher value of x(C), amorphous carbon and silicon carbide coexist in the films.     

Scope and Mechanistic Study of the Coupling Reaction of α, β-Unsaturated Carbonyl Compounds with Alkenes: Uncovering Electronic Effects on Alkene Insertion vs Oxidative Coupling Pathways

The cationic ruthenium-hydride complex [(C(6)H(6))(PCy(3))(CO)RuH](+)BF(4) (-) (1) was found to be a highly effective catalyst for the intermolecular conjugate addition of simple alkenes to α,β-unsaturated carbonyl compounds to give (Z)-selective tetrasubstituted olefin products. The analogous coupling reaction of cinnamides with electron-deficient olefins led to the oxidative coupling of two olefinic C-H bonds in forming (E)-selective diene products. The intramolecular version of the coupling reaction efficiently produced indene and bicyclic fulvene derivatives. The empirical rate law for the coupling reaction of ethyl cinnamate with propene was determined as: rate = k[1](1)[propene](0)[cinnamate](-1). A negligible deuterium kinetic isotope effect (k(H)/k(D) = 1.1±0.1) was measured from both (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) and (E)-C(6)H(5)CD=C(CH(3))CONHCH(3) with styrene. In contrast, a significant normal isotope effect (k(H)/k(D) = 1.7±0.1) was observed from the reaction of (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) with styrene and styrene-d(10). A pronounced carbon isotope effect was measured from the coupling reaction of (E)-C(6)H(5)CH=CHCO(2)Et with propene ((13)C(recovered)/(13)C(virgin) at C(β) = 1.019(6)), while a negligible carbon isotope effect ((13)C(recovered)/(13)C(virgin) at C(β) = 0.999(4)) was obtained from the reaction of (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) with styrene. Hammett plots from the correlation of para-substituted p-X-C(6)H(4)CH=CHCO(2)Et (X = OCH(3), CH(3), H, F, Cl, CO(2)Me, CF(3)) with propene and from the treatment of (E)-C(6)H(5)CH=CHCO(2)Et with a series of para-substituted styrenes p-Y-C(6)H(4)CH=CH(2) (Y = OCH(3), CH(3), H, F, Cl, CF(3)) gave the positive slopes for both cases (ρ = +1.1±0.1 and +1.5±0.1, respectively). Eyring analysis of the coupling reaction led to the thermodynamic parameters, Δ H(?) = 20±2 kcal mol(-1) and S(?) = -42±5 e.u. Two separate mechanistic pathways for the coupling reaction have been proposed on the basis of these kinetic and spectroscopic studies.     

超高纯乙烯的制备

综述了超高纯乙烯(C2H4)的制备工艺,提出了通过精馏加吸附的纯化方法,将含有氧(O2)、二氧化碳(CO2)、一氧化碳(CO)、乙烷(C2 H6)、乙炔(C2 H2)、氢气(H2)、甲烷(CH4)、碳三及以上等杂质的粗C2 H4提纯到99.9995％以上.利用Aspen Plus模拟软件分析,确定超高纯C2 H4制备的...     

超临界干燥法制备催化剂合成单壁纳米碳管及表征

采用超临界干燥法制备了活性高、比表面大的Fe/Mo/Al₂O₃催化剂.通过超临界干燥,催化剂的比表面由294m²/g提高到401m²/g.在1000℃下用该催化剂催化裂解甲烷, 合成了大产量、高质量的单壁纳米碳管(SWNTs).利用SEM、TEM、HRTEM、TGA 和Raman等手段对所制备的SWNTs进行了表征.结果表明:超临界法制备催化剂合成的粗产品中SWNTs含量在30%以上,大大高于同一配方催化剂采用常规干燥法的产率(约2%); SWNTs的管径分布在0.8-1.0nm之间,其形态以束状为主.     

Super-low friction and super-elastic hydrogenated carbon films originated from a unique fullerene-like nanostructure

Hydrogenated carbon films were grown by a plasma-enhanced chemical vapor deposition (PECVD) technique using CH(4) and H(2) as feedstock at ambient temperature. The microstructure of the films was characterized by high resolution transmission electron microscopy (HRTEM). The images showed the presence of curved basal planes in fullerene-like arrangements. An apparent amorphous graphene structure with nm-sized packages of basal planes in a turbostratic feature was observed. The fabricated fullerene-like hydrogenated carbon films (FL-C:H) possess superior mechanical properties, i.e.?high hardness (19?GPa) and high elasticity (elastic recovery of 85%). More importantly, the films exhibit ultra-low friction (μ = 0.009) under ambient conditions with 20% relative humidity.     

Auto-ignition hazard of mixtures of ammonia,hydrogen, methane and air in a urea plant

The auto-ignition of NH(3)/CH(4)/H(2)/air mixtures constitutes a hazard that is of much concern in urea plants. In this study, the auto-ignition behaviour of NH(3)/CH(4)/H(2)/air mixtures is investigated experimentally for pressures up to 7500 kPa. The experiments were carried out in a closed spherical vessel with a volume of 8 dm(3). The concentration and the pressure dependence of the auto-ignition temperature (AIT) were determined for four types of mixtures: NH(3)/air, NH(3)/CH(4)/air, NH(3)/H(2)/air and NH(3)/CH(4)/H(2)/air. The most ignitable NH(3)/air mixtures were situated between stoichiometry and the upper flammability limit. Small amounts of methane and hydrogen decrease the AIT of NH(3)/air mixtures to a large extent. The pressure dependence of the AIT could be correlated by a Semenov relationship. For the multi-fuel mixtures, a distinct deviation from the Semenov correlation was observed at the lowest temperatures. With respect to the explosion hazard in urea plants, the experimental results were used to assess realistic AIT values in the pool reactor and the ammonia scrubber, operating at a pressure of 15,000 kPa.     

Cutting single-walled carbon nanotubes

A two-step process is utilized for cutting single-walled carbon nanotubes (SWNTs). The first step requires the breakage of carbon-carbon bonds in the lattice while the second step is aimed at etching at these damage sites to create short, cut nanotubes. To achieve monodisperse lengths from any cutting strategy requires control of both steps. Room-temperature piranha and ammonium persulfate solutions have shown the ability to exploit the damage sites and etch SWNTs in a controlled manner. Despite the aggressive nature of these oxidizing solutions, the etch rate for SWNTs is relatively slow and almost no new sidewall damage is introduced. Carbon-carbon bond breakage can be introduced through fluorination to ～C(2)F, and subsequent etching using piranha solutions has been shown to be very effective in cutting nanotubes. The final average length of the nanotubes is approximately?100?nm with carbon yields as high as 70-80%.     

Growth of Single‐Walled Carbon Nanotubes with Different Chirality on Same Solid Cobalt Catalysts at Low Temperature

Currently, designing solid catalysts at high temperature is the main strategy to realize single‐walled carbon nanotubes (SWNTs) with specific chirality, meaning it is very hard and challenging to create new catalysts or faces to fit new chirality. However, low temperatures make most catalysts solid, and developing solid catalysts at low temperature is desired to realize chirality control of SWNTs. A rational approach to grow SWNTs array with different chiralities on same solid Co catalysts at low temperature (650 °C) is herein put forward. Using solid Co catalysts, near‐armchair (10, 9) tubes horizontal array with ≈75% selectivity and (12, 6) tubes array with ≈82% are realized by adopting a small amount of ethanol and large amount of CO respectively. (10, 9) tubes are enriched for thermodynamic stability and (12, 6) tubes for kinetics growth rate. Both kinds of tubes show a similar symmetry to the Co (1 1 1) face with threefold symmetry for the symmetry matching nucleation mechanism proposed earlier. This method provides a new strategy to study the nucleation mechanism and more possibilities for preparing new solid catalysts to control the structure of SWNTs.     

Effects of Annealing on High-Magnetoresistance Tunnel Junctions Using Co75Fe25 Ferromagnetic Electrodes

1. IntroductionSpin tunneling magnetoresistive effect in ferromagnet / insulat or / ferromagnet (FM / I / F M ) j "net ionshas been the subject of intense study since the discovery of large tunneling magnetoresistance (TMR) inFe/Alzos/Fe and CoFe/Alzos/Co junctions at roomtemperature (RT)[',']. TMR ratio of FM/I/FM junctions at the early period 'was achieved only a fewpercent at RT due to the restriction of fabricationtechnology and TMR junction structure and area[3-6].Recently, re…     

Decomposition of benzene in the RF plasma environment. Part I. Formation of gaseous products and carbon depositions

This study employed radio-frequency (RF) plasma for decomposing benzene (C6H6) gas, and examined both gaseous products and solid depositions after reaction. The reactants and products were analyzed mainly by using both an on-line Fourier transform infrared (FT-IR) spectrometer and a gas chromatography. The analyses for solid deposition included electron spectroscopy for chemical analysis (ESCA), element analysis and heat value analysis. The C2H2, C2H4, C2H6, CH4, CO2 and CO were detected and discussed. The analytical results demonstrate that in the C6H6/Ar plasma, C2H2 is the sole gaseous product being detected. The fraction of total carbon input converted into C2H2 YC2H2 increased with increasing C6H6 feed concentration, but decreased with increasing input power. In the C6H6/H2/Ar system, besides C2H2, CH4, C2H4 and C2H6 were also detected, and their yields increased with increasing H2/C6H6 ratio. The above results indicated that the addition of H2 (auxiliary gas) achieves the benefit of creating hydrogen-rich species like CH4, C2H4 and C2H6. In the C6H6/O2/Ar system, C6H6 could be totally oxidized into CO2, CO and H2O, and no measurable phenol was found. Analyses of solid depositions revealed that the carbon depositions were similar to those of Anthracite. The carbon deposition has a heat value of 7000 kcal/kg. Additionally, the possible reaction pathways were also built up and discussed.     

Towards a ‘catalyst activity map’ regarding the nucleation and growth of single walled carbon nanotubes

Quantification using scanning electron microscopy (SEM) of single walled carbon nanotubes (SWNTs) grown per unit area using a Co-Fe (50:50) catalyst system, prepared by the incorporation of the appropriate metal salts into a Spin-On Glass substrate, at 900°C. The effects of substrate, as well as catalyst precursor concentration, were investigated. SWNT growth density is maximised with a catalyst precursor concentration of ≥2.5 mM, associated with the formation of catalyst nanoparticles of a critical size for SWNT nucleation. Samples were subjected to secondary growth, using a range of H₂:CH₄ ratios to determine the optimum precursor composition. It was found that nucleation and growth stages are optimal under different conditions. Optimum conditions for nucleation resulted in >10× increase in SWNT density. Optimisation is dependent on temperature and the partial pressure of reagent gas species.     

单壁碳纳米管在基底表面的离散生长

通过旋涂硝酸铁异丙醇溶液于P型硅表面以获得均匀分布的催化剂颗粒,以CH4为反应气体采用CVD方法即可在P型硅表面均匀生长单壁碳纳米管,并且部分碳纳米管呈直立状.研究了催化剂浓度、生长基底、反应温度对单壁碳纳米管表面生长情况的影响.研究表明,催化剂浓度升高或采用二氧化硅替代P型硅为生长基底时,都会导致单壁碳纳米管生长的密度加大,而碳纳米管长度变短且更易贴附基底表面生长;随反应温度的提高碳纳米管的生长效率降低,并使得碳纳米管更易贴附基底表面生长.采用此方法制备的生长有直立碳纳米管的硅片作为扫描基底,在原子力显微镜敲击模式下利用拾取法成功制备了碳纳米管原子力显微镜针尖.     

温度对BCl3-CH4-H2化学气相沉积掺硼碳沉积过程的影响

以三氯化硼、甲烷和氢气的混合气体为前驱体,利用磁悬浮天平热重系统研究了850～1200℃区间内化学气相沉积掺硼碳的原位动力学.探索了温度对沉积速率的影响,计算了该温度区间内沉积过程的表观活化能,同时借助SEM和EDS技术.测试了不同温度点(900℃、1000℃、1100℃和1200℃)沉积产物的微观结构和成分.结果表明,化学气相沉积掺硼碳属于典型的热激活反应过程;在所研究的温度区间内存在5种不同的反应控制机制;随着温度的升高,沉积产物的n(B)/n(C)和堆积密度都显著变小,说明高n(B)/n(C)和高致密度的掺硼碳涂层应在较低的温度下制备.