N掺杂多孔碳材料研究进展

通过掺杂氮原子对多孔碳材料进行功能化,可强化多孔碳材料固有的优异性能并赋予其新功能,从而拓宽其在各领域的应用范围。近年来,研究者相继开发了一系列技术方法,已制备得到多种结构特异、性能优异的氮掺杂多孔碳材料。本文基于氮掺杂多孔碳材料的最新研究进展,详细介绍了利用液相模板法、化学气相沉积法、氨气后处理法、化学活化法和水热法等制备氮掺杂多孔碳材料的方法,评述了各种方法的特点及局限性,并简要介绍了该类材料在电池催化、气体吸附分离、储氢及污染气体脱除等方面的应用,指出了氮掺杂多孔碳材料工业应用的规模化制备发展方向。     

氮化硼纳米管的合成与表征

以氧化铁和无定型硼粉为原料,反应气氛为碳气氛,在1 400℃下利用化学气相沉积法（CVD）制备出氮化硼纳米管。X射线研究表明,对应着六方氮化硼晶面的特征衍射峰非常清晰。采用扫描电子显微镜（SEM）对样品的结构与形貌进行表征,结果表明,样品属于一端开口的竹节状BN纳米管。     

BN纳米管制备研究进展

BN纳米管(BNNTs)是一种与碳纳米管相似的管状结构材料,因其优异的力学强度、高的热导率、良好的热稳定性及化学稳定性、超疏水性及优异的电绝缘性等性能,在冶金、化工、环境、催化及生物医学等领域具有广泛的应用前景.简要综述了电弧放电法、化学气相沉积法与球磨氮化反应法制备BNNTs的优缺点及影响因素,并对今后BNNTs的研...     

软模板法聚苯胺微/纳米管的制备与表征

用化学氧化法中的软模板法,选择同时带有磺酸根(—SO3-)和羧酸根(—COO-)的酸性媒介深黄GG(AMY GG)为掺杂剂,制备出了具有一维微/纳米结构的聚苯胺(PANI)。运用扫描电镜(SEM)、透射电镜(TEM)对产物的微观形貌进行了表征。当盐酸和苯胺摩尔比〔n(HCl)/n(ANI)〕分别为0.5、0.75和1时,得到聚苯胺微/纳米管结构。用傅里叶红外光谱(FTIR)和X射线衍射谱图(XRD)对产物的结构进行了表征,可以看出,AMY GG的两个功能基团—COO-和—SO3-已经掺杂到了聚苯胺分子链上;当n(HCl)/n(ANI)=1时所得产物XRD的衍射峰与其摩尔比为0.2、0.5时所得产物衍射峰有明显差别。     

氮化硼纳米管问世

据报道，中科院物理所微加工实验室与日本物质材料研究机构合作，近日采用化学气相沉积法获得了N型的氮化硼半导体纳米管。     

爆炸法合成中空碳纳米颗粒

采用爆炸辅助化学气相沉积法,以N,N-二甲基甲酰胺(DMF)为原料,在金属催化剂作用下合成了粒径分布在20 nm～40 nm的中空碳纳米颗粒.更为重要的是,发现中空碳纳米颗粒可在无金属催化剂作用下自组装形成.在此过程中,控制炸药和碳源的比例对于碳颗粒的结构和尺寸有重要影响.当炸药与碳源的摩尔比例合适时,产物中中空碳纳米颗粒的含量达到95%以上,且粒径分布均匀,约为10 nm.     

碳纳米带的催化生长及其机理的研究

采用热化学气相沉积法(thermal chemical vapor deposition,TCVD)在经过高温氨气处理后的硅基铁纳米薄膜表面实现片状碳纳米带的催化生长.通过场发射扫描电子显微镜(field emission scanning electron microscopy,FESEM)的观察可知,生成的碳材料是一种准二维材料,表面具有垂直于其长度方向的纹理,厚(z方向)约几十纳米,宽(Y方向)几百纳米,类似于一种"搓板"状的结构.而其宽度沿着其长度方向则有较大的变化,时宽时窄,没有固定的规律.这种带状碳纳米纤维材料的边缘光滑,比中间略宽,类似于一种镶边结构.通过高分辨透射电子显微镜(high resolution transmission electron microscopy,HRTEM)的观察可知,碳纳米带的碳层沿着垂直于碳纳米带长度的(002)方向有统一的排列,其边缘都弯曲折叠成封闭结构.有序排列的碳层被层错和断点分割成许多微区.在对催化剂研究的基础上,本文认为片状碳纳米带的生长是通过碳原子在片层状催化剂颗粒中的扩散、析出来实现的.碳层从催化剂片层侧面中一层一层地析出,形成带状外观.     

中空碳纳米洋葱的制备

碳纳米洋葱是一种零维碳纳米材料,由于其优异的理化性能,使其在能源、催化等众多领域有着广泛的应用。在某些应用领域,中空结构的碳纳米洋葱比其它结构的碳纳米洋葱的性能更加优异。目前,中空结构的碳纳米洋葱的规模化制备仍然是一个难题。本文总结了目前制备中空结构碳纳米洋葱的方法,包括电弧放电、化学气相沉积、热解法等等。此外,对每种制备方法的优缺点进行评述并对未来的制备方法做出展望。     

不同硼含量的硼掺杂各向同性热解炭制备及微观结构研究

以CH4、H2和BCl3为原料,利用化学气相沉积方法制备了硼掺杂各向同性热解炭材料。研究了制备工艺及硼元素掺杂对热解炭微观结构和抗氧化性能的影响。结果表明,硼元素能够均匀地掺入热解炭中,其含量随着BCl3流量的增大而增加;硼掺杂并未改变热解炭的各向同性性质,但随着BCl3流量的增加,硼掺杂各向同性热解炭的结构由球形颗粒状结构逐渐向卷曲片层状结构转变,硼在热解炭中的存在形式则由单一形式(取代)逐渐过渡到混合形式(取代硼和碳化硼);硼元素的掺杂能有效抑制热解炭的氧化,大幅提高材料的起始氧化温度,显著降低氧化损失。     

Electrochemical properties of N-doped hydrogenated amorphous carbon films fabricated by plasma-enhanced chemical vapor deposition methods

Nitrogen-doped hydrogenated amorphous carbon thin films (a-C:N:H, N-doped DLC) were synthesized with microwave-assisted plasma-enhanced chemical vapor deposition widely used for DLC coating such as the inner surface of PET bottles. The electrochemical properties of N-doped DLC surfaces that can be useful in the application as an electrochemical sensor were investigated. N-doped DLC was easily fabricated using the vapor of nitrogen contained hydrocarbon as carbon and nitrogen source. A N/C ratio of resulting N-doped DLC films was 0.08 and atomic ratio of sp³/sp²-bonded carbons was 25/75. The electrical resistivity and optical gap were 0.695 Ω cm and 0.38 eV, respectively. N-doped DLC thin film was found to be an ideal polarizable electrode material with physical stability and chemical inertness. The film has a wide working potential range over 3 V, low double-layer capacitance, and high resistance to electrochemically induced corrosion in strong acid media, which were the same level as those for boron-doped diamond (BDD). The charge transfer rates for the inorganic redox species, Fe^2+/3+ and Fe(CN)₆^4−/3− at N-doped DLC were sufficiently high. The redox reaction of Ce^2+/3+ with standard potential higher than H₂O/O₂ were observed due to the wider potential window. At N-doped DLC, the change of the kinetics of Fe(CN)₆^3−/4− by surface oxidation is different from that at BDD. The rate of Fe(CN)₆^3−/4− was not varied before and after oxidative treatment on N-doped DLC includes sp² carbons, which indicates high durability of the electrochemical activity against surface oxidation.     

一种新颖结构的煤基定向碳薄膜的制备与表征

以宏源精选煤为原料在微波等离子体条件下制备出一种新颖结构的碳材料,运用场发射扫描电子显微镜、透射电子显微镜和能量色散谱技术对产物进行表征.结果表明：产物形状似莴笋状,外层石墨化程度较好,其最大宽度约为170 nm,长度则为4～5 μm,且呈定向排列.这种新颖结构的纳米碳材料有望在场发射、增强材料等方面显示出巨大的应用潜力.     

Chemistry and kinetics of chemical vapor deposition of pyrocarbon: VI. influence of temperature using methane as a carbon source

The chemical vapor deposition of carbon from methane was investigated at an ambient pressure of about 100 kPa, a methane partial pressure of 10 kPa and temperatures ranging from 1050–1125°C. Carbon deposition rates and compositions of the gas phase as a function of residence time have been determined using a substrate with a surface area/reactor volume ratio of 40 cm⁻¹. Increasing temperatures lead to strongly increasing deposition rates, decreasing partial pressures of ethane and increasing partial pressures of ethene, ethine and benzene. The overall activation energy of carbon deposition, determined from the initial deposition rates at a residence time versus zero amounts to 446 kJ/mol as compared to 431.5, 448 and 452.5 kJ/mol reported in earlier papers. Two possible rate-limiting steps are discussed, namely dissociation of methane, which is favored in the earlier papers, and dissociation of carbon–hydrogen surface complexes.     

Synthesis of photoluminescent SiC-SiOx nanowires using coal tar pitch as carbon source

SiC-SiOx nanowires (NWs) with core-shell and chain-bead structures were synthesized via a catalyst-free chemical vapor deposition (CVD) route without Ar gas, using silicon and coal tar pitch powders as raw materials. The SiC-SiOx NWs with sharp tips formed by solid-vapor between Si (s) and CO (g) or C (s) and SiO (g), liquid-vapor between Si (l) and CO (g), and vapor-vapor between SiO (g) and CO (g) growth process along the [111] direction. The NWs were several millimeters in length, and the average diameters of the chains and beads were 40–90 nm and 325 nm, respectively. The obtained NWs had good blue-green photoluminescence property owing to the stacking faults and amorphous SiOx. This novel CVD route is simple, low cost and suitable for large-scale production.     

Contribution to the study of carbon deposition in coke ovens

The formation of carbon deposits from coal pyrolysis in a two-stage reactor has been studied for several cracking temperatures from 850 to 1000 °C. The weight of the carbon deposit was monitored continuously during pyrolysis by a thermogravimetric balance. Four successive periods of deposition can be distinguished:

1. (1) no weight uptake;

2. (2) a slow increase in weight;

3. (3) a sharp increase in weight;

4. (4) constant weight.

From the data, three distinct deposition rates have been calculated at different cracking temperatures: germination rate, growth rate and overall deposition rate. The general tendency is an increase in all three deposition rates with temperature. Scanning electron and polarized light micrographs of these deposits show that they have a laminar structure. There are two (sometimes three) cone layers, the first being formed during the liberation of water contained in the coal charge, indicating that water plays the role of an inhibitor in the formation of carbon deposits. The structure of the deposits is independent of the temperature at which deposition takes place. The mechanism of this carbon formation is discussed.     

Synthesis of multiwalled carbon nanotubes on Al2O3 supported Ni catalysts in a fluidized‐bed

Multiwalled carbon nanotubes (MWNTs) were synthesized on Al₂O₃ supported Ni catalysts from C₂H₂ and C₂H₄ feedstocks in a fluidized bed. The influence of the ratio of superficial gas velocity to the minimum fluidization velocity (U/U_mf), feedstock type, the ratio of carbon in the total quantity of gas fed to the reactor, reaction temperature, the ratio of hydrogen to carbon in the feed gas, and nickel loading were all investigated. Significantly, the pressure drop across the fluidized‐bed increased as the reaction time increased for all experiments, due to the deposition of MWNTs on the catalyst particles. This resulted in substantial changes to the depth and structure of the fluidized bed as the reaction proceeded, significantly altering the bed hydrodynamics. TEM images of the bed materials showed that MWNTs, metal catalysts, and alumina supports were predominant in the product mixture, with some coiled carbon nanotubes as a by‐product. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

生物质热解催化剂积炭问题的研究进展

生物质催化热解获得生物油等高质产品是最有前途替代传统化石能源的方法之一,但在热解过程中存在着严重的催化剂失活问题,其中积炭是导致催化剂失活的最主要因素。本文对近年来生物质催化热解领域的催化剂积炭问题进行综述,重点介绍催化剂积炭失活原因及表征方法、积炭的影响因素分析（催化剂结构、催化剂酸性与反应温度）、抑制催化剂积炭的方法 （催化剂改性、高压反应条件等）以及积炭催化剂再生方法 （氧化灼烧再生、臭氧低温再生、非热等离子体再生等）,并介绍了近年来新兴的微波催化热解技术对催化剂积炭的抑制和消除作用,然后针对该领域目前所面临的困难和发展方向进行展望,以期为生物质催化热解过程中催化剂积炭问题研究提供理论基础。     

氮掺杂微孔活性炭制备及其超级电容性能

以土豆为碳源,乙二胺为氮源,氢氧化钾为活化剂制备具有微孔结构高比表面积氮掺杂活性炭。通过N_2物理吸附、扫描电镜、透射电镜、拉曼光谱和元素分析研究活性炭比表面积、孔结构、形貌及元素组成,并测试其电化学性能。结果表明,当碱碳质量比为5∶1时(NC600-800-5),活性炭材料比表面积最高2 440 m~2·g~(-1)、孔容最大1.07 cm~3·g~(-1)、孔径最大0.82 nm和1.80 nm。电流密度1 A·g~(-1)时比电容可达370 F·g~(-1),经3 000次循环充放电后,比电容保持率为95.2%。     

A time‐dependent multiphysics,multiphase modeling framework for carbon nanotube synthesis using chemical vapor deposition

A time‐dependent multiphysics, multiphase model is proposed and fully developed here to describe carbon nanotubes (CNTs) fabrication using chemical vapor deposition (CVD). The fully integrated model accounts for chemical reaction as well as fluid, heat, and mass transport phenomena. The feed components for the CVD process are methane (CH₄), as the primary carbon source, and hydrogen (H₂). Numerous simulations are performed for a wide range of fabrication temperatures (973.15–1273.15 K) as well as different CH₄ (500–1000 sccm) and H₂ (250–750 sccm) flow rates. The effect of temperature, total flow rate, and feed mixture ratio on CNTs growth rate as well as the effect of amorphous carbon formation on the final product are calculated and compared with experimental results. The outcomes from this study provide a fundamental understanding and basis for the design of an efficient CNT fabrication process that is capable of producing a high yield of CNTs, with a minimum amount of amorphous carbon. © 2009 American Institute of Chemical Engineers AIChE J, 2009