Synthesis,characterization, and electrical properties of nitrogen-doped single-walled carbon nanotubes with different nitrogen content

Nitrogen-doped single walled carbon nanotubes (SWCNTs) have been synthesized via the thermal decomposition of ferrocene using different ratios of acetonitrile/ethanol feedstock mixtures during the chemical vapor deposition process. The experiments were performed at 950 °C and 2 bar. The concentration of acetonitrile in the mixtures was varied from 0% to 100%. High resolution transmission electron microscopy and Raman spectroscopical measurements revealed the formation of SWCNTs for all mixtures. X-ray photoelectron spectroscopical analysis show nitrogen doping levels of up to 2 at.%. The doping levels increase as the acetonitrile concentration increases. The nitrogen incorporation is predominantly in the pyridine form. Electrical conductivity measurements show the dependence of conductivity as a function of nitrogen incorporation in the SWCNTs.     

Synthesis and characterization of superhard aluminum carbonitride thin films

Oxygen-free aluminum carbonitride thin films were grown on Si (100) substrates by reactive magnetron sputtering of Al target with the gas mixture of Ar, CH₄ and N₂ as precursor. A complementary set of techniques including X-ray photoelectron spectroscopy, energy-dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy and atomic force microscopy was employed for the characterization of the deposit chemistry, structure as well as morphology. Film growth proceeds along the preferred [0001] direction with the basal planes twisted because of the frustration in arranging the building blocks for aluminum carbonitrides. Under given conditions, the deposits show a declining tendency of crystallization with increasing carbon content. Strong covalent bonding and structural disorder give the film's extreme mechanical rigidity: Berkovich hardness is over 27.0 GPa for all the deposits, and an extreme value of 53.4 GPa was measured in Al₄₇C₂₀N_33.     

Synthesis and characterization of carbon aerogels doped with the anatase form of titanium oxide

TiO₂-doped carbon aerogels (CAs) were synthesized by sol–gel polymerization of a mixture of resorcinol, formaldehyde and tetrabutyl orthotitanate, followed by gelation and supercritical drying and carbonization in N₂ gas atmosphere. The morphology of these TiO₂-doped CAs was characterized by transmission electron microscopy. X-ray diffraction and Brunauer–Emmett–Teller methods were employed to determine the microstructure and surface characteristics of samples. It was found that the doped TiO₂ had no significant effect on the surface area of the samples, whereas the pore and mesopore volumes were increased by the addition of TiO₂. The TiO₂ particles were kept still as anatase in samples carbonized at 900 °C, and did not transform into rutile on heating. Electrochemical performance of the samples as electrode materials was studied by cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge/discharge measurements. The results showed that the specific capacitance of CA electrodes had been improved by TiO₂ doping, and the samples with wider pore diameters have higher capacitance values.     

Synthesis and characterization of phosphorus–nitrogen doped multiwalled carbon nanotubes

Phosphorus–nitrogen doped multiwalled carbon nanotubes (CN_xP_y) were prepared using a floating catalyst chemical vapor deposition method. Triphenylphosphine (TPP), as phosphorus (P) precursor, was used to control the structure of the CN_xP_y. Transmission electron microscope (TEM) observation indicated that with the increase of TPP amount, the outer diameter and wall thickness of the CN_xP_y gradually increased, while their inner diameter decreased. TEM and backscattered electron imaging revealed that structural changes of the nanotubes could be attributed to the shape change of the catalyst particles, from conical for nitrogen-doped carbon nanotubes (CN_x) to elongated for CN_xP_y, with the addition of TPP. X-ray photoelectron spectroscopy analysis demonstrated that the P content in CN_xP_y can reach as high as 1.9 at.%. Raman analysis indicated that CN_xP_y had a lower crystallinity than CN_x.     

Synthesis and characterization of ruthenium-containing ordered mesoporous carbon with high specific surface area

A Ru-containing ordered mesoporous carbon with a high specific surface area of 2186 m²/g was synthesized through evaporation-induced multi-constituent co-assembly method, wherein soluble resol polymer is used as the carbon precursor, silicate oligomers as the inorganic precursor, triblock copolymer as the template, and RuCl₃ · 3H₂O as the Ru precursor. The resultant sample was characterized by X-ray diffraction, nitrogen sorption, transmission electron microscopy and scanning electron microscopy. The results showed that the carbon material exhibited highly ordered mesoporous structure, and the ruthenium particles with sizes of ∼2 nm were uniformly distributed in the carbon matrix. The sample was used to catalyze benzene hydrogenation, which displayed high efficiency for this reaction.     

高比表面积三维有序大孔炭材料的合成与表征

将粒径为540nm的SiO2胶体微球通过自然沉积组装为胶体晶体模板,以葡萄糖的水溶液为前体填充模板间隙,高温炭化后,以HF溶液溶去模板,得到三维有序大孔炭材料。根据SEM检测,大孔以六方有序的方式排列,其孔径及孔径收缩率分别为510nm和5.6%。大孔之间由小窗口连通,构成内部三维交联的大孔网络。低温N2吸附测试表明,大孔孔壁上存在2～10nm为主的中孔孔隙,同时由于前体的表面复制作用,使样品BET比表面积达到948m2/g。XRD表征显示,所制备的3DOM材料由无序石墨结构的炭质组成。     

Synthesis and characterization of multiwalled carbon nanotubes-protoporphyrin IX composites using acid functionalized or nitrogen doped carbon nanotubes

In this research we describe the synthesis and characterization of composite materials based on multiwalled carbon nanotubes and protoporphyrin IX. We compare the results of using three types of carbon nanotubes: pristine (diameter < 10 nm), acid functionalized (diameter < 10 nm), and nitrogen doped carbon nanotubes (diameter ≈ 20 nm). Carbon nanotubes were mixed with protoporphyrin IX via two simple and straightforward methods using sonication, or heating-stirring. The characterization of the composites was done by Raman spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, ultraviolet-visible and fluorescence spectroscopy and infrared spectroscopy. A diversity of coatings of the nanotubes by protoporphyrin were obtained depending on the type of nanotube used or the method of synthesis. Some carbon nanotubes increased their diameter up to 40% after the reaction with protoporphyrin. Percentages by weight up to 20% of protoporphyrin were measured by thermogravimetric analysis. We obtained experimental evidences by different techniques of the electronic interaction and the formation of covalent bonds between both constituents, above all for the composites using nanotubes < 10 nm in diameter. Some of these evidences were ~ 98% of fluorescence quenching, reduction in the intensity of the absorption bands in ultraviolet visible spectroscopy, strong reduction in the intensity of some bands in Raman spectroscopy, red and blue shifts, as well as the presence of new absorption bands in infrared spectroscopy. Nitrogen doped carbon nanotubes showed low chemical reactivity to protoporphyrin IX, perhaps due to their lower acceptor character as they could have charge transfer from nitrogen dopants to the nanotube network, or because of their metallic character.     

Synthesis of niobium carbonitride by self-propagating combustion of Nb–C system in nitrogen

An experimental investigation on the preparation of niobium carbonitrides by self-propagating high-temperature synthesis (SHS) was conducted using compacted samples of niobium and carbon powders ignited in gaseous nitrogen. Effects of the carbon content, nitrogen pressure, and NbN addition on the combustion behavior and the degree of conversion were studied. Due to the nature of reaction in the combustion front, steady propagation of the combustion wave is observed in the sample of Nb + 0.3C, whereas the flame front associated with the samples of Nb + 0.5C and Nb + 0.7C travels in an oscillatory manner. Moreover, the flame-front propagation velocity was found to decrease with an increase in the carbon content of the sample. For the samples of Nb + 0.3C and Nb + 0.5C, after the passage of the combustion front the reaction continues lengthily in an afterburning stage, resulting in the nitridation percentage as high as about 80% that is nearly unaffected by the variation of nitrogen pressure. However, due to the lack of afterburning combustion the degree of nitridation in the sample of Nb + 0.7C was decreased to between 53 and 67%. The XRD analysis of final products indicates that in addition to the dominant phase of Nb(C,N), there exist small amounts of Nb and carbon left unreacted.     

Synthesis and characterization of carbon aerogels with different catalysts

Journal of Porous Materials - Carbon aerogels were synthesized by a sol–gel process by polycondensation of phloroglucinol, resorcinol and formaldehyde, using sodium hydroxide, calcium...     

Synthesis,characterization and application of surface active initiators

Surface active azo initiators have been synthesized starting from 2,2′-azoisobutyronitrile (AIBN) and different a, o-diols. Values of the production rate of free radicals from these initiators (2fkd) were obtained from ESR investigations of initiator solutions with a spin labelling technique as well as from solution polymerization of acrylonitrile and from emulsion polymerization of vinyl chloride under monomer starved conditions. The 2fkd values from the polymerization experiments were higher than those from the ESR investigations. Furthermore, the results show an influence on the kinetic constants and latex properties of the initiator structure. The emulsion polymerization of styrene was investigated at temperatures from ambient to 373 K with different initiator-emulsifier systems (IES) including persulphate, AIBN and surface active initiators. From these data were obtained Arrhenius plots for the mean degree of polymerization (DP) and for the particle number (N ), and overall activation energies were estimated. These activation energies show a strong dependence on the IES employed.     

The characterization of activated carbons with oxygen and nitrogen surface groups

The physicochemical properties and the surface chemical structure of the carbon materials obtained by the modification of the commercial activated carbon D43/1 (Carbo-Tech, Essen, Germany) were studied. The previously de-ashed activated carbon was subjected to the following modification procedures: high-temperature treatment (1000 K) under vacuum; oxidation with conc, nitric acid; and ammonia-treatment of annealed and oxidised carbons at high temperatures. The porous structure and the surface area of the five different carbon samples obtained were estimated by means of mercury porosimetry and from low-temperature nitrogen adsorption data. The thermogravimetric analysis and the quantitative determination of surface functional groups by selective neutralisation of bases and pH-metric titration were carried out. FTIR spectra (transmission) and X-ray photoelectron spectra (Cls, Ols and Nls) were obtained for all the carbon samples and compared with one another. The changes in the porosity and the chemical properties of the carbon surface caused by the modification were analysed. Some possible surface functional species, their structure and surface state are discussed.     

Mechanochemically assisted synthesis of titanium carbonitride from metal and organic precursor

Ultrafine TiC_0.29N_0.38 powders with a particle size of approximately 170 nm were synthesized by mechanochemical synthesis combined with moderate-temperature annealing using Ti and ethylenediamine as raw materials. Ethylenediamine plays a versatile role in the fabrication of ultrafine TiC_xN_y powders. It can serve as not only carbon and nitrogen sources, but also a process control agent, that facilitates the generation of ultrafine particles. A dense TiC_0.3N_0.39 ceramic with a high hardness of 16.7 GPa was obtained by spark plasma sintering at a considerably reduced temperature of 1100°C. This simple, energy-efficient method is a novel approach to synthesizing valuable TiC_xN_y.     

Synthesis, characterization, and electrochemical testing of carbon nanotubes derivatized with azobenzene and anthraquinone

Multi-walled and single-walled carbon nanotubes were side-wall functionalized with azobenzene and anthraquinone residues, i.e., chemical groups possessing redox activity, for potential utilization in functional catalysis and memory storage devices. Solvent-free synthesis was performed with diazonium salts generated in situ where it was found that it was simple and effective method. Nanotube functionalization was confirmed and characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). It is worth noting, that single-walled carbon nanotubes (SWCNTs) functionalized with azobenzene produced Raman modes typical of substituted azobenzenes with spectral peaks at ∼1137, 1412, and 1447 cm⁻¹. The nanotubes containing electroactive substituents were transferred onto electrode substrates using the Langmuir-Blodgett approach and characterized by cyclic voltammetry. The amount of electroactive groups per mg of nanotubes was calculated based on the peak of cathodic current. A highly reproducible voltammetric response was obtained with a single nanotube layer or multiple nanotube/octadecanol layers. It is believed that devices such as these will be invaluable for future high-performance electrodes.     

Synthesis and characterization of microporous titanosilicate ETS-10 with different titanium precursors

This work was aimed to identify the influence of different titanium sources, namely nano-sized Degussa TiO₂ (commercially known as P25), TiCl₃, TiF₄, and (NH₄)₂F₆Ti, on the crystallization of micropoprous titanosilicate ETS-10. The characterization results of XRD, FESEM, Raman, and FTIR showed that the morphology, particle size, and purity of the final products were strongly dependant on the titanium sources because of the different crystallization mechanisms of ETS-10 in the presence of different titanium precursors. The different coordination states of Ti atoms and anions of the titanium precursors were observed to play a role in the formation of ETS-10.     

Synthesis and characterization of microporous titanosilicate ETS-10 with different titanium precursors

This work was aimed to identify the influence of different titanium sources, namely nano-sized Degussa TiO₂ (commercially known as P25), TiCl₃, TiF₄, and (NH₄)₂F₆Ti, on the crystallization of micropoprous titanosilicate ETS-10. The characterization results of XRD, FESEM, Raman, and FTIR showed that the morphology, particle size, and purity of the final products were strongly dependant on the titanium sources because of the different crystallization mechanisms of ETS-10 in the presence of different titanium precursors. The different coordination states of Ti atoms and anions of the titanium precursors were observed to play a role in the formation of ETS-10.     

碳热还原氮化法制备碳氮化钛粉末

以物质的量比为1∶2.5的TiO_2粉和活性炭粉为原料,于N2气氛下采用碳热还原氮化法在不同的合成温度(分别为1500℃、1600℃、1650℃、1700℃、1750℃,N2压力固定为0.1MPa)和N2压力(分别为0.05MPa、0.1MPa、0.15MPa、0.2MPa,温度1700℃)下保温3h合成了碳氮化钛粉末。研究结果表明提高合成温度和降低N2压力有利于合成碳含量高的碳氮化钛粉末;在N2压力为0.1MPa的条件下,于1700℃保温3h热处理后,可以获得平均粒径为2μm的碳氮化钛粉末。     

新型含氮取代茂钛络合物的合成

合成了两个新型含氮茂钛络合物,经过元素分析、核磁共振、质谱确证结构。一个络合物单晶经过X－射线测试。