Evaluating the hydrogen chemisorption and physisorption energies for nitrogen-containing single-walled carbon nanotubes with different chiralities: a density functional theory study

The hydrogen adsorption energies for nitrogen-containing carbon nanotubes (N-CNTs) and for bare carbon nanotubes were calculated using the density functional theory methods at the B3LYP/6–31-G(d) level, including dispersion force corrections. The N-CNTs were finite saturated and non-saturated single-walled carbon nanotubes that contained one or more pyrimidine units, the relative positions of which defined the different configurations of the nanotube. The chemisorption of atomic hydrogen to a full exocyclic monolayer of zigzag, armchair, and chiral N-CNTs was studied as a function of the structural parameters. Zigzag N-CNTs of any configuration, with a larger number of nitrogen atoms, a small diameter and a small length, are more reactive compared to chiral and armchair N-CNTs. The presence of nitrogen in the carbon nanotubes enhances their reactivity to chemisorb atomic hydrogen, showing exothermic energy values. In contrast, the physisorption of molecular hydrogen was endothermic for most of the studied saturated N-CNTs, even when including corrections for van der Waals interactions. The endothermicity was greatest for zigzag nanotubes, then decreased for chiral nanotubes and decreased again for armchair nanotubes. In general, the endothermicity decreased for longer nanotubes, which have larger diameters, and a small number of nitrogen atoms. The results of this study suggest that, with saturated bare carbon nanotubes, saturated, and unsaturated N-CNTs could potentially have a higher capacity as hydrogen-storage media than the corresponding unsaturated carbon nanotubes.     

Nitrogen-doped carbon nanotubes for heat transfer applications

In this research, it is aimed to enhance the heat transfer properties of the carbon nanotubes through nitrogen doping. To this end, nitrogen-doped multiwall carbon nanotubes (N-CNTs) were synthesized via chemical vapor deposition method. For supplying carbon and nitrogen during the synthesis of N-CNTs, camphor and urea were used, respectively, at 1000 °C over Co–Mo/MgO nanocatalyst in a hydrogen atmosphere. N-CNTs with three different nitrogen loadings of 0.56, 0.98, and 1.38 mass% were synthesized, after which, water/N-CNT nanofluids of these three samples with concentrations of 0.1, 0.2, and 0.5 mass% were prepared. To obtain a stable nanofluid, N-CNTs were functionalized by nitric acid followed by stabilizing in water by employing the ultrasonic bath. Investigation on the stability of the samples showed a high stability level for the prepared water/N-CNT nanofluids in which the zeta potential of ??43.5 mV was obtained for the best sample. Also for studying the heat transfer properties, the thermal conductivity in the range of 0.1–0.5 mass% and convection heat transfer coefficients of nanofluids in the range of 0.1–0.5 mass%, and Reynolds number in the range of 4000–9000 were evaluated. The results showed 32.7% enhancement of the convection heat transfer coefficients at Reynolds number of 8676 and 27% increase in the thermal conductivity at 0.5 mass% and 30 °C.

     

氮掺杂碳纳米管负载的Ru和Pd催化剂上异丙醇的转化(英文)

Ru and Pd (2 wt%) loaded on pure and on Ndoped carbon nanotubes (NCNTs) were prepared and tested using the isopropyl alcohol decomposition reaction as probe reaction. The presence of nitrogen functionalities (pyridinic, pyrrolic, and quaternary nitrogen) on the nitrogen doped support induced a higher metal dispersion: Pd/NCNT (1.8 nm) Pd/CNT (4.9 nm), and Ru/NCNT (2.4 nm) Ru/CNT (3.0 nm). The catalytic activity of the supports was determined first. Isopropyl alcohol conversion produces acetone on CNTs while on NCNTs it led to both dehydration and dehydrogenation products. At 210 °C and in the presence of air, the isopropyl alcohol conversion was higher on the NCNTs (25%) than on the CNTs (11%). The Pd loaded catalysts were more active and more selective than the Ru ones. At 115 °C, the Pd catalysts were 100% selective towards acetone for a conversion of 100%, whereas the Ru catalysts led to dehydration and dehydrogenation products. The nitrogen doping induced the appearance of redox properties when oxygen is present in the reaction mixture.     

氮掺杂碳纳米管包覆碳化硅作为不含金属的催化剂(英文)

A hierarchical metal-free catalyst consisting of nitrogen-doped carbon nanotubes decorated onto a silicon carbide (N-CNTs/SiC) macroscopic host structure was prepared. The influence of N-CNTs incorporation on the physical properties of the support was evaluated using different characterization techniques. The catalyst was tested as a metal-free catalyst in the selective oxidation of H2S and steam-free dehydrogenation of ethylbenzene. The N-CNTs/SiC catalyst exhibited extremely good desulfurization performance compared to a Fe2O3/SiC catalyst under less conducive reaction conditions such as low temperature, high space velocity, and a low O2-to-H2S molar ratio. For the dehy-drogenation of ethylbenzene, a higher dehydrogenation activity was obtained with the N-CNTs/SiC catalyst compared to a commercial K-Fe/Al2O3 catalyst. The N-CNTs/SiC catalyst also displayed good stability as a function of time on stream for both reactions, which was attributed to the strong anchoring of the nitrogen dopant in the carbon matrix. The extrudate shape of the SiC support allowed the direct macroscopic shaping of the catalyst for use in a conventional fixed-bed reactor without the problems of catalyst handling, transportation, and pressure drop across the catalyst bed that are encountered with nanoscopic carbon-based catalysts.     

The influence of nitrogen sources on nitrogen doped multi-walled carbon nanotubes

A range of nitrogen doped carbon nanotubes (N-CNTs) was produced by a nebulised floating catalyst method at 850 °C using a mixture of toluene and 1-8% nitrogen containing reagents (a range of amines and amides). The carbon nanotube (CNT) products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), CHN analysis as well as Raman spectroscopy. Differences due to the different N containing reagents were noted but in general all reagents gave aligned CNTs that at low concentration (1%) were longer and wider than those produced without nitrogen. Increased N content in the reactant mixture gave doped tubes that became shorter and showed more disorder. Treatment of the N-CNTs with nitric acid (microwave, 30 min) gave samples that were chemically modified by the acid (loss of alignment, narrower tubes and more facile oxidation). It appears in general that the amount of N in the nitrogen containing reagent is more important than the source and type of the N atoms used as revealed by trends in the morphology (diameter, length) of the N-CNTs produced.     

N-CNTs/NiCo-LDH复合材料的制备及电化学性能

通过高温碳化聚吡咯纳米管制备了氮掺杂碳纳米管(N-CNTs), 并采用共沉淀法将镍钴层状双氢氧化物(NiCo-LDH)原位生长在N-CNTs上, 制备出具有三维互联网状结构的N-CNTs/NiCo-LDH复合材料. 研究了镍钴摩尔比对N-CNTs/NiCo-LDH复合材料形貌结构和电化学性能的影响. 结果表明, 当镍钴摩尔比为1∶2时, N-CNTs/Ni₁Co₂-LDH具有最佳的电化学性能. 在1 A/g电流密度下, 其比电容可达1311.8 F/g; 当电流密度为 10 A/g时, 电容保持率高达88.3%, 展现出优异的倍率性; 在经过2500次循环后, 电容保持率仍可达76.4%, 具有良好的循环稳定性.由N-CNTs/Ni₁Co₂-LDH与活性炭(AC)电极所构建的N-CNTs/Ni₁Co₂-LDH//AC水系混合型超级电容器, 在750 W/kg功率密度下, 具有27.19 W·h/kg的高能量密度.     

CVD synthesis of nitrogen doped carbon nanotubes using ferrocene/aniline mixtures

Nitrogen doped carbon nanotubes (N-CNTs) have been synthesized by the chemical vapour deposition (CVD) floating catalyst method using either 4-ferrocenylaniline or mixtures of varying concentrations of ferrocene/aniline together with toluene as added carbon source. The N-CNTs produced are less stable (thermal gravimetric analysis measurements), less graphitic and more disordered (transmission electron microscope measurements) than their undoped counterparts. The ratio of the Raman D- and G-band intensities increase with the nitrogen concentration used during the CNT growth. Furthermore, the transmission electron microscope (TEM) studies reveal that the CNTs are multi-walled (MW), and that the diameters of the N-MWCNTs can be controlled by systematically varying the concentrations of the nitrogen source. The TEM analysis also revealed that when ferrocenylaniline and ferrocene/aniline reactions are compared at similar Fe/N ratios, higher N doping levels are achieved (ca. 2-5×) when ferrocenylaniline is the catalyst.     

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes(CNTs),as one-dimensional nanomaterials,show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer.However,the security risks,time-consuming and high cost of the preparation process hinder its further application.Here,we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs(Co/N-CNTs) by using cobalt zeolitic imidazolate framework(ZIF-67) as a precursor,in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs.Importantly,the obtained Co/N-CNTs,with high content of pyridinic nitrogen and abundant graphitized structure,exhibit superior catalytic activity for oxygen reduction reaction(ORR) with half-wave potential(E_1/2) of 0.85 V and durability in terms of the minimum current loss(2%) after the 30,000 s test.Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.     

Enhanced electrocatalytic performance of functionalized carbon nanotube electrodes for oxygen reduction in proton exchange membrane fuel cells

Although nitrogen doped CNTs (N-CNTs) are considered as a promising alternative to platinized carbon for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs), the origin of the enhanced ORR activity with N-CNTs is not clear at present. Among several plausible reasons, the exposure of edge plane and creation of impurity band/surface states near the Fermi level are considered as major causes behind the catalytic activity. However, CNTs without nitrogen doping are not known to catalyze the ORR. In this work, we study the ORR activity of functionalized carbon nanotubes with different functional groups, such as sulfonic acid and phosphonic acid, in order to understand the role of surface functionalities in catalyzing the reaction. Functionalized CNTs show significantly enhanced activity towards the ORR, while CNTs without such surface functional groups do not reveal any such special ORR activity. Linear sweep voltammetry experiments with different rotation rates show diffusion controlled limiting current values for functionalized CNTs, and the 'n' values derived from Koutecky-Levich plots are 3.3 and 1.7 for S-MWCNTs and P-MWCNTs, respectively. This work demonstrates the ORR activity of functionalized MWCNTs, which opens up new strategies for electrocatalyst design in PEMFCs.     

The synthesis of nitrogen-doped carbon nanotubes/gold composites and their application to the detection of thioridazine

Nitrogen-doped carbon nanotubes (N-CNTs)/gold composites were synthesized through a simple self-assembly method. The morphology, composition, and optical properties of the resulted composites were investigated by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Raman spectra, ultraviolet–visible absorption spectrum, and X-ray photoelectron spectroscopic. This nanocomposite combines the advantages of N-CNTs and gold nanoparticales showing many excellent properties such as good dispersibility in water and satisfactory biocompatibility. Cyclic voltammogram experiment shows that N-CNTs/gold composite has high conductivity. Based on these aspects, N-CNTs/gold-modified electrode was applied to the voltammetric determination of thioridazine hydrochloride (TH) successfully. The linear calibration range for the TH sensor was 12?~?850?μM with a detection limit of 1.3?μM at a signal-to-noise ratio of 3, long-term stability, and good reproducibility.     

Electrochemical oxidation of catecholamines and catechols at carbon nanotube electrodes

The differences in the electrochemical oxidation of two commonly known catecholamines, dopamine and norepinephrine, and one catechol, dihydroxyphenylacetic acid (DOPAC), at three different types of carbon based electrodes comprising conventionally polished glassy carbon (GC), nitrogen-doped carbon nanotubes (N-CNTs), and non-doped CNTs were assessed. Raman microscopy and X-ray photoelectron spectroscopy (XPS) were employed to evaluate structural and compositional properties. Raman measurements indicate that N-CNT electrodes have ca. 2.4 times more edge plane sites over non-doped CNTs. XPS data show no evidence of oxygen functionalities at the surface of either CNT type. N-CNTs possess 4.0 at. % nitrogen as pyridinic, pyrrolic, and quaternary nitrogen functionalities that result in positively charged carbon surfaces in neutral and acidic solutions. The electrochemical behavior of the various carbon electrodes were investigated by cyclic voltammetry conducted in pH 5.8 acetate buffer. Semiintegral analysis of the voltammograms reveals a significant adsorptive character of dopamine and norepinephrine oxidation at N-CNT electrodes. Larger peak splittings, DeltaE(p), for the cyclic voltammograms of both catecholamines and a smaller DeltaE(p) for the cyclic voltammogram for DOPAC at N-CNT electrodes suggest that electrostatic interactions hinder oxidation of cationic dopamine and norepinephrine, but facilitate anionic DOPAC oxidation. These observations were supported by titrimetry of solid suspensions to determine the pH of point of zero charge (pH(pzc)) and estimate the number of basic sites for both CNT varieties. This study demonstrates that carbon purity, the presence of exposed edge plane sites, surface charge, and basicity of CNTs are important factors for influencing adsorption and enhancing the electrochemical oxidation of catecholamines and catechols.     

3D analysis of the morphology and spatial distribution of nitrogen in nitrogen-doped carbon nanotubes by energy-filtered transmission electron microscopy tomography

We present here the application of the energy-filtered transmission electron microscopy (EFTEM) in the tomographic mode to determine the precise 3D distribution of nitrogen within nitrogen-doped carbon nanotubes (N-CNTs). Several tilt series of energy-filtered images were acquired on the K ionization edges of carbon and nitrogen on a multiwalled N-CNT containing a high amount of nitrogen. Two tilt series of carbon and nitrogen 2D maps were then calculated from the corresponding energy-filtered images by using a proper extraction procedure of the chemical signals. Applying iterative reconstruction algorithms provided two spatially correlated C and N elemental-selective volumes, which were then simultaneously analyzed with the shape-sensitive reconstruction deduced from Zero-Loss recordings. With respect to the previous findings, crucial information obtained by analyzing the 3D chemical maps was that, among the two different kind of arches formed in these nanotubes (transversal or rounded ones depending on their morphology), the transversal arches contain more nitrogen than do the round ones. In addition, a detailed analysis of the shape-sensitive volume allowed the observation of an unexpected change in morphology along the tube axis: close to the round arches (with less N), the tube is roughly cylindrical, whereas near the transversal ones (with more N), its shape changes to a prism. This relatively new technique is very powerful in the material science because it combines the ability of the classical electron tomography to solve 3D structures and the chemical selectivity of the EFTEM imaging.     

Nitrogen-doped carbon nanotube spheres as metal-free catalysts for the partial oxidation of H2S

Nitrogen-doped carbon nanotubes (N-CNTs) with macroscopic shaping were synthesized by a coagulation route using alginate as a coagulating agent and the as-synthesized sample was used as metal-free catalysts in the partial oxidation of H₂S into elemental sulfur. The N-CNT beads display a relatively high desulfurization activity along with a high stability as a function of time on stream. The desulfurization performance of the N-CNT beads was also measured and compared to that of the Fe₂O₃/SiC catalyst. The N-CNT beads display a higher desulfurization activity under the similar reaction conditions with, however, lower sulfur selectivity due to the problem of diffusion of the reactant through the bead porosity.     

限域NiCo合金纳米颗粒高效催化生物质衍生物水相加氢脱氧

将储量丰富的生物质及其衍生物转化为具有高附加值的燃料和化学品被认为是一种有前景的绿色途径,可以极大地减少人们对传统化石资源的依赖.作为木质纤维素热解的直接产物和生物油升级的模型化合物,香草醛可以通过加氢脱氧(HDO)过程选择性地转化为2-甲氧基-4-甲基苯酚(MMP).MMP是一种有价值的化学品,常用于香料和药物等重要中间体的合成.在过去十年里,大量的金属催化剂被用来催化香草醛HDO转化为MMP.其中,贵金属(Pt,Pd,Ru和Au)虽然活性高,但是其储量低、价格昂贵,不利于工业化应用;而非贵金属(Fe,Co,Ni和Cu)的催化活性普遍较低,需要苛刻的反应条件来提高转化效率和选择性.此外,这类HDO反应大都在有机溶剂中进行,容易造成环境污染.因此,开发高效、稳定的非贵金属催化剂用于水相HDO反应是一个巨大的挑战.一般来说,合金纳米颗粒(NPs)具有强烈的协同效应,能产生良好的配位结构和电子环境,从而显著提升催化活性和选择性.基于此,本文首次采用了一种简单可控的合成方法来制备三聚氰胺海绵负载的氮掺杂碳纳米管(N-CNTs)限域的Ni-Co合金NPs(NiCo@N-CNTs/CMF)催化剂.该催化剂具有优异的HDO性能,在2 MPa H2,120oC反应6 h条件下,能在水相中将生物质衍生的香草醛高效转化为MMP,转化率和选择性均达到100％.相比于单金属的Ni@N-CNTs/CMF和Co@N-CNTs/CMF催化剂,香草醛转化率和MMP选择性都有大幅度的提高.而且,在温和的反应条件下,该催化剂对香草醛衍生物和其他芳香醛类化合物同样表现出优异的HDO性能,拥有100％的转化率以及较高的MMP选择性(91.5％～100％).XPS结果表明,Ni-Co形成合金后发生了电子结构的偏移,即Co原子可以从邻近的Ni原子处得到电子,提高Co电子云密度,从而促进对香草醛中C=O键的吸附.DFT计算结果表明,相比于单金属的Ni和Co,Ni-Co合金化后能显著提高对C=O键的选择性吸附和活化.同时,H2解离后形成的活性H*物种在Ni-Co合金NPs表面更容易脱附并参与催化反应.因此,Ni-Co@N-CNTs/CMF催化剂优异的HDO性能主要是由于Ni-Co合金NPs的协同作用大大促进了其对C=O键的选择性吸附和活化,以及活化氢物种的脱附.本文为设计和制备高效的非贵金属催化剂应用于水相的HDO反应提供了一个新策略.     

Tailoring the morphology of Pd nanoparticles on CNTs by nitrogen and oxygen functionalization

The influence of N and O functionalization of CNT on the morphology of supported Pd-PVA nanoparticles is studied with respect to the catalytic activity in the liquid phase oxidation of benzyl alcohol to benzaldehyde. The impact of specific N and O sites on the carbon surface induced by the high temperature N-functionalization in the temperature range 673-873 K was observed by HRTEM as increased nanoparticles dispersion and enhanced metal wetting at the carbon surface. Those small nanoparticles that stabilized at the N-CNTs surface are beneficial for improving catalytic performance. The interaction of O(2) with the metal surface was studied by microcalorimetry. At 353 K, the PVA shell hinders the dissociative oxygen chemisorption at the surface of the fresh catalyst. Differently, a very high (maximum for Pd/N-CNT873K 750 kJ mol(-1)) and oscillating exothermic differential heat is registered for the washed samples. Such high differential heat on the "washed" sample is due to the sum of oxygen chemisorption and PVA oxidation. Thereby, it is demonstrated that the PVA overlayer suppresses the total combustion reaction pathway. This contribution has highlighted the impact of the dynamic change of morphology of these Pd nanoparticles under the reaction conditions on the catalytic performance and how this is modulated by the nature of the support as well as the PVA. The support with its varying ability to strongly bind Pd regulates the morphology of the nanoparticles on which the sub-surface penetration of O, H, C from the reactants depends, all modulating the electronic structure and thus the reactivity.     

上游水库水体中氨氮、亚硝酸盐氮、硝酸盐氮、总氮的测定和关系探究

采用紫外分光光度法测定上游水库固定监测点位近两年采集样品的总氮、硝酸盐氮、氨氮、亚硝酸盐氮含量.对测试结果进行分析比较,探讨了上游水库水中总氮、硝酸盐氮、氨氮、亚硝酸盐氮的关系,从而为上游水库水质数据分析和综合评价提供一定参考.     

非金属元素氮的同素异形体概述

依据全氮物质的研究进展对非金属氮元素的同素异形体进行了归纳,按结构不同可将其分为分子氮、聚合氮、金属氮和原子簇氮等4类.分别对各种同素异形体的组成、结构、存在与合成进展以及应用进行了综合介绍,为丰富氮元素的教学和扩展应用研究提供重要素材.     

Determination of Total Nitrogen,Ammonia, and Nitrite in River Water by Near-infrared Spectroscopy and Chemometrics

Total nitrogen, ammonia nitrogen, and nitrite nitrogen were determined in river water during intermittent aeration by near-infrared spectroscopy with a back-propagation neural network. Near-infrared spectra were obtained for 138 samples. A total of 116 samples were used as the calibration set and the remainder as the test set. The spectral region was from 4000 to 12,500?cm^?1. Principal component analysis was used as a preprocessing method of the near-infrared spectra to eliminate redundant information. The six principal components were extracted through principal component analysis. Back-propagation neural network models of total nitrogen, ammonia nitrogen, and nitrite nitrogen showed that the correlation coefficients were 0.9816, 0.9783, and 0.9562, respectively, with root-mean-square error of cross validation values of 0.04735, 0.03689, and 0.03766. The results of the back-propagation neural network models of total nitrogen, ammonia nitrogen, and nitrite nitrogen indicated that the correlation coefficients were 0.9752, 0.9690, and 0.9524, respectively, with root-mean-square errors of prediction equal to 0.05763, 0.04537, and 0.04157. This study showed that the described approach accurately determined total nitrogen, ammonia nitrogen, and nitrite nitrogen. The concentrations of total nitrogen, ammonia nitrogen, and nitrite nitrogen were 0.64–54.25, 0.57–45.04, and 0.05–31.40?mg?·?L^?1 in river water, respectively.     

Reactions of nitrile oxides with nitrogen oxides. 2. Reactions with nitrogen monoxide and nitrogen sesquioxide

We have studied the reactions of aromatic nitrile oxides with nitrogen monoxide and nitrogen sesquioxide. It was shown that nitrogen monoxide removes an oxygen atom from the nitrile oxide with formation of the corresponding nitrile and nitrogen dioxide. The reaction products with nitrogen sesquioxide are formed as a result of reactions of the nitrile oxide with nitrogen monoxide and nitrogen tetroxide.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1623–1625, July, 1990.     

Fermentation Characteristics of <Emphasis Type="Italic">Mortierella alpina</Emphasis> in Response to Different Nitrogen Sources

The fermentation characteristics of Mortierella alpina were investigated in response to various nitrogen sources. Influences on nitrogen source and glucose uptake rate, mycelial morphology of M. alpina, and pH of medium in relation to different nitrogen sources were discussed. Effects of different nitrogen sources on cell growth, fatty acid composition, arachidonic acid (ARA), and total lipid concentration were also evaluated. It revealed that the maximum nitrogen source uptake ratio was obtained when corn steep liquor was used as nitrogen source. When yeast extract was used as the sole nitrogen source, glucose was completely exhausted at the end of fermentation. The maximum dry cell weight obtained from medium with yeast extract as nitrogen source had the highest total lipid concentration. Sodium nitrate was the favorable nitrogen source for ARA accumulation, and the highest ARA percentage in total fatty acids was obtained, 35.9%. Urea was identified as the favorable nitrogen source for ARA production, the highest ARA concentration obtained from urea was 5.8 g/l. Compared with inorganic nitrogen sources, organic nitrogen compounds are favorable for both cell growth and total lipids accumulation.