Redox-active nickel in carbon nanotubes and its direct determination

The presence of residual metal-catalyst impurities in carbon nanotubes is responsible for their toxicity. It is important to differentiate between the total amount of impurities and the redox-active (bioavailable) amount of such impurities because only the bioavailable impurities exhibit toxic effects. Herein, we report a simple and specific method for quantifying the amount of redox-active Ni present in various commercial samples of CNTs. It is based on the electrochemical oxidation of Ni(OH)(2) that is formed in alkaline solutions when Ni impurities are opened to the surrounding environment. Metallic Ni impurities play an extremely active role in toxicological assays as well as in undesired catalytic processes, and thus a method to rapidly quantify the amount of redox-active Ni is of great importance.     

Redox‐Active Nickel in Carbon Nanotubes and Its Direct Determination

The presence of residual metal‐catalyst impurities in carbon nanotubes is responsible for their toxicity. It is important to differentiate between the total amount of impurities and the redox‐active (bioavailable) amount of such impurities because only the bioavailable impurities exhibit toxic effects. Herein, we report a simple and specific method for quantifying the amount of redox‐active Ni present in various commercial samples of CNTs. It is based on the electrochemical oxidation of Ni(OH)₂ that is formed in alkaline solutions when Ni impurities are opened to the surrounding environment. Metallic Ni impurities play an extremely active role in toxicological assays as well as in undesired catalytic processes, and thus a method to rapidly quantify the amount of redox‐active Ni is of great importance.     

Direct Voltammetric Determination of Redox‐Active Iron in Carbon Nanotubes

With the advances in nanotechnology over the past decade, consumer products are increasingly being incorporated with carbon nanotubes (CNTs). As the harmful effects of CNTs are suggested to be primarily due to the bioavailable amounts of metallic impurities, it is vital to detect and quantify these species using sensitive and facile methods. Therefore, in this study, we investigated the possibility of quantifying the amount of redox‐available iron‐containing impurities in CNTs with voltammetric techniques such as cyclic voltammetry. We examined the electrochemistry of Fe₃O₄ nanoparticles in phosphate buffer solution and discovered that its electrochemical behavior could be affected by pH of the electrolyte. By utilizing the unique redox reaction between the iron and phosphate species, the redox available iron content in CNTs was determined successfully using voltammetry.     

Impurities within carbon nanotubes govern the electrochemical oxidation of substituted hydrazines

Electrochemistry and electrocatalysis on carbon nanomaterials is at the forefront of research. The presence of carbonaceous and metallic impurities within carbon nanotubes (CNTs) is a persistent problem. Here we show that the electrochemistry of the entire group of hydrazine compounds is governed by impurities within single-walled, double-walled and few-walled CNTs. The oxidation of organic substituted hydrazines at CNTs is driven by nanographitic impurities, in contrast to unsubstituted hydrazine, for which the electrochemistry is driven by metallic impurities within CNTs. This finding is unexpected, as one would assume that a whole group of compounds would be susceptible to "electrocatalysis" by only one type of impurity. This discovery should be taken into account when predicting the susceptibility of whole groups of compounds to electrocatalysis by metallic or nanographitic impurities. Our findings have strong implications on the electrochemical sensing of hydrazines and on the use of hydrazines as fuels for nanomotors.     

Signal transducers and enzyme cofactors are susceptible to oxidation by nanographite impurities in carbon nanotube materials

Carbon nanotubes (CNTs) are often employed in biofuel cells, artificial photosystems and bioelectronics in order to enhance electron transfer and to efficiently shuttle electrons between redox active molecules and the electrode surface. However, it should be noted that typical CNTs are highly heterogeneous materials, containing large amounts of impurities. Herein, we report the influence of nanographite impurities contained within CNTs upon the redox properties of signal transducers and enzyme cofactors that are vital for the functioning of biofuel cells, artificial leaves and bioelectronics as well as for the survival of living organisms. We investigate the susceptibility of tyrosine and tryptophan, amino acids involved in electron transfer and biorecognition reactions as well in the synthesis of neurotransmitters, in addition we also consider the susceptibility of the principal electron carrier β-nicotinamide adenine dinucleotide. We conclude that nanographite impurities within CNTs are responsible for the "electrocatalytic" oxidation of NADH and two amino acids involved in signal transduction, tyrosine and tryptophan. Our findings are of high importance for both industrial and biomedical applications.     

Bioavailability of metallic impurities in carbon nanotubes is greatly enhanced by ultrasonication

Metallic impurities within carbon nanotubes (CNTs) are considered as the main cause of their toxicity. Ultrasonication is a common procedure used to purify and obtain homogeneous dispersions of CNTs as well as to mix them with other components for further processing into composites. Herein, the influence of ultrasonication upon the bioavailability of metallic impurities in CNTs was investigated. We showed that even ultrasonication times as short as 5?min significantly enhanced the bioavailability of metallic impurities, which can therefore interact more actively with biologically important molecules. These findings will have profound impact on the processing of CNTs as well as on nanotoxicity studies.     

Nanographite impurities in carbon nanotubes: their influence on the oxidation of insulin, nitric oxide, and extracellular thiols

There has been growing interest in the use of modified-carbon-nanotube electrodes in applications such as the electrochemical detection of biologically significant compounds, owing to their apparent "electrocatalytic" properties and ability to enhance oxidative signals. In spite of their salient properties, little work has been done to further examine the reasons for these reported characteristics. In this report, we present clear evidence that the presence of nanographite impurities within carbon nanotubes (CNTs) is responsible for providing the previously reported enhanced electrochemical response. We have demonstrated this effect on homocysteine, N-acetyl-L-cysteine, nitric oxide, and insulin, which are important biological agents in the body. Moreover, we also showed that the influence of nanographite impurities on the electrochemistry of carbon nanotubes is prevalent among a variety of CNTs, such as single-walled CNTs, double-walled CNTs, and few-walled CNTs. Our findings will have a profound influence upon the biomedical applications of CNTs.     

Ion beam analyses of carbon nanotubes

The utility of ion beam analysis (IBA) techniques to quantitatively determine impurities in carbon nanotubes (CNTs) over a wide range of atomic numbers is demonstrated. Such techniques have not previously been used to monitor impurities and their effects in this unique material. Despite the difficulty in mounting the samples (which generally are formed into a powdery aggregate rather in a thin film), it is shown that reliable and accurate measurements of impurity concentrations can be achieved. Particle-induced X-ray emission (PIXE) and elastic recoil detection (ERD) analyses were used to characterize both metallic and very light (e.g., hydrogen) impurities in CNTs. This paper reports the first direct measurement of hydrogen in CNTs using an IBA technique. This is significant because CNTs are being actively investigated for hydrogen storage technology for energy applications.     

高温退火一步非破坏性纯化碳纳米管

针对催化化学气相法合成的碳纳米管含有金属、金属氧化物和碳杂质, 且缺陷较多进行了非破坏性纯化研究. 基于碳纳米管与碳杂质间结构、性质的微小差异, 1800 ℃使粗制的碳纳米管高温退火3 h, 为避免碳纳米管氧化, 高温退火过程在氩气气氛中完成. 运用扫描电镜、透射电镜观察碳纳米管的形貌和结构, 发现高温退火后, 碳纳米管的端帽大部分被打开. 能谱检测显示, 粗制的碳纳米管中的杂质(Al, Si, Ni, Cu 质量分数w分别为4.67%, 0.27%, 40.12%和1.34%)退火后被除去. 拉曼分析表明, 退火前后石墨D, G峰面积S_D, S_G分别从1314900降至474921, 767157降至566292, 退火不仅有效地去除了样品中的碳杂质, 而且使碳纳米管的缺陷得到一定程度的修复, 石墨化度随之大大提高. 研究提出了一种简单的、非破坏性的、便于规模化的纯化方法.     

Carbon nanotubes for supercapacitors:Consideration of cost and chemical vapor deposition techniques

In this topic,we first discussed the requirement and performance of supercapacitors using carbon nanotubes(CNTs) as the electrode,including specific surface area,purity and cost.Then we reviewed the preparation technique of single walled CNTs(SWNTs) in relatively large scale by chemical vapor deposition method.Its catalysis on the decomposition of methane and other carbon source,the reactor type and the process control strategies were discussed.Special focus was concentrated on how to increase the yield,selectivity,and purity of SWNTs and how to inhibit the formation of impurities,including amorphous carbon,multiwalled CNTs and the carbon encapsulated metal particles,since these impurities seriously influenced the performance of SWNTs in supercapacitors.Wish it be helpful to further decrease its product cost and for the commercial use in supercapacitors.     

Anomalous electrochemical dissolution and passivation of iron growth catalysts in carbon nanotubes

Catalytically synthesized carbon nanotubes (CNTs) such as those prepared via chemical vapor deposition (CVD) contain metallic impurities including Fe, Ni, Co, and Mo. Transition metal contaminants such as Fe can participate in redox cycling reactions that catalyze the generation of reactive oxygen species and other products. Through the nature of the CVD growth process, metallic nanoparticles become encased within the CNT graphene lattice and may still be chemically accessible and participate in redox chemistry, especially when these materials are utilized as electrodes in electrochemical applications. We demonstrate that metallic impurities can be selectively dissolved and/or passivated during electrochemical potential cycling. Anomalous Fe dissolution and passivation behavior is observed in neutral (pH=6.40+/-0.03) aqueous solutions when using multiwalled CNTs prepared from CVD. Fe particles contained within these CNTs display intriguing, potential-dependent Fe redox activity that varies with supporting electrolyte composition. In neutral solutions containing dibasic sodium phosphate, sodium acetate, and sodium citrate, FeII dissolution and surface confined FeII/III redox activity are significant despite Fe being encapsulated within CNT graphene layers. However, no apparent Fe dissolution is observed in 1 M potassium nitrate solutions, suggesting that the electrolyte composition plays an important role in observing FeII dissolution, passivation, and surface confined FeII/III redox activity. Between potentials of 0 and -1.1 V versus Hg/Hg2SO4, the primary redox-active Fe species are surface FeII/III oxides/oxyhydroxides. This FeII/III surface oxide redox chemistry can be completely suppressed by passivating Fe through repeated cycling of the CNTs in supporting electrolyte. By increasing the potential to more negative values (>-1.3 V), FeII dissolution may be induced in electrolyte solutions containing acetate and phosphate and inhibited by addition of sodium benzoate, which adsorbs on exposed Fe particles, effectively passivating them. Finally, we observe that the FeII/III redox chemistry or subsequent passivation does not affect the onset of oxygen reduction at nitrogen-doped CNTs, suggesting that the surface-bound FeII species is not the primary catalytically active site for oxygen reduction in these materials.     

Assessment of chemical purity of 10B-enriched p-boronophenylalanine by high-performance liquid chromatography coupled on-line with inductively coupled plasma optical emission spectrometry

A dual-detection technique, consisting of a combination of reversed-phase high-performance liquid chromatography and on-line detection of elemental boron in the column effluents by inductively coupled plasma optical emission spectrometry, was tested for drug analysis. The method was applied to assessing the chemical purity of p-boronophenylalanine (BPA), isotopically enriched in ¹⁰B. This compound is employed as a fructose complex solution for biodistribution studies in laboratory and clinical trials of boron neutron capture therapy. Besides the determination of the content of BPA, required for chemical quality controls of solutions of the complex used for infusions, resolution of mixtures of BPA and two usually accompanying residual impurities (phenylalanine and tyrosine) was achieved with UV detection. The limits of detection (in solution) were 1.5 and 0.6 ng ml⁻¹, respectively. In addition, by monitoring a sensitive-element emission wavelength it was possible to jointly observe the elution of boron-containing compounds that may be transparent to UV radiation or to confirm the presence of boron in potential impurities accompanying the drug. Those impurities may arise from the BPA synthesis or may be produced by degradation during the aging of the solutions. Chromatographic peaks corresponding to the amino acids and also to a related inorganic compound were detected in BPA–fructose complex solutions that were stored for different times and under different conditions. An increase in the areas of the peaks attributed to tyrosine and phenylalanine was observed for BPA–fructose solutions stored refrigerated for 1 month to 1 year, suggesting that degradation processes able to reduce the amount of bioavailable BPA could be active. In memoriam Dr. Daniel Batistoni.     

A Review on the Effects of Introducing CNTs in the Modification Process of Electrochemical Sensors

This review summarizes some developments in the fabrication of modified sensors and biosensors through the incorporating the carbon nanotubes (CNTs) in their modification ingredients. A large number of papers have paid attention towards the application of carbon nanotubes (CNTs) as electrode constituents and studied its electrochemical behavior. Here, we survey the achievements in the detection of various substances with high selectivity and sensitivity provided using CNTs based electrodes. Moreover, modified electrodes by CNTs have demonstrated the electrocatalytic features and higher sensitivity in detection of analytes. The improved characteristics arises from the large surface area and good conductivity of CNTs. However, it should be considered that the use of single walled carbon nanotubes (SWCNTs) or multi‐walled carbon nanotubes (MWCNTs), the presence of impurities, and the chemical procedures adopted are effective on the performance of the modified sensors.     

The Significant Role of Carboxylated Carbonaceous Fragments in the Electrochemistry of Carbon Nanotubes

Carbon nanotubes (CNTs) have been widely employed as electrode materials in diverse branches of electrochemistry, which are claimed to display dramatically improved electrochemical behaviour compared to the conventional carbon materials. But a series of recent publications have demonstrated that the electrocatalysis of CNTs might be due to the presence of some impurities, such as metallic catalysts, nanographitic particles and amorphous carbon. For this reason, CNTs are usually purified or treated with nitric acid or nitric and sulphuric acid prior to their versatile applications. However, the strong acidic and oxidative conditions are so aggressive that serious erosion of the tube structures has inevitably taken place, which creates defects on the sidewalls and gives rise to numerous molecular byproducts, commonly referred as carboxylated carbonaceous fragments (CCFs). The adsorption of CCFs on CNTs greatly alters the surface conditions of CNTs which may significantly impact on their electrochemical properties. To this end, we wish to disclose whether the electrocatalysis of the nitric acid purified CNTs is affected by the adsorption of the CCFs. Ascorbic acid (AA) and β‐nicotinamide adenine dinucleotide (NADH) as selected as the targeting benchmarks that are known to be insensitive to the presence of metallic impurities, which may guarantee the preclusion of the promoting contributions from the metallic catalysts resident in CNTs. We have demonstrated that the electrocatalytic activities of the CNTs are actually dominated by the adsorbed CCFs generated during the acidic pre‐treatment. After removal of the CCFs by base rinse, the electrocatalytic properties of CNTs are greatly deteriorated and degraded to the level similar to the conventional graphite powder. We believe this finding is particularly meaningful to uncover the mysterious electrocatalysis of CNTs.     

Nanoparticle-Assisted Alignment of Carbon Nanotubes on DNA Origami

Aligning carbon nanotubes (CNTs) is a key challenge for fabricating CNT-based electronic devices. Herein, we report a spherical nucleic acid (SNA) mediated approach for the highly precise alignment of CNTs at prescribed sites on DNA origami. We find that the cooperative DNA hybridization occurring at the interface of SNA and DNA-coated CNTs leads to an approximately five-fold improvement of the positioning efficiency. By combining this with the intrinsic positioning addressability of DNA origami, CNTs can be aligned in parallel with an extremely small angular variation of within 10°. Moreover, we demonstrate that the parallel alignment of CNTs prevents incorrect logic functionality originating from stray conducting paths formed by misaligned CNTs. This SNA-mediated method thus holds great potential for fabricating scalable CNT arrays for nanoelectronics.     

Nanoparticle‐Assisted Alignment of Carbon Nanotubes on DNA Origami

Aligning carbon nanotubes (CNTs) is a key challenge for fabricating CNT‐based electronic devices. Herein, we report a spherical nucleic acid (SNA) mediated approach for the highly precise alignment of CNTs at prescribed sites on DNA origami. We find that the cooperative DNA hybridization occurring at the interface of SNA and DNA‐coated CNTs leads to an approximately five‐fold improvement of the positioning efficiency. By combining this with the intrinsic positioning addressability of DNA origami, CNTs can be aligned in parallel with an extremely small angular variation of within 10°. Moreover, we demonstrate that the parallel alignment of CNTs prevents incorrect logic functionality originating from stray conducting paths formed by misaligned CNTs. This SNA‐mediated method thus holds great potential for fabricating scalable CNT arrays for nanoelectronics.     

Cytotoxicity of carbon nanotubes

With large-scale production and application at large scale, carbon nanotubes (CNTs) may cause ad-verse response to the environment and human health. Thus, study on bio-effects and safety of CNTs has attracted great attention from scientists and governments worldwide. This report briefly summa-rizes the main results from the in vitro toxicity study of CNTs. The emphasis is placed on the descrip-tion of a variety of factors affecting CNTs cytotoxicity, including species of CNTs, impurities contained, lengths of CNTs, aspect ratios, chemical modification, and assaying methods of cytotoxicity. However, experimental information obtained thus far on CNTs' cytotoxicity is lacking in comparability, and some-times there is controversy about it. In order to assess more accurately the potential risks of CNTs to human health, we suggest that care should be taken for issues such as chemical modification and quantitative characterization of CNTs in cytotoxicity assessment. More importantly, studies on physical and chemical mechanisms of CNTs' cytotoxicity should be strengthened; assaying methods and evaluating criteria characterized by nanotoxicology should be gradually established.     

毛细管色谱法在苯产品馏程分析中的应用研究

 对苯产品中的烃类杂质含量与苯的馏程之间的相关性进行研究。结果表明 ,当苯中烃类杂质含量在一定范围内时 ,根据毛细管色谱法对苯中烃类的分析结果 ,可以准确地反映出苯馏程是否合格 ,从而提出了以苯中烃类杂质含量的测定取代苯馏程的测定。使苯馏程分析由经典的蒸馏法改为毛细管色谱分析法 ,并在实际生产分析中得以实施应用。     

A determination method of pristine multiwall carbon nanotubes in rat lungs after intratracheal instillation exposure by combustive oxidation-nondispersive infrared analysis

This paper describes a method for determination of multiwall carbon nanotubes (MWCNTs) in rat lungs after intratracheal instillation exposure. The MWCNTs were quantitatively decomposed to CO₂ by combustive oxidation and were then determined by non-dispersive infrared analysis. Samples were pretreated by acid digestion, muffle ashing and in situ preheating to remove interferences due to coexisting biological carbon from the lung tissue sample, while preserving the MWCNTs as in its their original form. The preservation was confirmed by transmission electron microscopic observation of the pretreated samples of exposed lung tissues and by the fact that the recoveries of MWCNTs spiked to the lung tissues were close to 100%. The detection limit for MWCNTs obtained by the proposed method was 0.30 μg and the repeatability as expressed by the relative standard deviation was 5.6% (n = 4). The method was sufficiently sensitive and precise to apply to real samples of rat lung to investigate the in vivo persistence of intratracheally instilled MWCNTs. To our knowledge, this is the first report of this type of sample pretreatment and direct determination of pristine MWCNTs without modification or tagging. Conventional indirect methods use tagging with other compounds or metal impurities in the CNTs for detection, and the detachment of these tags can increase uncertainties in the determination of the CNTs. The tags can also change how the CNTs persist in vivo, which can lead to an incorrect understanding of the persistence of pristine CNTs in vivo.     

Influence of Carbon Nanotubes on Phase Composition,Thermal and Post-Heating Behavior of Cementitious Composites

This paper experimentally investigates the influence of carbon nanotubes (CNTs) on phase composition, microstructure deterioration, thermal behavior, and residual mechanical strengths of cementitious composites exposed to elevated temperatures. Cement mortars with small dosages of CNTs, 0.05% and 0.2% by weight of cement, were prepared and then heated at 25 °C, 150 °C, 200 °C, 450 °C, and 600 °C for two hours before being tested. The results show positive impact of the CNTs on the hydration process of cement mortar at room temperature and at higher temperatures up to 200 °C. Decomposition of the hydration products is obvious at 450 °C, whereas sever deterioration in the microstructure occurs at 600 °C. The nano reinforcement and bridging effect of the CNTs are obvious up to 450 °C. Thermal behavior characterization shows that CNTs incorporation enhances the thermal conductivity of the unheated and heat-treated mortar specimens. The decomposition of the hydration products needs more heat in the presence of CNTs. Finally, presence of CNTs significantly enhances the residual compressive and flexural strengths of heated mortar specimens for all studied temperatures.