Carbon nanotube immobilized polar membranes for enhanced extraction of polar analytes

We demonstrate for the first time that carbon nanotubes (CNTs) can be readily immobilized on the surface of a solid polymeric membrane which can lead to enhanced enrichment factor and extraction efficiency. The effectiveness of the CNT mediated process is demonstrated by micro-scale membrane extraction via direct solvent enrichment of polar and nonpolar organics. The enrichment factor measured as the ratio of concentrations in the acceptor to the donor phases was as high as 282 and the enhancement over the unmodified membrane was as much as 92%. In addition, the solvent retention in the carbon nanotube immobilized membrane (CNIM) increased by as much as 29%. Overall, the CNT incorporation provided enhanced solute transport and thus led to overall performance enhancement.     

Direct amperometric detection of glucose on a multiple-branching carbon nanotube forest

We show here that a re-structured carbon nanotube (CNT) forest can be used 'as-received' for high selectivity, non-enzymatic glucose detection without the need to incorporate catalytic metal nanoparticles or an exclusion polymeric membrane. Direct amperometric sensing of glucose has been achieved by using multiply-branched CNTs prepared by growing secondary or tertiary 'offshoot' CNTs on top of the existing CNT layer. The increased roughness factor on these re-structured CNTs enhances the amperometric detection sensitivity for glucose by a factor of 20x over that of interfering species like ascorbic acid or uric acid. A sensitivity of 60 microA mM(-1) cm(-2) and a detection limit of 1 microM, with a linear detection range of 1-11 mM (R(2) = 0.999), could be attained on the re-grown CNTs. When the re-grown CNTs were subjected to further anodization in acid to introduce a highly-charged interface, the sensitivity to glucose was enhanced to 157 microA mM(-1) cm(-2).     

Effects of size constraint on water filling process in nanotube

Molecular dynamics (MD) simulation and the potential of mean force (PMF) analysis are used to investigate the structural properties of water molecules near the end of nanotube for the whole process from the initial water filling up to the configuration stabilization inside the carbon nanotubes (CNTs). Numerical simulations showed that when a small-sized nanotube is immersed into the water bath, the size constraint will induce a prevailing orientation for the water molecule to diffuse into the tube and this effect can persist approximately 3.3 angstroms from the end of CNT. As the structure within the CNTs stabilizes, the ambient structural properties can indirectly reflect their corresponding properties inside the nanotube. Our results also showed that there exists a close correlation between the PMF analysis and the results of MD simulations, and the properties at nanometer scale are closely related to the size-constraint effect.     

多孔基体负载的碳纳米管复合膜制备及其气体渗透性能

采用改进的浮动催化法在多孔Al2O3基体上制备了垂直取向的碳纳米管阵列, 并用旋转喷涂法将聚苯乙烯填充于碳纳米管的空隙, 进一步将其制备成复合碳纳米管膜, 研究了H2和CO2单组分在碳纳米管复合膜中的渗透性能, 实验结果表明, H2/CO2的理想分离系数随着复合膜中碳管管径的减小而增大, 在管径较小的复合膜中, 气体渗透分离系数高于努森扩散限制, 达到6.25, 具有一定的分离效果. 两种气体在复合膜中的渗透率随着渗透温度的增加而减小.     

Poly(2,5-benzoxazole)/carbon nanotube composites via in situ polymerization of 3-amino-4-hydroxybenzoic acid hydrochloride in a mild poly(phosphoric acid)

Poly(2,5-benzoxzole) (ABPBO)/carbon nanotube (CNT) composites were prepared via in situ polycondensation of “protonated” AB monomer, 3-amino-4-hydroxybenzoic acid hydrochloride, in a mildly acidic poly(phosphoric acid) medium. In situ generated hydrochloric acid during the dehydrochlorination process provided additional acidity to the reaction medium. The enhanced acidity was advantageous for both the purification and dispersion of CNTs. Specifically, it was evident for the purification of as-received single-walled carbon nanotube (SWCNT), which was contained a large portion of impurity (60-70 wt%). On the basis of the data obtained from elemental analysis (EA), thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) as well as scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the resultant composites implicated that individual tube of multi-walled carbon nanotube (MWCNT) and bundles of SWCNT were homogeneously dispersed into the ABPBO matrix. After in situ polymerization in harsh temperature at 175 °C and subsequent work-up processes, CNTs were remained structurally intact in a mild reaction medium. Thus, the PPA medium is indeed viable for the preparation of composite.     

碳纳米管膜分离Li+/Mg2+的分子动力学模拟

采用"扶手椅"型碳纳米管建立了连续的碳纳米管膜模型,利用分子动力学模拟方法研究了Li+和Mg2+在膜中的传导行为.模拟研究了不同管径的碳纳米管CNTs(7,7),(8,8),(9,9),(10,10),(11,11)对Li+和Mg2+的通透性,检测了两种离子进入管内时的平均力势,探索了两种离子在碳纳米管内的径向、轴向密度分布,观测了个别离子在管内的运动轨迹.结果表明,模拟中CNTs(9,9)用于有效分离Li+和Mg2+的效果较好.管径不同,导致Li+和Mg2+通量不同,平均力势(PMF)差值不同,同时离子的轨迹和径向、轴向密度分布也有所差异.总之,碳纳米管是一种可将Li+和Mg2+分离的潜在材料.     

Carbon nanotube capsules self-assembled by w/o emulsion technique

Carbon nanotube capsules (CNCs) with the diameter of 5-10 microm were fabricated from acid-modified multiwalled carbon nanotubes (CNTs) using water-in-oil (W/O) emulsion technique. The effects of the content of CNTs in water, the extent of acid treatment, and the length of CNTs used on the formation and morphology of CNCs were investigated. It was found that the amount of CNTs in water and the length of CNTs are the crucial factors for the formation of carbon nanotube capsules.     

Effect of chirality and length on the penetrability of single-walled carbon nanotubes into lipid bilayer cell membranes

The ability of carbon nanotubes to enter the cell membrane acting as drug-delivery vehicles has yielded a plethora of experimental investigations, mostly with inconclusive results because of the wide spectra of carbon nanotube structures. Because of the virtual impossibility of synthesizing CNTs with distinct chirality, we report a parametric study on the use of molecular dynamics to provide better insight into the effect of the carbon nanotube chirality and the aspect ratio on the interaction with a lipid bilayer membrane. The simulation results indicated that a single-walled carbon nanotube utilizes different time-evolving mechanisms to facilitate their internalization within the membrane. These mechanisms comprise both penetration and endocytosis. It was observed that carbon nanotubes with higher aspect ratios penetrate the membrane faster whereas shorter nanotubes undergo significant rotation during the final stages of endocytosis. Furthermore, nanotubes with lower chiral indices developed significant adhesion with the membrane. This adhesion is hypothesized to consume some of the carbon nanotube energy, thus resulting in longer times for the nanotube to translocate through the membrane.     

Development of carbon‐nanotube‐assisted electromembrane extraction in the two‐phase mode combined with GC for the determination of basic drugs

In this work, carbon‐nanotube‐assisted electromembrane extraction in the two‐phase mode combined with GC was developed for the preconcentration and determination of basic drugs in body fluids. The multiwalled carbon nanotubes dispersed in organic solvent are held in the pores of the porous fiber wall by capillary forces and sonification. The membrane with immobilized carbon nanotubes acts as a sorbent and provides an additional pathway for analyte transport. This study demonstrates that the immobilization of carbon nanotubes in the supported liquid membrane is an excellent approach to enhance the performance of the extraction. Optimization of the variables affecting this method was carried out in order to achieve the best extraction efficiency. Optimal extractions were accomplished with octanol as the extraction solvent, 50 V as the driving force and pH 7.4 in the sample solution with the whole assembly agitated at 1000 rpm for 20 min. Under the optimized extraction conditions, the proposed technique provided good linearity (R² > 0.9990), repeatability (3.5–3.8%), low LODs (1.5 ng/mL), good preconcentration factors (292–316) and high recoveries (80–87%). Finally, this method was successfully used for the determination of tramadol and methadone in different body fluids including plasma and urine samples.     

Anodic oxidation of hydrazine at carbon nanotube powder microelectrode and its detection

Carbon nanotube powder microelectrodes (CNTPMEs) were used to study the anodic oxidation of hydrazine at Carbon nanotube (CNT)-the novel carbon material. It was found that the electrochemical behaviours were greatly improved at CNTs, indicating that the anodic oxidation could be catalyzed at CNTs. The kinetics parameters of this process were calculated, the heterogeneous electron transfer rate constant k was 0.0019 cm s(-1), (1-alpha)n(alpha) was 0.22. The CNTPMEs were also found with high sensitivity for hydrazine detection, could be used as hydrazine sensors.     

不同结构碳纳米管的电磁波吸收性能研究

研究了单壁、多壁碳纳米管(聚团状、阵列状)以及未纯化与纯化后碳纳米管在2～18 GHz范围内的电磁波吸收性能. 通过测定不同结构碳纳米管粉体的介电常数以及磁导率, 得到损耗因子及衰减常数大小顺序为: 阵列状多壁碳纳米管>原生聚团状多壁碳纳米管>纯化聚团状多壁碳纳米管>原生单壁碳纳米管>纯化后单壁碳纳米管. 相比多壁碳纳米管, 单壁碳纳米管衰减常数随频率变化较小, 且具有较宽的吸收峰. 模拟计算和实验测试结果都表明, 碳纳米管/聚合物复合材料具有优良的电磁吸波性能.     

硅胶负载碳纳米管分离富集水中痕量银

以NaOH为沉淀试剂,将水样中的Ag+在线生成Ag2O沉淀,并即时被滞留在硅胶负载的碳纳米管表面。被吸附的Ag2O沉淀用HNO3(10%,V/V)洗脱,并用火焰原子吸收法检测。当进样体积为5.4mL时,线性范围为1～120μg/L,富集系数为34.5;检出限为0.35μg/L;相对标准偏差为0.5%(40μg/L,n=7),采样频率为47次/h。结果表明:本方法的富集系数、检出限及精密度均明显优于以纯碳纳米管和纯硅胶微珠为吸附剂收集Ag2O的体系。将此系统应用于实际水样中银的测定,加标回收率在96%～108%之间。     

Carbon nanotube bags: catalytic formation, physical properties, two-dimensional alignment and geometric structuring of densely filled carbon tubes

The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO3)3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well-arranged two-dimensional order. The tubes have the morphology of bags or fibers, since they are completely filled with smaller helicoidal CNTs. This morphology has so far not been reported for CNTs. Owing to the dense filling of the outer mother CNTs with small helicoidal CNTs, the resulting CNT fibers appear to be stiff and show no sign of inflation, as sometimes observed with hollow CNTs. The fiber morphology was observed by raster electron microscopy (REM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The carbon material is graphitic as deduced from spectroscopic studies (X-ray diffraction, Raman and electron energy-loss spectroscopy (EELS)). From M?ssbauer studies, the presence of two different oxidation states (Fe0 and FeIII) of the catalyst is proven. Geometric structuring of the template by two different methods has been studied. Inkjet catalyst printing shows that the tubes can be arranged in defined areas by a simple and easily applied technique. Laser-structuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the microm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported.     

Synthesis of ZrO2-carbon nanotube composites and their application as chemiluminescent sensor material for ethanol

ZrO2-carbon nanotube (CNT) composites have been successfully synthesized via decomposition of Zr(NO3)4.5H2O in supercritical carbon dioxide-ethanol solution with dispersed CNTs at relatively low temperatures. The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) analyses. It was demonstrated that CNTs were fully coated with an amorphous ZrO2 layer, and the coating layer was nominally complete and uniform. In addition, the thickness of the coating sheath could be readily controlled by tuning the Zr(NO3)4.5H2O/CNTs ratio used. Furthermore, the chemiluminescent sensor prepared from ZrO2-carbon nanotube composites exhibited dramatic sensitivity as well as high stability and selectivity to ethanol.     

Surfactant-directed polypyrrole/CNT nanocables: synthesis, characterization, and enhanced electrical properties.

We describe here a new approach to the synthesis of size-controllable polypyrrole/carbon nanotube (CNT) nanocables by in situ chemical oxidative polymerization directed by the cationic surfactant cetyltrimethylammonium bromide (CTAB) or the nonionic surfactant polyethylene glycol mono-p-nonylphenyl ether (Opi-10). When carbon nanotubes are dispersed in a solution containing a certain concentration of CTAB or Opi-10, the surfactant molecules are adsorbed and arranged regularly on the CNT surfaces. On addition of pyrrole, some of the monomer is adsorbed at the surface of CNTs and/or wedged between the arranged CTAB or Opi-10 molecules. When ammonium persulfate (APS) is added, pyrrole is polymerized in situ at the surfaces of the CNTs (core layer) and ultimately forms the outer shell of the nanocables. Such polypyrrole/CNT nanocables show enhanced electrical properties; a negative temperature coefficient of resistance at 77-300 K and a negative magnetoresistance at 10-200 K were observed.     

Electrochemical Introduction of Active Sites into Super-long Carbon Nanotubes for Enhanced Capacitance

Electrochemical cyclic voltammetric(CV)scan was applied to inducing the partial oxidation and defects of carbon nanotubes(CNTs).The electrochemically induced functional groups and physical defects were...     

Nitrogen adsorption characterization of aligned multiwalled carbon nanotubes and their acid modification

Aligned multiwalled carbon nanotube (CNT) arrays were synthesized by using an iron-based sol-gel catalyst and acetylene as the precursor. These CNTs show high purity, uniform diameters and pore-wall thickness. Low temperature nitrogen adsorption was employed to characterize the structural and surface properties of the as-synthesized sample and that modified with boiling concentrated nitric acid. The adsorption characteristics of the as-synthesized and modified CNTs were thoroughly investigated. High-resolution comparative alpha(s)-plot showed that the nitrogen adsorption on CNTs takes place via a multistage mechanism closely related to their structures. It was also found that the acid modification significantly increased the adsorption energy and enhanced the adsorption capacity under low pressures. High-resolution comparative method provided valuable insights about the surface and pore structures of CNTs.     

Direct measurements of interactions between polypeptides and carbon nanotubes

The interactions of various polypeptides with individual carbon nanotubes (CNTs), both multiwall (MW) and single wall (SW), were investigated by atomic force microscopy (AFM). While adhesion forces arising from electrostatic attraction interactions between the protonated amine groups of polylysine and carboxylic groups on the acid-oxidized multi-wall carbon nanotubes (Ox-MWCNTs) dominate the interaction at a low pH, weaker adhesion forces via the hydrogen bonding between the neutral -NH2 groups of polylysine and -COO- groups of the Ox-MWCNTs were detected at a high pH. The adhesion force was further found to increase with the oxidation time for Ox-MWCNTs and to be negligible for oxidized single-wall carbon nanotubes (Ox-SWCNTs) because carboxylate groups were only attached onto the nanotube tips in the latter whereas onto both the nanotube tips and sidewall in the former. Furthermore, it was demonstrated that proteins containing aromatic moieties, such as polytryptophan, showed a stronger adhesion force with Ox-MWCNTs than that of polylysine because of the additional pi-pi stacking interaction between the polytryptophan chains and CNTs.     

Solid-phase extraction-capillary electrophoresis-mass spectrometry for the determination of tetracyclines residues in surface water by using carbon nanotubes as sorbent material

Last years chemical properties of carbon nanotubes (CNTs) have attracted high interest. One of the most important issues is the capability of CNTs to adsorb analytes on its surface. In this work, such property has been used to preconcentrate trace tetracyclines from environmental water samples at the trace level. Multi-walled carbon nanotubes (MWNTs) have showed higher capacity than other two single-walled carbon nanotubes (SWNTs). Preconcentration of the samples was performed in a flow system at-line coupled to the CE-MS equipment. The preconcentration of tetracyclines on MWNTs followed by capillary electrophoresis-mass spectrometry allows the detection of 0.30-0.69 microg/L of tetracyclines for the analysis of 10 mL of samples. Recoveries for the analysis of spiked samples ranged from 98.6 to 103.2% and the precision from 5.4 to 8.2%. Separation of tetracylines in the electrophoretic system was achieved using 50 mM formic acid at pH 2.0 as a background electrolyte. Atmospheric pressure electrospray ionization mass spectrometry detection was accomplished using 50:50 (v/v) methanol/water containing 0.5% (v/v) formic acid as a sheath liquid.     

正渗透过程中纳米碳管膜的盐水通道行为

以纳米碳管(CNT)仿生构筑正渗透(FO)膜, 采用分子动力学模拟的方法考察水和盐在由CNT(6,6)、CNT(7,7)、CNT(8,8)、CNT(9,9)、CNT(10,10)、CNT(11,11)等不同尺寸纳米碳管构筑膜中, 于2.5、3.75、5.0mol·L^-1等不同汲取液浓度下的传递行为. 纳秒级的模拟得到水分子在不同尺寸纳米碳管膜内的分布, 水通量的变化以及盐截留等情况. 模拟结果表明, 由CNT(8,8)构筑的正渗透膜表现出优异的通水阻盐性能.