Overcoming the insolubility of carbon nanotubes through high degrees of sidewall functionalization

The use of carbon nanotubes in materials applications has been slowed due to nanotube insolubility and their incompatibility with polymers. We recently developed two protocols to overcome the insoluble nature of carbon nanotubes by affixing large amounts of addends to the nanotube sidewalls. Both processes involve reactions with aryl diazonium species. First, solvent-free functionalization techniques remove the need for any solvent during the functionalization step. This delivers functionalized carbon nanotubes with increased solubility in organic solvents and processibility in polymeric blends. Additionally, the solvent-free functionalization process can be done on large scales, thereby paving the way for use in bulk applications such as in structural materials development. The second methodology involves the functionalization of carbon nanotubes that are first dispersed as individual tubes in surfactants within aqueous media. The functionalization then ensues to afford heavily functionalized nanotubes that do not re-rope. They remain as individuals in organic solvents giving enormous increases in solubility. This protocol yields the highest degree of functionalization we have obtained thus far-up to one in nine carbon atoms on the nanotube has an organic addend. The proper characterization and solubility determinations on nanotubes are critical; therefore, this topic is discussed in detail.     

Surface structure and adsorption properties of multiwalled carbon nanotubes

The pore structure, sorption parameters, and chemical composition of the surface of multiwalled carbon nanotubes synthesized by catalytic pyrolysis were determined. The dependences of the amount of cholic acid adsorbed by the nanotube surface on time, pH, and concentration of an equilibrium solution were studied. Physical adsorption of cholic acid is mainly the outcome of nonspecific interactions between the acid and the surface of the nanotubes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1712–1715, October, 2006.     

Oxygen adsorption characteristics on hybrid carbon and boron‐nitride nanotubes

In this work, first‐principles density functional theory (DFT) is used to predict oxygen adsorption on two types of hybrid carbon and boron‐nitride nanotubes (CBNNTs), zigzag (8,0), and armchair (6,6). Although the chemisorption of O₂ on CBNNT(6,6) is calculated to be a thermodynamically unfavorable process, the binding of O₂ on CBNNT(8,0) is found to be an exothermic process and can form both chemisorbed and physisorbed complexes. The CBNNT(8,0) has very different O₂ adsorption properties compared with pristine carbon nanotubes (CNTs) and boron‐nitride nanotube (BNNTs). For example, O₂ chemisorption is significantly enhanced on CBNNTs, and O₂ physisorption complexes also show stronger binding, as compared to pristine CNTs or BNNTs. Furthermore, it is found that the O₂ adsorption is able to increase the conductivity of CBNNTs. Overall, these properties suggest that the CBNNT hybrid nanotubes may be useful as a gas sensor or as a catalyst for the oxygen reduction reaction. © 2014 Wiley Periodicals, Inc.     

碳纳米管吸附水溶液中双酚A的热力学

以甲醇和去离子水组成的体系（体积比90∶10）为流动相,建立了以香烟过滤嘴作吸附剂,固相萃取（SPE）与高效液相色谱（HPLC）联用测定水中双酚A(Bisphenol A,BPA)的新方法。研究了水溶液中碳纳米管(CNTs)吸附双酚A的热力学特性,测定了不同温度下的吸附等温线,并探讨了其可能的吸附机理。结果表明,CNTs对BPA 的吸附主要以快速吸附为主,常温下,碳纳米管对于70 mg·L-1的双酚A水溶液的吸附量可达到 24.65 mg g-1,吸附量随初始浓度的增加而增加,随温度的降低而增大,采用Freundlich和Langmuir方程拟合,相关系数均大于0.99,热力学函数ΔG、ΔH及ΔS分别为-39.48 ~ -43.51 KJ·mol-1、-18.06 KJ·mol-1、71.73 J·mol-1·K-1,吸附为放热、熵增的自发过程,降低温度有利于吸附,并且具有物理吸附特征。     

Fluoride and lead adsorption on carbon nanotubes

The properties and applications of CNT have been studied extensively since Iijima discovered them in 1991[1,2]. They have exceptional mechanical properties and unique electrical property, highly chemical stability and large specific surface area. Thus far, they have widely potential applications in many fields. They can be used as reinforcing materials in composites[3], field emissions[4], hydrogen storage[5], nanoelectronic components[6], catalyst supports[7], adsorption material and so on.…     

非离子型表面活性剂Tween 60用于碳纳米管的双水相分离

单壁碳纳米管以其优异的电学和光学性能受到了广泛的关注,高性能器件等应用要求使用性质均一的单壁碳纳米管.因此,不同结构的单壁碳纳米管的分离具有重要意义.双水相萃取是一种能够对单壁碳纳米管进行结构分离的新方法,分离结果稳定可靠,且不需要复杂的设备,具有简捷、高效、易扩大规模等特点.本文通过调节脱氧胆酸钠(DOC)和非离子型...     

Removal of anionic and cationic dyes from wastewater by adsorption using multiwall carbon nanotubes

This paper evaluated the efficiency and reusability of multiwall carbon nanotubes (MWNTs) on removal of cationic and anionic dyes under effect of pH, dose of MWNTs and concentration of dyes. The characterization of MWNTs is characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectra and BET (Brunauer, Emmett and Teller) surface area. SEM and TEM analyses showed that MWNTs had size within nano scale range of 10–50 nm. The experimental results indicated that the efficiency of removal of MWNTs increase under condition of normal pH, at contact time 60 min with agitation speed 240 rpm and initial concentration of dyes 10 mg/l. Under these optimal conditions, the removal reached 98.7% and 97.2% for anionic dyes and cationic dyes, respectively. For economic use, MWNTs can be used more than one time where the same experiments with the already used MWNTs was repeated and it was found that the percent removal is almost the same.     

Influence of single-wall carbon nanotubes on Langmuir–Blodgett films of ferroelectric liquid crystals as studied by atomic force microscopy

Langmuir–Blodgett films of ferroelectric liquid crystal (LC) doped with low concentration of single-wall carbon nanotubes have been prepared and characterised. Pressure–area isotherms show that the films are stable and have good spreading properties. The interaction between nanotubes and LC molecules in the monolayer was increased during barrier compression, resulting in increased surface pressure. We observed phase change with increasing nanotube concentration in ferroelectric LC matrix. Atomic force microscopy profiles indicate uniform deposition of material on single crystal silicon wafer.     

Effect of substitutionally boron‐doped single‐walled semiconducting zigzag carbon nanotubes on ammonia adsorption

We investigate the binding of ammonia on intrinsic and substitutionally doped semiconducting single‐walled carbon nanotubes (SWCNTs) on the side walls using density functional calculations. Ammonia is found to be weakly physisorbed on intrinsic semiconducting nanotubes while on substitutional doping with boron its affinity is enhanced considerably reflected with increase in binding energies and charge transfer. This is attributed to the strong chemical interaction between electron rich nitrogen of ammonia and electron deficient boron of the doped SWCNT. On doping, the density of states are changed compared to the intrinsic case and additional levels are formed near the Fermi level leading to overlap of levels with that of ammonia indicating charge transfer. The doped SWCNTs thus are expected to be a potential candidate for detecting ammonia. © 2014 Wiley Periodicals, Inc.     

Enhanced separation of Compound Xueshuantong capsule using functionalized carbon nanotubes with cationic surfactant solutions in MEEKC

A novel additive of multi‐walled carbon nanotubes (MWNTs) dispersed with cationic surfactants or mixed cationic/anionic surfactants was used for MEEKC separation of eight phenolic compounds, four glycosides, and one phenanthraquinone. In this context, several parameters affecting MEEKC separation were studied, including the dispersion agents of MWNTs, MWNTs content, oil type, SDS concentration, and the type and concentration of cosurfactant. Compared with conventional MEEKC, the addition of all types of MWNTs dispersions using single or mixed cationic surfactant solutions in running buffers was especially useful for improving the separation of solutes tested, as they influenced the partitioning between the oil droplets and aqueous phase due to the exceptional electrical properties and large surface areas of MWNTs. Use of cationic surfactant‐coated MWNTs (6.4 μg/mL) as the additive in a microemulsion buffer (0.5% octanol, 2.8% SDS, 5.8% isopropanol, and 5 mM borate buffer) yielded complete resolution of 13 analytes. The proposed method has been successfully applied for the detection and quantification of the studied compounds in a complex matrix sample (Compound Xueshuantong capsule).     

Supramolecular hybrids of [60]fullerene and single-wall carbon nanotubes

Noncovalent interactions between purified HiPCO single-wall carbon nanotubes (SWNT) and a [60]fullerene-pyrene dyad, synthesized through a regioselective double-cyclopropanation process, produce stable suspensions in which the tubes are very well dispersed, as evidenced by microscopy characterization. Cyclic voltammetry experiments and photophysical characterization of the suspensions in organic solvents are all indicative of sizeable interactions of the pyrene moiety with the SWNT and, therefore, of the prevalence in solution of [60]fullerene-pyreneSWNT hybrids.     

Triply fused Zn(II)-porphyrin oligomers: synthesis, properties, and supramolecular interactions with single-walled carbon nanotubes (SWNTs)

The photophysical, electrochemical, and self-assembly properties of a novel triply fused Zn(II)-porphyrin trimer were investigated and compared to the properties of a triply fused porphyrin dimer and the analogous monomer. The trimer exhibited significantly red-shifted absorption bands relative to the corresponding monomer and dimer. Electrochemical investigations indicated a clear trend in redox properties amongst the three porphyrin structures, with the lowest oxidation potential and the lowest HOMO-LUMO gap exhibited by the triply fused trimer. This electrochemical behavior is attributed to the extensive pi-electron delocalization in the trimeric structure relative to the monomer and dimer. Additionally, it was found that the trimer forms extremely strong and nearly irreversible supramolecular interactions with single-walled carbon nanotubes (SWNTs), resulting in stable solutions of porphyrin-nanotube complexes in THF. Formation of these complexes required the addition of trifluoroacetic acid (TFA) to the solvent. This allowed the oligomers to make close contact with the nanotubes, enabling the formation of stable supramolecular assemblies. Atomic force microscopy (AFM) was used to observe the supramolecular porphyrin-nanotube complexes and revealed that the porphyrin trimer formed a uniform coating on the SWNTs. Height profiles indicated that nanotube bundles could be exfoliated into either individual tubes or very small bundles by exposure to the porphyrin trimer during sonication.     

Hydrogen adsorption in carbon nanostructures: comparison of nanotubes, fibers, and coals

Single-walled carbon nanotubes (SWNT) were reported to have record high hydrogen storage capacities at room temperature, indicating an interaction between hydrogen and carbon matrix that is stronger than known before. Here we present a study of the interaction of hydrogen with activated charcoal, carbon nanofibers, and SWNT that disproves these earlier reports. The hydrogen storage capacity of these materials correlates with the surface area of the material, the activated charcoal having the largest. The SWNT appear to have a relatively low accessible surface area due to bundling of the tubes; the hydrogen does not enter the voids between the tubes in the bundles. Pressure-temperature curves were used to estimate the interaction potential, which was found to be 580+/-60 K. Hydrogen gas was adsorbed in amounts up to 2 wt % only at low temperatures. Molecular rotations observed with neutron scattering indicate that molecular hydrogen is present, and no significant difference was found between the hydrogen molecules adsorbed in the different investigated materials. Results from density functional calculations show molecular hydrogen bonding to an aromatic C[bond]C that is present in the materials investigated. The claims of high storage capacities of SWNT related to their characteristic morphology are unjustified.     

Selective isolation of acidic proteins with a thin layer of multiwalled carbon nanotubes functionalized with polydiallyldimethylammonium chloride

The selective isolation of acidic proteins using a thin layer of multiwalled carbon nanotubes (MWNTs) functionalized with polydiallyldimethylammonium chloride (PDDA) was demonstrated. A certain amount (20 ml) of a suspension of PDDA-functionalized MWNTs that had been well dispersed by sonication was filtered through an MF-Millipore membrane with a pore aperture of 1.2 μm, and a uniform layer of PDDA-MWNT composites with a thickness of ca. 5 μm formed on the membrane. A 4 × 1 cm piece of the obtained membrane was supported by a stainless steel wire mesh and was then sandwiched between two PTFE films with grooved flow-through channels to form an extraction module. This module with a flow inlet and outlet was incorporated into a sequential injection system for performing the on-line separation and preconcentration of acidic protein, i.e., bovine serum albumin (BSA), and the BSA retained on the layer was eluted with a citrate buffer used as stripping reagent. In addition to a significant reduction in flow resistance, a dynamic sorption capacity of 3.8 mg mg⁻¹ or 1.4 mg cm⁻² for BSA was achieved using the layer-based system—a 146-fold improvement over that obtained using a packed microcolumn mode. A sample volume of 2.0 ml yielded an enrichment factor of 17, a retention efficiency of 100% and a recovery of 95%, along with a sampling frequency of 20 h⁻¹ and a RSD value of 2.8% at 25 μg ml⁻¹ for BSA. The practical applicability of the system was demonstrated by isolating acidic proteins (especially human serum albumin) from whole blood. Figure Selective isolation of acidic proteins with a composite thin layer of multi-walled carbon nanotubes functionalized with poly-diallyldimethylammonium chloride     

Selective oxidation of semiconducting single-wall carbon nanotubes by hydrogen peroxide

Selective oxidation of single-wall carbon nanotubes (SWCNTs) by H2O2 was conducted at varying heating times and monitored by UV-vis-NIR spectroscopy. A major increase in the relative absorption intensity indicated a higher than 80% concentration of metallic SWCNTs in the final product. Here, it is suggested that semiconducting SWCNTs are more reactive than metallic SWCNTs because of hole-doping by H2O2, resulting in faster oxidation.