Nanotubes In Aqueous Solution Research Articles

Vx-Na2TiOSiO4 MWNTs for uranium extraction from seawater and recovery from nuclear waste

Uranyl ion pollution is a serious environmental problem, and developing novel adsorption materials is essential for uranyl ion removal. V-doped Na2TiOSiO4 multiwalled nanotubes (Vx-Na2TiOSiO4 MWNTs) were prepared by an effective hydrothermal process and their uranyl ion adsorption properties were investigated. The special morphology, high specific surface area, and surface potential made MWNTs an excellent adsorbent. Appropriate doping can further improve the adsorption performance of nanotubes. The saturated adsorption capacities of nanotubes in aqueous solution and simulated seawater were 593.2 and 236.9 mg/g, respectively, and can reach 684.6 and 287.0 mg/g after appropriate doping. Proposed and proved the adsorption mechanism of nanotubes was the surface electrostatic adsorption mechanism, the Na+ replacement, and uranyl ion crystallization. In addition, nanotubes have excellent selectivity and recyclability. The finding in this work provides a fundamental understanding of the efficient usage of Vx-Na2TiOSiO4 MWNTs in practical applications.

Cluster Adsorption of L-Histidine on Carbon Nanotubes in Aqueous Solutions at Different Temperatures

Adsorption isotherms are obtained for L-histidine on carbon nanotubes using aqueous solutions at temperatures of 25, 35, 45, 55, 65, and 80°C. The isotherms are interpreted by using the cluster adsorption model and analyzing the dependence of the strength of the bond nanotube–amino acid on temperature. Equations of the adsorption isotherms are obtained for all temperatures. The calculated results indicate that L-histidine is fixed on a nanotube’s surface in the form of monomers and different clusters. The equilibrium characteristics of adsorption are found to change as the temperature rises. Values obtained for the coefficients of equilibrium are used to calculate apparent enthalpy ΔH* of L-histidine adsorption by nanotubes, according to the van’t Hoff equation.

Optimization of Binary Polymer Concentration for Dispersion of Multiwalled Carbon Nanotubes in Aqueous Solution

AbstractThe dispersion of carbon nanotubes (CNTs) is a challenging step in the preparation of conducting composites. Stabilizing CNT suspensions in a liquid solution with surfactants and polymers as dispersants is the most common method. This study aimed to investigate a systematic route to the degree of dispersion of functionalized multiwalled carbon nanotubes (F‐MWCNTs) in aqueous solution, assisted by four types of binary dispersants (i.e., polymer/surfactant). A UV‐Vis spectroscopy‐based method was employed to accurately determine the optimum F‐MWCNTs concentration in blended binary polymer with application of the Boltzmann sigmoidal model. The model represents the concentration of dispersed F‐MWCNTs attained versus the initial concentration of F‐MWCNTs used, and it was found that the model fits the experimental data. The significance of the parameters related to the Boltzmann sigmoidal model for the dispersion behavior of F‐MWCNTs is discussed. The model could be a tool to prepare optimally dispersed F‐MWCNTs in various types of liquid solutions.

On the adsorption of volatile organic compounds on hydroxyl-functionalized carbon nanotubes in aqueous solution

Volatile organic compounds (VOCs) are among the primary concerns due to their practical threatening on living environment and human health. This work aims at examining the physical adsorption behavior of four representative VOC species on hydroxyl-functionalized CNTs in terms of molecular dynamics simulations. Simulation results indicate that the adsorption affinities of these four VOC species follow the order of toluene > ether > acetone > methanol for both the unfunctionalized and hydroxyl-functionalized CNTs. This adsorption preference is endorsed by the binding energy calculations based on the umbrella sampling algorithm. The surface modifications due to the introduction of hydroxyl groups affect both the adsorption mechanism and equilibrium configuration. The hydrogen-bond network near the adsorption region is rebuilt for stabilizing the adsorption kinetics. Compared to the dominant van der Waals interaction, the electrostatic interaction between the charged hydroxyl groups and the VOC molecules are found to be much less significant. With the increase of hydroxyl concentration, the adsorption affinity decays for all four VOC species. This conclusion is confirmed by both the binding free energies and the number of successfully adsorbed VOC molecules. The fundamental mechanism is due to the reduction of the originally hydrophobic area of CNTs surface and the additional bonding competition from water molecules. This work presents a molecular insight on the interaction between VOC molecules and hydroxyl-functionalized CNTs in aqueous solution. It can also benefit the development and design of smart filtration devices of VOC molecules for their early removal in aqueous solutions.

Selective separation of single-walled carbon nanotubes in aqueous solution by assembling redox nanoclusters.

The selective separation of soluble and individual single-walled carbon nanotubes (SWCNTs) in aqueous solution is a key step for harnessing the extraordinary properties of these materials. Manipulating the strong van der Waals intertube interactions between the SWCNT bundles is very important in selective separation, which is a long-standing challenge. Here we reported the ability of redox polyoxometalate clusters to modulate the intertube π-π stacking interaction through electron transfer and achieved the diameter-selective separation of SWCNTs in a surfactant aqueous solution. The large-diameter SWCNTs concentrated at ∼1.3-1.4 nm were selectively separated when ∼1 nm clusters encapsulated within the tube cavity, and the dispersion of subnanometer ∼0.7-0.9 nm SWCNTs was boosted when clusters were adsorbed on the outer surface of small-diameter nanotubes. The mechanism of diameter-selective separation of SWCNTs associated with the size-dependent interaction between cluster-tubes and the steric hindrance effect of clusters was revealed by optical absorption and Raman spectroscopy. This simple method thus enables the selective separation of individual high-quality SWCNTs in aqueous solutions without harsh sonication with the potential for other separation applications.

Study of adsorption of histidine enantiomers on carbon nanotubes in aqueous solution based on different adsorption models

Study of adsorption of histidine enantiomers on carbon nanotubes in aqueous solution based on different adsorption models

Dispersion of Functionalized Multi-Walled Carbon Nanotubes in Aqueous Solution

Dispersion of Functionalized Multi-Walled Carbon Nanotubes in Aqueous Solution

On the Adsorption of Volatile Organic Compounds on Hydroxyl-Functionalized Carbon Nanotubes in Aqueous Solution

On the Adsorption of Volatile Organic Compounds on Hydroxyl-Functionalized Carbon Nanotubes in Aqueous Solution

A Discrete Platinum(II) Amphiphile: Construction, Characterization, and Controllable Self-Assembly in Different Solvents.

"Coordination-driven self-assembly" offers us an efficient method to fabricate 3D metallacages and 2D metallacycles with controllable shape and size via simple building blocks. Herein, a new discrete platinum(II) amphiphile (AOM), which contains hydrophilic tris(ethylene oxide) chains and a hydrophobic porphyrin unit, was constructed successfully by using "coordination-driven self-assembly". From various characterization methods, such as UV-vis spectroscopy, dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and small-angle X-ray scattering, we found that AOM can self-assemble into vesicles, curved vesicles with open ends, and at last stable bilayer nanotubes in aqueous solution at room temperature and flexible cross-linked structures at about 60 °C. In contrast, AOM formed rigid bilayer nanosheets of micrometers in width and millimeters in length in n-hexane. We hope this investigation will pave the way for the fabrication of controllable soft materials.

Electrochemical fingerprint of cytochrome c on a polymer/MWCNT nanocomposite electrode

The electroactivity of cytochrome c on screen-printed graphite electrodes modified with stable dispersions of multi-walled carbon nanotubes in aqueous solution of amphiphilic poly(n-butyl acrylate)100-block-poly(acrylic acid)140 diblock copolymers was estimated. Using a broad potential window, the reduction and oxidation of heme iron at a near-zero potential, the electrooxidation of Tyr and Trp at +0.6 V and the electrooxidation of heme at +0.8 V were detected in a wide concentration range of 1–100 μm with a limit of detection of 1–2 μm. Such a multipoint detection can be used as an electrochemical fingerprint of cytochrome c for its electrochemical recognition and quantification in complex (bio)chemical analytes.

A systematic investigation of dispersion concentration and particle size distribution of multi-wall carbon nanotubes in aqueous solutions of various dispersants

Surfactant-assisted exfoliation of multi-walled carbon nanotubes (MWNTs) in aqueous solution have become a common procedure to generate high fraction of individualized nanotubes. Since well-controlled experimental methodologies and reliable comparative metrics are scarce, a systematic research was conducted in order to analyze the dispersibility and the dispersing mechanisms of MWNTs in aqueous solutions of various surfactants. The concentration of dispersed MWNTs was accurately measured for a wide range of surfactant concentration, using combined UV–vis spectroscopy and thermogravimetric analysis (TGA). The obtained dispersibility results indicated that the highest dispersion concentration and efficiency is achieved in the SDBS-assisted MWNTs dispersion. Furthermore, the nanotube morphology and surfactant properties can be evaluated and rationalized by analyzing the dispersed nanotube mass and the surfactant amount per nanotube surface area. The amount of dispersed MWNTs remaining after varying levels of sonication and centrifugation was investigated, and a controllable sonication-centrifugation method for the preparation of well-dispersed MWNTs was established. The experimental data of the concentration of MWNTs dispersions versus centrifugation speed (ω) are fitted reasonably well by a Boltzmann function. The SDBS-assisted MWNTs dispersion will be more susceptible to the high centrifugal speed,while PVP-assisted MWNTs dispersion will be sediment fast at the mild centrifugation. The distributions of diameter and length of MWNTs at maximum dispersibility show that the sizes for the MWNTs dispersed by SDBS are much more polydisperse. The results further suggest that preparation of controllable carbon nanotubes morphology and design of rational configuration of surfactants are the key factors for increasing the dispersion stability and maximum concentration of well-dispersed MWNT.

The aging effect on the enhancement of thermal stability, mechanical stiffness and fluorescence properties of histidine-appended naphthalenediimide based two-component hydrogels.

A histidine attached naphthalenediimide (NDI)-containing amphiphilic molecule (NDIP) self-assembles into nanotubes in aqueous solution at pH 6.6 as revealed by high-resolution transmission electron microscopy studies. This histidine-appended NDI forms a two-component hydrogel in the presence of tartaric acid at a molar ratio of 1 : 2. A morphological transformation was observed from a nanotube structure in the non-gel aggregated state of histidine appended NDI to interconnected cross-linked nanofibers of the two-component hydrogel in the presence of tartaric acid. Interestingly, the gel exhibits an unusual behavior upon aging compared to the fresh gel. It is found that the thermal stability and gel stiffness increase very significantly upon aging. Another important feature noted is that the very weak fluorescence of the fresh gel is transformed into bright greenish fluorescence upon aging. These results suggest that intermolecular interactions among the gelator molecules and tartaric acid in the gel phase slowly increase with time to form a mechanically very stiff and thermally robust gel.

Humic acid assisted stabilization of dispersed single-walled carbon nanotubes in cementitious composites

AbstractSignificant research has been done in recent decades in the field of the dispersion of carbon nanotubes in aqueous solutions and the reinforcement of ordinary Portland cement (OPC). However, the cementitious mixture, as an alkaline environment, easily leads to the re-agglomeration of dispersed single-walled carbon nanotubes (SWCNTs) and influences their enhancing effects. Humic acid (HA) is a type of natural organic matter which can assist the stabilization of dispersed single-walled carbon nanotubes in cementitious composites. The present study characterizes the influence of HA in stabilizing the dispersion of SWCNTs by means of ultraviolet spectrophotometer tests. The fluidity of fresh cement slurry and mechanical performance of hardened OPC pastes were measured to better illustrate the dispersion of SWCNTs in real cement composites. The results not only reveal that the addition of an alkaline environment to the SWCNT suspensions results in a rapid decrease of the dispersion, but also suggest that the appropriate content of HA (0.12 wt.%) can play a significant role in stabilizing the dispersion of SWCNTs. When the mixed hybrid of SWCNTs and HA with a concentration of HA/c equal to 0.05 wt.% is used, the fluidity of the fresh cement slurry experiences a maximum decline and this mixture content of materials will dramatically increase the compressive and flexural strength by about 31% and 48%, which indicates that more SWCNTs are in a dispersed state under this concentration. SEM images further prove that a suitable HA/c can inhibit the expansion of cracks in the cementitious composites.

Biocatalytic hydrogenations on carbon supports.

We describe the use of carbon as a versatile support for H2-driven redox biocatalysis for NADH-dependent CX bond reductions in batch and flow reactions. In each case, carbon is providing an electronic link between enzymes for H2 oxidation and reduction of the biological cofactor NAD+, as well as a support for a multi-enzyme biocatalysis system. Carbon nanopowders offer high surface areas for enzyme immobilization and good dispersion in aqueous solution for heterogeneous batch reactions. Difficulties in handling multi-wall carbon nanotubes in aqueous solution are overcome by growing them on quartz tubes to form carbon nanotube column reactors, and we show that these facilitate simple translation of H2-driven biocatalysis into flow processes. Using this flow reactor design, high conversions (90%) and total enzyme turnover numbers up to 54,000 could be achieved. Use of an entirely heterogeneous biocatalysis system simplifies recovery and re-use of the enzymes; combined with highly atom-efficient cofactor recycling, this means that high product purity can be achieved. We demonstrate these methods as platform approaches for overcoming challenges with NADH-dependent biocatalysis.

Robust technique for dispersion of single-walled carbon nanotubes in aqueous solutions with tRNA

Stable dispersions of single-walled carbon nanotubes (SWCNTs) demonstrated great prospects for applications in biomedical engineering, including bioelectronics, nanoparticle-based drug delivery and imaging in vivo. Prolonged stability of individual SWCNTs in suspensions is crucial for these applications. Here we report the method for efficient stabilization of SWCNT dispersions with transfer ribonucleic acid (tRNA). We optimized the SWCNTs/tRNA mass ratio for dispersion of CoMoCAT and HiPCO tubes and studied them by optical absorbance and photoluminescence (PL) spectroscopy. Cryo-TEM and AFM imaging and PL spectroscopy of suspensions prepared even without any ultrasonic treatment confirmed the presence of individual SWCNTs in the dispersions. We propose a straightforward SWCNT/tRNA dipsersion preparation by either mild sonication or even without ultrasonic treatment will boost the biomedical applications due to simplicity of the procedure and minimal damage of tRNA and SWCNTs.

Probing the degradation of carbon nanotubes in aqueous solution by liquid cell transmission electron microscopy

Understanding the degradation of carbon nanotubes (CNTs) is critically important for their potential biological and environmental applications. In this work, the chemical degradation of CNTs in aqueous solution in the presence of strong oxidizing hydroxyl radicals was directly investigated through liquid cell transmission electron microscopy. The real-time observation on degradation of CNTs revealed three types of degradation behaviors: (Ι) the radial shrinkage of CNTs; (ΙΙ) the rupture of CNTs caused by perforation degradation; (ΙΙΙ) the axial disappearance of CNTs initiated from both end caps of CNTs and newly formed defects. Among them, the axial degradation was found to be predominant based on statistic results. Moreover, the degradation mechanism and its dependence on the structure of CNTs were explicated. This work provides insights to further understand the microscopic mechanisms governing the degradation of CNTs in solution, and will shed the light on the practical applications of CNTs.

Polymeric surfactants with tricyclic rigidity from natural rosin: Synthesis and dispersion of single-walled carbon nanotubes in aqueous solution

Polymeric surfactants from natural rosin containing a unique tricyclic rigid structure were prepared and their structures were characterized by IR, 1H NMR and GPC. Their surface activities including hydrophile—lipophile balance values (HLB), emulsification properties, foaming properties, critical micelle concentration (CMC) and the minimum surface tension (γCMC) were evaluated. With the increase in ratio of hydrophobic to hydrophilic in polymeric surfactant, the CMC values of the surfactants decreased, and the emulsification and foaming properties of these surfactants increased, and the HLB values of them decreased. This type of polymeric surfactants was used to disperse single-walled carbon nanotubes (SWCNTs) in water, and their dispersal capacities were comparatively determined by UV-visible absorption spectroscopy. Thermogravimetric analysis (TGA) was used to quantify the amount of surfactant attached onto the nanotubes. More intuitive image of their dispersion states were obtained by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results showed that this type of polymeric surfactants had good dispersion capacity and dispersion stability to SWCNTs in water through strong hydrophobic attraction and weak van der Waals interactions.

Retracted: Kinetic resistance of carbon nanotubes in aqueous solution

It has come to our attention that the article titled ‘Kinetic resistance of carbon nanotubes in aqueous solution’ DOI: 10.1049/mnl.2010.0188 published in Micro & Nano Letters in November 2011 (received on 8th November 2010; revised on 24th November 2010 in Micro & Nano Letters) duplicates the results of an already published manuscript in the Chinese Journal of Computational Mechanics and has been retracted to ensure the authenticity of the academic record.

Capillary electrophoresis analysis of affinity to assess carboxylation of multi-walled carbon nanotubes

Surface oxidation improves the dispersion of carbon nanotubes in aqueous solutions and plays a key role in the development of biosensors, electrochemical detectors and polymer composites. Accurate characterization of the carbon nanotube surface is important because the development of these nano-based applications depends on the degree of functionalization, in particular the amount of carboxylation. Affinity capillary electrophoresis is used to characterize the oxidation of multi-walled carbon nanotubes. A polytryptophan peptide that contains a single arginine residue (WRWWWW) serves as a receptor in affinity capillary electrophoresis to assess the degree of carboxylation. The formation of peptide-nanotube receptor-ligand complex was detected with a UV absorbance detector. Apparent dissociation constants (KD) are obtained by observing the migration shift of the WRWWWW peptide through background electrolyte at increasing concentrations of multi-walled carbon nanotubes. A 20% relative standard deviation in method reproducibility and repeatability is determined with triplicate analysis within a single sample preparation and across multiple sample preparations for a commercially available carbon nanotube. Affinity capillary electrophoresis is applied to assess differences in degree of carboxylation across two manufacturers and to analyze acid treated carbon nanotubes. The results of these studies are compared to X-ray photoelectron spectroscopy and zeta potential. Affinity capillary electrophoresis comparisons of carbon nanotube samples prepared by varying acid treatment time from 30 min to 3 h yielded significant differences in degree of carboxylation. X-ray photoelectron spectroscopy analysis was inconclusive due to potential acid contamination, while zeta potential showed no change based on surface charge. This work is significant to research involving carbon nanotube-based applications because it provides a new metric to rapidly characterize carbon nanotubes obtained from different vendors, or synthesized in laboratories using different procedures.

Controlled dispersion of multiwalled carbon nanotubes modified by hyperbranched polylysine

ABSTRACTHyperbranched polymers have been found effective in controlling the dispersibility of carbon nanotubes in aqueous solutions. In this study, hyperbranched polylysine (HBPL) was synthesized using lysine and N,N′‐methylenebisacrylamide as precursors via Michael addition. The HBPL then was used to noncovalently modify multiwalled carbon nanotubes (MWCNTs) to prepare MWCNTs‐HBPL. The obtained MWCNTs‐HBPL composites were characterized using FTIR spectroscopy, Raman spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The results showed that the HBPL was successfully attached to the surface of MWCNTs via noncovalent interactions. The dispersibility of the MWCNTs‐HBPL composites in aqueous solutions was investigated using digital photographs, ultraviolet–visible absorption spectroscopy, and zeta potential measurements. The results demonstrated that both the mass ratio of MWCNT to HBPL and the pH of the solution had a significant impact on the dispersibility of the MWCNTs/HBPL solution, suggesting that HBPL treatment is an effective method of controlling the dispersibility of MWCNTs in aqueous solutions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46249.