Effects of modification groups and defects on the desalination performance of multi-walled carbon nanotube (MWNT) membranes

A new class of valves for membranes is based on the formation of nanobubbles at the pore entrances of carbon nanotube (CNT) membranes. Nanobubble stabilization is achieved by electrochemically etching CNTs into a polymer matrix to form a well that can be reversibly filled. Such valves have applications in flow battery systems where high-energy chemicals can be stored indefinitely. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

In this work, we have presented a comprehensive analysis of the performance of copper (Cu) and existing carbon nano tube (CNT) bundle structures (i.e. SWCNT, DWCNT and MWCNT) across nanometer technology nodes like 45, 32, 22 and 16 nm at local, intermediate and global level interconnects. Double walled carbon nano tubes (DWCNTs) and multi walled carbon nano tubes (MWCNTs) are modeled like simple single walled carbon nano tube (SWCNT) equivalent model with high accuracy. The analytical closed form delay expressions for SWCNT, DWCNT and MWCNT bundles have been found out. It has been observed that sparse SWCNT bundle interconnects show about 50 % performance improvement for 20 $$\upmu $$ μ m long local level interconnects over Cu in 16 nm technology node, whereas the performance advantage numbers for MWCNT and sparse DWCNT bundles are 50 and 35 % respectively. For 200 $$\upmu $$ μ m long intermediate level interconnects, the performance advantage numbers are 85, 80 and 75 % for dense SWCNT, MWCNT and dense DWCNT bundles respectively in 16 nm node. For 10 mm long global level interconnects, the performance advantage numbers are 85, 85 and 75 % for dense SWCNT, MWCNT and dense DWCNT bundles respectively in 16 nm node. It is also observed that the performance numbers improve with scaling for all levels of interconnects. It is also shown that the ratio of delay of CNT bundles and Cu for various levels of interconnects agree well with the existing work.

Carbon Nanotubes Applications on Electron Devices 406 of the active membrane pore density.In contrast, there are few, if any, reports of "bamboo" structure formation or catalyst migration in SWNTs or double-walled carbon nanotubes (DWNTs).However, it has been difficult to produce vertically aligned carbon nanotubes of this size uniformly and at large scale (Kalra 2003;Hata, Futaba et al. 2004).The major challenges also lie in finding a conformal deposition process to fill the gaps in this nanotube array, as well as in designing a selective etching process to open up the nanotube channels without producing voids in the membrane.These challenges in nanomanufacturing are one of the major reasons for the imbalance between the number of reports from computational and experimental studies, offering great research opportunities in the area of experimental Carbon Nanotube Nanofluidics.This book chapter is intended to provide an intermediate level overview of Carbon Nanotube Nanofluidics to the beginners and scientists who are interested in this emerging research field.For that purpose, we write discussions of Carbon Nanotube Nanofluidics with respect to transporting entities.In section 2, we discuss water transport under the CNT nanoconfinement in view of the unique transport phenomena including spontaneous water filling, fast water transport and mechanisms behind it.In section 3, we discuss the various aspects of gas transport in CNT.We present fundamental findings of Carbon Nanotube Nanofluidics for the gas transport, followed by a perspective of gas separation using CNT membranes.In section 4, we introduce recent achievements made by theoretical and experimental studies focusing on the behavior of ions in CNT including transport of ions under the CNT nanoconfinement, and ion exclusion and selectivity in association with CNT membrane technology.Finally, we will conclude several aspects of Carbon Nanotube Nanofluidics in section 5.

Electrophoretic transport of proteins across electrochemically oxidized multi-walled carbon nanotube (MWCNT) membranes has been investigated. A small charged protein, lysozyme, was successfully pumped across MWCNT membranes by an electric field while rejecting larger bovine serum albumin (BSA). Transport of lysozome was reduced by a factor of about 30 in comparison to bulk mobility and consistent with the prediction for hindered transport. Mobilities between 0.33 and 1.4 × 10(-9) m(2) V(-1) s(-1) were observed and are approximately 10-fold faster than comparable ordered nanoporous membranes and consistent with continuum models. For mixtures of BSA and lysozyme, complete rejection of BSA is seen with electrophoretic separations.

Separation of hydrogen isotopic water by multi-walled carbon nanotube (MWCNT) membrane and graphene oxide (GO)-MWCNT composite membranes

Substantive work has been carried out on microscopic and one–dimensional carbon nanotubes (CNTs), owing to their outstanding mechanical and electrical properties and their attractive application potential. Macroscopic CNTs are also essential for diverse applications, such as composites, conductors, sensors, and catalyst templates. After the first preparation of 40 cm long single–walled CNT (SWCNT) strands, macroscopic CNT yarns have been fabricated by spinning well–aligned CNT arrays, directly spinning and pulling of CNTs in a reaction furnace, and chemical infiltration of CNTs. However, for applications with large two–dimensional lateral surface areas, such as field–emission displays, fuel cells, and supercapacitors, it is desirable to grow or transfer nanotubes directly onto an appropriate surface to form film–like structures with a controlled thickness. As a relatively new form of nanotubes, double–walled CNTs (DWCNTs) have attracted great research interest in recent years because of their unique coaxial structure and promising mechanical, electrical, optical, and thermal properties compared to SWCNTs and multiwalled CNTs (MWCNTs). Recent advances in the large–scale synthesis of DWCNTs have made them attractive for a variety of applications. DWCNT “buckypapers”, about 2.5 cm in diameter and more than tens of micrometers in thickness, were obtained by infiltrating purified DWCNTs. We have previously developed a two–step purification protocol to obtain pure and clean DWCNT films, which retain their film–like structures after H2O2 and HCl treatments. It is well known that the Langmuir–Blodgett (LB) technique can produce mono– and multilayered organic–molecule membranes, with controlled thicknesses ranging from about 1 nm up to tens of micrometers. LB films consisting of microscopic SWCNTs have indeed been fabricated from organic solutions. In this communication, we report a novel and simple approach, similar to the LB technique, to controllably fabricate two–dimensional DWCNT membranes of only a few tens of nanometers in thickness. The raw DWCNT samples, containing several to tens of thin layers, were prepared by a chemical vapor deposition (CVD) method, described in detail in our recent paper. The black and sticky films with a thickness of several micrometers are comprised mainly of DWCNT bundles, together with amorphous carbon and catalyst particles coated with several layers of graphenes. Ultrathin DWCNT membranes could be obtained via a post–purification treatment and the generation process is illustrated in Figure 1. The raw DWCNT films (DWCNT–1) were first immersed into a H2O2 solution (30 %) for 72 h (DWCNT–2), which was followed by treatment in HCl solution (37 %) (DWCNT–3). The treated samples were then rinsed in distilled water until a pH value of 7 was reached. Addition of a few drops of ethanol or acetone to the purified DWCNT in water led to the rapid flotation of a DWCNT film to the water surface, which subsequently extended to a large thin film. The resulting film can be collected easily from the water surface with any substrate, such as a silicon wafer, copper grid, foil, or hollow metal ring, for further characterization and use. The thickness of the DWCNT film was effectively reduced by the H2O2 and HCl purification processes as the amorphous carbon and metal catalyst particles were successfully removed. The resulting membranes are so thin that they appear to be fully transparent. This was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization, which showed a single–layered structure and, thus, these films differ significantly from the as–prepared DWCNT samples. In order to understand the fundamentals behind the property changes of the DWCNT surface during the purification C O M M U N IC A IO N S

An electric field was applied across a deionized water droplet placed on a multi-walled carbon nanotube (MWCNT) membrane. Droplets of different size were tested by varying the voltage applied from 3 to 25 V during the electrowetting process. After electrowetting, it was observed that the topography of the membrane deformed from vertical alignment to a grouped pattern due to bubbles appearing during the electrowetting process, indicating the occurrence of electrolysis. For the droplet size ranging from 2 to 3.5 μl, the contact angle (CA) for smaller droplets reduced more dramatically than for larger droplets at the same voltage, and the contact angle saturation condition also varied in response to the droplet size. To reveal the droplet size effect, the Young-Lippmann equation is modified to simulate CA reduction on a MWCNT membrane.

Carbon nanotubes (CNTs) are widely used and may pose potential environmental risks to soil and groundwater systems. Therefore, it is important to improve current understanding of the fate and transport of CNTs in porous media. In this study, the transport behavior of multi-walled carbon nanotubes (MWCNTs) with different surface modifications were examined in water-saturated sand columns under different pH (5 and 7) and ionic strength (0.1, 1, and 5mM) conditions. COOH-MWCNTs have the strongest mobility among the five types of MWCNTs, followed by pristine MWCNTs. NH2-MWCNTs, Cu-MWCNTs, and Fe-MWCNTs have the weaker mobility. The transport of five types of MWCNTs decreased with the increase of ionic strength, while increased with the increase of pH value. The results suggested that the transport of MWCNTs can be affected by the electrostatic attraction between the functional groups on the surface of MWCNTs and quartz sand. Moreover, the pH and ionic strength of the solution also played an important role in enhancing the transport of MWCNTs, which have great significance for evaluating the transport and fate of MWCNTs in natural environment.

Double-wall carbon nanotubes (DWCNTs), single-wall carbon nanotubes (SWCNTs), and multi-wall carbon nanotubes (MWCNTs) were investigated as an alternative for platinum in counter-electrodes for dye-sensitized solar cells. The counter-electrodes were prepared on fluorine-doped tin oxide glass substrates by the screen printing technique from pastes of carbon nanotubes and organic binder. The solar cells were assembled from carbon nanotubes counter-electrodes and screen printed anodes made from titanium dioxide. The cells produced with DWCNTs, SWCNTs or MWCNTs have overall conversion efficiencies of 8.0%, 7.6% and 7.1%, respectively. Electrochemical impedance spectroscopy measurements revealed that DWCNTs displayed the highest catalytic activity for the reduction of tri-iodide ions. The large surface area and superior chemical stability of the DWCNTs facilitated the electron-transfer kinetics at the interface between counter-electrode and electrolyte and yielded the lowest transfer resistance, thereby improving the photovoltaic activity. A short-term stability test at moderate conditions confirmed the robustness of solar cells based on the use of DWCNTs, SWCNTs or MWCNTs.

The continuous miniaturization of very large-scale integration devices impacts the performance of integrated circuits. The performance of existing interconnect materials such as copper has become saturated beyond the deep-submicron technology node, motivating the search for new interconnect materials that could be efficiently employed in such circuits. In this study, a temperature-dependent analysis is performed to determine the propagation delay, power dissipation, and power–delay product of copper, single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), double-walled carbon nanotubes (DWCNTs), and mixed (multi- and double-wall) carbon nanotube bundle (MDCB) structures. The performance of these bundled structures is examined with the help of a complementary metal–oxide–semiconductor driver interconnect load system at various temperatures (200–500 K) and technology nodes (22 and 16 nm). The proposed novel mixed structure with MWCNTs at the periphery and DWCNTs in the center is interesting due to the combination of the excellent conducting properties of DWCNTs and the reduction of the net capacitive coupling due to the MWCNTs. Indeed, it is observed that this MDCB interconnect structure can outperform not only copper interconnects but also the SWCNT, MWCNT, and DWCNT structures. Such mixed structures could be used as interconnect materials in high-speed integrated circuits at future nanotechnology nodes.

Carbon nanotubes (CNTs) [1,2] have excellent thermal conductivity [3], extremely high current-carrying capacity (ampacity), i.e., stable electrical resistance in the presence of high currents [4], and superior mechanical properties [5,6]. Metal/CNT composites are therefore expected to be potential functional materials, and there have been many investigations concerning the fabrication of metal/CNT composites [7,8]. Composite plating is one promising process for the fabrication of metal/CNT composite films, and its application to such has been investigated [9]. In particular, Cu/CNT composite films are expected to be used for electronics applications. CNTs are generally categorized into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs). CNTs have anisotropic electrical and thermal conductivity, i.e., they have higher electrical and thermal conductivity in the axis direction than in the direction perpendicular to the axis direction. In this study, Cu/MWCNT and Cu/SWCNT composite films were fabricated using composite plating techniques, including electroplating and electroless plating. The dispersibility of CNTs in the plating baths is extremely important for composite plating with CNTs that are hydrophobic. Polyacrylic acid (mean molecular weight 5000) is an effective dispersant for MWCNTs in an acidic copper sulfuric bath [10], and Cu/MWCNT composite films with a homogeneous MWCNT distribution have been formed by electroplating using such a Cu/MWCNT composite bath [11,12]. Metal/MWCNT composite films, including the Cu/MWCNT composite film, intrinsically have a tendency toward a bumpy surface morphology due to the (anisotropic) electrical conductivity of MWCNTs [13]. However, a relatively flat surface morphology could be obtained using appropriate current densities (cathode overpotentials) [14] or surfactants [15]. In addition, reverse current electrodeposition could be used to increase the MWCNT content in Cu/MWCNT composite films [16]. Cu/MWCNT composite films have also been obtained by electroless plating using an alkaline bath. Ethylenediaminetetraacetic acid (EDTA), glyoxylic acid and sodium dodecyl sulfate (SDS) + hydroxypropyl cellulose (HPC) were used as a complexing agent, a reducing agent and surfactants for MWCNTs, respectively [17]. The Cu/MWCNT composite films were also successfully fabricated on an acrylonitrile butadiene styrene resin substrate [18]. SWCNTs have the smallest diameter among CNTs and have a tendency to form a characteristic aggregate known as a bundle. This bundle cannot be disintegrated to a primary particle, i.e., single SWCNTs, with the addition of dispersants alone. The use of both a powerful mechanical disintegration method and a dispersant is effective for the disintegration of SWCNT bundles. The selection of dispersants for SWCNTs is also important. In this study, trimethyl stearyl ammonium chloride (TMSAC), which is a cationic surfactant, was selected to prepare a Cu/SWCNT composite electroplating bath [19]. Cu/SWCNT composite films with relatively homogeneous SWCNT distribution were formed by electroplating. Cu/SWCNT composite films with homogeneously dispersed SWCNTs were also fabricated by electroless plating using a bath containing EDTA, glyoxylic acid, SDS+HPC (Fig. 1) [20]. References A. Oberlin, M. Endo and T. Koyama, J. Cryst. Growth, 32, 335 (1976).S. Iijima, Nature, 354, 56 (1991).S. Berber, Y.K. Kwon and D. Tomanek, Phys. Rev. B, 84, 4613 (2000).Z. Yao, C.L. Kane and C. Dekker, Phys. Rev. Lett., 84, 2941 (2000).M.F. Yu, O. Lourie, M.J. Dyer, K. Moloni, T.F. Kelly and R.S. Ruoff, Science, 287, 637 (2000).J.P. Lu, Phys. Rev. Lett., 79, 1297 (1997).S. Cho, K. Kikuchi, T. Miyazaki, K. Takagi, A. Kawasaki and T. Tsukada, Scr. Mater., 63, 375 (2010).A.K. Shukla, N. Nayan, S.V.S.N. Murty and S.C. Sharma, Mater. Sci. Eng. A, 560, 365 (2013).X.H. Chen, J.C. Peng, X.Q. Li, E.M. Deng, J.X. Wang and W.Z. Li, J. Mater. Sci. Lett., 20, 2057 (2001).S. Arai and M. Endo, Electrochem. Commun., 5, 797 (2003).S. Arai and M. Endo, Electrochem. Solid-State Lett., 7(3), C25 (2004).S. Arai and M. Endo, Electrochem. Commun., 7, 19 (2005).S. Arai, M. Endo and N. Kaneko, Carbon, 42, 641 (2004).S. Arai, T. Saito and M. Endo, J. Electrochem. Soc., 157(3), D147 (2010).S. Arai, T. Saito and M. Endo, J. Electrochem. Soc., 157(3), D127 (2010).S. Arai, Y. Suwa and M. Endo, J. Electrochem. Soc., 158(2), D49 (2011).S. Arai and T. Kanazawa, ECS J. Solid State Sci. Technol., 3, P201 (2014).S. Arai and T. Kanazawa, J. Electrochem. Soc., 162 (1), D68 (2015).T. Ogasawara, M. Shimizu and S. Arai, Proc. ADMETA Plus 2017, pp. 54-55 (2017).S. Arai, T. Osaki, M. Hirota and M. Uejima, Mater. Today Commun., 7, 101 (2016). Figure 1

This paper deals with electrostatically actuated Double Walled Carbon Nanotubes (DWCNT) cantilevered resonators. The governing equations for the motion of the DWCNT are derived through Euler-Bernoulli beam model assumptions that account for inertial and viscoelastic effects. The DWCNT is a specific type of multi-walled carbon nanotube (MWCNT) that is comprised of two coaxially concentric carbon nanotubes. Electrostatic, damping, and intertube van der Waals forces act on the outer tube of the DWCNT, while only intertube van der Waals force acts on the inner tube. A soft AC voltage provides the electrostatic actuation. The nonlinear behavior and phenomena in the system are provided by the electrostatic and intertube van der Waals forces. The DWCNT is subjected to nonlinear parametric dynamics. The Method of Multiple Scales (MMS) is employed to investigate the system under soft excitations and/or weak nonlinearities. The frequency-amplitude response is found in the case of parametric resonance. The resulting nonlinear dynamic behavior is important to improve DWCNT resonator sensitivity in the application of mass sensing.

Introduction In an emerging field of nanotechnologies, assessment of exposure is an integral component of occupational and environmental epidemiology, risk assessment and management, as well as regulatory actions. This review focuses occupational exposure to carbon nanotubes (CNT). Methods PubMed and Scopus databases were searched for period 2000–2017 using all keywords combinations based on the following structure: ‘assessment’ and ‘exposure’ and ‘carbon nanotube’. The words ‘assessment’ and ‘exposure’ were alternatively replaced by ‘measurement’ and by ‘human’ and ‘occupational’, respectively. The word ‘carbon nanotube’ was alternatively replaced by ‘single-walled carbon nanotube’, ‘double-walled carbon nanotube’, ‘multi-walled carbon nanotube’, and their abbreviations. Only field-studies conducted in occupational settings were included. The quality of the exposure measurement protocol and results reporting were reviewed. The results were compared with the current NIOSH recommended exposure limit (REL) of 1 µg/m 3 respirable elemental carbon (EC) mass-concentration as an 8 hour time-weighted average. Result Twenty-five studies conducted in R and D laboratories, small-scale pilot-production facilities, and, more rarely, large-scale primary or secondary manufacturer/user facilities in the USA (eleven), the Republic of Korea (four), Japan (four), Russia (one) and Europe (four) were reviewed. Open handling of CNT powder during the sieving, mechanical work-up, packaging, and clean-up work-tasks was classified at highest likelihood of exposure. Fourteen most recent studies measured EC concentration, although using different methods and aerosol fractions. All but one studies observed EC values exceeding the REL. The quantification of CNT agglomerates and/or CNT-contained particles lacks methodological standardisation and precluded any comparison of results. Discussion Currently available occupational-exposure data are limited, because production and use of CNT are relatively recent and workforce sizes remain small. Due to high variability of methods and instruments used for exposure sampling and analysis and of criteria used for interpreting their results, results are difficult to compare. Further effort of methodological standardisation is warranted.

Introduction In an emerging field of nanotechnologies, assessment of exposure is an integral component of occupational and environmental epidemiology, risk assessment and management, as well as regulatory actions. This review focuses occupational exposure to carbon nanotubes (CNT). Methods PubMed and Scopus databases were searched for period 2000–2017 using all keywords combinations based on the following structure: ‘assessment’ and ‘exposure’ and ‘carbon nanotube’. The words ‘assessment’ and ‘exposure’ were alternatively replaced by ‘measurement’ and by ‘human’ and ‘occupational’, respectively. The word ‘carbon nanotube’ was alternatively replaced by ‘single-walled carbon nanotube’, ‘double-walled carbon nanotube’, ‘multi-walled carbon nanotube’, and their abbreviations. Only field-studies conducted in occupational settings were included. The quality of the exposure measurement protocol and results reporting were reviewed. The results were compared with the current NIOSH recommended exposure limit (REL) of 1 µg/m3 respirable elemental carbon (EC) mass-concentration as an 8 hour time-weighted average. Result Twenty-five studies conducted in R and D laboratories, small-scale pilot-production facilities, and, more rarely, large-scale primary or secondary manufacturer/user facilities in the USA (eleven), the Republic of Korea (four), Japan (four), Russia (one) and Europe (four) were reviewed. Open handling of CNT powder during the sieving, mechanical work-up, packaging, and clean-up work-tasks was classified at highest likelihood of exposure. Fourteen most recent studies measured EC concentration, although using different methods and aerosol fractions. All but one studies observed EC values exceeding the REL. The quantification of CNT agglomerates and/or CNT-contained particles lacks methodological standardisation and precluded any comparison of results. Discussion Currently available occupational-exposure data are limited, because production and use of CNT are relatively recent and workforce sizes remain small. Due to high variability of methods and instruments used for exposure sampling and analysis and of criteria used for interpreting their results, results are difficult to compare. Further effort of methodological standardisation is warranted.

Multiwalled carbon nanotube membranes for water purification