Diameter Of Carbon Nanotubes Research Articles

Effect of carbon nanotube diameter on water transfer through disjoint carbon nanotubes in the lateral electric fields

The lateral electric field affects a single-file water molecules transport through a disjoint carbon nanotube (DCNT). Nevertheless, it is not clear whether this phenomenon still exists when the diameter of the DCNT gradually increases. Herein, we use molecular dynamics simulations to investigate the transport of water molecules through the DCNTs with different diameters under the influence of the lateral electric fields. We find that the occupancy of water molecules, the flow rate and the flux rate within the large DCNTs decrease greatly when the lateral electric field increases from 0V/nm to 1.0V/nm, whereas the occupancy of water molecules, the flow rate and the flux rate within the small DCNTs decrease slightly when the lateral electric field increases from 0V/nm to 1.0V/nm. Our results are beneficial to understand the diameter effect of the DCNT on water transport and design novel nanoscale devices.

Formation of One-Dimensional van der Waals Heterostructures via Self-Assembly of Blue Phosphorene Nanoribbons to Carbon Nanotubes

Van der Waals heterostructures composed of low-dimensional atomic layers host rich physics for new device applications, such as magic-angle twisted bilayer graphene and coaxial multi-walled hetero-nanotubes. Aside from exploring their abnormal physical behavior, fabrication of such structures also presents a great challenge to this area, owing to the subtle and sensitive interactions among neighboring layers. Here we show by molecular dynamics simulations that narrow blue phosphorene nanoribbons can be encapsulated into carbon nanotubes driven by van der Waals interactions and form one-dimensional heterostructures. It shows that by varying carbon nanotube diameters and nanoribbon width, the nanoribbons can either retain their original straight structures or twist into tubular structures. Wrapping phases are also observed for large-sized blue phosphorus. It is found that the underlying mechanism originates from the competition between van der Waals energy and bending energy induced by tube curvature. A phase diagram of the resultant 1D structure is thus obtained based on a simple analysis of energetics. The results are expected to stimulate further experimental efforts in fabricating one-dimensional van der Waals heterostructues with desired functionality.

High performance of carbon nanotube elastocaloric refrigerators over a large temperature span

Compression of greenhouse gases still dominates the market of refrigeration devices. Although well stablished and efficient, this technology is neither safe for the environment nor able to be scaled down to nanoscale. Solid-state cooling technologies are being developed to overcome these limitations, including studies at nanoscale. Among them, the so-called elastocaloric effect (eC) consists of the thermal response, $\Delta T$, of a material under strain deformation. In this work, fully atomistic molecular dynamics simulations of the eC in carbon nanotubes (CNTs) are presented over a large temperature span. The efficiency of the CNTs as solid refrigerators is investigated by simulating their eC in a model of refrigerator machine running under Otto-like thermodynamic cycles (two adiabatic expansion/contraction plus two isochoric heat exchange processes) operating at temperatures, $T_\mbox{O}$, ranging from 300 to 2000 K. The coefficient-of-performance (COP), defined as the ratio of heat removed from the cold region to the total work performed by the system per thermodynamic cycle, is calculated for each value of $T_\mbox{O}$. Our results show a non-linear dependence of $\Delta T$ on $T_\mbox{O}$, reaching a minimum value of about 30 K for $T_\mbox{O}$ between 500 and 600 K, then growing and converging to a linear dependence on $T_\mbox{O}$ for large temperatures. The COP of CNTs is shown to remain about the same and approximately equal to 8. These results are shown to be weakly depend on CNT diameter and chirality but not on length. The isothermal entropy change of the CNTs due to the eC is also estimated and shown to depend non-linearly on $T_\mbox{O}$ values. These results predict that CNTs can be considered versatile nanoscale solid refrigerators able to efficiently work over a large temperature span.

Characteristic Control of SWCNT-FET by Varying Its Chirality and Dimensions

Carbon nanotube (CNT) has witnessed great importance due to its electronic and mechanical properties. The CNTFET was designed to provide high-performance electronic devices. Therefore, the carbon nanotube is representing a potential material for future microelectronic devices. In this paper, COMSOL Multiphysics was used to design and a simulate single-walled carbon nanotube field-effect transistor with a back gate. The insulation layer used in the model was silicon dioxide. The influence of changing its thickness on the drain current was discussed. In addition, the specification of carbon nanotubes was investigated in terms of changing their diameter and length. Moreover, this paper reveals the current transport of CNTFET for different applied gate voltage and drain voltage. In our work, the CNTFET behaves as n-type FET with transconductance g m ≈1.25uA and electron mobility equal to 4.77×10-26cm2v-1s-1. To obtain semiconducting properties for the CNT material, it must consider the chirality when altering the carbon nanotubes diameter. In the proposed device, the diameter values range from 1nm to 4.5nm. It was found that increasing the diameter range resulted in decreasing bandgap from 0.497 eV to 0.110 eV and increasing drain current from 4.075 uA to 31.33 uA.

Predicting mechanical properties of carbon nanotube-reinforced cementitious nanocomposites using interpretable ensemble learning models

Compressive and flexural strength are important characteristics that indicate the efficiency of utilizing carbon nanotube (CNT) in cementitious nanocomposites. Preparing numerous test samples and conducting mechanical tests at different ages is costly and time-consuming, so a predictive model appears essential. Due to the complexity of recent building materials, experimental and statistical models do not function well for such complex materials, so machine learning techniques were adopted in this study. From the results of experiments performed in the literature, separate comprehensive data sets for compressive and flexural strength were collected, and water to cement ratio (W/C), CNT type, CNT content, CNT length, CNT diameter, sand to cement ratio for mortars (S/C), surfactant type, dispersion method, curing days (age) and compressive or flexural strengths of the control sample (C0 or F0) considered as input variables. Four ensemble learning-based algorithms, including random forest, AdaBoost, Gradient Boost, and XGBoost, were developed alongside a standalone model, the decision tree. To assess the sensitivity of input variables, four methodologies, including the Gini importance, permutation importance, F score, and mean of relative Shapely additive explanation (SHAP) values, were obtained, and compressive or flexural strengths of the control sample and CNT content identified overall as the most influential variables. The results revealed that XGBoostprovides more reliable and accurate results for compressive and flexural characteristics and better maps the relationships between input variables. In addition, SHAP analysis was performed to explain the contribution of each input according to its value on the output of XGBoost.

Shock loading of carbon nanotube bundle

A single-walled carbon nanotube (CNT) bundle under shock loading in lateral direction is studied by means of the chain model with reduced number of degrees of freedom. One or two compressive shock waves are initiated by a piston moving at a constant speed V0. At lower piston speeds, only the faster wave front resulting in an elliptization of CNTs propagates, while at higher speeds this is followed by the slower wave front resulting in CNT collapse. Time evolution of the CNT bundle structure during compression is investigated in detail. Energy absorption rate W as a function of the piston speed V0 is evaluated for bundles having CNTs of different diameter D. Bundles with smaller CNT diameter demonstrate a higher energy absorption rate scaling as W∼D−3. The rate of energy absorption increases bilinearly with V0, and in the regime of CNT collapse the slope of the line is twice as high as in the case when only elliptization takes place. The obtained results can be useful for the development of new types of elastic dampers.

Nanoporous Membranes of Densely Packed Carbon Nanotubes Formed by Lipid-Mediated Self-Assembly.

Nanofiltration technology faces the competing challenges of achieving high fluid flux through uniformly narrow pores of a mechanically and chemically stable filter. Supported dense-packed 2D-crystals of single-walled carbon nanotube (CNT) porins with ∼1 nm wide pores could, in principle, meet these challenges. However, such CNT membranes cannot currently be synthesized at high pore density. Here, we use computer simulations to explore lipid-mediated self-assembly as a route toward densely packed CNT membranes, motivated by the analogy to membrane-protein 2D crystallization. In large-scale coarse-grained molecular dynamics (MD) simulations, we find that CNTs in lipid membranes readily self-assemble into large clusters. Lipids trapped between the CNTs lubricate CNT repacking upon collisions of diffusing clusters, thereby facilitating the formation of large ordered structures. Cluster diffusion follows the Saffman-Delbrück law and its generalization by Hughes, Pailthorpe, and White. On longer time scales, we expect the formation of close-packed CNT structures by depletion of the intervening shared annular lipid shell, depending on the relative strength of CNT-CNT and CNT-lipid interactions. Our simulations identify CNT length, diameter, and end functionalization as major factors for the self-assembly of CNT membranes.

Unveiling the Influence of Carbon Nanotube Diameter and Surface Modification on the Anchorage of L-Asparaginase

L-asparaginase (ASNase, EC 3.5.1.1) is an amidohydrolase enzyme known for its anti-cancer properties, with an ever-increasing commercial value. Immobilization has been studied to improve the enzyme’s efficiency, enabling its recovery and reuse, enhancing its stability and half-life time. In this work, the effect of pH, contact time and enzyme concentration during the ASNase physical adsorption onto pristine and functionalized multi-walled carbon nanotubes (MWCNTs and f-MWCNTs, respectively) with different size diameters was investigated by maximizing ASNase relative recovered activity (RRA) and immobilization yield (IY). Immobilized ASNase reusability and kinetic parameters were also evaluated. The ASNase immobilization onto f-MWCNTs offered higher loading capacities, enhanced reusability, and improved enzyme affinity to the substrate, attaining RRA and IY of 100 and 99%, respectively, at the best immobilization conditions (0.4 mg/mL of ASNase, pH 8, 30 min of contact time). In addition, MWCNTs diameter proved to play a critical role in determining the enzyme binding affinity, as evidenced by the best results attained with f-MWCNTs with diameters of 10–20 nm and 20–40 nm. This study provided essential information on the impact of MWCNTs diameter and their surface functionalization on ASNase efficiency, which may be helpful for the development of innovative biomedical devices or food pre-treatment solutions.

Influence of Ni on the structural evolution of polymer-derived SiOC ceramics

Polymer derived ceramics (PDCs) technique is an advanced method for preparing high performance ceramics, in which pyrolysis process is an important step. In order to study the effect of the Ni transition metal on the pyrolysis process of polysiloxane, different contents of Ni acetate tetrahydrate (Ni(ac)2·4H2O)-impregnated polysiloxane (PSO) precursors were pyrolyzed in argon atmosphere between 1000 °C and 1300 °C. The organic-inorganic conversion behavior of precursors, the elemental and structural characterization of the Ni-free and Ni-containing SiOC ceramics were investigated. The results revealed that the presence of Ni not only enabled the growth of carbon nanotubes (CNTs) but also promoted the crystallization of carbon and SiC phase during the pyrolysis process. Additionally, high Ni content and pyrolysis temperature raised the diameters of CNTs and crystallinity of turbostratic layer carbon and SiC.

Low power high-speed CNFET-based full adder

This study proposes a 1-bit Full Adder using Carbon Nanotube-FET (CNFET) with low power, fast speed, and excellent performance for a range of electrical applications. The suggested Full Adder has two elements: sum and cout (FA). This design likewise exploits the advantagesof the unique characteristics ofmetal oxide-FETs like CNFETs. These CNFETs have the ability to change their threshold voltage by altering the diameter of carbon nanotubes to obtain their required voltage levels and great performance. The simulations presented in this paper use 32-nm CNFET technology in the Cadence Virtuoso EDA tool. When compared to the classical Si MOSFET-based Full Adder, simulation outcomes demonstrate the suggested design is better in aspects of speed, power, and energy.

Forecasting carbon nanotube diameter in floating catalyst chemical vapor deposition

Carbon nanotube (CNT) diameter control is essential for many conductive and structural applications; to date, a general diameter methodology applicable to all floating catalyst chemical vapor deposition (FC-CVD) reactors is not yet established. Single-walled CNT (SWCNT) diameter was robustly controlled by systematically exploring an extensive variety of fundamental FC-CVD reactor parameters (631 experiments) including: CO2, H2, and Ar flowrates; fuel flowrate; added H2O (up to an unprecedented 30% of fuel by mass); ferrocene concentration; reactor temperature (covering temperatures with solid and liquid floating catalyst); and quartz reactor tube age. As a function of these experimental input factors, across three Raman wavelengths, validated statistical models robustly predicted: 1) diameter of SWCNTs, via the weighted average of the radial breathing modes (RBMs); 2) the conditions which led to SWCNT growth, via the categorical appearance of viable RBMs. This is noteworthy because it illustrates a new paradigm of FC-CVD reactor control, accounting for interaction between reactor input factors, system noise, and other non-linear responses. Oxidative influences (including laboratory humidity) yield smaller CNT diameters, although H2O becomes important only at higher temperatures and CO2 is countered by H2 addition. Increasing reactor temperature increased diameters. Pyrolysis calculations showed species inside the reactor differ substantially from species injected. A kinetic-thermodynamic model of catalyst particle size and chemical state revealed that adding oxidative species kept the active catalyst particles small, explaining the resulting small CNT diameters. The powerful combination of our multivariate statistical approach with kinetic-thermodynamic modeling enables unprecedented insight and control over CNT synthesis.

Phosphorus and nitrogen codoped entangled carbon nanotubes forming spongy materials: Synthesis and characterization

Carbon sponges are of great interest of the scientific community given their potential in advanced applications such as water cleaning, catalysis, energy storage, and mechanical reinforcement. These carbon nanomaterials improve their attributes for unexpected properties and applications by doping with foreign atoms. Nitrogen‑phosphorus-codoped and functionalized carbon nanotube sponges (NP-CNTSs) were synthesized, using the aerosol-assisted chemical vapor deposition (AACVD) method. We used acetonitrile and triphenylphosphine (TPP) as nitrogen and phosphorus precursors. According to our results, the NP-CNTSs were formed by entangled multi-walled carbon nanotubes (MWCNTs) of diameters ranging between 60 and 300 nm with Fe2P and Fe3C nanoparticles in the walls and inside the carbon nanotube sponges (CNTSs) respectively. The Fourier transform infrared (FTIR) characterization revealed the vibrational modes of aromatic and aliphatic CH, PO, PH, and OCN bonds. The NP-CNTSs undergo a quasi-reversible hydroquinone/quinone redox process as revealed by cyclic voltammetry studies. They also efficiently retain organic solvents, absorbing up to 40 times their weight for dichlorobenzene. The XPS and Raman characterizations show the presence of pyridinic nitrogen, which might be responsible for the formation of cavities in the wall of the CNTSs and the entanglement of carbon nanotubes, which promotes the growth of the NP-CNTSs. To study the role of nitrogen and phosphorus in the electronic properties of carbon materials, we carried out calculations proposed in the density functional theory (DFT) for phosphorus‑nitrogen codoping bilayer graphene and carbon nanotube junctions containing pentagonal, hexagonal, and heptagonal carbon rings.

Catalyst-free growth of single- to few-layered graphene and carbon nanotubes on an ionic liquid surface

Carbon atoms can form many allotropes, which makes it as one of the most noticeable elements in the Periodic Table. Here, we report that single- to few-layered graphene, single- to multi-wall nanotubes and nested closed fullerenes may be fabricated on ionic liquid surfaces by a modified LP-CVD method without the assistance of metallic catalysts and near room temperature. The average size of the graphene platelets is about 300–500 nm, and the outer diameter of the single-wall carbon nanotube is 1.39 nm. The multi-wall nanotubes with semicircular closed end and fullerenes were fabricated for the first time on the ionic liquid surfaces, and the inner diameters of both the nanotubes and fullerenes are on the order of several nanometers. Based on the experimental results, the growth mechanism of the allotropes of carbon is presented uniformly.

Localized Liquid Zones Assisted Highly Crystalline Single-Wall Carbon Nanotube Sheets: Implications for Conducting Shields in Coaxial Cables

The electrical conductivity of carbon nanotube (CNT) macro assemblies can be influenced by their crystallinity. Herein, we present the synthesis of high-quality SWCNT sheets for which an appropriate optimization parametric research of synthesis temperature, precursor flow rate, and H2 flow rate was carried out in this approach. It was found that highly crystalline SWCNT sheet (IG/ID = 180.3) was synthesized by floating catalyst chemical vapor deposition technique at 12 mL/h precursor flow rate and 1000 sccm H2 flow rate. Three distinct Raman laser wavelengths (514, 532, and 785 nm) were used to study the as-synthesized sheet, and the maximum calculated IG/ID ratio was found to be 180.3 (@ λ = 514 nm). Due to high concentration of H2 gas, the number of localized liquid zones or CNT nucleation sites increased which has an impact on both the quality as well as the diameter of CNTs. The I–V characteristics of CNT sheet were studied via four-probe technique, yielding a measured value of electrical conductivity of 9.21 × 106 S/m. Further, the R-T measurement showed the positive temperature coefficient up to the 108 K which indicates the metallicity of as produced CNT sheets. These highly conducting SWCNT sheets are the best solution for a wide range of applications in many fields, including conducting shields in coaxial cables, flexible and nano scale electrical and electronic devices, displays, biosensors, field-effect transistors and gas sensing materials.

Aerosol based synthesis of highly conducting carbon nanotube macro assemblies by novel mist assisted precursor purging system

Taking hardware complexity into consideration of traditional continuous precursor purging systems for synthesis of few wall carbon nanotubes (CNTs) is a big challenge. Therefore, a novel precursor purging system for aerosol formation is designed to achieve uniform diameter distribution of CNTs, with the aerosol flow rate controlled either by number of ultrasonic mist makers or flow rate of carrier gas. Large droplets are turned into aerosol via an as-customized mist-producing system without the use of temperature or any chemical reaction. A built-in atomized gas valve is used to introduce the aerosol into a floating catalyst chemical vapour deposition (FCCVD) reactor. After an influential comparison of as-customized purging systems to the mostly used complex and big-budget systems for uniform diameter distribution, the quality of these CNT assemblies, synthesized using two different carrier gases (argon and hydrogen) is examined. Herein, CNT sheets with mostly fewer walls CNTs (diameter 2–10 nm) have been synthesized using this approach, with the controlled size of catalyst nanoparticles, under H2 atmosphere exhibiting low sulphur impurities, as evidenced by Raman, EDS, and XPS spectra, and have a fourteen-fold greater electrical conductivity (5.78 × 104S/m) than those synthesized under Ar atmosphere. Moreover, these sheets are also twisted and wrapped by insulating heat shrink tubes. The maximum current density of these conducting CNT wires having 250 µm diameter is 8.15 × 106A/m2. Further, one of the domestic applications of LED bulb (3–45 W) lightning is also demonstrated which shows the suitability of these conducting wires in numerous hi-profile applications.

Enhanced Ion Rejection in Carbon Nanotubes by a Lateral Electric Field.

Reverse osmosis membranes hold great promise for dealing with global water scarcity. However, the trade-off between ion selectivity and water permeability is a serious obstacle to desalination. Herein, we introduce an effective strategy to enhance the desalination performance of the membrane. A series of molecular dynamics simulations manifest that an additional lateral electric field significantly promotes ion rejection in carbon nanotubes (CNTs) under the drive of longitudinal pressure. Specifically, with the increase in the electric field, the ion flux shows a deep linear decay, while the water flux decreases only slightly, resulting in a linear increase in ion rejection. The energy barriers of ions around the CNT inlet are obtained by calculating the potentials of mean force to explain enhanced ion rejection. The lateral electric field uniformly raises the energy barriers of ions by pushing them away from the CNT inlet, corresponding to the enhanced ion velocity in the field direction. Furthermore, with the increase in CNT diameter, there is a significant increase in the flux of both ions and water; however, the lateral electric field can also obviously enhance the ion rejection in wider CNTs. Consequently, the enhancement of ion rejection by lateral electric fields should be universal for different CNT diameters, which opens a new avenue for selective permeation and may have broad implications for desalination devices with large pore sizes.

Supramolecular Self-Assembly of Dipalmitoylphosphatidylcholine and Carbon Nanotubes: A Dissipative Particle Dynamics Simulation Study.

Dissipative particle dynamics simulations were performed to investigate the self-assembly of dipalmitoylphosphatidylcholine (DPPC) as a model lipid membrane on the surface of carbon nanotubes (CNTs). The influence of surface curvature of CNTs on self-assembly was investigated by performing simulations on solutions of DPPC in water in contact with CNTs of different diameters: CNT (10, 10), CNT (14, 14), CNT (20, 20), and CNT (34, 34). DPPC solutions with a wide range of concentrations were chosen to allow for formation of lipid structures of various surface densities, ranging from a submonolayer to a well-organized monolayer and a CNT covered with a lipid monolayer immersed in a planar lipid bilayer. Our results are indicative of a sequence of phase-ordering processes for DPPC on the surface of CNTs. At low surface coverages, the majority of hydrocarbon tail groups of DPPC are in contact with the CNT surface. Increasing the surface coverage leads to the formation of hemimicellar aggregates, and at high surface coverages close to the saturation limit, an organized lipid monolayer self-assembles. An examination of the mechanism of self-assembly reveals a two-step mechanism. The first step involves densification of DPPC on the CNT surface. Here, the lipid molecules do not adopt the order of the target phase (lipid monolayer on the CNT surface). In the second step, when the lipid density on the CNT surface is above a threshold value (close to saturation), the lipid molecules reorient themselves to form an organized monolayer around the tube. Here, the DPPC molecules adopt stretched conformations normal to the surface, the end hydrocarbon groups adsorb on the surface, and the head groups occupy the outermost part of the monolayer. The saturation density and the degree of lipid ordering on the CNT surface depend on the surface curvature. The saturation density increases with increased surface curvature, and better-ordered structures are formed on less curved surfaces.

Energy Efficient Tri-State CNFET Ternary Logic Gates

Power consumption and especially leakage power are the main concerns of nano MOSFET technology. On the other hand, binary circuits face a huge number of interconnection wires, which results in power dissipation and area. Researchers introduced emerging nanodevices and multiple-valued logic (MVL) as two feasible solutions to overcome the challenges mentioned above. Carbon nanotube field-effect transistor (CNFET) is one of the emerging technologies that has some unique properties and advantages over MOSFET, such as adjusting the carbon nanotube (CNT) diameters to have the desired threshold voltage and have the same mobility as P-FET and N-FET transistors. In this paper, we present a novel method for designing ternary logic circuits based on CNFETs. Each of our designed logic circuits implements a logic function and its complementary via a control signal. Also, these circuits have a high impedance state, which saves power while the circuits are not in use. Moreover, we designed a two-digit adder/ subtractor and a power-efficient ternary logic arithmetic logic unit (ALU) based on the proposed gates. The proposed ternary circuits are simulated using HSPICE via standard 32 nm CNFET technology. The simulation results indicate the designs’ correct operation under different process, voltage, and temperature (PVT) variations. Also, simulation results show that the two-digit adder/ subtractor using our proposed gates has 12X and 5X lower power consumption and power-delay product (PDP), respectively, compared to previous designs.

Carbon nanotube assisted highly selective separation of organic liquid mixtures

Carbon nanotubes (CNTs) are prominent candidates for the separation of various polar and non-polar liquid mixtures. Numerous studies report the application of CNTs for isolating the binary aqueous liquid mixtures, but very few demonstrate the separation of organic liquid mixtures. Here, we investigate the selective permeation of cosolvents such as ethanol, isopropanol, n-butanol, acetone, and tetrahydrofuran into the CNTs from the binary mixtures of benzene using molecular dynamics simulations. Our findings reveal that extremely small-sized (11,0) CNTs achieve almost 100% cosolvent capture selectivity in all five equimolar binary mixtures. In considerably bigger-sized CNTs such as (20,0), benzene accumulates inside along with the cosolvent, however, forms a well-distinguishable layer close to the interior wall of CNTs analogous to the second layer of a double-walled CNT. The results confirm that the liquid capture and selectivity are governed by the polarity and molecular size of the solvents as well as the CNT diameters.

Optimal electrical conductivity and interfacial polarization induced by loaded nanoparticles on carbon nanotubes for excellent electromagnetic wave absorption performance

Carbon materials have aroused wide attention in the field of electromagnetic wave absorption because of their advantages of good electrical conductivity, low density and adjustable structure. To obtain enhanced performance of electromagnetic wave absorption, the elaborate design of structures for carbon materials has become essential. In this work, the nitrogen-doped and large diameter carbon nanotubes modified with cobalt nanoparticles (M-Co/C-CNTs) composites were successfully prepared by adsorption and carbonization of the gases generated by organic matter pyrolysis. It is concluded that the enhanced conduction loss and polarization loss are attributed to the interfacial electronic engineering induced by the sensibly loaded cobalt nanoparticles and nitrogen doping. As a result, the samples achieved a broad effective absorption bandwidth of 4.56 GHz, and a strong reflection loss of −52.2 dB with a thin thickness of 2.1 mm. This work proposes a tailored way to fabricate the large diameter carbon nanotube composites and enhance electromagnetic wave absorption through novel structural modulation.