Large-diameter Carbon Nanotubes Research Articles

A molecular simulation study on the adsorption and separation performance of carbon nanotubes for SO2 in flue gas

To control the emission of SO2 from flue gas into the atmosphere while considering the capture and collection of greenhouse gas CO2, the adsorption behavior of a binary mixture of SO2 and other gases in flue gas (O2/N2/H2O/CO[Formula: see text] in (10, 10) carbon nanotube (CNT) was simulated using grand canonical Monte Carlo (GCMC) simulation. The adsorption and separation performance of SO2 in CNTs with a diameter range of 0.81–1.63 nm for the five-component mixture gas was also analyzed. The findings suggest that the adsorption and separation of SO2 are primarily influenced by CO2 (reduction of adsorption capacity by about 50%, separation coefficient of SO2/CO2 is lowest) with this effect being more pronounced under high pressure. Meanwhile, it was observed that CNTs with larger pipe diameters exhibit higher SO2 adsorption capacity, but relatively lower SO2/CO2 selectivity and lower stability. On the other hand, CNTs with smaller diameters have relatively lower adsorption capacity for SO2, but exhibit good selectivity and stability (under different pressure) for SO2/CO2. Based on the statistical analysis of SO2 adsorption capacity and SO2/CO2 selectivity, it was determined that (6, 6) CNT with a diameter of 0.81[Formula: see text]nm can exhibit excellent SO2 adsorption and separation performance at atmospheric pressure, while appropriate large diameter CNTs should be selected for flue gas treatment under high pressure.

Carbon Nanotube-Encased FeNi Alloy/N-Doped Carbon ORR Catalyst: High Efficiency and Stability

The efficient reduction of oxygen in fuel cell technology using platinum group metals (PGMs) faces challenges like sluggish kinetics, high costs, and poor durability. To overcome these limitations, PGM-free oxygen reduction reaction (ORR) electrocatalysts are sought after. Transition-metal-based electrocatalysts, specifically metal-nitrogen co-doped carbon (M-N/C, M = Fe, Co, etc.), have emerged as promising alternatives due to their abundant pore structures, high surface area, conductivity, and cost-effectiveness. This review explores various non-precious metal electrocatalysts for ORR, highlighting pyrolyzed transition metal nitrogen-containing complexes on carbon (M–Nx/C) as outstanding candidates, with Fe-N/C demonstrating remarkable performance. In this study, we introduce a novel approach to construct Fe-Nx doped large-diameter carbon nanotubes (Fe,Ni-N/C) by pyrolyzing zeolitic imidazolium frameworks-8 (ZIF-8) functionalized with nickel acetate. This approach capitalizes on strong intercalation between acetate and metal ions, promoting Fe-Nx active site formation while generating large-diameter carbon nanotubes. The resulting catalyst facilitates rapid mass transport and maximizes active site exposure, nearing the performance of Pt/C. Our catalyst exhibits an initial potential of 1.03 V, a half-wave potential of 0.88 V, and a limit current of 5.5 mA cm−2. Remarkably, it retains 85.7% of its initial performance in a 36,000 s chronoamperometry test, demonstrating superior durability and methanol toxicity resistance compared to Pt/C. Large-diameter carbon nanotubes offer a potential alternative electrocatalyst, eliminating the need for templates, simplifying mass production for applications like sensors, supercapacitors, and lithium-ion batteries. Furthermore, our Fe,Ni-N/C catalyst outperforms commercial Pt/C, making it a promising choice for ORR applications in fuel cells.

Impact of Cr doping on the performance of Ni/Al2O3 catalyst through methane decomposition into COx-free hydrogen and carbon nanomaterials

The co-production of clean hydrogen and nanostructured carbon materials via methane decomposition is a desirable alternative route for energy savings and environmental considerations. In the current study, Al2O3 supported monometallic 50%Ni and bimetallic 40%Ni-10%Cr catalysts were prepared and evaluated for this reaction. The as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), and N2 physisorption, and Raman spectroscopy. Meanwhile, the spent catalysts were characterized by XDR, SEM, and Raman spectroscopy. According to XRD, TPR, and SEM results, the incorporation of Cr2O3 into the Ni/Al2O3 catalyst improved metal dispersion and reduction behavior compared to the un-promoted catalyst. As a result, the Ni-Cr/Al2O3 catalyst exhibited exceptional activity in terms of hydrogen yield throughout the whole reaction periods. Furthermore, the Cr2O3 inclusion enhanced catalyst stability by preventing the aggregation of active metal sites during the decomposition process. In contrast, the presence of agglomerated NiO particles on the surface of the Al2O3 support was the primary cause of deteriorating the activity of Ni/Al2O3 catalyst over a long reaction period. Both catalysts produced 79 % hydrogen at the start of the reaction (10 min), but by the end of the reaction (180 min), the hydrogen yield was 57 % and 76 % for Ni/Al2O3 and Ni-Cr/Al2O3 catalysts, respectively. In addition, the addition of Cr2O3 raised the accumulated carbon yield from 9.2 to 13.5 gC/gNi for both catalysts, respectively. SEM images showed that thin carbon nanotubes were deposited on the Ni-Cr/Al2O3 catalyst, whereas large-diameter carbon nanotubes were grown on the Ni/Al2O3 catalyst.

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.

Computationally Guided Design of Large-Diameter Carbon Nanotube Bundles for High-Strength Materials

Large-diameter carbon nanotubes (CNTs) synthesized by floating-catalyst chemical vapor deposition (FC-CVD) assemble into bundles and subsequently into aerogel networks from which yarns and sheets are mechanically drawn. The CNT bundles exhibit unique microstructures with collapsed CNT packing, not found in other types of CNT yarns. At the same time, the bundle structure is not homogeneous and the wide variability of CNT cross-sectional shapes reflects the bundling process. Transmission electron microscopy (TEM) images allow detailed quantification of CNT diameters, shapes, and number of walls. Molecular dynamics (MD) simulations of CNT assemblies are subsequently built to match the observed CNT shape characteristics and mass densities. Contrary to an established notion of an applied “buckling” pressure requirement for radial collapse, MD demonstrated that interacting large-diameter CNTs can collapse spontaneously, suggesting that collapse can occur during bundling. Computational explorations of this mechanism yield conditions for large double-walled CNTs (with a mean diameter around 7.8 nm) to assemble into phases with significantly increased packing efficiencies and Young’s moduli approaching 1 TPa. The results may play a guiding role in advancing FC-CVD aerogel synthesis and processing methods to yield yarn and sheets with larger densities and superior mechanical properties.

Hollow “graphene” microtubes using polyacrylonitrile nanofiber template and potential applications of field emission

We report a simple process to connect graphene sheets forming graphene hollow microtubes (GHMs), where the tube diameter can be adjusted in the 100–500 nm range by changing reaction conditions. We discovered that graphene sheets can be seamlessly linked to each other if C atoms are substituted for N atoms at the edges of the sheets during annealing of graphene oxide(G-O)-coated electrospun PAN carbon fibers in ammonia atmosphere. The G-O/carbon hybrid nanofibers framework served as a confining template around which graphene sheets curved to form tubular structures. The GHMs formed by this process are similar to (very) large diameter carbon nanotubes (CNTs) with relatively low curvature whose electron field-emission properties include a low turn-on voltage of 0.18 V/μm (at J = 10 μA/cm2), low threshold field of 0.35 V/μm (at J = 10 mA/cm2), and high field-emission stability. This process to produce GHMs can be scaled up to fabricate GHMs of variable diameter in bulk quantities.

Insights into the π - π interaction driven non-covalent functionalization of carbon nanotubes of various diameters by conjugated fluorene and carbazole copolymers.

We investigate the interaction of polyfluorene and fluorene/carbazole copolymers bearing various functional groups and side chains with small to large diameter-from 1.7 nm to 9 nm-carbon nanotubes (CNTs) in vacuo. We use variable-charge molecular dynamics simulations based on the reactive force field ReaxFF. We show that non-covalent functionalization of nanotubes, driven by π - π interactions, is effective for all the polymers studied, thanks to their conjugated backbone and regardless of the presence of specific functional groups. The geometry at equilibrium of these polymer/CNT hybrids is analyzed in detail at the scale of each fluorene or carbazole unit. The role of both the functional groups and the alkyl chain length is analyzed in detail. Adsorption of the polymers on the nanotube sidewalls is shown to be either complete-with the whole chain physisorbed-or partial-due to intrachain coiling or interchain repulsion-depending on the initial geometry, number of polymers, and nanotube diameter. Energetic arguments supplement the described geometric features. Both energetic and geometric adsorption features are derived here for the first time for large diameter carbon nanotubes (up to 9 nm) and fluorene/carbazole copolymers having up to 30 monomers and bearing different functional groups. The force field ReaxFF and its available parameterization used for the simulations are validated, thanks to a benchmark and review on higher-level quantum calculations-for simple π - π interacting compounds made up of polycyclic aromatic molecules adsorbed on a graphene sheet or bilayer graphene. Although it is shown that the influence of the nanotube chirality on the adsorption pattern and binding strength cannot be discussed with our method, we highlight that an available force field such as ReaxFF and its parameterization can be transferable to simulate new systems without specific re-parameterization, provided that this model is validated against reference methods or data. This methodology proves to be a valuable tool for optimal polymer design for nanotube functionalization at no re-parameterization cost and could be adapted to simulate and assist the design of other types of molecular systems.

Towards the development of nanosprings from confined carbyne chains

Abstract The synthesis of long and stable carbyne chains inside carbon nanotubes (CNTs) have recently drawn renewed attention to this linear one-dimensional carbon allotrope. Carbyne's mechanical properties are predicted to exceed that of CNTs and graphene, making it a very suitable structural component for many nanoscale applications. While carbyne's mechanical behavior under tensile loading is excellent, this carbon chain readily buckles under compressive loading. Taking this effect into account, here we study the compressive behavior of carbyne chains under the bracing effect of confinement in small diameter CNTs such as (5,5) and (6,6) and the formation of helix-shaped springs of carbyne under compressive loading in larger diameter CNTs such as (7,7) and (8,8), using molecular dynamics simulations (MD). The Young's modulus of confined carbyne chains under compression was estimated in average to be 4029 GPa when confined in (5,5) CNT and 3858 GPa when confined in (6,6) CNT, showing slight increases with chain length. We found that for looser confinements carbyne chains can buckle into a coiled helix-shaped spring with properties that depend on confinement radius and chain length. The behavior of these nanosprings follows Hooke's law and may be envisaged for applications in nanodevices .

Mechanical properties of carbon-nanotube-reinforced cementitious materials: database and statistical analysis

This paper aims to provide guidelines for selecting the correct type of carbon nanotube (CNT) to improve the mechanical properties of cementitious materials. Previous researchers have discussed the effect of CNT characteristics on their dispersion quality. However, the effect of these characteristics on the mechanical properties of CNT-reinforced cementitious materials is not fully understood. To clarify this, the study reported in this paper was conducted in two phases. In the first phase, a database was established from the literature to study the influences of three different parameters associated with CNTs (length, diameter and concentration based on the weight percent of cement powder (c-wt%)) on compressive and flexural strengths. The analyses revealed that short and small-diameter CNTs could be beneficial for increasing compressive strength. Conversely, relatively long and large-diameter CNTs were more effective in increasing flexural strength. In general, an average CNT length of 10–20 μm and an average diameter of 20–32·5 nm resulted in the highest overall mechanical performance. The optimal upper limit concentrations for flexural and compressive strengths were found to be 0·15 and 0·20 c-wt%, respectively. In the second phase of this study, the statistical analyses were experimentally verified using the CNT optimum length, two diameters and three levels of concentrations.

Elastic constants of graphene: Comparison of empirical potentials and DFT calculations

The capacity of popular classical interatomic potentials to describe elastic properties of graphene is tested. The Tersoff potential, Brenner reactive bond-order potentials REBO-1990, REBO-2000, REBO-2002 and AIREBO as well as LCBOP, PPBE-G, ReaxFF-CHO and ReaxFF-C2013 are considered. Linear and non-linear elastic response of graphene under uniaxial stretching is investigated by static energy calculations. The Young's modulus, Poisson's ratio and high-order elastic moduli are verified against the reference data available from experimental measurements and ab initio studies. The density functional theory calculations are performed to complement the reference data on the effective Young's modulus and Poisson's ratio at small but finite elongations. It is observed that for all the potentials considered, the elastic energy deviates remarkably from the simple quadratic dependence already at elongations of several percent. Nevertheless, LCBOP provides the results consistent with the reference data and thus realistically describes in-plane deformations of graphene. Reasonable agreement is also observed for the computationally cheap PPBE-G potential. REBO-2000, AIREBO and REBO-2002 give a strongly non-linear elastic response with a wrong sign of the third-order elastic modulus and the corresponding results are very far from the reference data. The ReaxFF potentials drastically overestimate the Poisson's ratio. Furthermore, ReaxFF-C2013 shows a number of numerical artefacts at finite elongations. The bending rigidity of graphene is also obtained by static energy calculations for large-diameter carbon nanotubes. The best agreement with the experimental and ab initio data in this case is achieved using the REBO-2000, REBO-2002 and ReaxFF potentials. Therefore, none of the considered potentials adequately describes both in-plane and out-of-plane deformations of graphene.

Probing the mechanics of aqueous two-phase extraction using large diameter single-walled carbon nanotubes

We have demonstrated that large diameter (1.8 ± 0.4 nm) carbon nanotubes (CNTs) can be separated by means of the aqueous two-phase extraction (ATPE). This rapid and convenient tool has enabled us to isolate fractions of particular CNT diameter distribution. We have shown how a range of parameters can be used to fine tune the characteristics of the isolated material. Interestingly, by varying the pH of the medium, we have suppressed the extraction of low diameter CNTs and only large diameter CNTs were obtained. A number of other factors such as selected surfactant concentration steps, temperature or amount of starting CNT material have been found to have a significant effect on the end result of the CNT differentiation. The findings have provided us with more insight regarding the underlying mechanics of ATPE for processing polydisperse CNT mixtures.

Unraveling the influence of grain boundaries on the mechanical properties of polycrystalline carbon nanotubes

The ability to produce homogeneous defect-free carbon nanotubes (CNTs) represents a major challenge in terms of utility and cost. Specifically, the existence of grain boundaries (GBs) are ubiquitous in large diameter CNTs obtained by various large-scale growth methods and their effects on the mechanical properties of CNTs are not fully explored. Understanding the influence of the grain size and the GB orientation upon the mechanical behavior of CNTs is crucial for their functional and structural applications. The significance and novelty of the current work lies in its ability to establish the mechanical properties and the fracture behavior of CNTs containing grain boundaries of varied size, orientation and structure to an applied uniaxial load using comprehensive molecular dynamics simulations. A specially developed program, using Voronoi tessellation method and Delaunay triangulation, was implemented to generate the atomistic descriptions of the considered polycrystalline CNTs with a variety of GB morphology. Our results reveal that the mechanical performance of CNTs is significantly affected by the orientations of the GBs, diameter and temperature. In terms of the fracture strength, the resulting failure patterns indicate that the polycrystalline CNTs fail in a brittle fashion and that pentagon-heptagon defects along the GBs serve as crack nucleation sites.

Universal Selective Dispersion of Semiconducting Carbon Nanotubes from Commercial Sources Using a Supramolecular Polymer.

Selective extraction of semiconducting carbon nanotubes is a key step in the production of high-performance, solution-processed electronics. Here, we describe the ability of a supramolecular sorting polymer to selectively disperse semiconducting carbon nanotubes from five commercial sources with diameters ranging from 0.7 to 2.2 nm. The sorting purity of the largest-diameter nanotubes (1.4 to 2.2 nm; from Tuball) was confirmed by short channel measurements to be 97.5%. Removing the sorting polymer by acid-induced disassembly increased the transistor mobility by 94 and 24% for medium-diameter and large-diameter carbon nanotubes, respectively. Among the tested single-walled nanotube sources, the highest transistor performance of 61 cm2/V·s and on/off ratio >104 were realized with arc discharge carbon nanotubes with a diameter range from 1.2 to 1.7 nm. The length and quality of nanotubes sorted from different sources is compared using measurements from atomic force microscopy and Raman spectroscopy. The transistor mobility is found to correlate with the G/D ratio extracted from the Raman spectra.

Mechanical properties of single-walled carbon nanotubes: a comprehensive molecular dynamics study

There is inconsistent information across the literature related to tensile and compressive mechanical properties of carbon nanotubes (CNTs). This inconsistency arises from different sources such as the technical difficulties associated with testing and measuring the CNTs mechanical properties in the laboratory or the use of different input parameters (e.g. CNT wall thickness or boundary conditions) in numerical simulations. To address this inconsistency, an extensive series of molecular dynamics (MD) simulations is carried out in this study to investigate the influences of major factors including chirality, size, aspect ratio and slenderness ratio of CNTs on their mechanical properties, which have not been examined as extensively in previous studies. Numerical simulations are repeated for different temperatures of 100 K, 300 K and 500 K to investigate the influence of temperature in different practical applications. The agreements between the findings of this study and those from related previous studies are discussed in detail in the paper. Results on compressive behavior show the emergence of secondary and tertiary buckling modes as the slenderness ratio of the CNT increases, especially at higher temperatures. In addition, chiral CNTs are found to buckle at lower stresses and strains. Results on tensile behavior indicate a nonlinear-elastic response for all CNTs examined. Larger-diameter CNTs are found to fail at lower values of tensile stress and strain.

Selective synthesis of large diameter, highly conductive and high density single-walled carbon nanotubes by a thiophene-assisted chemical vapor deposition method on transparent substrates

Selective synthesis of single-walled carbon nanotubes (SWNTs) with controlled properties is an important research topic for SWNT studies. Here we report a thiophene-assisted chemical vapor deposition (CVD) method to directly grow highly conductive SWNT thin films on substrates, including transparent ones. By adding low concentration thiophene into the carbon feedstock (ethanol), the as-prepared carbon nanotubes demonstrate an obvious up-shift in the diameter distribution while the single-walled structure is still retained. In the proposed mechanism, the change in the diameter is sourced from the increase in the carbon yield induced by the sulfur-containing compound. Such SWNTs are found to possess high conductivity with 95% SWNTs demonstrating on/off ratios lower than 100 in transistors. More importantly, it is further demonstrated that this method can be used to directly synthesize dense SWNT networks on transparent substrates which can be utilized as transparent conductive films (TCFs) with very high transparency. Such TCFs can be applied to fabricate a light modulating window as a proof-of-concept. The present work provides important insights into the growth mechanism of SWNTs and great potential for the preparation of TCFs with high scalability, easy operation and low cost.

Confinement effects on the shape and composition of bimetallic nano-objects in carbon nanotubes.

CoPt and FePt nanostructures have been efficiently confined in carbon nanotubes (CNTs). A marked confinement effect has been evidenced, both on bimetallic nano-object shape and composition. In large diameter CNTs small Co- and Fe-rich nanoparticles are formed, while in small diameter CNTs Pt-rich nanowires are selectively produced.

Biomimetic modification of large diameter carbon nanotubes and the desalination behavior of its reverse osmosis membrane

Based on the fact that wide diameter carbon nanotube (CNTs) has higher water conductance and lower cost than narrow one, this paper built a set of RO membranes with modified 1.35nm diameter CNTs (10,10) and calculated their desalinating properties by molecular dynamics simulations. Inspired by the structure of biological membrane which has perfect ion selectivity, different charged and polar groups (CONH2, NH3+, COO‐, OH) were added to the interior of CNTs. The potential of mean force (PMF), conductance and axial density distributions of water and ions in CNTs were examined under hydrostatic pressure. Results showed that water flux of 1.35nm diameter (10,10) unmodified CNTs was about 3 times of 1.1nm diameter (8,8) CNTs (Chen S. and Corry B., 2009) [1]. Compared to CNTs with functional groups at entrance, water flux of CNTs with modified groups in the interior decrease slightly, while salt rejection greatly improved. With certain number, type and position of functional groups (CONH2, NH3+, COO−), 100% salt rejection could be achieved without affecting water conductance evidently. Water flux of 100% salt rejection modified CNTs was from 146% to 167% of unmodified (8,8) CNT (Chen S. and Corry B., 2009) [1]. Compared to four functional groups (COO−, CONH2, OH) in the interior, one functional group added at entrance and four functional groups added in the interior could obtain both higher desalination and high water conductance.

Carbon nanotube feedback-gate field-effect transistor: suppressing current leakage and increasing on/off ratio.

Field-effect transistors (FETs) based on moderate or large diameter carbon nanotubes (CNTs) usually suffer from ambipolar behavior, large off-state current and small current on/off ratio, which are highly undesirable for digital electronics. To overcome these problems, a feedback-gate (FBG) FET structure is designed and tested. This FBG FET differs from normal top-gate FET by an extra feedback-gate, which is connected directly to the drain electrode of the FET. It is demonstrated that a FBG FET based on a semiconducting CNT with a diameter of 1.5 nm may exhibit low off-state current of about 1 × 10(-13) A, high current on/off ratio of larger than 1 × 10(8), negligible drain-induced off-state leakage current, and good subthreshold swing of 75 mV/DEC even at large source-drain bias and room temperature. The FBG structure is promising for CNT FETs to meet the standard for low-static-power logic electronics applications, and could also be utilized for building FETs using other small band gap semiconductors to suppress leakage current.

Diameter-dependent release of a cisplatin pro-drug from small and large functionalized carbon nanotubes.

The use of platinum-based chemotherapeutic drugs in cancer therapy still suffers from severe disadvantages, such as lack of appropriate selectivity for tumor tissues and insurgence of multi-drug resistance. Moreover, drug efficacy can be attenuated by several mechanisms such as premature drug inactivation, reduced drug uptake inside cells and increased drug efflux once internalized. The use of functionalized carbon nanotubes (CNTs) as chemotherapeutic drug delivery systems is a promising strategy to overcome such limitations due to their ability to enhance cellular internalization of poorly permeable drugs and thus increase the drug bioavailability at the diseased site, compared to the free drug. Furthermore, the possibility to encapsulate agents in the nanotubes' inner cavity can protect the drug from early inactivation and their external functionalizable surface is useful for selective targeting. In this study, a hydrophobic platinum(IV) complex was encapsulated within the inner space of two different diameter functionalized multi-walled CNTs (Pt(IV)@CNTs). The behavior of the complexes, compared to the free drug, was investigated on both HeLa human cancer cells and RAW 264.7 murine macrophages. Both CNT samples efficiently induced cell death in HeLa cancer cells 72 hours after the end of exposure to CNTs. Although the larger diameter CNTs were more cytotoxic on HeLa cells compared to both the free drug and the smaller diameter nanotubes, the latter allowed a prolonged release of the encapsulated drug, thus increasing its anticancer efficacy. In contrast, both Pt(IV)@CNT constructs were poorly cytotoxic on macrophages and induced negligible cell activation and no pro-inflammatory cytokine production. Both CNT samples were efficiently internalized by the two types of cells, as demonstrated by transmission electron microscopy observations and flow cytometry analysis. Finally, the platinum levels found in the cells after Pt(IV)@CNT exposure demonstrate that they can promote drug accumulation inside cells in comparison with treatment with the free complex. To conclude, our study shows that CNTs are promising nanocarriers to improve the accumulation of a chemotherapeutic drug and its slow release inside tumor cells, by tuning the CNT diameter, without inducing a high inflammatory response.

Thermal rectification of heterojunction nanotubes

Using non-equilibrium molecular dynamics method, we have studied the thermal rectification of heterojunction nanotubes (HCNTs). All of these HCNTs, composed of two 4 nm long carbon nanotubes (CNTs), only have a pentagon-heptagon defects pair. Here the positive direction is defined as the direction where the heat flux flows from the large diameter CNTs to the small diameter CNTs. We have found that the thermal rectification depends on the diameter, the chirality and the temperature.#br#Diameter effect: We fix the diameter on one side and changed it on another side, i.e., the left side of the HCNTs is (3, 3) while the right side of the HCNTs is (n, n), in which n changes from 4 to 9. It is found that the thermal rectification efficiency of HCNTs increases with n (also with the diameter difference). If considering the temperature field of (3, 3)-(4, 4) HCNTs, one can find that there exists a region near the HCNT where the temperature changes sharply. This region when the flux is positive is similar to that when the flux is negative. However, if taking into consideration the (3, 3)-(9, 9) HCNTs, we find that the distribution of temperature field shows different behaviors when the directions of the heat flux are different, and the length of this region becomes longer than (3, 3)-(4, 4). It can be explained that the thermal rectification is caused by different temperature distributions in HCNTs.#br#Chirality effect: We keep the chirality unchanged on one side of HCNTs and change the chirality of the other side, namely, the chirality of the left side of HCNTs are (3, 3) and the right side are (9, 9), (11, 7), (13, 4) and (15, 1), all of their diameters are close to 4.1 Å. We can find that the intersection angle between two CNTs decreases when the right side of HCNTs changes from (9, 9) to (15, 1), and the thermal rectification efficiency will be enhanced. It can be explained that the phonon is scattered and absorbed more effectively at the hetero-junction as the intersection angle decreases.#br#Temperature effect: We have constructed a HCNT (3, 3)-(9, 9) and changed its average temperature from 200 to 400 K. Our results show that the thermal rectification efficiency will be weakened with the rise in average temperature because of increasing heat flux in the negative direction.#br#This research may be helpful to the research in nanoscale thermal diodes, thermal logical gates and controlling heat flux.