Outer Surface Of Carbon Nanotubes Research Articles

Fabrication of highly catalytic active α-Fe2O3-carbon nanotube composites for thermal decomposition of ammonium perchlorate by light and temperature control strategy

For alleviating agglomeration of α-Fe2O3 nanoparticles and improving their catalytic activities as burning rate catalysts (BRCs) in solid propellants, Fe(CO)5 as the iron source was encapsulated into the inner space and/or loaded onto the outer surface of carbon nanotubes (CNTs) via ultrasonication with visible light and temperature control strategy. The Fe(CO)5-CNTs composites were subsequently transformed into α-Fe2O3-CNTs nanocomposites by Fe(CO)5 pyrolysis. The as-synthesized α-Fe2O3-CNTs composites were utterly characterized by HRTEM, SEM, BET, XPS, FTIR, Raman, and XRD. The catalytic combustion results show that the nanocomposites are highly active in boosting the thermal degradation of ammonium perchlorate (AP). α-Fe2O3&CNTs(S1) nanocomposite, the most excellent one, shifts left the peak temperature of the high-temperature decomposition (HTD) region of AP by 103.7 °C and increases its release heat by 190 %. Moreover, a carbon nanotube with a smaller outer diameter and higher iron content is conducive to enhancing AP thermal deterioration. A possible mechanism of AP decomposition with the addition of the nanocomposites was investigated by thermal decomposition dynamics, in-situ solid-state FTIR, and gas phase FTIR-MS technique. The mechanistic research implies that the produced NH3 and HClO4 gases can be absorbed on the nanocomposite surfaces to form more superoxide anions (O2−) during AP decomposition, accelerating the generation of NO from N2O and facilitating AP disintegration at a lower temperature. A tentative AP decomposition mechanism in the presence of the α-Fe2O3-CNTs nanocomposites is therefore proposed.

Tailoring the separation performance of a carbon nanotube-based mixed matrix membrane decorated with metal–organic framework

Synthesis of mixed matrix membranes (MMM) using carbon nanotubes (CNTs) has shown great prospects for achieving excellent selective separation because of its special structure. Nevertheless, the preparation of highly selective MMM faces challenges, which is attributed to the obstacles encountered by CNTs dispersion in polymer matrix and elimination of interface defects. A novel CNT-based composite decorated with metal–organic framework (MOF) was synthesized and applied to the preparation of MMM. MOF was post modified, and then carboxyl groups were inserted on the outer surface of CNTs. The synthetic MMM (Cu-MOF-en@MWCNT) not only has selective adsorption on dyes, but also has selective photodegradation on dyes. The method of using CNTs to wrap the outside of MOF has great potential in dye separation. The performance of MMM was further improved by decorating MOF on the filler to improve the selectivity to the designated dye.

Singlet oxygen mediated photocatalytic Antimonite decontamination in water using nanoconfined TiO2

The development of advanced strategies to decontaminate water polluted with emerging contaminants (e.g., antimony (Sb)) is considered a priority. Herein, we synthesized and evaluated nanoscale photocatalysts with TiO2 confined within and on the outer surface of carbon nanotubes (i.e., TiO2-in/out-CNT) for the simultaneous detoxification of toxic Sb(III) and adsorption of less toxic Sb(V). Under simulated solar irradiation, the TiO2-in-CNT system exhibited a Sb(III) removal efficiency of 100% over 40 min with 1O2 as the dominant reactive species. In contrast, HO• was identified as the species contributed to the Sb(III) conversion in the unconfined TiO2-out-CNT system. In addition, the TiO2-in-CNT system exhibited faster Sb(III) removal kinetics (4 times) compared with that of TiO2-out-CNT. The system efficacy was tolerant of a wide pH range (3.2–9.5), and showed good selectivity and performance in the presence of several coexisting anions (e.g., NO3–, Cl−, HCO3–) and different water matrices. The outcomes of this study are dedicated to providing an effective design for the decontamination of highly toxic heavy metal ions in water by integrating a state-of-the-art nanoconfinement effect and photocatalysis.

Two-electron oxygen reduction on fullerene C60-carbon nanotubes covalent hybrid as a metal-free electrocatalyst

Nanocarbon materials are considered to be active for electrochemical oxygen reduction reaction (ORR) for hydrogen peroxide (H2O2) synthesis. In the present work, a new type of fullerene 60 (C60)-carbon nanotubes (CNTs) hybrid with covalently attached C60 onto outer surface of CNTs was synthesized. The structure of C60-CNT hybrid was confirmed by physical and chemical characterizations and its conformation is proposed featuring the covalent incorporation of CNTs and C60 derivative. C60-CNT hybrid showed high efficiencies on electro-generating H2O2, owing to huge surface area and intermolecular electron-transfer in the hybrid structure. A high H2O2 production rate of 4834.57 mg L−1 h−1 (426.58 mmol L−1) was achieved at − 0.2 V vs saturated calomel electrode (SCE).

Encapsulated metal catalyst for selective hydrogenation of quinoline under atmospheric conditions

Simultaneous high activity and selectivity are highly desired in heterogeneous catalysis of various important organic intermediate compounds. In the present investigation, we realized ultra-high selective hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline (py-THQ) under atmospheric conditions by encapsulating 7 ± 2 nm Pd nanoparticles (PdNPs) inside the 10 ± 2 nm nanochannels of carbon nanotubes (CNTs). For the prepared Pd@CNTs catalysts, the encapsulated PdNPs was found to selectively absorb the nitrogen heterocyclic ring of quinoline, which led to the increase of average length of CC bonds in the heterocyclic ring, further resulting in selective activation of the heterocyclic ring and ~100% selectivity to py-THQ. The DFT calculations confirmed the selective hydrogenation feature of Pd@CNTs. In contrast, the Pd-CNTs catalyst with PdNPs supported on the outer surface of CNTs is incapable of selectively activate the heterocyclic ring of quinoline, showing poor selectivity and catalytic activity. The Pd@CNTs catalysts also exhibited universal ultra-high selectivity to other quinoline derivatives (7-Methylquinoline, quinaldine and quinoxaline) and oxygen heterocyclic compounds (2,3-benzofuran). Due to the confined effect, the Pd@CNTs catalysts presented superior cycling stability to the Pd-CNTs and activated carbon (AC) impregnated with Pd (Pd-AC) catalysts. The Pd@CNTs catalyst was also found to highly stable in air storage for months, without loss of activity.

Carbon Nanotubes Enhance the Radiation Resistance of bcc Iron Revealed by Atomistic Study.

With extra space, a carbon nanotube (CNT) could serve as an absorber of point defects, including helium interstitials, and outgas the accumulate helium via “nano-chimneys”. The radiation resistance of CNT/Fe has still not been fully understood. Herein, we investigated the influence of CNTs on low-energy helium irradiation resistance in CNT/Fe composites by molecular dynamic simulations. CNTs reduced the small and medium He clusters in the Fe matrix. When the incident energy of the He atoms was 300 eV, the He atoms aggregated at the outer surface of CNTs. CNTs postponed the formation of He bubbles. When the irradiation energy was higher than 600 eV, He atoms could penetrate the walls of CNTs and form clusters inside the single-walled CNTs or the space in double-walled CNTs—the latter presented better performance. The reduction of Frenkel pair point defects suggested the enhancement of radiation resistance by the presentation of CNTs. Our results might be useful for the material design of advanced steels for radiation resistance.

Comparison of SnO2-carbon nanotubes composite and the SnO2-carbon black mixture as an anode for Li-ion batteries

This article reports a comparative study on the electrochemical properties between SnO2-carbon nanotubes (CNTs) composite and SnO2-carbon black (CB) mixture. The SnO2-CNTs composite was directly synthesized by a sol-gel method with purified multi-walled carbon nanotubes and tin chloride. The SnO2-CB mixture was obtained by mixing carbon black with the previously prepared SnO2. XRD profiles of SnO2-CNTs and the obtained SnO2 have shown the pure tin dioxide phase for the composite and the mixture. TEM images confirmed that SnO2 nanoparticles with average particle size of 3-20 nm are deposited on the outer surface of carbon nanotubes, while the SnO2 obtained for the mixture indicate larger average particle size than that of in the SnO2-CNTs composite. These samples were used as anode materials for the lithium ion battery. The SnO2-CNTs composite showed an initial charge capacity of 810 mAg−1 which slightly reduced to 500 mAg−1 after 100 cycles. The SnO2-CB mixture had a smaller capacity, i.e., an initial charge capacity of 350 mAg−1, and decreased to 230 mAg−1 after 100 cycles. A reversible capacity at 0.2 Ag−1 was recovered for both samples after the cycling at different current densities, which implies excellent rate performance of the materials.

Preparation of palladized carbon nanotubes encapsulated iron composites: highly efficient dechlorination for trichloroethylene and low corrosion of nanoiron.

A method developed based on the capillary effect and capillary condensation theory was used to synthesize an innovative Fe/C/Pd composite in this study. This composite (Fe@CNTs@Pd) consists of carbon nanotubes (CNTs) with nanoscale zerovalent iron (NZVI) on the inner surface and palladium nanoparticles supported on the outer surface of CNTs. This structure successfully addresses the problems of high iron corrosion rate and lower utilization rate of hydrogen in the application of bimetal nanoparticles for trichloroethylene (TCE) removal. TCE degradation experiments and electrochemical tests were conducted to investigate the material properties and reaction mechanisms of the composite. It is found that the prepared composite material contribute a high level of TCE dechlorination rate and substantially reduced hydrogen production during iron corrosion in water compared with the conventional CNTs-supported bimetal materials (Fe/Pd@CNTs). Hydrogen spillover effect helps the reactivity of Fe@CNTs@Pd for TCE degradation and suppressed the galvanic cell effect, which results in a stronger resistance to corrosion. Although the Kobs of Fe@CNTs@Pd was 16.87% lower than that of Fe/Pd@CNTs, the hydrogen production rate of Fe@CNTs@Pd was 10 times slower than that of Fe/Pd@CNTs. Therefore, Fe@CNTs@Pd shows a significant reduction in the corrosion rate at a cost of slightly slower degradation of TCE. In sum, the prepared composites demonstrate important characteristics, including alleviating NZVI agglomeration, maintaining high TCE removal efficiency and reducing the corrosion of NZVI.

Confining SnS2 Ultrathin Nanosheets in Hollow Carbon Nanostructures for Efficient Capacitive Sodium Storage

Summary Tin disulfide (SnS 2 ) is a promising anode material for sodium-ion batteries because of its high specific capacity. However, the low conductivity and large volume change during reaction with Na + ions greatly limit its practical application. Herein, a multistep templating method has been exploited for the rational design and synthesis of SnS 2 nanosheets confined in carbon nanotubes (SnS 2 @CNTs). To demonstrate the universality of this method, SnS 2 nanosheets confined in carbon nanoboxes (SnS 2 @CNBs) and hollow carbon nanospheres (SnS 2 @CNSs) have also been synthesized by simply changing the template in the reaction system. Due to their unique structural merits, the SnS 2 @CNTs, SnS 2 @CNBs, and SnS 2 @CNSs show improved sodium storage performance in terms of high specific capacity, good cycling stability, and superior rate capability.

Oleuropein interactions with inner and outer surface of different types of carbon nanotubes: Insights from molecular dynamic simulation

Due to the special properties of carbon nanotubes (CNT) including size, huge surface area and high cellular uptake, they are important in drug delivery and separation. On the other hand, oleuropein (oleu), according to the pharmaceutical properties such as anti-cancer, anti-inflammatory, anti-microbial and anti-hypertensive has attracted many attentions. In this study, we investigated adsorption of oleuropein at two positions inside and outside of the different types of single-walled carbon nanotubes including the chiral, zigzag and armchair with different diameter. According to radial distribution functions graph and the amount of Lennard-Jones energy between oleuropein and nanotubes, oleuropein is adsorbed on all nanotubes. Interaction between CNT and oleu is stronger on the inner surface rather than the outer surface. The strongest interaction belongs to inner surface with a diameter of 1.3Å. Chirality of nanotubes has no effect on interaction energy between CNT and oleu. However, interaction between CNT and oleu on the inner surface becomes weaker with increasing the diameter of CNT but this interaction on the outer surface of CNT does not change significantly. The strong interaction of the oleuropein adsorbed on the outer surface of the nanotubes with solvent leads to improve the solubility of the nanotubes.

The Structure of Carbon Nanotube Exohedral Complexes with Lithium in a Wide Range of Concentrations

The sorption properties of the outer surface of carbon nanotubes with respect to lithium are studied in connection with the search for new materials for lithium battery electrodes. The regularities of the atom ensemble structure with the increased adsorbate concentration have been investigated using ab initio method of computer modeling. Carbon nanotubes (7.7) fragment containing 112 carbon and up to 50 lithium atoms was studied. It is shown that the process of the sequential filling of the nanotube surface by adsorbate consists of two stages. The first of them (the concentration of Li is less than 8 – 9 at. %): distribution of adsorbate atoms on the surface of the tube is determined by the Coulomb repulsion of lithium ions. Chemical interaction between lithium atoms becomes significant at concentration 9 at. %. It leads to the formation of structures such as trimers and tetramers of lithium.

Wettability on Inner and Outer Surface of Single Carbon Nanotubes.

The surface wettability of a liquid on the inner and outer surface of single carbon nanotubes (CNTs) was experimentally investigated. Although these contact angles on both surfaces were previously studied separately, the available data are of limited help to elucidate the effect of curvature orientation (concave or convex) on wettability due to the difference in surface structure. Here, we report on the three-phase contact region and wettability on the outer surface of CNT during the dipping and withdrawing experiment of CNT into an ionic liquid. Furthermore, the wettability on the inner surface was measured using a liquid within the same CNT. Our results show that the contact angle on the outer surface of the CNT is larger than that on the flat surface and that on the inner surface is smaller than that on the flat one. These findings suggest that the surface curvature orientation has a noticeable effect on the contact angle at the nanoscale because both inner and outer surfaces expose the same graphite wall structure and the contact line tension will be negligible in this situation. The presented results are rationalized using the free energy balance of liquid on curved surfaces.

Large-scale synthesis of cobalt sulfide/carbon nanotube hybrid and its excellent electrochemical capacitance performance

In this paper, cobalt sulfide (CoS) in-situ hybridized with carbon nanotube (CNT) is achieved through a hydrothermal process with the presence of polyvinylpyrrolidone (PVP). The morphology and structure of CoS/CNT hybrids are investigated by using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that the product consists of CoS nanoparticles with the diameter of 30–50nm that well dispersed on the outer surface of CNTs. Furthermore, CoS/CNT hybrid has shown excellent electrochemical capacitance and exhibited favorable electrochemical cycling stability with 93.4% capacitance retention over 1000 cycles. Therefore, the CoS/CNT hybrids can be considered as promising electrode materials for supercapacitor.

A theoretical study on the interaction of amphetamine and single-walled carbon nanotubes

The adsorption of 1-phenyl-2-aminopropane (amphetamine) on the (4,4), (5,5), (6,6), and (7,7) single-walled carbon nanotubes (SWCNTs) has been theoretically investigated. The molecule has been located in different modes including parallel, perpendicular, and oblique on the outer surface of carbon nanotubes. The physisorption of amphetamine onto SWCNT sidewall is thermodynamically favored; as a consequence, it modulates the electronic properties of pristine nanotube in the vicinity of Fermi region. The adsorption energies for the parallel and oblique modes found in the range of −1.13 to −1.88 and −1.27 to −2.01kcal/mol, respectively. Projected density of states (PDOS) and frontier orbital analysis in the vicinity of Fermi level region suggest the electronic states to be contributed from SWCNT rather than amphetamine molecule.

Carbon nanotubes modified with ZnO nanoparticles: High-efficiency electromagnetic wave absorption at high-temperatures

Carbon nanotube–ZnO composite powders, which act as high-temperature electromagnetic wave absorbents, are prepared by homogeneous precipitation. Carbon nanotube–ZnO/glass composites are fabricated by pressureless sintering. ZnO nanoparticles are assembled on the surface of carbon nanotubes, which produces heterostructure and enhances polarization at heterogeneous interface. Owing to the consumption of an amorphous carbon layer on the outer surface of carbon nanotubes and the generation of oxygen vacancies in ZnO during sintering, a higher concentration of charge carriers is produced in ZnO, which causes more relaxation polarization and dielectric loss in electromagnetic field. Owing to the shortened relaxation time, and the increase of relaxation polarization, permittivity and dielectric loss increases with the increase in testing temperature. Reflection coefficient of the obtained composite reaches −70dB. The special integration of multiwalled carbon nanotubes modified with some metal oxide semiconductor nanoparticles provides an effective approach to design high-temperature electromagnetic absorbing materials.

O2 activation on the outer surface of carbon nanotubes modified by encapsulated iron clusters

Using first-principles calculations, the structural, magnetic, and electronic properties of the (6, 6) single-walled carbon nanotubes (SWCNT) with the confined small Fe cluster are systematically studied. We find that Fe–C interactions can induce the transfer of the electrons from the confined Fe to the carbon surface of the SWCNT considerably, and consequently the reduction of the local work function of the region in contact with the Fe. The charging of the carbon surface and the reduction of the work function make the adsorption of the O2 molecule much more energetically favorable on the outer surface of the SWCNT. Furthermore, the energy barrier of the rate-determining step, i.e., the approaching of the O2 towards the modified carbon surface, for the O2 dissociation is less than 0.8eV, indicating that the process can proceed readily at room temperature.

Catalytic Hydroxyl Radical Generation by CuO Confined in Multi-Walled Carbon Nanotubes

A DFT study of the catalytic properties of CuO/CNT and CuO@CNT complexes for the heterogeneous catalytic ozonation has been performed. We illustrated the atomistic details of CuO/CNT and CuO@CNT with a quantitative and qualitative discussion within such an electronic structure characteristics. Ozone was catalytically decomposed into an atomic oxygen species and oxygen molecule on both the surface inner and outer CuO@CNT complex, while ozone can only decompose over CuO on the outer surface of CuO/CNT, with partial electrons transfer from CuO/CNT and CuO@CNT complexes to the adsorbate. Then the atomic oxygen reacted with the water molecule to form two hydroxyl groups on the surface, promoting the reaction chain for the generation of•OH which, in turn, lead to an increase in the catalytic ozonation efficiency. Results show synergetic confinement effect of metal oxide nanoparticles inside CNT could also lead to an acceleration of ozone decomposition and the generation of •OH on the inner and outer surface of carbon-nanotube containing catalytic particles.

High performance of carbon nanotubes confining gold nanoparticles for selective hydrogenation of 1,3-butadiene and cinnamaldehyde

This work reports a striking enhancement of catalytic performance of gold nanoparticles (NPs) with average diameter of 3.2nm partially (ca. 32–40%) confined in the cavity of carbon nanotubes (CNTs) for the gas-phase hydrogenation of 1,3-butadiene (BD), as well as liquid-phase hydrogenation of cinnamaldehyde (CAL). The reaction rates and turnover frequencies of the CNTs confining gold NPs exceed those with a similar size deposited on the outer surface of CNTs and activated carbon by more than one to two orders of magnitude in both two reactions. The selectivity to monobutenes and hydrocinnamaldehyde is up to 100% and 91% at 100% and 95% conversions of BD and CAL, respectively. Au/CNTs catalysts were characterized in depth to establish their structure–property relationship. The peculiar interaction of confined gold NPs with the surface of CNTs facilitates the dissociation/activation of H2, which is the rate-determining step for hydrogenation reactions demonstrated by kinetic studies.

Effects of Catalytic Site Position on the Performance and Lifetime of Carbon Nanotubes Supported Cobalt Fischer-Tropsch Synthesis Nano Catalyst

The effects of confinement in carbon nanotubes on the performance and lifetime of carbon nanotubes (CNT) supported cobalt Fischer–Tropsch (FT) catalysts are reported. A method was developed to control the position of the catalytic sites on either inner or outer surface of carbon nanotubes. TEM analyses revealed that about 80-85% of cobalt oxide particles can be controlled to be positioned at inner or outer surface of the nanotubes. Deposition of cobalt oxide inside the nanotube pores decreased the average size of the cobalt oxide particles from 16.6 to 7.2 nm and shifted the reduction peak temperature of cobalt oxide species to lower temperatures (from 330 to 318oC, and 446 to 428oC) and improved the reducibility of the catalyst by 7%. The catalysts were assessed in terms of their activity, selectivity and lifetime in a fixed-bed micro reactor. The catalyst with catalytic sites inside the pores showed 30.5% higher initial activity than the catalyst with catalytic sites outside the pores. Also, the catalyst with cobalt particles inside the pores exhibited higher selectivity to heavier hydrocarbons (79.5% vs. 76.2% C5 + selectivity). Deposition of cobalt particles on interior surface of the nanotubes resulted in a more stable catalyst, while its counterpart experienced 50.4% deactivation within a period of 20 days due to catalytic sites sintering. It is concluded that encapsulation of the catalytic metal nanoparticles inside the nanotubes prevents the catalytic site agglomeration. Keywords: Fischer-Tropsch, cobalt nano particles, Carbon nanotubes, Confinement, Activity, Selectivity, Deactivation

Synthesis of polyfluorenes bearing lateral pyreneterminated alkyl chains for dispersion of single-walled carbon nanotubes

Two kinds of polyfluorenes bearing two lateral pyrene terminated alkyl chains and two alkyl chains per repeating unit were synthesized by Suzuki polycondensation and used to disperse single-walled carbon nanotubes (SWCNT) in organic solvents. Stable polymer-SWCNT complex can be formed via the multivalent π-π stacking interaction of the lateral pyrene functional groups and the polyfluorene backbone with the outer surface of carbon nanotubes; meanwhile the lateral alkyl chains can impart good solubility to the complex. As expected, polyfluorenes bearing lateral pyrene functional groups and octyl chains exhibited much higher carbon nanotube solubility in common organic solvents than the corresponding polyfluorenes bearing only octyl chains. Photophysical studies indicated that the formation of polymer-SWCNT complex can effectively quench the fluorescence of polyfluorenes.