Cailu Xu

Direct synthesis of long single-walled carbon nanotube strands

In the processes that are used to produce single-walled nanotubes (electric arc, laser ablation, and chemical vapor deposition), the typical lengths of tangled nanotube bundles reach several tens of micrometers. We report that long nanotube strands, up to several centimeters in length, consisting of aligned single-walled nanotubes can be synthesized by the catalytic pyrolysis of n-hexane with an enhanced vertical floating technique. The long strands of nanotubes assemble continuously from arrays of nanotubes, which are intrinsically long.

Adsorption of cadmium(II) from aqueous solution by surface oxidized carbon nanotubes

Carbon nanotubes (CNTs) were oxidized with H2O2, KMnO4, and HNO3. Their physicochemical properties were investigated by BET N-2 adsorption, laser particle examination, Boehms titration, zeta potential measurement and cadmium(II) adsorption. The experimental results suggest that cadmium(II) adsorption capacities for three kinds of oxidized CNTs increase due to the functional groups introduced by oxidation compared with the as-grown CNTs. The cadmium(II) adsorption capacity of the as-grown CNTs is only 1.1 mg g(-1), while it reaches 2.6, 5.1 and 11.0 mg g(-1) for the H2O2, HNO3 and KMnO4 oxidized CNTs, respectively, at the cadmium(II) equilibrium concentration of 4 mg 1(-1). Adsorption of cadmium(II) by CNTs was strongly pH-dependent and the increase of adsorption capacities for HNO3 and KMnO4 oxidized CNTs is more obvious than that of the as-grown and H2O2 oxidized CNTs at lower pH regions. The experiments of CNT dosage effect on the cadmium(II) adsorption show that the adsorption capacity for KMnO4 oxidized CNTs has a sharper increase at the CNT dosage from 0.03 to 0.08 g per 100 ml than the as-grown, H2O2 and HNO3 oxidized CNTs and its removal efficiency almost reaches 100% at CNT dosage of 0.08 g per 100 ml. Analysis revealed that the KMnO4 oxidized CNTs hosted manganese residuals, and these surely contributed to cadmium sorption to a yet-undefined extent

COMPETITIVE ADSORPTION OF PB2+, CU2+ AND CD2+ IONS FROM AQUEOUS SOLUTIONS BY MULTIWALLED CARBON NANOTUBES

Abstract The individual and competitive adsorption capacities of Pb 2+ , Cu 2+ and Cd 2+ by nitric acid treated multiwalled carbon nanotubes (CNTs) were studied. The maximum sorption capacities calculated by applying the Langmuir equation to single ion adsorption isotherms were 97.08 mg/g for Pb 2+ , 24.49 mg/g for Cu 2+ and 10.86 mg/g for Cd 2+ at an equilibrium concentration of 10 mg/l. The competitive adsorption studies showed that the affinity order of three metal ions adsorbed by CNTs is Pb 2+ >Cu 2+ >Cd 2+ . The Langmuir adsorption model can represent experimental data of Pb 2+ and Cu 2+ well, but does not provide a good fit for Cd 2+ adsorption data. The effects of solution pH, ionic strength and CNT dosage on the competitive adsorption of Pb 2+ , Cu 2+ and Cd 2+ ions were investigated. The comparison of CNTs with other adsorbents suggests that CNTs have great potential applications in environmental protection regardless of their higher cost at present.

Study on poly(methyl methacrylate)/carbon nanotube composites

Carbon nanotubes (CNTs) can be used to compound poly (methyl methacrylate)/carbon nanotube (PMMA/CNT) composites by an in situ process. The experimental results show that CNTs can be initiated by AIBN to open their π-bonds, which imply that CNTs may participate in PMMA polymerization and form a strong combining interface between the CNTs and the PMMA matrix. Through the use of an improved in situ process, the mechanical properties and the heat deflection temperatures of composites rise with the increase of CNTs. The dispersion ratio of CNTs in the PMMA matrix is proportional to the reaction time of polymerizing MMA before CNTs are added into the PMMA mixture.

Lead adsorption on carbon nanotubes

Carbon nanotubes (CTNs) show exceptional adsorption capability and high adsorption efficiency for lead removal from water. The adsorption is significantly influenced by the pH value of the solution and the nanotube surface status, which can be controlled by their treatment processing. The adsorption isotherms are well described by both Langmuir and Freundlich models, Our results suggest that CNTs can be good Pb2+ adsorbers and have great potential applications in environmental protection

Adsorption of fluoride from water by amorphous alumina supported on carbon nanotubes

A new candidate for fluoride adsorption from water, amorphous Al2O3 supported on carbon nanotubes (Al2O3/CNTs), is reported in this Letter. The adsorption isotherms show that the best fluoride adsorption of Al2O3/CNTs occurs at a pH range of 5.0-9.0. The adsorption capacity for Al2O3/CNTs is about 13.5 times higher than that of AC-300 carbon, 4 times higher than that of gamma-Al2O3 at equilibrium fluoride concentration of 12 mg/l. The broad range of the pH values and high adsorption capacity of Al2O3/CNTs make it very suitable for potential applications in fluoride removal from water

Adsorption of fluoride from water by aligned carbon nanotubes

Aligned carbon nanotubes (ACNTs), a new type of carbon material, were prepared by catalytic decomposition of xylene using ferrocene as catalyst. The kinetics experiment of ACNTs shows that fluoride adsorption rate is fast in the first 60 min and the adsorption capacity reaches 3.0 mg/g rapidly, then it decreases and adsorption achieves equilibrium gradually in about 180 min. The fluoride adsorption of ACNTs depends slightly on the solution pH value. The highest adsorption capacity of ACNTs occurs at pH 7 and reaches 4.5 mg/g at equilibrium fluoride concentration of 15 mg/l. The experimental results indicate that ACNTs are promising candidate materials for fluoride removal

Fabrication of aluminum-carbon nanotube composites and their electrical properties

Abstract Aluminum–carbon nanotube (CNT) composites were fabricated by hot-pressing the respective powders. The microstructural characteristics and the distribution of carbon nanotubes in the aluminum matrix were investigated. The electrical resistivities of the composites were measured from room temperature down to 4.2 K. The electrical resistivity at room temperature increases slightly with increasing volume fraction of the carbon nanotubes in the aluminum. From room temperature to ∼80 K all the composites exhibit the typical metallic decrease of the electrical resistivity upon lowering the temperature. At about 80 K their resistivities abruptly drop by more than 90%; at lower temperatures the resistivity does not show any fluctuation.

Study of electrochemical capacitors utilizing carbon nanotube electrodes

Several types of block-form porous tablets of carbon nanotubes are fabricated to use as polarizable electrodes in electrochemical capacitors (ECs). These tablets are prepared by using moulded mixtures comprising carbon nanotubes and phenolic resin powders. Comparison of the effect of different processing on the performance of the capacitors is specifically investigated. Using these polarizable electrodes, ECs with a specific capacitance of about 15 to 25 F cm−3 are obtained with 38 wt.% H2SO4 as the electrolyte.

Rapid growth of well-aligned carbon nanotube arrays

Abstract Vertically aligned carbon nanotube (CNT) arrays with high density were synthesized on quartz substrates in large areas ( 100×40 mm 2 ) by catalytic decomposition of a ferrocene–xylene mixture at 850 °C in a quartz tube reactor. The nanotubes grow at a high growth rate of ∼50 μm /min, and reach 1.5 mm in length in 30 min. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations reveal that the nanotubes are high-purity multi-wall CNTs with well-ordered graphene sheets, and about 30–60 nm in diameter. This provides a simple way to synthesize well-aligned CNTs in large areas. A continuous rapid growth model is suggested for the CNTs in high growth rate under our experimental conditions.