Yuefeng Zhu

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.

Alignment of multiwalled carbon nanotubes in bulk epoxy composites via electric field

We demonstrate the alignment of multiwalled carbon nanotubes in bulk epoxy matrices by application of external electric field. The composites were prepared by a macro-layer-by-layer method; UV light was used to rapidly polymerize the epoxy and preserve the aligned nanotube network. The nanotube alignment generated strong anisotropy in the composite’s properties. The composite’s storage modulus was increased by ∼50%, and the electrical conductivity was improved by four orders of magnitude in the direction of nanotube alignment. Compared to pristine nanotubes, amine functionalized nanotubes showed enhanced storage modulus but reduced electrical conductivty. The enhanced modulus for amine functionalized nanotubes is an artifact of their enhanced compatibility with the epoxy, while their reduced conductivity may result from the shortening of the nanotube length during functionalization. In addition to the rapid alignment of nanotubes parallel to the field direction, we also report a tendency for lateral agglo...

Formation of carbon nanotubes in water by the electric-arc technique

A simplified arc discharge apparatus was used for growing carbon nanotubes, required only water (solution) in a glass container with no need for vacuum, water-cooled chamber. Carbon nanotubes with highest purity (20%) and highest yield (7 mg/min) were obtained when using salt solution as the medium. Resonance Raman spectrum of multi-walled carbon nanotubes (MWNTs) presented in as-grown materials was measured and RBM peaks originating from very thin core nanotubes were observed. The results show that high-quality MWNTs can be effectively prepared in water-arcing process.

Heterogeneity in Epoxy Nanocomposites Initiates Crazing: Significant Improvements in Fatigue Resistance and Toughening

Crazing is a failure mode of bulk polymers and occurs under predominant uniaxial tensile load when the bulk eventually forms denser ligaments (or fibrils) while preserving its continuity. [1‐2] The bridging of cracks by such fibrils is an importantmechanismforenergydissipationandtougheningin thermoplastic polymers. However, craze phenomena are not observed [3‐5] in thermosetting polymers such as epoxies due to the high crosslinking density of the epoxy chains, which limits molecular mobility and inhibits craze fibril formation. Such thermosetting epoxies typically display a brittle failure. [6‐7] We demonstrate here that thermosetting epoxies reinforced with amido-amine-functionalized multiwalled carbon nanotubes (A-MWNTs) exhibit crazing. We show order of magnitude reduction in fatigue crack growth rates as a result of the crazing. The fracture toughness and ductility of the brittle epoxy is also significantly enhanced by the crazing. Importantly these enhancements in fatigue resistance and toughness are achieved without any softening of the material. In fact, the Young’s modulus of the nanocomposite is � 30% greater and the average hardness of the nanocomposite is � 45% higher than the baseline (pristine) epoxy. We show that this effect is related to heterogeneous curing of the epoxy, which results in localized pockets of uncrosslinked epoxy that are trapped (or frozen) at the nanotube‐matrix interfaces. Under mechanical loading, these localized regions of high molecular mobility can evolve (or coalesce) to generate conditions that are favorable for crazing. Recently, in a very interesting study, [8] crazing has been reported for a poly(lactide

New Fabrication and Mechanical Properties of Styrene-Butadiene Rubber/Carbon Nanotubes Nanocomposite

A novel technology to prepare styrene-butadiene rubber (SBR)/carbon nanotubes (CNTs) composites was developed by combining a spray drying method and a subsequent mechanical mixing process. The cross-linking degrees of the vulcanized composites increased gradually with the additive CNTs contents. By comparing with those of the pure SBR composites, the mechanical properties such as tensile strength, tear strength and hardness of the composites filled with CNTs at certain contents were dramatically improved almost by 600%, 250% and 70%, respectively. The fabrication of the CNTs filled with SBR composites by combination of the spray drying method and subsequent mechanical mixing process was effective for enhancing the reinforcement effects of CNTs in rubbers. The novel technology can also open a new route for the modification and reinforcement on the nanocomposites with large amount of CNTs.

Influence of AC Electric Field on Macroscopic Network of Carbon Nanotubes in Polystyrene

CVD‐grown multiwall carbon nanotubes are dispersed in styrene monomer. During the polymerization of styrene, an AC electric field is applied to induce the CNTs to align along the electric field line to form a macroscopic nanotube network in polystyrene matrix. The dielectrophoresis force and the electric field redistribution at the CNTs apexes are responsible for alignment of the CNTs as well as bonding between the CNTs. Parameters such as field strength and nanotube weight fraction are varied. The results indicate that the macroscopic CNTs alignment along electric field direction can be observed only if the AC voltage reaches or is higher than certain values, and the higher the electric field frequency is, the more uniformly the CNTs align along electric field direction. In addition, nanotube concentration also affects the alignment of CNTs. According to the results of this study, the CNTs will align into a developed network in polystyrene matrix under a proper combination of three parameters of the electric field voltage, frequency, and the CNTs concentration.

Macroscopic Networks of Carbon Nanotubes in PMMA Matrix Induced by AC Electric Field

It has been proven that electric fields can be used to improve the dispersion and alignment of carbon nanotubes (CNTs) in liquid media. In this article, an AC electric field is applied to blending of suspension of CNTs in methlmethacrylate (MMA) monomer during the polymerization of the MMA monomer initiated by 2 2‐azoisobytyronitrile (AIBN). Polymethlmethacrylate (PMMA) composites with macroscopic CNTs networks are prepared. It is found that morphologies of the CNTs networks are strongly dependent on the electric field parameters and polymerization conditions, such as the voltage, frequency, exerting time of the electric field, shapes of the electrodes for introducing the electric field, and the polymerization temperature. Increased voltage and frequency are found to be beneficial for the improvement of the CNTs dispersion and alignment, while fine CNTs networks are formed with optimized polymerization temperature and exerting time of the electric field.

Influence of Functional Groups on the Dispersion of TiO2 Particles on Carbon Nanotube

In this work, the functional groups on acid-treated and heat-treated carbon nanotubes (CNTs) were investigated by Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. The morphology of the TiO2 particles decorated on the two kinds of CNTs was also studied, respectively. The results indicated that the functional groups could adsorb ions in the aqueous solution due to their electronegativity and benefit for the well dispersion of TiO2.The mechanism of TiO2 well dispersion on CNTs surface was also discussed.

Effects of forced flow on morphology of Al-CuAl2 eutectic solidified with electromagnetic stirring

Acad Sinica, Inst Met Res, State Key Lab Rapidly Solidified Nonequilibrium A, Shenyang 110015, Peoples R China.;Zhang, W (reprint author), Liaoning Univ Engn & Technol, Dept Mat Sci & Engn, 47 Zhonghua Rd, Fuxin 123000, Peoples R China