Fu Liu

Preparation of short carbon nanotubes by mechanical ball milling and their hydrogen adsorption behavior

Abstract Short multi-wall carbon nanotubes (MWNTs) with open tips were obtained by mechanical ball milling. The microstructure characteristics of MWNTs before and after ball milling were checked by transmission electron microscopy (TEM). The effect of ball milling on the hydrogen adsorption behavior of the MWNTs was studied. The hydrogen adsorption experiments were carried out at room temperature under a pressure of 8–9 MPa. The hydrogen adsorption capacity of carbon nanotubes milled for 10 h was 0.66 wt%, which was about six times that of MWNTs without milling. For the carbon nanotubes milled with MgO for 1 h, a hydrogen adsorption capacity of 0.69 wt% was obtained. The enhancement of hydrogen adsorption might result from the increase of defects and surface area of the MWNTs caused by ball milling.

Continuous Ni-layer on multiwall carbon nanotubes by an electroless plating method

Abstract Electroless plating has been successfully applied for nickel coatings on multiwall carbon nanotubes (MWNTs) grown by chemical vapor deposition (CVD). The samples before and after coating were checked using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that the coating process can be divided into two steps: nickel was first deposited as nanoparticles at the activated sites on the pre-treated surface of carbon nanotubes in the initial stage; it was then thickened later, as the reaction time increased and eventually formed a continuous layer. Finally a uniform Ni-layer on individual tubes with thickness of 20–40 nm can be obtained after coating. A simple model for the mechanism of the coating is also discussed.

Purification of CVD synthesized single-wall carbon nanotubes by different acid oxidation treatments

Different acid oxidation methods were systematically carried out to purify the SWNTs synthesized by CVD. The results show that the best purification process can produce over 98% pure single-wall carbon nanotubes within 2 h. In this process, it is found by Raman characterization that the amount of nanotubes with small diameters do not diminish within 3 h.

The effect of pretreatments on hydrogen adsorption of multi-walled carbon nanotubes

Abstract Hydrogen adsorption of multi-walled carbon nanotubes (MWNTs) was investigated under moderate pressure (12xa0MPa) at room temperature. The effects of annealing and doping on the hydrogen adsorption of carbon nanotubes have been discussed. It is showed that both heat-treatment and doping play an important role in the hydrogen adsorption of carbon nanotubes. Even when doped with the same element, the hydrogen uptake property was greatly different when the concentration of the doping solution changed. An optimal result (3.2xa0wt.%) was achieved for carbon nanotubes annealed in N 2 at 500xa0°C and soaked in 1.0xa0M KNO 3 solution.

Synthesis of carbon nanotubes filled with Fe3C nanowires by CVD with titanate modified palygorskite as catalyst

Multi-walled carbon nanotubes (MWCNTs) have been successfully synthesized with titanate-modified palygorskite as catalyst and acetylene as carbon source by chemical vapor deposition (CVD) at high temperature. Transmission electron microscopy (TEM) studies showed that there were a lot of carbon nanotubes partially filled with elongated foreign material in their inner cavities. X-ray energy dispersive spectrum (EDS) analyses and selected area electron diffraction (SAED) investigations on the encapsulated material revealed that it was single crystalline iron carbide (Fe3C) derived from ferric precursors in the mineral. The yield of carbon nanotubes was influenced by preparation temperature based on thermal gravimetric analyses (TGA). The relative quantity of Fe3C nanowires was influenced by the temperature and the local structure of nanotubes upon TEM observations. A growth mechanism is also proposed in the paper.

Free-standing α-Co(OH)2/graphene oxide thin films fabricated through delamination and reassembling of acetate anions intercalated α-Co(OH)2 and graphene oxide in water.

A novel hydrothermal process is demonstrated to prepare acetate anions intercalated α-Co(OH)2 that can be delaminated in water without any additional anion exchange processes. Positively charged Co(OH)2 nanosheets with lateral size of hundreds of nanometers and thickness less than 2 nm can be obtained by dispersing the as-obtained α-Co(OH)2 into water followed by sonication. The exfoliated Co(OH)2 nanosheets can be restacked into its original structure with different interlayer d-spacings. A flexible free-standing film with stacking Co(OH)2 nanosheets and graphene oxide (GO) layers can be obtained through flocculation of the Co(OH)2 nanosheets with GO nanosheets suspensions followed by a vacuum filtration, but the content of Co(OH)2 has to be kept under a low value so as to obtain films with flexible nature. Electrochemical tests show that this kind of film is not suitable to be used as electrode material for supercapacitor and lithium ion battery, because the content of active material is not high and the compacted junction between opposite charged nanosheets will prevent the electrolyte from diffusing into the interlayer space.

Cocatalyzing Pt/PtO Phase-Junction Nanodots on Hierarchically Porous TiO2 for Highly Enhanced Photocatalytic Hydrogen Production

Phase-junctions between a cocatalyst and its semiconductor host are quite effective to enhance the photocatalytic activity and are widely studied, while reports on the phase-juncted cocatalyst are still rare. In this work, we report the deposition of the Pt/PtO phase-juncted nanodots as cocatalyst via NaOH modification of an interconnected meso-macroporous TiO2 network with high surface area and inner-particle mesopores to enhance the performance of photocatalytic H2 production. Our results show that NaOH modification can largely influence Pt/PtO phase-juncted nanodot formation and dispersity. Compared to the TiO2 nanoparticles, the hierarchically meso-macroporous TiO2 network containing 0.18 wt % Pt/PtO phase-juncted cocatalyst demonstrates a highest photocatalytic H2 rate of 13 mmol g-1 h-1 under simulated solar light, and possesses a stable cycling activity without obvious decrease after five cycles. Such high H2 production performance can be attributed to both the phase-juncted Pt/PtO providing more active sites while PtO suppresses the undesirable hydrogen back reaction, and the special hierarchically porous TiO2 network with inner-particle mesopores presenting short diffusion path lengths for photogenerated electrons and enhanced light harvesting efficiency. This work suggests that Pt/PtO phase-juncted cocatalyst on hierarchically porous TiO2 nanostructures is a promising strategy for advanced photocatalytic H2 production.

Preparation of CNTs-supported Fe3O4 and Fe3C Nano-particles and the Investigation on their Magnetic Properties

Magnetite (Fe3O4) nanoparticles uniformly loaded on multi-walled carbon nanotubes (MWCNTs) were synthesized by a wet chemistry method, and then carbon coated Fe3C nanoparticles supported by MWCNTs were prepared by heat-treatments subsequently in nitrogen at 600 degC and in acetylene atmosphere at 500 degC. The as-prepared nanoparticles were all single crystals with a size distribution ranging from 10 to 60nm upon TEM and XRD measurements. The magnetic properties of these two kinds of nanoparticles were measured using vibrating sample magnetometer (VSM) at room temperature. The results show that above materials are useful for magnetic materials, and the method to produce magnetic nanoparticles coated with graphite is rather simple

Hydrothermal Fabrication of Spindle-type alpha-Fe 2 O 3 Nanoparticle and its Magnetic Property

Spindle-type α-Fe₂O₃ nanoparticles have been synthesized via a hydrothermal method, using Fe(NO₃)₃, NH₄Cl and ethylene glycol as starting precursors. The resultant products were characterized by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM). The results indicate that the synthesized individual spindle-type α-Fe₂O₃ nanoparticles are single crystals, and their hysteresis loops show that they have two kinds of magnetic properties, diamagnetism and paramagnetism

Controllable Synthesis of CNTs Using Pd Catalyst

High yields of multi-walled carbon nanotubes are synthesized by chemical vapor deposition of acetylene on palladium nanoparticles supported on porous SiO2. HRTEM results reveal that the carbon nanotubes have novel conical inner structure. By changing the content of palladium in the catalyst, we obtained palladium nanoparticles with different diameter distribution. It was found that the apex angles of cones, the outer diameter and the length have a dependence on the diameter of the palladium nanoparticles. Due to the presence of open graphite layers, these novel carbon nanotubes have fascinating potential for energy storage, filed emission and composites