Tonghua Wang

A novel form of carbon micro-balls from coal

Abstract A novel form of ball-like carbon material with its size in micrometer range was prepared from coal with nickel as catalyst by arc plasma method. The carbon material has been systematically studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and ultraviolet laser Raman spectroscopy. The SEM observation shows that the novel carbon material exists in various forms such as individual balls, net-like and plate-like forms, all of which have a quite smooth surface. The diameters of these carbon spheres are quite uniform and in a narrow range of 10–20 μm. The EDS analysis reveals that the ball-like carbon material contains more than 99.5% of carbon and a little amount of other elements such as nickel, silicon and aluminum. The XRD and UV–Raman results reveal that the novel carbon material is a kind of highly graphitized carbon. The growth mechanism of the ball-like carbon material was proposed and discussed in terms of arc plasma parameters and the chemical structure of coal-based carbon.

High-purity single-wall carbon nanotubes synthesized from coal by arc discharge

Dalian Univ Technol, Dept Mat Sci & Chem Engn, Ctr Nano Mat & Sci, Carbon Res Lab, Dalian 116012, Peoples R China. Chinese Acad Sci, Met Res Inst, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Qiu, JS (reprint author), Dalian Univ Technol, Dept Mat Sci & Chem Engn, Ctr Nano Mat & Sci, Carbon Res Lab, 158 Zhongshan Rd,POB 49, Dalian 116012, Peoples R China

Bamboo-Shaped Carbon Tubes from Coal

Abstract Bamboo-shaped carbon tubes (BCTs) were first synthesized in high yields from iron-loaded carbon electrodes prepared from coal by arc discharge. The BCTs were characterized by scanning electron microscopy and transmission electron microscopy (TEM). The TEM characterization reveals that the tubes have bamboo-like structures consisting of hollow compartments separated with conical shaped graphite layers. The diameters of BCTs are in the range of 40–60 nm with their length being about several micrometers. For some BCTs, the hollow compartments are quite uniform with a size of 100 nm. A growth model is suggested to explain the formation of bamboo structure in tubes.

A novel carbon/ZSM-5 nanocomposite membrane with high performance for oxygen/nitrogen separation

A novel carbon/ZSM-5 nanocomposite membrane is successfully prepared by incorparating nano-sized ZSM-5 into polymeric precursor(polyimide), which shows excellent permselectivities for separation of oxygen/nitrogen gas pairs.

Towards the Preparation of Ordered Mesoporous Carbon/ Carbon Composite Membranes for Gas Separation

Carbon/carbon composite membranes (CCMs) were made using the blend of polyimide with ordered mesoporous carbon (OMC) as precursor at a pyrolysis temperature of 650°C. The thermal stability of precursors, the structure evolution, and the morphology and gas separation performance of CCMs were investigated. The results have shown that the CCMs are one of the most attractive membrane materials for gas separation. The thermal stability of the precursor is improved by the addition of OMC. OMC can tightly embed in the membrane matrix due to the carbonaceous homology of matrix. As a result of the addition of OMC into carbon membranes, the gas permeability of O2 increases ten times, together with the O2/N2 selectivity significantly boosting from 10.3 to 12.9.

Dynamic characteristic testing for MEMS micro-devices with base excitation

The study of the dynamic characteristics of MEMS micro-devices depends on relevant testing facilities. Testing with a base excitation method was studied and employed in practical tests. A system for the dynamic characteristic testing of MEMS micro-devices was built based on a PZT transducer as the shock excitation source. A high voltage power source for the PZT transducer, which can provide large transient current, was developed for impact generation. Experiments for testing micro piezoelectric cantilevers were accomplished with the base excitation method. The impact response, i.e. electric charge signal generated by the micro piezoelectric cantilever, was acquired. By performing spectral analysis and comparison of the result with another cantilever having different resonance frequencies, the resonance frequency of the tested microstructure was determined. For comparison, simulation of the piezoelectric cantilever with a finite element analysis (FEA) method was carried out. Because the theory analysis is in good agreement with the experiment results, it can be used to estimate the actual resonance frequency of the tested microstructure. The base excitation method was also applied in the dynamic testing of microstructures under a high-g force environment. By the exclusion of the resonance peaks of PZT transducer and noise frequencies, the resonance frequency of the tested microstructure was determined. The applicability and the limitation of the method were briefly discussed.

Fabrication and gas permeation of CMS/C composite membranes based on polyimide and phenolic resin

Carbon molecular sieving (CMS) membranes were fabricated on a support of phenolic resin-based carbon sheets, using a 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene-1,2,3,4-cyclobutanetetracarboxylic dianhydride type polyimide as a precursor, through coating, drying and pyrolysis. The thermal stability of the precursor, the morphology, functional groups, porous structure and microstructure of the CMS/C membranes were characterized by thermogravimetric analysis, electron microscopy, infrared spectroscopy, nitrogen adsorption and X-ray diffraction, respectively. The effects of coating times, pyrolysis temperature, and permeation temperature and pressure on the gas permeation of the CMS/C membranes were investigated. In addition, zeolite ZSM-5 was also utilized as an additive to adjust the microstructure and gas permeation of the CMS/C membranes. The results show that the best gas permeability and selectivity could be attained for the CMS/C membranes under the fabrication condition of coating six times and a pyrolysis temperature of 650 °C. The permeability of the CMS/C membranes improves with an increase in the permeation temperature or a decrease in the pyrolysis temperature. Also, the incorporation of ZSM-5 reduces the thermal stability of the precursor and the gas permeability of the resultant CMS/C membranes.

Effect of membrane-casting parameters on the microstructure and gas permeation of carbon membranes

In this work, membrane-casting parameters including solvents and drying methods were investigated to adjust the microstructure and gas permeation of poly(phthalazinone ether sulfone ketone) (PPESK) based carbon membranes. The structure and properties of the membrane samples were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, transmittance electron microscopy, single gas and mixed gas permeation. Results have shown that the membrane-casting parameters greatly influence the physico-chemical properties of the polymeric membranes, so as to affect the structure and gas permeation of their derived carbon membranes. Under the same drying conditions, the selection of a solvent with a high boiling point is beneficial to the thermal degradation of the polymeric membrane during pyrolysis. In addition, the adoption of a solvent with a close solubility parameter to PPESK is favorable to improving the permeability of carbon membranes. Compared to common warm air drying, cold drying is more favorable for the improvement of the thermal stability of the precursor membranes. With variation of the pyrolysis temperature from 650 °C to 850 °C, the best selectivities of carbon membranes are obtained at 850 °C for refrigerate-drying and at 750 °C for freeze-drying, respectively. All the gas separation data of the present carbon membranes made by cold drying surpass the Robesons upper bound.

Preparation of composite carbon-zeolite membranes using a simple method

Zeolite thin films and composites supported on different materials have been widely used as highly selective membrane separators, membrane reactors, chemical sensors, and microdevices [1–11]. In particular, zeolite membranes supported on polymers and ceramics as supports are universally studied. However, polymers are vulnerable to organic solvents and could not tolerate high temperatures. Ceramics provide better mechanical strength and thermal stability, but are more difficult to fabricate and therefore are more expensive. Moreover, ceramics also have a little etching of aluminum by a strong alkaline solution [1]. Porous carbon materials are promising candidates as supports for zeolite membranes because they not only possess comparable mechanical strength, thermal characteristics of metallic supports, and excellent resistance to chemical attack, but also exhibit organic substrate’s flexibility of forms and lower capital cost [10, 11, 12]. Zeolite films grown on porous carbon materials can modify the nature of the porous carbon itself and present different potential advantages in a number of applications. On the other hand, the pores of porous carbon materials can be narrowed down to a desired uniform subnanometer size by the zeolite growth on the porous carbon surface, which is one of the most difficult but a fascinating task that carbon researchers have to attempt [12]. The main difficulty is that there are few nucleation centers on the hydrophobic carbon supports, which make it difficult for zeolites to nucleate and grow on them from the hydrophilic zeolite synthesis solution. Up to now, there are few studies on the growth of zeolites on the activated carbon and hollow fibers as supports by using the oxidizing pretreatment of the carbon materials to increase the oxygen functional groups and the surface change in the carbon materials with a cationic polymer for the zeolite growth [11, 13–15]. Recently, continuous zeolite/carbon composites are obtained by electrophoretic deposition of zeolite nanocrystals on porous carbon disks, then followed by hydrothermal synthesis [16]. In this communication, we report a simple and effective method for preparation of continuous carbonsilicalite-1 membranes on porous carbon tubes. A 1%wt zeolite silicalite-1 colloidal suspension in ethanol prepared from the recipes described by Yeung and coworkers [9]. Porous carbon tubes prepared at Dalian University of Technology have 9 mm OD, 5 mm ID, 75 mm long, and a nominal pore size of 0.3 μm. Prior to use, the tubes were rinsed with DDI water and then dried at 393 K for 10 hr. A thin layer of zeolite seeds was coated onto the inner surface of the tubes using a slip-casting technique in 1wt% seed suspension for 30 s contact time. The seeded supports were dried at room temperature overnight and calcined in air at 523 K for 6 hr. After calcination, the seeded tubes were immersed vertically in the clear synthesis solution with a molar composition of 20SiO2:2.5 (TPA)2O:10 000H2O at 403 K for 36 hr. After the synthesis, the sample was characterized by scanning electron microscopy (SEM, JEOL JSM-6300F) and X-ray powder diffraction (XRD, Philips PW 1030). Fig. 1 is the SEM images of the prepared carbon– zeolite composites. Without seeding, no zeolite film is formed on the untreated carbon support except for the very few crystal deposits (Fig. 1a). This reflects that the carbon surface is extremely inert and zeolites are unable to grow on the untreated carbon support. It is clear from Fig. 1b that after the support is seeded by using slip-casting in seed ethanol suspension, the seeds are successfully introduced onto the carbon surface. The carbon surface is fully covered with 5 μm thick layer of silicalite-1 seeds. This not only makes the carbon surface even and smooth, but also provides anchoring centers for zeolite growth, which both favors forming a continuous and dense membrane on the carbon support. After hydrothermal synthesis, a continuous zeolite membrane of 5–6 μm thickness is formed on this seeded support as shown in Fig. 1c. The zeolite crystals grow outward from the surface of the seed layer. From the surface (Fig. 1c inset), the zeolite membrane is well intergrown and possesses a smooth and uniform surface. Under the conditions of 1 bar and room temperature, the membrane shows no N2 permeation. This fully proves that the carbon–zeolite membrane is dense and perfect. XRD patterns of the samples in Fig. 2 show that both the seeded carbon support and the membrane have strong characteristic peaks with a silicalite-1 structure [17], but with different relative peak intensities. This confirms the existence of a seed layer on the support and the formation of the silicalite-1 zeolite layer on the seeded support.

Preparation and applications of microfiltration carbon membranes for the purification of oily wastewater

ABSTRACT Microfiltration carbon membranes for oily wastewater treatment were fabricated from phenolic resin. The effects of oil concentration, running time, additives and regeneration on the removal of oil from wastewater were investigated. The as-obtained microfiltration membranes possess a macroporosity of 39.0% and meso and microporous volumes of 0.134 m3/g, along with two major pore size distributions around 0.1 μm and 20 nm. They are, respectively, attributed to the constituted particles’ stacking and the precursor pyrolysis. The results showed that the microfiltration membranes can efficiently remove the oil in wastewater. In the presence of ethanol as an additive in solution, the oil concentration is dramatically reduced from initial 200 mg/L in feed to below 10 mg/L in permeate, with an oil rejection of 95.3%.