Carbon nanotubes (CNTs) have attracted intensive interests of researchers for a long time due to their fascinating physical and chemical properties promising for various potential applications, including advanced ceramics, nanoelectronic devices, nanoscale sensors, solar cells, battery electrode, field emitters, etc.. This review summarized the synthetic methods of CNTs, with an emphasis on the chemical vapor deposition (CVD) method, especially catalytic CVD. Although there still are some challenges in the way, with the development of the technology, a hope for widespread applications always exists.
Abstract:The porous ceramics based on Al 2 O 3 -TiO 2 /ZrO 2 -SiO 2 from particle-stabilized wet foam by direct foaming were discussed. The initial Al 2 O 3 -TiO 2 suspension was prepared by adding TiO 2 suspension to partially hydrophobized colloidal Al 2 O 3 suspension with equimolar amount, to form Al 2 TiO 5 on sintering. The secondary ZrO 2 -SiO 2 suspension was prepared using the equimolar composition, and to obtain ZrSiO 4 , ZrTiO 4 , and mullite phases in the sintered samples, the secondary suspension was blended into the initial suspension at 0, 10, 20, 30, and 50 vol%. The wet foam exhibited an air content up to 87%, Laplace pressure from 1.38 to 2.23 mPa, and higher adsorption free energy at the interface of approximately 5.8×10 8 to 7.5×10 8 J resulting an outstanding foam stability of 87%. The final suspension was foamed, and the wet foam was sintered from 1400 to 1600 ℃ for 1 h. The porous ceramics with pore size from 150 to 400 μm on average were obtained. The phase identification was accomplished using X-ray diffraction (XRD), differential thermal analysis (DTA), and thermogravimetric analysis (TGA), and microstructural analysis was performed using field emission scanning electron microscopy (FESEM).
Monodisperse magneticFe3O4nanoparticles (NPs) with the size of ca. 3.5 nm were prepared and used as the catalysts for the synthesis of vertically aligned carbon nanotube (VACNT) arrays. A silicalite-1 microcrystal monolayer was used as the support layer between catalyst NPs and the silicon substrate. Compared to our previous report which used radio-frequency- (rf-) sputteredFe2O3film as the catalyst,Fe3O4NPs that were synthesized by wet chemical method showed an improved catalytic ability with less agglomeration. The silicalite-1 crystal monolayer acted as an effective “buffer” layer to prevent the catalyst NPs from agglomerating during the reaction process. It is believed that this is the first report that realizes the vertical alignment of CNTs over the zeolite monolayer, namely, silicalite-1 microcrystal monolayer, instead of using the intermediate anodic aluminum oxide (AAO) scaffold to regulate the growth direction of CNT products.
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