J. Phys. Chem. B 2006, 110, 11237-11240
11237
Thermal Decomposition of Commercial Silicone Oil to Produce High Yield High Surface Area SiC Nanorods V. G. Pol,† S. V. Pol,† A. Gedanken,*,† S. H. Lim,‡ Z. Zhong,‡ and J. Lin‡ Department of Chemistry and Kanbar Laboratory for Nanomaterials at the Bar-Ilan UniVersity Center for AdVanced Materials and Nanotechnology, Bar-Ilan UniVersity, Ramat-Gan 52900, Israel, and Institute of Chemical Engineering and Sciences, No.1 Pesek Road, Jurong Island, Singapore, 627833 ReceiVed: March 7, 2006; In Final Form: April 24, 2006
This article reports on the synthesis of high surface area (563m2/g) β-SiC nanorods by thermal decomposition of commercial silicone oil at a relatively low reaction temperature (800 °C) in a closed Swagelok cell. High yield (75%) of SiC nanorods are obtained in this one-stage, solvent-, catalyst-, and template-free synthesis technique that runs at a relative low temperature and employs cheap single-precursor. The morphological (TEM, HR-SEM), compositional (CHNS, EDX, SAEDX]), structural (XRD, HR-TEM, and ED), thermal (TGA) characterizations and surface area analysis are carried out for the obtained SiC nanorods. The possibility of hydrogen storage in this high surface area nano-SiC rods are also tested and reported for the first time.
Introduction The high-thermal conductivity, resistance toward oxidation, mechanical strength, and chemical inertness of silicon carbide (SiC) have numerous applications in fields such as biomaterials, lightweight/high strength structure, and catalyst support1. Moreover, as an important wide band gap semiconductor with high electron mobility, β-SiC nanowires would be favorable for applications in high temperature, high power, and highfrequency nanoelectronic devices2. Dai3 et al. first succeeded in the synthesis of SiC nanorods in 1995 through the reaction of carbon nanotubes with SiO or Si + I2. Meng4 et al. synthesized β-SiC nanorods by carbothermal reduction reaction, and Zhou5 et al. fabricated SiC nanowires by the hot filament CVD method. Recently, Li6 et al. synthesized SiC nanowires by using a SiC rod as the anode- to-arc discharge. However, these methods use various reactants and require high reaction temperatures (usually above 1200 °C) and high pressure7 to synthesize pure SiC nanorods and nanowires. Also, in many syntheses for SiC nanowires, metal catalysts are employed.8-10 The low maximum attainable specific surface area has limited the application of silicon carbide as a catalyst carrier or as a support for various chemical reactions.11 Ultrafine β-SiC has been synthesized with a highest surface area reported so far (150 m2/g) by the inflight processing12a of charred rice husks in a plasma reactor operating at atmospheric pressure. Hiroaki et al. reported the formation and mechanical properties of betasilicon-carbide whiskers by thermal decomposition of sulfurcontaining silicone oils.12b Our research work is the continuation of the work carried out by Hiroaki et al. According to our literature search, hydrogen storage in SiC nanomaterial or high surface area SiC has not yet been reported. In this article, we report on the synthesis of high surface area (563m2/g) β-SiC nanorods by thermal decomposition of commercial silicone oil at a relatively low reaction temperature (800 * Corresponding author e-mail:
[email protected]. † Department of Chemistry and Kanbar Laboratory for Nanomaterials at the Bar-Ilan University center for Advanced Materials and Nanotechnology. ‡ Institute of Chemical Engineering and Sciences.
°C) in a closed Swagelok cell. High yield (75%) of SiC nanorods are obtained in this one-stage, solvent-, catalyst-, and templatefree synthesis that runs at a relative low temperature and employs cheap single-precursor. The possibility of hydrogen storage in this high surface area nano-SiC rods is also tested and reported for the first time. Experimental Section In a typical synthesis, 2 g or 2 mL of commercial silicone oil (Solufix) was introduced into a 4 mL stainless steel reactor at room temperature under nitrogen. Poly(dimethylsiloxane) (silicone oil) is a colorless, odorless, chemically inert lubricant, with excellent thermal stability. The filled cell was closed tightly with the other plug13 and the temperature was raised to 800 °C at the rate of 10 °C/min and heating continued for 3 h. The reaction took place at an autogenic pressure of the precursor. The Swagelok-reactor heated at 800 °C was gradually cooled (∼5 h) to room temperature, opened, and 0.152 g of gray powder was obtained. The total yield of the obtained SiC nanorods was 75%, referred to the starting silicone oil. Similar one-stage, catalyst-free, efficient, and the simplest economic RAPET (Reactions under Autogenic Pressure at Elevated Temperature) reactions were also reported14-20 for the fabrication of various interesting nanostructures. Figure 1a shows the XRD diffraction pattern (Bruker AXSD* advanced powder X-ray diffraction) of the SiC nanorods. The SiC nanorods sample shows the reflection lines at 2Θ ) 35.73, 41.49, 60.12, 71.95, and 75.69, which are assigned as (111), (200), (220), (311), and (222). These values are in good agreement with the diffraction peaks, peak intensities, and cell parameters of crystalline fcc β-SiC (space group F-43m (216)). These values match very well with the literature values of PDF no. 73-1665. The commercial silicone oil is composed of C, H, O, and Si elements. The carbon, hydrogen, and sulfur contents in the reactant (commercial silicone oil) and the formed product (SiC nanorods) are measured by C, H, N, S analysis (Eager 200). Figure 1b demonstrates the CHNS analysis of the commercial silicone oil and shows only the presence of carbon and hydrogen. The analysis measured 32.8 element % of carbon
10.1021/jp061407e CCC: $33.50 © 2006 American Chemical Society Published on Web 05/20/2006
11238 J. Phys. Chem. B, Vol. 110, No. 23, 2006
Pol et al.
Figure 1. (a) XRD pattern of SiC nanorods. (b) The C, H, N, and S analysis of the commercial silicone oil.
and 8.2 element % of hydrogen in the commercial silicone oil. This confirms the purity of silicone oil and the absence of sulfur impurity. The carbon content in the product (SiC nanorods) is 24.9 element % that matches well with that of the SiC powder (26%) received from Alfa-Aesar. The measured amount of hydrogen in SiC nanorods is 0.6%. The energy-dispersive X-ray analysis (attached to a JEOLJSM 840 scanning electron microscope) is presented in Figure 1b shows 1:1 molar percentage of Si and C. A small amount of oxygen (
