Controlled deposition of covalently bonded tantalum oxide on carbon supports by solvent evaporation sol–gel process Yongsoon Shin * , Jin Yong Kim * , Chongmin Wang, Jeff F. Bonnet, K. Scott Weil Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99354, United States article info Article history: Received 10 April 2009 Accepted for publication 6 May 2009 Available online 22 May 2009 Keywords: Tantalum oxide Sol–gel Covalent bond Nanocomposite: carbon abstract A simple strategy for covalently attaching Ta 2 O 5 particles onto functionalized graphitic carbon supports has been developed to fabricate hybrid nanocomposites. In this process, tantalum ethoxide was directly reacted with functional groups on the carbon surface to form covalent bonding, which caused the car- bonyl stretches of the carbon supports to be blue-shifted to 50–70 cm 1 after Ta 2 O 5 particle deposition. Homogeneously deposited Ta 2 O 5 particles on the carbon supports have been studied by X-ray diffraction (XRD), FT–IR spectroscopy, scanning electron microscopy (SEM), and transmission electron microscope (TEM). Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction High surface area carbon materials with graphitic nature have attracted intensive research focuses due to their possible applica- tions in the areas of adsorbents, catalyst supports, electrode mate- rials, and energy storage media [1,2]. Main studies have been focused on the control of the nanostructures of porous carbons including, surface area, pore size, and nature of the carbon frame- work, to meet the particular requirements of specific applications [3,4]. Furthermore, many studies have been focused on depositing metal or metal oxide on the carbon surface [5]. However, chemical inertness and poor solubility of carbon materials essentially make it very difficult to modify surface functionality. Therefore, in order to establish a uniform coverage of metal or metal oxide nanoparti- cles on the surfaces of the carbon materials, it is necessary to acti- vate the surfaces. Usually, the surfaces of the carbon materials can be functionalized using different acid treatments [6,7] or plasma [8] to create carboxylic, carbonyl, and hydroxyl groups that are able to kind different nanomaterials. Tantalum oxide (Ta 2 O 5 ) has recently attracted much attention due to its possible enhancement of activity and selectivity in the selective oxidation of hydrocarbons on various oxide catalysts [9]. Ta 2 O 5 has been also widely used as a key material of antireflec- tive coating layer, impedance under high temperature, capacitor due to its high reflective index, high chemical stability, and high dielectric constant [10]. Ta-based porous mixed oxides have been recently found to be highly active for water decomposition under UV irradiation [11,12]. Mesoporous Ta 2 O 5 has been extensively synthesized by the ligand-assisted templating method for its pho- tocatalytic application [13]. However, the ordered mesopore net- work was easily collapsed under low calcination temperature [14]. In this work, we demonstrate a facile one-step method for fabri- cating Ta 2 O 5 /carbon hybrid composite materials, where Ta 2 O 5 par- ticles are homogeneously distributed on carbon supports, through covalent interaction as shown Scheme 1. The strategy demon- strated that combined sol–gel process with solvent evaporation process is effective for the formation of Ta 2 O 5 , which was covalently bonded onto carbon surface. Electron microscopes techniques and FT–IR are the key techniques to observe surface morphologies and chemical bonding of Ta 2 O 5 particles on the carbon surface. 2. Experimental Tantalum ethoxide [Ta(OEt) 5 ] and thionyl chloride (SOCl 2 ) was purchased from Aldrich Chemical Co. and carbon nanoparticle (30 nm) was procured from Asbury Carbons (Grade #: 5345R). The carbon sample (C0) was dispersed in a mixture of concentrated nitric acid and sulfuric acid (5:3 vol. ratio) and refluxed for 1 h. The sample was repeatedly washed with deionized water until the solution reached a pH value of 7. The filtered carbon solid was dried under vacuum for 24 h at 70 °C. Dried carboxylate-function- alized carbon (C1) was suspended in SOCl 2 and stirred for 24 h at 70 °C. The solution was filtered, washed with anhydrous THF, and dried under vacuum at room temperature (C2). For direct synthesis of Ta 2 O 5 on carbon supports, to 2.0 g of either C0 or surface modified carbons (C1 or C2) dispersed in 20 mL of ethanol, different amounts of Ta(OEt) 5 (8, 4, 2, or 1 mL, d = 1.57) were added, and stirred overnight at room temperature. EtOH retards rapid hydrolysis and condensation of Ta(OEt) 5 to form Ta 2 O 5 on the carbon surface because EtOH stabilizes Ta(OEt) 5 . 0039-6028/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2009.05.006 * Corresponding authors. Tel.: +1 509 375 2693; fax: +1 509 375 2186. E-mail addresses: yongsoon.shin@pnl.gov (Y. Shin), jin.kim@pnl.gov (J.Y. Kim). Surface Science 603 (2009) 2290–2293 Contents lists available at ScienceDirect Surface Science journal homepage: www.elsevier.com/locate/susc