Modified Sol-Gel Synthesis of Vanadium Oxide Nanocomposites Containing Surfactant Ions
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Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
EXPERIMENTAL A modified sol-gel method [10] was used to react a vanadium alkoxide with the surfactant dodecylphosphate. The air sensitive reagents required the use of a double manifold system with vacuum and argon gas lines, together with ground joint glassware. Also a means of cooling the violent or exothermic reactions is needed, and water or slush baths were used for this purpose. A reflux set up was used with a cooling bath of ice water to react 5 grams of sodium metal (Aldrich) with 300 ml of isopropanol (Aldrich) in 300 ml of diethyl ether (Aldrich). After completion of the reaction the alcohol and ether were removed by vacuum to leave the white needle like crystals of NaOCH(CH 3)2. The following synthesis, of the vanadium alkoxide, was modified from that of Turevskaya [I I ]. About 250 ml of dry diethyl ether was added, and a dry ice acetone bath was applied. 3.4 ml of VC14 (Aldrich) was added slowly via a syringe to the reaction vessel. The resulting NaCI was removed along with the ether to leave V[OCH(CH 3)2]4. Vanadium (IV) isopropoxide was then reacted with acetylacetone (also known as 2,4-pentanedione from Aldrich) with a 1:1 molar ratio in isopropanol. Acetylacetone acts as a chelating agent to slow down the hydrolysis reactions of the metal alkoxide. If hydrolysis occurs too fast then amorphous phases will be obtained. The isopropanol (iPrOH) was removed by vacuum. A 3.4 wt% aqueous solution of the surfactant was prepared by dissolving dodecylphosphate, from Lancaster, into pH5 adjusted water (with concentrated HC1). The reactants, in the molar ratio I V[OCH(CH 3)2]4 : 1 acetylacetone (acac) : 1 surfactant :I KCI were mixed and then heated at 800C for 5 days, washed with water, then dried at 120 0 C for I day. The product obtained will be called Material I. After drying the product was black in color suggesting partial reduction of the vanadium. This synthesis scheme is shown on the next page. Samples were characterized via X-ray powder diffraction on a Phillips PW3040-MPD powder diffractometer using CuKo• radiation, fitted with an Anton Paar heating stage model HTK-10 calibrated to the m.p. of lead. Thermal gravimetric analysis, to determine water and organic content as well as overall stability, was done on a Perkin Elmer TGA 7. Magic angle spinning NMR analysis was performed on a Bruker AC-300 MHz instrument set up for solids; concentrated phosphoric acid (aq) used as a reference for 31P NMR. Electron Microprobe analyses and SEM photographs were obtained on a JEOL 2000 Electron Microprobe. RESULTS AND DISCUSSION Material I upon drying was a black hardened gel with small variations in color, after grinding it became gray. Initial results from XRD indicated the presence of NaC1 and KCI salts, byproducts of the synthesis. These were removed by washing the sample with reverse osmosis water. Thermal gravimetric analysis was performed in both oxygen and nitrogen gas (fig 1) which revealed a weight loss of 9.25% for H20, and 42.6
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