Sonochemical Preparation of Silane-Coated Titania Particles Kurikka V. P. M. Shafi, †,‡ Abraham Ulman,* ,†,‡ Xingzhong Yan, ‡,§ Nan-Loh Yang, ‡,§ Michael Himmelhaus, | and Michael Grunze | Department of Chemical Engineering and Chemistry, Polytechnic University, Brooklyn, New York 11201, Department of Chemistry, CUNY at Staten Island, 2800 Victory Bulevard, Staten Island, New York 10314, The NSF MRSEC for Polymers at Engineered Interfaces, and Institute of Physical Chemistry, University of Heidelberg, INF 253, D-69120 Heidelberg, Germany Received August 30, 2000. In Final Form: December 21, 2000 We report that sonochemistry is a fast and efficient technique for coating of octadecyltrihydrosilane (CH3(CH2)17SiH3) on titania surfaces. Infrared spectroscopy as well as thermal analysis confirms that complete coating is achieved after 30 min. Solid-state 13 C NMR spectroscopy establishes the bonding of trihydrosilane to the titania particles. Raman microscopy gives the expected rutile structure and further confirms the presence of an octadecyl monolayer. X-ray diffraction confirms that the rutile structure of the titania particles has not changed during sonication. Anatase titania undergoes the same reaction when sonicated in the presence of octadecyltrihydrosilane. Introduction A recent communication by McCarthy and co-workers reported the reaction of trihydrosilanes (R-SiH 3 ) with titanium and other metal oxide surfaces. 1 This reaction represents a new type of self-assembly that can be used to functionalize nanoparticles by organic monolayers and thus may become important when the preparation of nanocomposites is limited by lack of compatibility between the inorganic nanoparticles and the organic matrix. The limitation of the reported route, however, is that maximum coverage is achieved only after a long reaction time, as was reported by the authors and was also found in our laboratory, thus making it less desirable for practical applications. We report here that a faster and more efficient coating of octadecyltrihydrosilanes (OTHS, CH 3 (CH 2 ) 17 SiH 3 ) on a titania surface (rutile) can be achieved by sonochemical means. Silica-coated titania particles can be further prepared by thermal decomposition of the silane-coated titania surfaces, removing the organic moieties and leaving a SiO 2 layer on the TiO 2 nanoparticle surface. The advantage of the new sonochemical method is that the reaction is completed within 30 min. Nanoparticles have been the subject of considerable interest because of their special properties, resulting from the nanoscale regime, such as a large surface-to-volume ratio, and increased surface reactivity as compared to that of the bulk material. This enables their use as catalysts, as well as in mechanical, electronic, and optical applica- tions. 2 Titanium dioxide is a most versatile material and has been extensively used over the past decade, because of its low cost, nontoxicity, photostability, and efficient photo- catalytic properties. 3 TiO 2 is both biologically and chemi- cally inert, and its photocatalytic properties are favorable for oxidation of hazardous chemicals, 4 reduction of heavily metal ions, 5 and photodestruction of bacteria and viruses in water. A high refractive index combined with a high degree of transparency in the visible region makes the TiO 2 a unique choice for the pigment industry. The scattering efficiency for the visible light imparts whiteness, brightness, and opacity to the coatings. These properties have made TiO 2 an important additive in cosmetic formulations as well. Sonochemistry has been used extensively to generate novel materials with unusual properties, 6 because the method results in the formation of amorphous nanopar- ticles. 7 The chemical effects of ultrasound are driven primarily from hot spots formed during acoustic cavitation, a process that dramatically concentrates the low-energy density of a sound field. Various experiments have demonstrated that the effective temperature reached during bubble collapse is 5000 K. 8 When liquids that contain solids are irradiated with ultrasound, related phenomena can occur. 9 There, cavita- tion occurs near an extended solid surface and cavity collapse is nonspherical and drives high-speed jets of liquid * To whom correspondence may be addressed. Phone: (718) 260- 3119. Fax: (718) 260-3125. E-fax: (810) 277-6217. E-mail: aulman@ poly.edu. † Polytechnic University. ‡ The NSF MRSEC for Polymers at Engineered Interfaces. § CUNY at Staten Island. | University of Heidelberg. (1) Fadeev, A. Y.; McCarthy, T. J. J. Am. Chem. Soc. 1999, 121, 12184. (2) (a) Agfeldt, A.; Gratzel, M. Chem. Rev. 1995, 95, 49. (b) Halperin, W. P. Rev. Mod. Phys. 1986, 58, 533. (c) Weller, H.; Eychmuller, A. Adv. Photochem. 1995, 165. (d) Serpone, N.; Khairutdinov, R. F. In Semiconductor Nanoclusters; Kamat, P. V., Meisel, D., Eds.; Studies in Surface Science and Catalysis, Vol. 103; Elsevier Science: New York, 1997; p 417. (e) Sailor, M. J.; Heinrich, J. L.; Lauerhaas, J. M. In Semiconductor Nanoclusters; Kamat, P. V., Meisel, D., Eds.; Studies in Surface Science and Catalysis, Vol. 103; Elsevier Science: New York, 1996; p 209. (3) Sawunyama, P.; Fujishima, A.; Hashimoto K. Langmuir 1999, 15, 3551. (4) Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemann, D. W. Chem. Rev. 1995, 95, 69. (5) Chen, L. X.; Rajh, T.; Wang, Z.; Thurnauer, M. C. J. Phys. Chem. B 1997, 101, 10688. (6) Ultrasound: Its Chemical, Physical and Biological Effects; Suslick, K. S., Ed.; VCH: Weinheim, Germany, 1988. (7) (a) Shafi, K. V. P. M.; Gedanken, A.; Prozorov, R. Adv. Mater. 1998, 10, 590. (b) Shafi, K. V. P. M.; Felner, I.; Mastai, Y.; Gedanken, A. J. Phys. Chem B 1999, 103, 3358. 1726 Langmuir 2001, 17, 1726-1730 10.1021/la001252g CCC: $20.00 © 2001 American Chemical Society Published on Web 02/01/2001