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Pore Fabrication in Various Silica-Based Nanoparticles by Controlled Etching Lan Zhao,† Yunfeng Zhao,‡ and Yu Han*,‡ †
Core Lab of Imaging and Characterization and ‡Advanced Membrane and Porous Materials Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Received May 15, 2010. Revised Manuscript Received June 6, 2010
A novel method based on controlled etching was developed to fabricate nanopores on preformed silica nanoparticles (150 nm). These particles tend to precipitate when dispersed in solvent and cannot form a stable homogeneous colloidal suspension.16-18 Suzuki et al. reported that they were able to synthesize well-ordered nanosized mesoporous particles.18 Although these particles were small, with diameters ranging from 20 to 50 nm, there was severe interparticle aggregation, which constitutes a major drawback for their applications. Only a few successful examples of preparing stable colloidal suspension of mesoporous nanoparticles have been reported, which are based on either highly diluted synthetic system or the addition of particle growth suppressant. For example, Lin et al. successfully synthesized well-dispersed mesoporous silica MCM-41 nanoparticles (∼100 nm) by carefully controlling the nuclei formation and particle growth in a diluted system. They also successfully developed multifunctional materials based on these mesoporous nanoparticles and demonstrated their applications as cell markers and magnetic resonance imaging (MRI) contrast agents.1,24 Using triethanolamine as additives, Bein’s group prepared (16) Han, Y.; Ying, J. Y. Angew. Chem., Int. Ed. 2005, 44, 288. (17) El Haskouri, J.; Ortiz de Zarate, D.; Guillem, C.; Beltran-Porter, A.; Caldes, M.; Marcos, M. D.; Beltran-Porter, D.; Latorre, J.; Amoros, P. Chem. Mater. 2002, 14, 4502. (18) Suzuki, K.; Ikari, K.; Imai, H. J. Am. Chem. Soc. 2004, 126, 462. (19) Moeller, K.; Kobler, J.; Bein, T. Adv. Funct. Mater. 2007, 17, 605. (20) Kobler, J.; M€oller, K.; Bein, T. ACS Nano 2008, 2, 791. (21) Vallet-Regi, M.; Balas, F.; Arcos, D. Angew. Chem., Int. Ed. 2007, 46, 7548. (22) Torney, F.; Trewyn, B. G.; Lin, V. S.-Y.; Wang, K. Nat. Nanotechnol. 2007, 2, 295. (23) Vivero-Escoto, J. L.; Slowing, I. I.; Wu, C.-W.; Lin, V. S.-Y. J. Am. Chem. Soc. 2009, 131, 3462. (24) Lin, Y.-S.; Wu, S.-H.; Chou, Y.-H.; Chang, C.; Lin, M.-L.; Tsai, C.-P.; Mou, C.-Y. Chem. Mater. 2006, 18, 5710.
Published on Web 06/17/2010
Langmuir 2010, 26(14), 11784–11789
Zhao et al.
Article
Figure 1. TEM micrographs of silica nanoparticles synthesized from the reverse microemulsion method with an average particle size of (a) 14 nm, (b) 35 nm, (c) 42 nm, and (d) 50 nm.
nonaggregated, colloidal suspensions of mesoporous silicas from concentrated solutions.19 This method allowed precisely tuning the particle size down to 50 nm and was extendable for the synthesis of various functionalized colloidal mesoporous silicas.20 The objective of this work is to integrate the merits of colloidal functional nanoparticles and mesoporous silica in one material. Herein, we demonstrate a general method to generate pores in various silica-based nanoparticles, including pure silica, fluorescent dye-doped silica, and magnetic silica-coated Fe2O3. This method consists of two steps. In the first step, silica-based nanoparticles are synthesized from reverse microemulsion systems. This allows us to prepare uniform, small particles (
