Surface Patterns by Solvent Evaporation of Colloidal Zeolite Suspension
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Surface Patterns by Solvent Evaporation of Colloidal Zeolite Suspension Huanting Wang, Zhengbao Wang, Limin Huang, Anupam Mitra and Yushan Yan* Department of Chemical & Environmental Engineering University of California Riverside, CA 92521, U. S. A. * Tel: (909) 787-2068, Fax: (909) 787-2425, E-mail: [email protected]. ABSTRACT Surface patterns of porous zeolite structures such as knotted-rope web and wrinkled honeycomb were obtained by dynamic self-assembly of zeolite nanoparticles during solvent evaporation of colloidal zeolite suspension. The study shows that extra ethanol in zeolite synthesis solution is crucial for pattern formation. The addition of ethanol helps produce zeolite nanoparticles with a specific range of particle size during the hydrothermal synthesis. It also provides uniform dynamic driving force for pattern formation during its preferential evaporation. In addition, surface patterns vary with suspension compositions. The patterned zeolite structures have a well-defined bimodal pore size distribution (i.e., 0.55 nm and 2.6 nm) with high BET surface area of 680~750m2/g. INTRODUCTION Patterned zeolite films have been recently fabricated by combining micromolding with selfassembly of monodisperse zeolite nanocrystals [1]. Solvent-evaporation from a thin layer of polymer solution has generated surface patterns in polymer films [2,3], which were interpreted as vitrification of flow patterns associated with Benard-Marangoni (surface-tension-driven) convection [4]. In this study we attempt to demonstrate that surface patterns of porous zeolite structures can spontaneously form through dynamic self-assembly of zeolite nanoparticles during solvent evaporation of colloidal suspensions. The effects of the composition of the suspension will be discussed. Detailed characterization of the porous material will be provided. EXPERIMENTAL DETAILS The zeolite silicalite nanoparticle suspensions used in this study were similarly synthesized hydrothermally as reported previously [1,5]. One major difference is that extra ethanol was deliberately added to the synthesis solution and the as-synthesized suspension was used directly without centrifugation separation. The molar composition of the synthesis solution is 1TPAOH/2.8SiO2/22.4EtOH/40H2O (TPAOH for tetrapropylammonium hydroxide, TEOS for tetraethyl orthosilicate, and EtOH for ethanol). Two batches (noted as A and B) of synthesis solution underwent different hydrothermal histories. Batch A was heated at 70°C for 9 days, and Batch B at 80 °C for 3 days. As a comparison, batch C was synthesized under the same conditions as batch B except that no extra amount of ethanol was added. The resulting colloidal suspensions were cooled to room temperature under stirring before use for pattern formation. Nitrogen adsorption-desorption measurements were carried out (Micromeritics ASAP 2010 instrument) to determine Brunaer-Emmett-Teller (BET) surface area and pore size distribution of calcined samples. Thermal decomposition of organic structure-directing agent (TPAOH) was Y1.4.
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