Delivered by Publishing Technology to: Chalmers Tekniska Hogskola (Chalmers University of Technology) IP: 114.86.54.136 On: Mon, 11 Jan 2016 15:34:33 Copyright: American Scientific Publishers Copyright © 2006 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 6, 726–730, 2006 Preparation of Vermiculite Nanoparticles Using Thermal Hydrogen Peroxide Treatment Zdenˇ ek Weiss, † Marta Valášková, ∗ Jana Seidlerová, Monika Šupová-Kˇ rístková, Ondˇ rej Šustai, Vlastimil Matˇ ejka, and Pavla ˇ Capková Institute of Materials Chemistry, Technical University Ostrava, 17. listopadu 2172, 708 33 Ostrava-Poruba, Czech Republic Powdered natural Mg-vermiculite (Letovice, Czech Republic), with the formula (Mg 035 K 002 Ca 001  (Mg 239 Fe 3+ 051 Fe 2+ 002 Al 008  (Si 264 Al 133 Ti 003  O 10 (OH) 2 · 497H 2 O and particle size <5 m, was used for the investigation of exfoliation after hydrogen peroxide and/or microwave treatment (600 W). A sample heated in the microwave oven for 40 min exhibits a 11% mass loss and reduction of the 001 peak intensity in the X-ray diffraction pattern. The basal 001 peak intensity of untreated Mg- vermiculite sample (I 001 = 100%) drops to 35% in the microwave treated sample. Only the sample treated for 5 h at 80  C fully rehydrated after 120 min at room temperature. A more pronounced reduction of the 001 peak intensity (to 8%) was observed after hydrogen peroxide treatment of the sample at 25  C. The combination of a five-hour hydrogen peroxide treatment at 80  C and subsequent microwave heating leads to an effective extinction of the 001 diffraction in the XRD pattern. The 001 diffraction profile becomes very diffuse with peak intensity less than 1%. The degree of reduction of the 001 diffraction intensity also depends on the time and temperature of hydrogen peroxide treatment and on the peroxide concentration. An even more pronounced reduction of the peak intensity is caused by exfoliation of particles to nano-domains coupled with a randomization of the c-axes. Keywords: Mg-Vermiculite, Exfoliation, Nano-Domains, Hydrogen Peroxide, Microwave, X-ray Diffraction. 1. INTRODUCTION The layered silicates (phyllosilicates) represent important native materials, which are utilized in different areas of industry. In recent years phyllosilicates have found wide exercise in the field of polymer/layered silicate nanocom- posites (PLSN). The advantages of PLSN include impro- ved stiffness, strength, toughness, and thermal stability as well as reduced gas permeability and coefficient of thermal expansion (e.g. Thostenson, 1 Alexandre, and Dubois. 2 ) The size of phyllosilicate nanoparticles is important parameter for manufacturing of this nanocomposites. The best properties are achieved when very fine phyllosilicate particles are homogenously dispersed in polymer matri- ces. For this reason new, more effective methods for the delamination/exfoliation of phyllosilicates are developed. Thermal and chemical treatment can be used for exfoliation/delamination of phyllosilicates. Especially suit- able are phyllosilicates containing molecular water in the interlayer, because their exfoliation results from a ∗ Author to whom correspondence should be addressed. spontaneous escape of the interlayer molecular water. Montmorillonite, hectorite, and saponite are among the most commonly used phyllosilicates for the prepara- tion of PLSN (Okamoto 3 ). Vermiculite is other kind of phyllosilicate that is abundant and much cheaper as compared with montmorillonite, hectorite, and saponite. Mg-vermiculite belongs to 2:1 phyllosilicates containing hydrated cations in the interlayer. According to its struc- ture determined by Shirozu and Bailey, 4 the interlayer Mg is octahedrally coordinated with water molecules form- ing a mon-octahedral sheet. The interlayer and the 2:1 layer thicknesses are equal to 7.5 Å and 6.6 Å, respec- tively. The removal of the interlayer water molecules dur- ing thermal decomposition leads to the formation of less hydrated vermiculite phases (e.g. Weiss and Rowland, 5 de la Calle et al., 6 Graf von Reichenbach and Beyer 7 8 ). Mg- vermiculite in equilibrium with a humid atmosphere at 25  C exhibits the first basal spacing at 14.36 Å. How- ever, the X-ray diffraction (XRD) patterns of dehydrated and rehydrated Mg-vermiculite in open-air humid atmo- sphere display a significant variation of the position of the 726 J. Nanosci. Nanotechnol. 2006, Vol. 6, No. 3 1533-4880/2006/6/726/005 doi:10.1166/jnn.2006.116