Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Research paper Comparable study of vermiculites from four commercial deposits prepared with fixed ceria nanoparticles Marta Valášková a,⁎ , Jana Kupková a , Gražyna Simha Martynková a , Jana Seidlerová a , Vladimír Tomášek a , Michal Ritz b , Kamila Kočí c , Volker Klemm d , David Rafaja d a Nanotechnology Centre, VŠB-Technical University of Ostrava, 17. listopadu 15/2172, Ostrava, Poruba 708 33, Czech Republic b Department of Chemistry, VŠB-Technical University of Ostrava, 17. listopadu 15/2172, Ostrava, Poruba 708 33, Czech Republic c Institute of Environmental Technologies, VŠB-Technical University of Ostrava, 17. listopadu 15/2172, Ostrava, Poruba 708 00, Czech Republic d Technical University Bergakademie Freiberg, Institute of Materials Science, Gustav Zeuner Str. 5, Freiberg 09599, Germany ARTICLE INFO Keywords: Raw vermiculites Structural alteration Vermiculite/CeO 2 nanoparticles composites X-ray diffraction (FR-IR) and Raman spectroscopy HRTEM ABSTRACT Four commercial macroscopic vermiculites (Ver) from different exploited deposits were investigated regarding their chemistry and structural transformation stage from mica (phlogopite), and compared with selected raw vermiculites and “hydrobioties” known from literature, in which the chemical analyzes verified the existence of iron as Fe 3+ and Fe 2+ . Subsequently prepared vermiculite/ceria (Ver/CeO 2 ) nanoparticles composites were compared from the point of view of the fixation of ceria nanoparticles by using stability test and regarding their photocatalytic activity in the decomposition of N 2 O. The experimental methods used for these studies were X-ray fluorescence spectrometry, atomic emission spectrometry, X-ray powder diffraction, infrared (FR-IR) and Raman spectroscopy and transmission electron microscopy with high resolution (HRTEM). Negative layer charge of vermiculites produced by the local charge balance and distribution of Fe 3+ in tetrahedral and octahedral sheets were related to the CeO 2 nanocrystals fixation and orientation. Among the four Ver/CeO 2 nanoparticles com- posite samples, the vermiculite in sample Ver-C/CeO 2 exhibited the highest negative layer charge. The CeO 2 crystallites were the smallest among all four samples. HRTEM found separated CeO 2 nanocrystallites and CeO 2 agglomerates of differently oriented nanocrystallites. Such forms of CeO 2 nanocrystals influenced the position of the Raman CeO 2 F 2g and suppressed ability for photocatalytic N 2 O conversion. 1. Introduction The macroscopic and microscopic types of raw vermiculites are major categories of clay mineral vermiculite occurring in ultrabasic and basic rocks of raw vermiculite deposits (Basset, 1963). Large crystalline plates of the macroscopic vermiculites are of secondary origin, as they are formed by weathering, hydrothermal action or percolating ground water from biotites, chlorites, pyroxenes, amphiboles, etc. In pyrox- enites and amphibolites, vermiculites were found together with biotite minerals, mainly phlogopite. On the contrary, vermiculites appearing in the carbonate type deposits together with magnesium and calcium salts are materials different from biotites showing interlayer basal d-value 1.4 nm in their X-ray diffraction patterns. Boettcher (1966) explored the chemical conditions necessary for the conversion of biotite to ver- miculite, both occurring in the Rainy Creek alkaline-ultramafic igneous complex near Libby, Montana, USA. The author concluded that biotite and biotite pyroxenite were the first zoned body crystallizing from the original ultramafic magma. Such a large amount of altered coarse- grained biotite pyroxenite is the major source of commercial vermicu- lite in the world. The considerations in literature suggest that trioctahedral biotite could weather to vermiculite under acid conditions and to vermiculite plus montmorillonite under neutral and alkaline conditions (Latimer, 1952). The oxidation of Fe 2+ to Fe 3+ under alkaline conditions causes a large decrease of the clay mineral surface charge and expansion of the crystal lattice that predetermines conditions for the formation of montmorillonite. Based on the analysis of vermiculites and “hydro- biotites”, Foster (1963) concluded that the composition, charge relation and cation exchange capacity in these vermiculites can be derived from phlogopite or magnesian biotite by replacement of K + by Mg 2+ . The term “hydrobiotite” was interpreted as regular 1:1 interstratification of biotite (or interlayer-deficient biotite) and vermiculite (Rieder et al., 1998). Vermiculites were classified as 2:1 phyllosilicates with clay mineral layer charge 0.6 < x < 0.9 eq/(Si,Al) 4 O 10 , arising mostly from the tetrahedral substitution of Si 4+ by Al 3+ (Bailey, 1980; Guggenheim http://dx.doi.org/10.1016/j.clay.2017.10.006 Received 30 June 2017; Received in revised form 31 August 2017; Accepted 8 October 2017 ⁎ Corresponding author. E-mail address: marta.valaskova@vsb.cz (M. Valášková). Applied Clay Science xxx (xxxx) xxx–xxx 0169-1317/ © 2017 Elsevier B.V. All rights reserved. Please cite this article as: Valášková, M., Applied Clay Science (2017), http://dx.doi.org/10.1016/j.clay.2017.10.006