Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels
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Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels Catherine Dejoiea,b,*, Pauline Martinettoa, Eric Dooryhéea,c, Ross Brownd, Sylvie Blancd, Patrice Bordatd, Pierre Strobela, Philippe Odiera, Florence Porchere,f, Manuel Sanchez del Riog, Elsa Van Eslandeh, Philippe Walterh, Michel Annea a
Institut Néel, (UPR 2940 CNRS), 25 avenue des Martyrs, BP 166, F-38042 Grenoble Cedex 9, France b Lawrence Berkeley National Laboratory, Advanced Light Source, 1 Cyclotron Road, Berkeley CA 94720, USA c National Synchrotron Light Source-II, Brookhaven, Upton, NY 11973, USA d Institut Pluridisciplinaire de Recherche sur l’Environnement et les Matériaux, CNRS, Hélioparc, 2 avenue Pierre Angot, F-64053 Pau Cedex 9, France e Laboratoire de Cristallographie, Résonnance Magnétique et Modélisation, UHP-CNRS Faculté des Sciences BP 70239 , F- 54506 Vandoeuvre-les-Nancy, France f Laboratoire Léon Brillouin, CEA-CNRS, F-91191 Gif-sur-Yvette, France g European Synchrotron Radiation Facility - 6 rue Jules Horowitz, F-38000 Grenoble, France h Centre de Recherche et de Restauration des Musées de France, CNRS, Palais du Louvre, Porte des Lions, 14 Quai François Mitterrand F-75001 Paris, France * Corresponding author: [email protected], [email protected] ABSTRACT The search for durable dyes led several past civilizations to develop artificial pigments. Maya Blue (MB), manufactured in pre-Columbian Mesoamerica, is one of the best known examples of an organic-inorganic hybrid material. Its durability is due to the unique association of indigo molecule and palygorskite, a particular fibrous clay occurring in Yucatan. Despite 50 years of sustained interest, the microscopic structure of MB and its relation to the durability remain open questions. Combining new thermogravimetric and synchrotron X-ray diffraction analyses, we show that indigo molecules can diffuse into the channel of the palygorskite during the heating process, replacing zeolitic water and stabilizing the room temperature phases of the clay. INTRODUCTION Due to the lack of natural stable blue pigments, ancient civilisations solved this problem by manufacturing various synthetic blue pigments. The first known artificial pigment is Egyptian Blue1 made in the second millennium BC. Chinese also produced a blue/purple pigment found on pottery2,3 and the terracotta soldiers of the First Emperor of Qin4. Production of Maya Blue in the Pre-Columbian Mesoamerica constitutes another example of the know-how of ancient people5,6. In the 1960s, the composition of this pigment was elucidated, and the durability of Maya Blue was imparted to the association of indigo heattreated with fibrous clays, such as palygorskite and sepiolite7. The exceptional chemical stability of Maya Blue is shown by the persistence of the blue colour in acidic and oxidizing conditions8,9. Maya Blue is now considered as one of the first ever artificial organic-inorganic hybrid10, and its exceptional stability is a source of inspiration in the design of new hybrid materials11,12,13,14,15. Palygor
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