Journal of Materials Science Research; Vol. 12, No. 1; 2023 ISSN 1927-0585 E-ISSN 1927-0593 Published by Canadian Center of Science and Education 36 Solid-State Characterization of Heteropolyacid-Phyllosilicate Complexes: Structural, Morphological and Thermal Properties Pascal Y. Vuillaume 1 , Asmae Mokrini 2 , Lucie Robitaille 2 , Philippe Bébin 1 & Lori Leblond 1 1 COALIA, 671 Blvd. Frontenac West, Thetford Mines, Qc, G6G 1N1 Canada 2 National Research Council Canada, Industrial Materials Institute, Boucherville, Qc, J4B 6Y4 Canada Correspondence: Pascal Vuillaume, COALIA, 671, Bould. Frontenac West, Thetford Mines, Qc, G6G 1N1 Canada. Tel: 1-418-814-8264. E-mail: pvuillaume@coalia.ca Received: April 16, 2023 Accepted: May 16, 2023 Online Published: May 23, 2023 doi:10.5539/jmsr.v12n1p36 URL: https://doi.org/10.5539/jmsr.v12n1p36 Abstract We have previously described the complex formation from a synthetic smectite clay, Sumecton SA (SSA), and the heteropolyacid (HPA), 12-phosphotungstic acid (PTA). Three new synthetic layered aluminosilicate clays of the smectite- [Lucentite SWN (SWN)] and (fluoro)mica-type [Tetrasilicic mica (TSM); Somasif ME100, (SME)] have been self-assembled with PTA, at a specific PTA-clay weight ratio of 5. New protogenic inorganic complexes have been prepared for the future fabrication of proton exchange membrane for fuel cell devices (PEMFC). Complex formation, thermal and structural properties of PTA-phyllosilicate complexes have been investigated using EDX, XRD, SEM, and DRIFT. EDX indicates that complexes incorporate a substantial amount of PTA (50-60% w/w) and that a moderate depletion of Mg 2+ ions from octahedral layers of micas clays occurs during the process compared to smectite ones. In contrast, a significant amount of F is removed from the octahedral framework of the mica clays. DRIFT experiments indicate that the Keggin structure is preserved within all complexes and that complex formation predominantly involves the external oxygen (W-O d ) of PTA. According to Patterson functions, coherence lengths - which reflect for the virgin clays the extent of the longitudinal platelet stacking (L c ) - of the two smectite clays (L c ~25 Å) are significantly lower than for their analogous of the mica type (L c = 180-225 Å). Clays in complexes are characterized by the loss of in-plane organization but are still partially ordered. The nature of the order is still speculative but could be related to the formation of a new inorganic PTA species formed during the complex formation. Compared to the virgin clays, the order of smectite complexes is maintained in the same range (L c = 27-42 Å) while for mica complexes, coherence lengths are dramatically reduced to ~ 60 Å. All PTA- activated complexes contain a substantial amount of amorphous silica, which tends to increase when heated at temperatures above 280 o C. However, the Keggin structure within the complexes is at least stable up to 280 o C and even, for the most robust TSM complex, up to 450 o C. Keywords: Clays, heteropolyacids, protogenic complexes, Patterson functions, coherence length 1. Introduction Phyllosilicates clays are layered self-assemblies built-up from silicate (Si-O) nanoplates. Within this class of inorganic materials are found the swelling smectite- and mica-type clays. Both have a similar structural edifice (see Figure 1); the distinction between the two groups is based on the surface charge density and elemental composition. Micas are characterized by a higher negative charge density (~1 per formula unit cell layer) than smectite (~0.2 to 0.6). (Note 1) Because of their low cost, availability and unusual intercalation properties, a large variety of natural swelling smectite and micas clays has been used for forming new functional materials (Sanchez, Julian, Belleville, & Popall, 2005). Some acid activated phyllosilicates clays have been used as catalytic supports (Yadav, 2005) or for the fabrication of proton exchange membrane for fuel cell devices (PEMFC) (Herring, 2006). In the PEMFC field, there is an immediate need to design viable polyelectrolyte membrane with high protogenic conductivity capable of operating at low humidity level and/or high temperature and durability (Herring, 2006).