Synthesis and Magnetic Properties of Iron Pillared Montmorillonites

Abstract

We have investigated the magnetic properties and structural changes of iron pillared montmorillonites in terms of likely exchange interactions between magnetic ions and/or magnetic ions separated by oxygen ions, as well as their distribution in the unit cell. Iron pillared montmorillonites were synthesized by two different methods. The first one consists of expanding Na⁺ and Ca²⁺ montmorillonite with ethylene glycol from 12.5 and 15 Å respectively to 17 Å. An iron polycation solution is prepared by hydrolyzing a solution of FeCl₃ with Na₂CO₃ to yield Fe _n (OH) _m ^(3n−m)+. The treated montmorillonite is then stirred into the polycation solution. The X-ray powder pattern shows an expansion to 24–25 Å. Secondly CO₂ is bubbled into a solution of tetrabutylammonium hydroxide (TBAOH) or tetramethylammonium hydroxide (TMAOH) and a solution of FeCl₃ is stirred into it. The montmorillonite is added to this solution. The X-ray powder pattern shows spacings varying from 17 Å (TBAOH) and 14 Å (TMAOH) to 15 Å and 16 Å. Both procedures yield montmorillonites containing intercalated iron in the gallery space. Quantitative spectrophotometric analyses of the intercalated phases show varying amounts of iron in the gallery spaces. The straight line sections of the curve of inverse magnetic susceptibility versus temperature show a negative Weiss constant for Na⁺ montmorillonite and for the phases prepared using the TBAOH and TMAOH solutions. A positive Weiss constant is seen for the montmorillonite material prepared with the polycation solutions.