Binnessites prepared by ion exchange. Structural evolution with temperature

Birnessites containing Na+ or K' in the interlayer have been prepared following a sol-gel method, with an initial glucose/cation ratio of 1 or 1.5. The solids have been submitted to ion exchange with Li+, Mg2+, and Cu2+, and all the materials have been characterised by several physicochemical techniques (elemental chemical analysis, X-ray diffraction, FT-IR spectroscopy, thermal analysis and specific surface area assessment). Total cation exchange was not achieved in my case, although sodium is better exchanged than potassium. Exchange is larger for Li', lower for Cu2+ and even lower for Mg2+. Ionic exchange is topotactic, and the layered structure is maintained in all cases, with an interlayer spacing close to 7 Angstrom. The samples are stable up to 600 degreesC; above this temperature cryptomelane (a 2x2 tunnel structure) is formed in most of the samples containing potassium, while LiMn2O4 spinel is formed is Li was present in the birnessite.