Changes in acidity of Fe-pillared/delaminated smectites on heat treatment

Hydroxy-iron smectites were prepared using solutions with a OH/Fe content of about 1.2 and 2.5. To study thermal stability, the samples were heated in air at temperatures between 473 and 873 K. Changes in surface chemistry imposed by heat treatment were evaluated using potentiometric titration. The pK(a) distributions revealed peaks characteristic for iran complexes (Fe-III) deposited on the surface of smectite. Heal treatment resulted in significant changes in the chemistry of the material and creation new species; however, the sorbents textural properties did not alter significantly. Data obtained from X-ray diffraction and sorption of nitrogen demonstrate that iron species are adsorbed mainly on the external surface of smectite and that the properties of the final products depend upon the OH/Fe ratio of hydroxy-iron solutions used in their preparation. (C) 1997 Academic Press.