The structures of Fe2+, Cr3+-, and Ti4+-modified montmorillonite prepared from ion exchange of the Na-clay with Fe2+, Cr3+, and Ti4+ were investigated. Conventional BET surface area and spectroscopic analysis by extended adsorption fine structure (EXAFS) were applied. It was shown that the BET surface area of Na-clay was similar to that of Fe-clay, but somewhat different from those of Cr- and Ti-clay; it decreased in the order Na- > Fe- > Ti- > Cr-montmorillonite. This sequence appeared to be consistent with the ion size Na+ (0.95 nm) > Fe2+ (0.65 nm) > Cr3+ (0.62 nm), except for Ti4+ (0.69 nm). EXAFS data showed that some Si atoms within montmorillonite were replaced by Ti atoms and that a neostructure of titanium oxide was formed. (C) 2004 Elsevier Inc. All rights reserved.