Layered hydrous titanium dioxide: potassium ion exchange and structural characterization

Abstract

which is obtained from potassium tetratitanate (K2Ti409), has been studied by examining the titration curve in relation to the structural change of the material. Structural characterization has also been performed for layered hydrous titanium dioxide and its potassium ion exchanged phases. The material has almost the same sheet structure of [Ti40$In as that of potassium tetratitanate, in which hydronium ions and hydroxylated protons are situated as exchangeable ones. The ion exchange proceeds stepwise through four stages (0-25, 25-50, 50-70, and 70-98% conversion), indicating that potassium ions replace the exchangeable protons one by one. During the process four solid phases appeared with different interlayer distances and cation/water contents: one-fourth-exchanged phase, &, SH1,5Ti409.0.6H20; half-exchanged phase, KHTi409.0.5H20; approximately three-fourths-exchanged phase, K1.4H,,6Ti409.1 .2H20 and fully exchanged phase, K2Ti409.2.2H20. The study of the unit cell dimensions of these phases indicates that the ion exchange takes place accompanied by a contraction/expansion of interlayer distances and a shift of adjacent sheets in relation to each other along the c axis. A lattice type change occurred during the process, which is considered to be due to the arrangement of potassium ions and/or water molecules incorporated in the interlayer space. A structural model is proposed for the fully exchanged phase in which interlayered potassium ions and water molecules occupy the sites arranged' in a double row and shifted above and below the levels at y = 0 and Models for the other ion-exchanged phases are also proposed to interpret the ion-exchange mechanism from a structural aspect.