Synthetic Inorganic Ion-exchange Materials. XXXVII. Ion-exchange Behaviors of Alkylammonium Ions on Hydrous Titanium Dioxide

Abstract

Abstract Ion-exchange behavior of alkali hydroxide and alkylamines having different sizes and forms on hydrous titanium dioxide ion exchanger (HTDO) were studied. The uptakes of all the cations by HTDO indicated the ion-exchange stoichiometry at a pH range studied. The pH titration curves vary, depending on the cation species and the strength of the bases used: amorphous HTDO(Am-HTDO) behaves as a bifunctional acid towards strong bases and as a monofunctional acid towards weak bases. Am-HTDO shows an affinity series in the increasing order: large ions((C2H5)3NH+, (CH3)4N+, and (n-C4H9)4N+)<ions in medium size (CH3NH+, n-C3H7NH3+, n-C4H9NH3+ etc.)<small ions(Na+, K+, and NH4+). The large ions suffer from a strong steric effect, because of the limited space of the ion-exchange site available. The results correlate with the pore size distribution: the pore radius ranged from 4 to 7 Å in Am-HTDO degassed at 40 °C by a rotary pump. The maximum volume occupied by the alkylammonium ions exchanged (0.2–0.3 cm3/g), calculated by assuming cations to be unhydrated, is in good agreement with the value determined by N2 gas adsorption (0.16 cm3/g). An anatase-type HTDO showed a larger steric effect for uptake of the alkylammonium ions than that by the Am-HTDO, due to a decrease in the ion-exchange cavity.