Transformation of ultrafine titanium dioxide particles from rutile to anatase at negatively charged colloid surfaces

The phase transition of TiO2 from rutile to anatase has not been reported below the transition temperature from anatase to rutile, This work reports the new observation that ultrafine rutile-type particles are transformed into anatase by contacting the strongly negatively charged colloid particles such as V2O5 . nH(2)O, MoO3, and H2WO4 . nH(2)O. The weakly negatively charged particles of silica and montmorillonite did not change the structure, More active Nb2O5 . nH(2)O and Ta2O5 . nH(2)O reacted chemically with TiO2 to produce new compounds, Conversely, anatase-type TiO2 was changed into rutile by contacting with HCl solution, From these facts it is concluded that chloride ions at the interface affect to form the rutile-type TiO2, although anatase is thermodynamically stable at low temperatures, It is concluded that the surface field of the strongly negatively charged crystalline particles in an acidic condition eases the TiO2 article to crystallize into a thermodynamically stable one. (C) 1997 Academic Press.