Formation of uniform size anatase nanocrystals from bis(ammonium lactato)titanium dihydroxide by thermohydrolysis
Bis(ammonium lactato)titanium dihydroxide decomposes in neutral aqueous solution at temperatures above 100 °C to produce anatase nanocrystals of preferentially oblate habitus, and with a very narrow size distribution. There is almost no dependence of size on precursor concentration, and a time dependence is observed only in the very beginning of crystal growth. The crystal size is mainly determined by the reaction temperature, increasing from ca. 2 nm at 120 °C to about 20 nm at 300 °C. We assume the temperature dependent formation of a layer of byproduct ammonium lactate at the crystallite surface where it interferes with growth reactions. After removal of this layer, continued heating yields larger crystallites in typical anatase shapes, indicating that Ostwald ripening has now become effective.