Sol-Gel Synthesis of Complex Titanates in Micro-Emulsions

Amorphous precursor nanopowders of zirconolite (CaZrTi 2 O 7 ) were prepared using a water-in-oil micro-emulsion synthesis, with Ti(O i C 3 H 7 ) 4 , Zr(O n C 3 H 7 ) 4 and either Ca(OC 2 H 5 ) 2 or an aqueous Ca(NO 3 ) 2 solution as precursors. The stoichiometry and structural evolution of the nanoparticles were investigated using a range of techniques, including ICP-MS, TEM, gas adsorption and vibrational spectroscopy. The use of Ca(OC 2 H 5 ) 2 led to slightly sub-stoichiometric nanopowders (Ca x ZrTi 2 O 6+x , x = 0.8), following washing. Lower values of x were obtained in the washed nanopowders when using Ca(NO 3 ) 2 , with x = 0.004, 0.022 or 0.52 at pH 2, 7 or 13, respectively. In the latter system, a comparison between the washed and unwashed nanopowders revealed that 25% of the calcium was lost during washing. The Ca(NO 3 ) 2 was found to form unstable tetraamine complexes within the reverse micelles at high pH, which transformed into Ca(OH) 2 on ageing. The Ca(OH) 2 can then interact with the hydrolysed titanium/zirconium alkoxides, and thus be integrated chemically into the final nanoparticle structure.