Microfluidic synthesis of titania shells on colloidal silica

Abstract

Coating colloidal silica core particles with titania layers of tunable thickness in a one-step, continuous flow process through controlled hydrolysis of titanium tetraethoxide (TEOT) is demonstrated. Silica particles were coated with titania layers of varying thicknesses by aging titanyl sulfate in the presence of silica particles. Thick, irregular layers were obtained via a multi-step coating process, involving repeated filtration and redispersion cycles. Thick coatings were obtained by the hydrolysis of titanium n-butoxide in ethanol. The methods to synthesize titania-silica particles include the use of polyelectrolyte-coated silica spheres as template for sol-gel reactions and the deposition of alternating coatings of cationic polyelectrolytes and anionic titania nanosheet on the silica surface. Photography-based microfabrication enables microfluidic designs that provide uniform addition through periodically spaced side inlets along the length of synthesis channel.