Continuous Synthesis of Monodisperse Yolk–Shell Titania Microspheres

A microfluidic strategy is developed for continuous synthesis of monodisperse yolk–shell titania microspheres. The continuous flow synthesis of titania microparticles is achieved by decoupling the microdroplet formation and interfacial hydrolysis reaction steps by utilizing a polar aprotic solvent as the continuous phase in the microreactor. The decoupling of the precursor microdroplet formation and the hydrolysis reaction allows titania synthesis throughputs an order of magnitude higher than those previously reported in a single-channel flow reactor (∼0.1 g/h calcined microparticles), without affecting the microreactor lifetime due to clogging. Flow synthesis and dynamics across a broad range of precursor flow rates are examined, while effects of flow synthesis parameters, including the precursor to continuous phase flow rate ratio, precursor composition, and calcination temperature on the surface morphology, size, and composition of the resulting titania microparticles, are explored in detail. Titania microparticle size can be controlled by variation in the precursor to continuous phase flow rate ratio. The surface morphology and porosity of the in-flow synthesized titania microparticles can be varied by adjusting the precursor composition, while the crystalline phase can be tuned by varying the calcination temperature.