Hollow TiO₂/SiO₂ composite microspheres through reactive assembly across immiscible liquid interfaces

Titania (TiO₂) based photocatalysts have shown tremendous potential in tackling important issues related to energy, the environment, and water purification. The tunable morphologies of the TiO₂ based multicomponent composites are promising for the improvement of photocatalytic characteristics for practical applications. In this work, we report a one-step facile approach to achieve hollow silica/titania microspheres through the process of reactive assembly at the immiscible interface of micrometer-sized droplets. Scanning electron microscopy and small-angle neutron scattering revealed the hierarchal structure of the microspheres. Elemental mapping of the composite microspheres provided direct evidence of the incorporation of silica nanoparticles into the microspheres. The diffusion of reactant molecules and hydrolysis/condensation reactions across the phase boundary of the interface of two immiscible liquids controls the morphology of the microspheres and the size of TiO₂ nanoparticles. The silica/titania composite microspheres show excellent thermal stability against the anatase to rutile phase transition caused by inhibition of the growth of TiO₂ nanoparticles due to proximity of the silica nanoparticles. The photoelectrochemical measurements show that TiO₂-SiO₂ microspheres exhibit superior photocatalytic characteristics compared to the TiO₂ microspheres. The kinetics of dye degradation for TiO₂-SiO₂ microspheres is found to be significantly faster compared to TiO₂ microspheres which confirms the superior photocatalytic properties of the composite microspheres.