Magnetically separable titania-coated nickel ferrite photocatalyst

A magnetically separable photocatalyst was prepared by a continuous multi-step spray pyrolysis process. In the first step, nickel ferrite core particles were prepared by an ultrasonic spray pyrolysis. In the second step, tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TTIP) were sequentially injected and coated on the surface of the core particles. The sequentially coated layers were decomposed to form silica and titania layers in a final furnace reactor. The titania–silica layered particles displayed higher photoactivity than particles coated only with titania and titania–silica mixture-coated particles. The photoactivity of the titania–silica layered particles remained unchanged after magnetic separation and washing. This confirms that the adhesion between the core particles and the coated layer is strong enough to withstand vigorous mixing. It also implies that the formation of free particles of silica or titania is negligible in the second reactor. The strong adhesion between the coated layer and the nickel ferrite core is attributed to the features of the multi-step process, wherein the core particles are exposed to high temperate in the second reactor for only a few seconds and transformation of the core particles into non-magnetic particles is prohibited.