Novel photocatalyst: Titania-coated magnetite. Activity and photodissolution

Magnetic photocatalysts were synthesized by coating titanium dioxide partic les onto colloidal magnetite and nano-magnetite particles. The photoactivit y of the prepared coated particles was lower than that of single-phase TiO2 and was found to decrease with an increase in the heat treatment. These ob servations were explained in terms of an unfavorable heterojunction between the titanium dioxide and the iron oxide core, leading to an increase in el ectron-hole recombination. Interactions between the iron oxide core and the titanium dioxide matrix upon heat treatment were also seen as a possible c ause of the observed low activities of these samples. Other issues consider ed include the physical and chemical characteristics of the samples, such a s surface area and the presence of surface hydroxyl groups. Depending on th e calcination conditions, these photocatalysts were found to suffer from va rying degrees of photodissolution. Photodissolution tests revealed the grea ter the extent of the heat treatment, the lower the incidence of photodisso lution. This was explained in terms of the stability of the iron oxide phas es present, as well as the photoactivity of the titanium dioxide matrix. Ou r studies revealed that the observed photodissolution was in fact to be ind uced photodissolution. That is, the photogenerated electrons elevated to th e conduction band of the titanium dioxide nanocrystals were being injected into the lower lying conduction band of the iron oxide core, leading to its reduction.