Study on a novel POM-based magnetic photocatalyst: Photocatalytic degradation and magnetic separation

The photocatalytic performance of a novel polyoxometalate (POM)-based magnetic photocatalyst was studied by photocatalytic degradation of a model compound (formic acid) in an annular fluidized bed photoreactor. Degradation rate, apparent quantum efficiency, and energy efficiency were evaluated and compared with suspended TiO2 fine particles (Degussa P25) and quartz sand supported TiO2 photocatalysts. All degradation experiments were conducted under fully irradiated photoreaction (FIP) conditions. Results showed that this novel POM-based magnetic photocatalyst exhibited 2.7–4.2 times higher initial degradation rate and 2.7–3.8 times higher apparent quantum efficiency than the quartz sand supported TiO2 photocatalyst, depending on the pH of the solution. Though it had lower degradation efficiency and apparent quantum efficiency than suspended P25, it was proved that this POM-based magnetic photocatalyst could be efficiently separated from treated water by high-gradient magnetic separation (HGMS), while the separation for P25 fine particles is quite difficult. The magnetic field/gradient in a lab-constructed HGMS was modeled and simulated by finite element analysis (FEA) to examine the particle capture feasibility. Experimental results proved that separation efficiency higher than 90.1% could be achieved under investigated conditions, i.e., flow velocity lower than 1.375 mm s−1 under the studied magnetic photocatalyst concentration.