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

Abstract

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 TiO 2 fine particles (Degussa P25) and quartz sand supported TiO 2 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 TiO 2 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.