P25 titanium dioxide coated magnetic particles: Preparation, characterization and photocatalytic activity

Abstract

The photocatalytic properties of magnetic iron(II,III) oxide particles coated with different wt% of commercially available P25 TiO2 (P25) using a simple wet impregnation method were measured. The produced materials were characterized by XRD, XPS, SEM, TEM, EDX, FTIR, ICP, Magnetic Property Measurement System (MPMS) and BET (N2). After calcination at 500°C of the magnetic particles that was loaded only with P25, the P25 was strongly bound through a redox reaction with the magnetic particles. It was found that the P25 surface coverage was almost complete (>95%) at a 1:1 mass loading ratio; at higher P25 mass ratios, a thicker coating was obtained. However, the photocatalytic degradation rates of terephthalic acid (TPA) and phenol for these particles at all P25 loadings was lower than those obtained for pure P25 on a per TiO2 mass basis. Precoating the magnetic particles with a SiO2 sol-gel layer prevented the electron hole migration and oxidation of magnetite to hematite, but also led to a weakly bound P25 layer that was removed by rinsing. This was overcome by adding a second TiO2 sol-gel on top of the SiO2 coated magnetic particles coating for anchoring the P25 particles to the surface. While magnetic particles consisting of a silica undercoat followed by a TiO2 sol-gel coating as the photocatalytic layer have been reported, our approach is to use the TiO2 sol-gel coating as an adhesion layer to anchor P25 particles. The P25 adhered strongly to this underlying TiO2 sol-gel layer without significant loss of surface area. In both P25 and our produced photocatalyst, during the photocatalytic reaction P25 is in direct contact with water and the process occurs on the P25 and water interface. As a result, the photocatalytic degradation rates of TPA and phenol by the P2- coated magnetic particles were found to be equivalent to those of P25. The pseudo-first order rate constants in the P25 mass basis for photocatalytic degradation of TPA were 0.0152±0.003min−1 and 0.0144±0.007min−1 using pure P25 and SiO2 sol-gel/TiO2 sol-gel/P25 coated magnetic particles, respectively. The rate constant for phenol photocatalytic degradation was reported 0.09±0.02min−1 for pure P25 and 0.10±0.04min−1 for SiO2 sol-gel/TiO2 sol-gel/P25 coated magnetic particles. The similar specific surface area of the P25 powder and the P25 anchored to the surface in SiO2 sol-gel/TiO2 sol-gel/P25 coated magnetic particles is the reason for these similarity for rate constants.