Catalytic Ozonation of 4-Nitrophenol in the Presence of Magnetically Separable Titanium Dioxide – Magnetite Composite

Abstract

This paper deals with determining catalytic activities of titania (TiO2) with various crystalline structures and magnetite (Fe3O4) during mineralization of 4-nitrophenol in aqueous media by ozonation. Among the titania samples under study, amorphized TiO2 was shown to have the highest catalytic activity, while magnetite was characterized by the lowest catalytic activity. A procedure is proposed to synthesize a magnetically separable composite (TiO2/Fe3O4) including amorphized titania and magnetite phases, which involves deposition of a catalytically active titania phase on preformed magnetite particles. We also studied the effect of mass ratio of titania and magnetite phases in the composite on its catalytic activity during 4-nitrophenol mineralization by ozonation. It was found that catalytic activity of composite increased as the amorphized titania phase was doped with magnetite phase up to 30% wt but as the magnetite portion in the composite catalyst was further increased, its activity decreased. According to Fourier transform infrared (FTIR) spectroscopy, content of catalytically active sites (hydroxyl groups of titania) in the composite catalyst decreases as compared to the pure phase of amorphized titania. Increase in catalytic activity of the composite as its magnetite content increases to 30% wt can be attributed to increase of accessibility of catalytically active sites (OH groups) for ozone, because specific surface area and total pore volume of the composite catalyst as determined by BET increase as compared to amorphized TiO2 and catalytically active titania phase is located mostly on surface of magnetite particles which is indicated by scanning electron microscopy (SEM) results and electrophoretic light scattering (ELS) data. It was shown that the obtained composite catalyst of optimized composition, in spite of its fine particles, can be easily recovered from aqueous phase by magnetic field and used repeatedly in ozonation in order to promote water purification process.

Keywords

• A – catalytic activity; C0 and C – initial and current total organic carbon concentrations in aqueous phase, respectively, mol/l; keff,c and keff – effective rate constants of 4-nitrophenol mineralization during ozonation with and without a catalyst, respectively, min−1; t – time, min.