Solar photocatalytic ozonation of emerging contaminants detected in municipal wastewater treatment plant effluents by magnetic MWCNTs/TiO2 nanocomposites

Abstract

Magnetically separable catalysts with high solar photocatalytic ozonation activity were successfully synthesized. First maghemite and then titania (anatase) nanoparticles were deposited onto the multiwalled carbon nanotubes (MWCNTs) by co-precipitation and sol–gel methods. The synthesized catalysts were characterized by XRD, N₂ adsorption/desorption, TEM, XPS and VSM, and were applied for the removal of emerging contaminants (ECs) existing in urban wastewater through photocatalytic ozonation. Ozone alone can completely remove a mixture of the four ECs in water, but the mineralization degree was very low (44.9%). Photocatalytic oxidation led to a higher level of mineralization (48.3% TOC removal) in the experimental conditions, but some intermediate products such as phenolic compounds and carboxylates which are toxic and difficult to degrade were generated during the photocatalytic oxidation process. Photocatalytic ozonation led to the highest removal efficiency for TOC (65.7%), which suggested a lower concentration of intermediate products accumulated during photocatalytic ozonation, the integration of ozonation and solar photocatalytic oxidation improved the mineralization efficiency.