Photocatalysis of S -metolachlor in aqueous suspension of magnetic cerium-doped mTiO 2 core–shell under simulated solar light

Magnetic cerium-doped mesoporous titanium dioxide was synthesized by combining sol–gel method and calcination using tetrabutanate and ammonium cerium nitrate as precursors and Pluronic P123 as a template coating on iron oxide covered with carbon in ethanol. The magnetic Ce-doped catalyst showed only anatase structure with a slight increase in lattice parameters compared to the undoped catalyst. The Ce L III -edge X-ray absorption near-edge spectroscopy (XANES) spectra showed Ce 3+ , and the cerium substitution doping into titanium dioxide was proposed. Degradation of S -metolachlor in aqueous magnetic photocatalyst suspension followed (pseudo) first-order kinetics in the presence of 0.5 g L −1 of γ-Fe 2 O 3 @C@0.16 mol% Ce-mTiO 2 with a half-life of 55.18 ± 1.63 min. Fifteen degradation products were identified, and their transformation routes of the photocatalytic degradation were then proposed. Complementary toxicity assessment of the treated S -metolachlor solution was undertaken with Environment Canada’s algal microplate assay measuring growth inhibition (72-h IC 50 ) in the freshwater chlorophyte Pseudokirchneriella subcapitata . This test method revealed a significant decrease in toxicity (1.7-fold reduction after 180 min of irradiation treatment), thereby confirming that the by-products formed following photocatalysis would be less harmful from an environmental point of view. Photocatalytic degradation of S -metolachlor thus appears to hold promise as a cost-effective treatment technology to diminish the presence of this herbicide in aquatic systems.