Synergism between peroxymonosulfate and LaCoO 3 ‐TiO 2 photocatalysis for oxidation of herbicides. Operational variables and catalyst characterization assessment

BACKGROUND This paper reports the use of novel coupled LaCoO 3 ‐TiO 2 as photocatalyst with double route of peroxymonosulfate ( PMS ) activation. First, as a photocatalyst due to titania; and second, through PMS heterogeneous decomposition onto LaCoO 3 particles. Thus, photocatalytical activity was tested for removing a mixture of four herbicides of different recalcitrance (metazachlor, tembotrione, tritosulfuron and ethofumesate). RESULTS The presence of light and PMS highly enhanced herbicides removal rate: 3.5–5 times increases were obtained with UVA light. Oxidant concentration, catalyst load, pH and temperature were assessed. Herbicides were completely oxidized depending on their recalcitrant nature and the operational variables. 55% TOC conversion was reached using Oxone® 5 × 10 −4 mol L −1 . Phytotoxicity assays denoted no inhibition after 180 min of photocatalytic treatment (∼80% initial inhibition). Solid properties of Co/Ti = 0.1:1 ratio were studied by means of SEM ( LaCoO 3 aggregates linked to a variety of shapes and sizes of TiO 2 ), XRF (6.1% of LaCoO 3 ), XPS (superficial Co 3+ , La 3+ and Ti 4+ ), XRD (anatase, rutile and rhombohedral LaCoO 3 ) and UV –vis diffuse reflectance (visible range absorption and bandgap of 2.88 eV for TiO 2 ). CONCLUSION Catalysts based on LaCoO 3 ‐TiO 2 combined with peroxymonosulfate seem to be suitable for removing organic pollutants, with a moderate conversion of TOC and elimination of toxicity. © 2017 Society of Chemical Industry