Synergism between peroxymonosulfate and LaCoO3‐TiO2 photocatalysis for oxidation of herbicides. Operational variables and catalyst characterization assessment

BACKGROUND This paper reports the use of novel coupled LaCoO3‐TiO2 as photocatalyst with double route of peroxymonosulfate (PMS) activation. First, as a photocatalyst due to titania; and second, through PMS heterogeneous decomposition onto LaCoO3 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 (LaCoO3 aggregates linked to a variety of shapes and sizes of TiO2), XRF (6.1% of LaCoO3), XPS (superficial Co3+, La3+ and Ti4+), XRD (anatase, rutile and rhombohedral LaCoO3) and UV–vis diffuse reflectance (visible range absorption and bandgap of 2.88 eV for TiO2). CONCLUSION Catalysts based on LaCoO3‐TiO2 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