S-doped TiO₂ photocatalyst for visible LED mediated oxone activation: Kinetics and mechanism study for the photocatalytic degradation of pyrimethanil fungicide

The degradation of pyrimethanil (PYR) was investigated through the activation of oxone by the S-TiO₂ (ST) photocatalyst under visible LED irradiation. The catalyst characterization revealed that the sulfur doping mechanism was based on the cation (S⁶⁺) substitution of Ti⁴⁺ in TiO₂ lattice. The optimal molar ratio of S/Ti at 0.25 was proven efficient in the PYR degradation. Influences of various reaction parameters including ST loading, oxone dosage, PYR concentration, and initial solution pH were examined. SO₄^•-, ^•OH, ¹O₂, O₂^•-, and h⁺ were found to be the reactive species generated in the ST/Oxone/Vis LED process. Different natural water constituents exerted dissimilar effects because of the generation of additional reactive species or their radical scavenging capabilities. Moreover, the reusability test indicates the ST photocatalyst is reusable and stable. A series of degradation intermediates was detected via four major degradation pathways. Overall, the ST/Oxone/Vis LED process was demonstrated to be a promising approach for the removal of organic pollutants.