Post-harvest treatment of carbendazim in Chinese chives using TiO₂ nanofiber photocatalysis with different anatase/rutile ratios

Carbendazim residues in Chinese chives were treated by photocatalysis using the following three electrospun TiO₂ nanofibers: TTiP/PVP, TTiP/PVAc, and TBOT/PVP. The as-spun fibers were calcined at 500–650 °C to achieve anatase/rutile (A/R) ratios of 100:0, 80:20, 70:30, 50:50, and 30:70. The obtained anatase crystallite sizes were in the range of 13.9–28.1 nm, while the rutile crystallite sizes were 21.1–30.6 nm. The experiments were conducted in glass reactors. These were filled with water and each type of the fiber and irradiated from above by black light lamps for 5 min. Then, 50 g of the samples of Chinese chives was immersed for 5, 15, 30, and 60 min. Carbendazim in the chives was extracted using the matrix solid-phase dispersion (MSPD) method and analyzed using UHPLC. The ˙OH formation from each fiber type was investigated using the coumarin fluorescent probe method.

An A/R ratio of 70:30 yielded the highest ˙OH formation, as well as the greatest carbendazim degradation. Rutile plays a crucial role in inhibition of electron-hole recombination and ˙O₂⁻ stabilization. The degradation efficiencies for carbendazim from TTiP/PVP, TTiP/PVAc, and TBOT/PVP fibers after a 60-min treatment were 98.6–99.5%, 91.2–97.1%, and 99.5–99.9%, respectively. The TTiP/PVP and TBOT/PVP fibers produced levels of retained carbendazim in the chives that were within EU maximum residue limits of 0.1 mg/kg. The thermal stability of the TTiP/PVAc fiber limited ˙OH formation and carbendazim degradation.