Preparation of TiO2-nanotube-based photocatalysts and degradation kinetics of patulin in simulated juice

Abstract

Patulin (PAT) is a heat-stable mycotoxin produced by several fungal species belonging to the genera Penicillium and Aspergillus, in damaged or moldy fruits. In this work, TiO2 nanotubes (TNTs) were prepared as photocatalysts for the degradation of PAT in simulated juice, by a hydrothermal method coupled with calcination treatment. Their physical, chemical, optical, and adsorption properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), photoluminescence (PL), and N2 adsorption–desorption isotherms, to optimize the preparation conditions. The photocatalytic activities of the TNTs were evaluated by the degradation of PAT in a simulated juice, under ultraviolet (UV) irradiation. The results showed that TNTs-450 calcinated at 450 °C for 2 h had high adsorption performance and photocatalytic activity in the amorphous state, and 1000 mg/L of TNTs-450 can completely degrade 1000 μg/L PAT in the simulated juice within 25 min. The kinetics of the photocatalytic degradation of PAT were then studied under various reaction conditions, showing that the photocatalytic degradation of PAT by TNTs-450 in the simulated juice followed first-order kinetics (R2 ≥ 0.97). However, the UV light intensity and the pH of the reaction system are the main factors affecting the rate of PAT degradation. In addition, the Langmuir–Hinshelwood model can explain the photocatalytic degradation of PAT by TNTs-450 well, following the adsorption-surface reaction-desorption step.