Efficient photodegradation of zearalenone: Unraveling the potential of photocatalysts based on kaolin group minerals

The widespread occurrence of zearalenone (ZEN) in a variety of grain products and animal feed, coupled with its capacity to accumulate in the food chain, poses a significant health risk for both humans and animals. Its ability to induce estrogen-like effects may disrupt the body's estrogen levels, thereby contributing to reproductive system diseases, even at very low concentrations. The removal of ZEN from aqueous environment is predominantly challenging due to its weakly polar nature, compounded by its high thermal stability. Photodegradation, especially when applying mineral-based photocatalysts, stands out as a promising strategy for environmentally friendly mycotoxin removal. It not only demonstrates cost-effectiveness but also entails the production of negligible secondary pollutants.

Our research employed platy kaolinite (M), synthetic calcined kaolinite nanotubes (MNC), and halloysite purchased from Sigma-Aldrich (HS) as supports for TiO₂, g-C₃N₄, or combination of TiO₂/g-C₃N₄ semiconductors. Each synthesis was designed to consistently yield ~20 wt% of the semiconductor or its mixture in the samples, maintaining a TiO₂ to g-C₃N₄ ratio of 1:1. The sol-gel method was used for TiO₂ synthesis [1], while porous g-C₃N₄ nanosheets were prepared by heating melamine at 550°C, with the addition of ammonium chloride in a 1:1 ratio. The structural, textural, morphological, and light absorption properties of the obtained samples were characterized through XRD, N₂ adsorption/desorption, UV-Vis DRS spectroscopy, Raman spectroscopy, SEM, and TEM..

The UV-induced photodegradation kinetics experiments (365 nm, 10 mW/cm²) were carried out at a consistent initial ZEN concentration of ~10 ppm. ZEN concentrations were determined with high-pressure liquid chromatography (HPLC). The TiO₂-loaded photocatalysts exhibited the slowest photodegradation kinetics, resulting in the final removal of ~41.9% by the M-based sample, ~63.4% by the HS-based sample, and ~86.9% by the MNC-based sample. Conversely, the impregnation with g-C₃N₄ and TiO₂/g-C₃N₄ led to materials exhibiting the fastest kinetics, effectively removing over ~99.9% of the initial ZEN concentration. Notably, the nanotubular-based photocatalysts demonstrated slightly faster kinetics than those observed for the M-based materials and were comparable to those noted for the pure g-C₃N₄. Analogous experiments under visible light irradiation highlighted the synergistic effect for the combination of  both semiconductors, characteristic of Z-scheme heterojunction structures. Among the MNC-based samples, the least efficient photodegradation was demonstrated by the g-C₃N₄-containing sample (~13.7%), slightly higher for the TiO₂-containing sample (~20.3%), and the most efficient removal was observed for the sample containing both semiconductors (~36.6%).

The conducted experiments revealed a significant potential of kaolinite and halloysite nanotubes as carriers for semiconductors in the effective removal of ZEN from aqueous solutions. Future aspects of our research will involve detailed investigations into the degradation pathways of ZEN and the electrochemical characterization of the materials used.

This project was supported by the National Science Centre Poland, under a research project awarded by Decision No. 2021/43/B/ST10/00868.

References:
[1] Dziewiątka K., Matusik J., Trenczek-Zając A., Cempura G. (2023). TiO₂-loaded nanotubular kaolin group minerals: The effect of mineral support on photodegradation of dyes as model pollutants. Applied Clay Science, Elsevier, volume 245, 107123.