Degradation of Glyphosate in Soil Photocatalyzed by Fe₃O₄/SiO₂/TiO₂ under Solar Light

Abstract: In this study, Fe₃O₄/SiO₂/TiO₂ photocatalyst was prepared via a sol-gel method, and Fe₃O₄ particles were used as the core of the colloid. Diffraction peaks of Fe₃O₄ crystals are not found by XRD characterization, indicating that Fe₃O₄ particles are well encapsulated by SiO₂. FTIR characterization shows that diffraction peaks of Ti-O-Si chemical bonds become obvious when the Fe₃O₄ loading is more than 0.5%. SEM characterization indicates that agglomeration occurs in the Fe₃O₄/SiO₂/TiO₂ photocatalyst, whereas photocatalysts modified by Fe₃O₄/SiO₂ present excellent visible light absorption performance and photocatalytic activity, especially when the Fe₃O₄ loading is 0.5%. Photocatalytic degradation of glyphosate in soil by these photocatalysts under solar irradiation was investigated. Results show that 0.5% Fe₃O₄/SiO₂/TiO₂ has the best photocatalytic activity. The best moisture content of soil is 30%~50%. Degradation efficiency of glyphosate reaches 89% in 2 h when the dosage of photocatalyst is 0.4 g/100 g (soil), and it increased slowly when more photocatalyst was used. Soil thickness is a very important factor for the photocatalytic rate. The thinner the soil is, the better the glyphosate degradation is. Degradation of glyphosate is not obviously affected by sunlight intensity when the intensity is below 6 mW/cm² or above 10 mW/cm², but it is accelerated significantly when the sunlight intensity increases from 6 mW/cm² to 10 mW/cm².