High-efficiency photo-Fenton Fe/g-C3N4/kaolinite catalyst for tetracycline hydrochloride degradation

Traditional homogeneous Fenton reactions can only be carried out under acidic conditions; however, visible light can greatly enhance the activity and stability of iron-doped semiconductor catalysts in the Fenton system. Therefore, in this study, a commercially applicable Fe/graphitic carbon nitride (g-C3N4)/kaolinite composite photocatalyst was prepared for the first time using an in-situ calcination process. The results showed that Fe ions and g-C3N4 were successfully loaded onto kaolinite with a two-dimensional uniform sheet structure. The as-synthesized Fe/g-C3N4/kaolinite composite containing 0.9 mmol of Fe (Fe/CN/K-0.9) showed a degradation efficiency of 89% for tetracycline hydrochloride (TCH) within 80 min in the photo-Fenton system. Compared with photocatalytic degradation (29.6%) and Fenton degradation (76.6%), a photo-Fenton degradation efficiency of 85% was maintained after three cycles. Free radical scavenging experiments also showed that hydroxyl radicals were the main active substances. The enhanced photocatalytic activity of the composite was attributed to the large specific surface area of kaolinite, which could effectively adsorb TCH. Furthermore, FeIII acted as a photo-generated electron acceptor, which not only avoided photo-generated electron-hole recombination but also effectively reduced the consumption of H2O2 to realize a stable FeII/FeIII cycle reaction, thus improving photo-Fenton catalytic activity.