Comparative studies on Fenton-like reactions catalyzed by Fe₃O₄ loaded inside and outside halloysite nanotubes for the removal of organic pollutants

In this work, Fe₃O₄ nanoparticles (NPs) loaded inside and outside halloysite nanotubes (HNTs) were prepared and developed as the heterogeneous Fenton-like catalysts for the removal of representative organic pollutants. Characterization results indicated that the samples with Fe₃O₄ NPs loaded outside the HNTs lumen (Fe₃O₄/HNTs) and inside the HNTs lumen (Fe₃O₄@HNTs) were successfully prepared. Both samples had typical magnetic hysteresis loops, while Fe₃O₄@HNTs exhibited higher magnetization intensity. The comparative experiments showed that Fe₃O₄@HNTs had better Fenton-like catalytic ability than that of Fe₃O₄/HNTs in the degradation of various organic pollutants. Taking Rhodamine B (RhB) as an example, the adsorption thermodynamics and kinetics of RhB onto Fe₃O₄/HNTs and Fe₃O₄@HNTs were also investigated. The comparative results demonstrated that the adsorption ability of Fe₃O₄/HNTs was better than that of Fe₃O₄@HNTs. Moreover, the dissolved concentration of Fe²⁺ and production amount of hydroxyl radical (·OH) in the Fe₃O₄@HNTs-H₂O₂ system were significantly higher than those in the Fe₃O₄/HNTs-H₂O₂ system. Based on aforementioned comparison, the nano-confinement effect in the Fe₃O₄@HNTs-H₂O₂ system was verified. This work provides meaningful guidance for the cheap and convenient design of nanoreactors for Fenton-like applications.