Preparation And Fenton-Like Reaction Mechanism Of Fe₃O₄@HNTs

In heterogeneous Fenton,nanoreactors with nano-confinement effect greatly improve the effectiveness for organic pollutants removal with shorter reactive oxygen species remove distance and longer free radicals life,compared with traditional heterogeneous Fenton catalysis.Citric Acid modified Fe²⁺cations with negative charges could spontaneously reside in the lumen of halloysite nanotubes（HNTs）via electrostatic interactions with negatively charged Al-OH layer located in the tube of the HNTs.In this study,this ligand-assisted principle was used for in-situ preparation of Fe₃O₄nanoparticles in the lumen of HNTs followed by water bath method,and a nanoreactor was obtained.The phase composition and microtopography of Fe₃O₄@HNTs nanoreactor were investigated by X-ray diffraction（XRD）,Fourier infrared spectroscopy（FT-IR）,scanning electron microscopy（SEM）,and transmission electron microscopy（TEM）.Specific surface area（SSA）was analyzed by Brunauer-Emmett-Teller（BET）,and the magnetism was measured by Vibration Sample Magnetometer（VSM）.The acid fuchsin（AF）was employed as the target pollutant.The Fenton reaction efficiency of Fe₃O₄@HNTs nanoreactor has been systematically evaluated,and the kinetics of this process has also been investigated.Combined with the UV absorption spectra（UV-vis）,the density functional theory（DFT）,the degradation of AF in different systems,the iron leaching,the decomposition efficiency of H₂O₂,the radicals quenching tests,and the generation efficiency of·OH,the heterogeneous Fenton reaction mechanism of Fe₃O₄@HNTs catalytic degradation of AF was proposed.The characterization results showed that the catalytic performance of Fe₃O₄@HNTs nanoreactor is the best when the content of Fe₃O₄is 50%,and the synthesis temperature and time are 95°C and 3h,respectively.When the initial p H,H₂O₂concentration,catalyst dosage,and AF concentration were 5.0,19.59 m M,0.5g/L,and 50 mg/L,respectively,the decolorization rate of AF was as high as 100%in120 minutes.The kinetic studies revealed that the AF degradation reaction in Fe₃O₄@HNTs-H₂O₂system followed the Behnajady-Modirshahla-Ghanbery（BMG）model.The radicals quenching testing demonstrated that the contribution of radicals to AF degradation were·OH and ¹O₂,but followed·OH>¹O₂.Mechanism studies have indicated that the degradation of AF molecules mainly included two steps:one is the diffusion and enrichment of dye molecules in the lumen of Fe₃O₄@HNTs,and the other is a heterogeneous Fenton reaction triggered by Fe₃O₄nanoparticles.The efficient and rapid rate of the Fenton reaction resulted from the“nano-confined”effect of nanoreactor Fe₃O₄@HNTs.The micro space has enlarged concentrations of effective radicals and shortened the Gibbs free energy of Fe²⁺/Fe³⁺.