Comparative Studies On Fenton-Like Reactions Catalyzed By Fe₃O₄ Loaded In And Out Of Halloysite Nanotubes

With the rapid modernization of society,pollution of the water environment has become a problem that must be addressed.Heterogeneous Fenton reaction systems have attracted the attention of researchers in recent years as a pollutant treatment method with high efficiency,simple operation,and no secondary contamination.However,the ultra-short lifetime of hydroxyl radical（·OH）in heterogeneous Fenton reaction is a factor that limits its degradation ability.In order to improve this problem,two catalysts,Fe₃O₄loaded outside of halloysite（HNTs）tube（Fe₃O₄/HNTs）and Fe₃O₄loaded inside HNTs tube（Fe₃O₄@HNTs）,were constructed in this study and their structural differences were analyzed by a series of characterization methods.With Rhodamine b（Rh B）as the target pollutant and Fe₃O₄/HNTs and Fe₃O₄@HNTs as catalysts,the influence of reaction conditions on the reaction efficiency of heterogeneous Fenton was systematically analyzed,and the half-life of Rh B was calculated by combining the reaction kinetics.The difference of adsorption between the two catalysts in the degradation process was analyzed by adsorption thermodynamics and adsorption kinetics.The relationship between the concentration difference of each molecule and the structure of catalyst in heterogeneous Fenton reaction is analyzed and discussed.Finally,analyzing the possible heterogeneous Fenton reaction mechanism.The phase composition,surface morphology,micro structure,and magnetic properties of Fe₃O₄/HNTs and Fe₃O₄@HNTs were analyzed using XRD,FTIR,SEM,TEM,and VSM.The analysis shows that Fe₃O₄in the Fe₃O₄/HNTs structure is loaded outside the HNTs tube,but not inside.In the Fe₃O₄@HNTs structure,Fe₃O₄can be efficiently loaded inside the HNTs tube with a particle size limited to about 7 nm.Both are known to have good magnetic properties.The results of the reaction efficiency of Fe₃O₄/HNTs and Fe₃O₄@HNTs heterogeneous Fenton system show that under the conditions of Fe₃O₄@HNTs 20°C room temperature,Rh B concentration of 30 mg/L,p H of solution 2,catalyst dosage of0.5 g/L,and 30%H₂O₂concentration of 3 ml/L,Within 120 min,the degradation of Rh B reached 92.91%,which was significantly better than that of Fe₃O₄/HNTs（69.95%）.The reaction process is first-order kinetic.The analysis results of adsorption thermodynamics and adsorption kinetics show that the adsorption of Fe₃O₄/HNTs is better than that of Fe₃O₄@HNTs.The adsorption isotherm equations satisfy the Langmuir model for both structural catalysts,and the adsorption process is monolayer homogeneous adsorption,which occurs at the catalyst surface and satisfies quasi-second order dynamics.Analysis of the concentration changes of each substance in the heterogeneous Fenton reaction of Fe₃O₄/HNTs and Fe₃O₄@HNTs shows that the structural differences do not affect the dissolution rate of total iron,but affect the catalytic degradation ability of the system by increasing the concentration of Fe²⁺and·OH in the Fe₃O₄@HNTs reaction system.It is easier for Fe³⁺to be reduced to Fe²⁺,and the reaction rate of Fe²⁺with H₂O₂to generate·OH is accelerated.The degradation mechanism of Rh B by Fe₃O₄/HNTs and Fe₃O₄@HNTs may be a combination of homogeneous Fenton reaction and heterogeneous Fenton reaction.The heterogeneous Fenton reaction of Fe₃O₄/HNTs occurs on the outer surface of HNTs tubes.The heterogeneous Fenton reaction of Fe₃O₄@HNTs occurs on the inner surface of the HNTs tube,and limiting the heterogeneous Fenton reaction in the tube enables Fe₃O₄@HNTs to have a more efficient degradation capacity.