Comparative studies on Fenton-like reactions catalyzed by Fe_(3)O_(4) loaded inside and outside halloysite nanotubes for the removal of organic pollutants

In this work,Fe_(3)O_(4) 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 Fe_(3)O_(4) NPs loaded outside the HNTs lumen(Fe_(3)O_(4)/HNTs)and inside the HNTs lumen(Fe_(3)O_(4)@HNTs)were successfully prepared.Both samples had typical magnetic hysteresis loops,while Fe_(3)O_(4)@HNTs exhibited higher magnetization intensity.The comparative experiments showed that Fe_(3)O_(4)@HNTs had better Fenton-like catalytic ability than that of Fe_(3)O_(4)/HNTs in the degradation of various organic pollutants.Taking Rhodamine B(RhB)as an example,the adsorption thermodynamics and kinetics of RhB onto Fe_(3)O_(4)/HNTs and Fe_(3)O_(4)@HNTs were also investigated.The comparative results demonstrated that the adsorption ability of Fe_(3)O_(4)/HNTs was better than that of Fe_(3)O_(4)@HNTs.Moreover,the dissolved concentration of Fe^(2+)and production amount of hydroxyl radical(·OH)in the Fe_(3)O_(4)@HNTs-H_(2)O_(2) system were significantly higher than those in the Fe_(3)O_(4)/HNTs-H_(2)O_(2) system.Based on aforementioned comparison,the nano-confinement effect in the Fe_(3)O_(4)@HNTs-H_(2)O_(2) system was verified.This work provides meaningful guidance for the cheap and convenient design of nanoreactors for Fenton-like applications.

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst： kinetics and Fenton-like mechanism

The kinetics and Fenton-like mechanism are two challenging tasks for heterogeneous Fenton-like catalytic oxidation of organic pollutants. In this study, three kinetic models were used for the kinetic studies of Fe3O4/MWCNTs-H2O2 Fenton-like reaction for MO degradation. The results indicated that this reaction followed the first- order kinetic model. The relationship of reaction rate constant and temperature followed the Arrhenius equation. The activation energy and frequency factor of this system were calculated as 8.2 kJ.mo1-1 and 2.72 s-1, respectively. The quantifications of Fe ions dissolution and ,OH radicals generation confirmed that the homogeneous and hetero- geneous catalyses were involved in Fe3O4/MWCNTs＇H2O2 Fenton-like reaction. The reaction rate constant was closely related with Fe ions dissolution and ,OH radicals generation. Fe3O4/MWCNTs nanocomposites had typical ferromagnetic property and could be easily separated from solution by an external magnet after being used. Furthermore, Fe3O4/MWCNTs nanocomposites exhibited good stability and recyclability. Finally, the Fenton-like mechanisms on homogeneous and heterogeneous catalyses were described.

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst： combination mechanism and affecting parameters

Multi-walled carbon nanotubes （MWCNTs） can act not only as a support for Fe3O4 nanoparticles （NPs） but also as a coworker with synergistic effect, accordingly improving the heterogeneous Fenton-like efficiency of Fe3O4 NPs. In this study, Fe3O4 NPs were in situ anchored onto MWCNTs by a moderate co-precipitation method and the as-prepared Fe3O4/MWCNTs nanocomposites were employed as the highly efficient Fenton-like catalysts. The analyses of XRD, FTIR, Raman, FESEM, TEM and HRTEM results indicated the formation of Fe3O4 crystals in Fe3O4/MWCNTs nanocomposites prepared at different conditions and the interaction between Fe3O4 NPs and MWCNTs. Over a wide pH range, the surface of modified MWCNTs possessed negative charges. Based on these results, the possible combination mechanism between Fe3O4 NPs and MWCNTs was discussed and proposed. Moreover, the effects of preparation and catalytic conditions on the Fenton-like catalytic efficiency were investigated in order to gain further insight into the heterogeneous Fenton-like reaction catalyzed by Fe3O4/MWCNTs nanocomposites.