Synthesis Of Magnetite-based Catalysts For Catalytic Degradation Of Organic Pollutants In Water

Magnetite (Fe3O4) has been observed to have efficient catalysis in heterogeneous Fentonsystem, which is assigned to the presence of Fe(II) species in magnetite structure initiating thereaction. Fe3O4has also been applied to the oxidation process of Fe3O4/persulfate owing to thesimilar structure of O-O bond was contained in H2O2and persulfate. Unfortunately, some ofthese systems do not show favorable catalytic activity, which is particularly due to that Fe3+cannot efficiently catalyze the generation of SO4, and the utilization efficiency of theperoxides and catalytic degradation rate of target substances is low. In order to solve thisproblem, Rhodamine B (RhB) was selected and different magnetite composites was preparedfor the degradation experiment. The main researches are concluded as follows:(1) Polyhydroquinone, an immobilized quinone, was synthesized by oxidativepolymerization of hydroquinone. The polymers obtained were characterized byFourier-transform infrared spectra and cyclic voltammetry. Polyhydroquinone is a redox-activepolymer with quinone/hydroquinone redox active units in the main chain. The influence ofpolyhydroquinone in the Fe3O4/persulfate system was examined. It was found that the additionof polyhydroquinone in Fe3O4/persulfate system increased the oxidation rate of RhB, whichwas ascribed to their role as an electron shuttle. The presence of polyhydroquinone successfullybuilds up two cycles, one semiquinone/quinone cycle, another cycle of Fe(III)/Fe(II) inducedby quinone. The presence of phenolic and quinonoid moieties in the structure ofpolyhydroquinone provide for their ability to reduce Fe(III), thereby assisting the redox cyclingof Fe and increasing degradation of the target substrate.(2) the polyhydroquinone/Fe3O4(pHQ/Fe3O4) was synthesized as heterogeneous catalystto activate persulfate to effectively degrade RhB. The synthetic pHQ/Fe3O4nanoparticles werecharacterized using X-ray powder diffraction (XRD) and Fouier-transform infrared spectra(FTIR). The results indicated that the pHQ/Fe3O4maintains quinone units and the presence ofquinone successfully accelerates the degradation compared to Fe3O4, owing to the role ofquinone assisting the redox cycling of Fe. Effects of pHQ/Fe3O4addition, persulfateconcentration, pH and temperature on the degradation of RhB by persulfate are examined inbatch experiments. Increasing the temperature may significantly accelerate the RhB degradation and the degradation is found to follow the pseudo-first-order kinetic model. At thesame time, the reusability of the catalyst was also studied. These phenomena suggest thatpHQ/Fe3O4-persulfate oxidation process may be an effective strategy to promote RhBdegradation.(3) the graphene coated Fe3O4(GS/Fe3O4) was synthesized by a hydrothermal method.The synthetic nanoparticles were characterized using X-ray diffraction (XRD),Fourier-transform infrared (FTIR) spectra and Brunauer-Emmett-Teller (BET) nitrogenadsorption. Effects of GS/Fe3O4addition, persulfate concentration, pH, and temperature on thedegradation efficiency of RhB by persulfate are examined in batch experiments. Resultsindicated that the presence of graphene successfully accelerates the degradation rate of RhB.The graphene and Fe3O4ratio1:5favored the RhB decomposition; the degradation rateincreased as the initial persulfate concentration increased; the degradation rate was low atneutral and alkaline conditions while acidic conditions was higher; increasing the temperaturemay significantly accelerate the RhB degradation, and the degradation is found to follow thepseudo-first-order kinetic model. The effect of radical scavengers on the degradation of RhBwas also studied, proving that SO4is the major radical and OH and O2－are the assistantradicals in this study.(4) the FeS/Fe3O4nanoparticles was synthesized using a hydrothermal method. Thesynthetic nanoparticles was used as heterogeneous catalyst to activate persulfate to effectivelydegrade RhB. A series experiments of reaction conditions were also performed, whichconfirmed that weak acidic, higher temperature, higher dosages of FeS/Fe3O4and PS. At thesame time, the reusability of the catalyst was also studied. These phenomena suggest that FeS/Fe3O4-persulfate oxidation process may be an effective strategy to promote RhB degradation.