Efficiency Evaluation On Heterogeneous Fenton Reaction Catalyzed By Nano-Fe₃O₄in Situ Assembled On Low Dimensional Carbon Materials

With the development of advanced oxidation technology applications in thefield of industrial wastewater treatment, Heterogeneous Fenton oxidation technologygradually has obtained more attentions. This technology effectively overcomes manyshortcomings of traditional Fenton technology, greatly improving the efficiency ofthe Fenton reaction. In this study, low-dimensional carbon materials such as multi-walled carbon nanotubes (MWCNTs) and graphene (RGO) were employed as thecarriers, on which in situ synthesized Fe3O4/carbon-based heterogeneous Fentoncatalyst by liquid phase deposition. The composite catalysts were all characterized byX-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Ramanspectroscopy, scanning electron microscope (SEM), transmission electronmicroscopy (TEM), specific suiface area (BET), Zeta potential and Vibrationmagnetometer. In the effectiveness evaluation of Fe3O4/carbon-based heterogeneousFenton reaction, central composite design (CCD) of response surface methodology(RSM) was used to optimize the process conditions based on the single factorexperiment. Meanwhile the kinetics of the Heterogeneous Fenton oxidation processwas carried out and further researched.The research results indicated that the Fe3O4/MWCNTs composite with20%MWCNTs content synthesized at95oC in2h exhibited the optimum catalyticactivity for the discoloration of MO and discoloration ratio could reach99.38%withthe catalyst dosage of2g/L. The Fe3O4/RGO composite with10%RGO contentsynthesized at95oC in2h exhibited the optimum catalytic activity for thediscoloration of MO and discoloration ratio could reach93.99%with the catalystdosage of1g/L. The experiments results indicated that the catalytic activity of thecomposite catalysts were higher than that of pure Fe3O4. The composite catalysts can be reused maintaining efficient catalytic activity, and recovered by magneticconveniently. The results of the UV-visible absorption spectroscopy showed that theMO molecules have been completely mineralized and degraded into H2O and CO2.The research of single factor experiments suggested that with the increasing ofinitial pH value and H2O2concentration, the discoloration rate of MO upgradedfirstly, then slow down. Nevertheless, as the catalyst dosage, reaction temperatureand MO initial concentration increased, the discoloration rate of MO also increased.Then on this basis, it finally obtained that the optimal parameters for theheterogeneous Fenton discoloration of MO by Fe3O4/MWCNTs were determined tobe initial pH value2.7,12.3mM H2O2concentration,2.9g/L catalyst dosage and39.3min reacrion time via creating a quadratic polynomial prediction model ofreaction with RSM, analysis of variance (ANOVA) and constructing contour plotsand3D response surface plots for the interactions between two variable. The actualMO discoloration rate was99.86%acquired by confirmatory experiments whichonly had1.99%difference comparing with the predictive value of101.85%. Itshowed that the model was accurate and reliable. The optimal parameters for theheterogeneous Fenton discoloration of MO by Fe3O4/RGO composite weredetermined to be initial pH value2.9,16.5mM H2O2concentration,2.5g/L catalystdosage and33.5min reaction time. The actual MO discoloration was99.98%attained via confirmatory experiments which only had0.338%difference comparingwith predictive value of100.336%. The model is accuracy and reliablility.Kinetic studies showed that the degradation process of MO by heterogeneousFenton reaction with Fe3O4/carbon-based complied with the characteristic of firstorder reaction kinetics under the different reaction conditions. The impacts of pHvalue, H2O2concentration, catalyst dosage, reaction temperature and MO initialconcentration on reaction rate constant k were studied, respectively. The resultsindicated that the relationships between k and the pH values, H2O2concentrationmeet the equation of k=exp (a+b*x+c*x2), while the relationship between k and thecatalyst dosage, reaction temperature, MO initial concentration fitted the Boltzmannfunction k=A2+(A1-A2)/(1+exp((x-x0)/dx)).