Preparation And Characterization Of Hydrogel Coated Fe₃O₄ Nanoparticles And Its Application For Catalytic Degradation Of Organic Wastewater

In this thesis,electrostatic self-assembly method was used to coat sodium carboxymethyl cellulose(CMC)on the surface of Fe3O4 Magnetic nanoparticle(Fe3O4 MNPs).Then Acrylic acid(AA)and acrylamide(AM)were cross-linked to CMC by the radical polymerization of N,N-methylene acrylamide(MBA)crosslinkers and ammonium persulfate(APS)initiators.Finally,composite microspheres(Fe3O4@hydrogel)with hydrogel as the outer layer and Fe3O4 magnetic nanoparticles(Fe3O4 MNPs)as the core were prepared.The physical and chemical properties of the composite were comprehensively analyzed by various characterization methods.The results showed that the hydrogel was successfully coated on the surface of Fe3O4 MNPs.The hydrogel copolymer content was about 17.7%and the saturation magnetization was 44.80 emu/g.The BET surface area is 73.52 m2/g,and the average pore diameter is 5.5 nm.Acid Red 73(AR73)was used to simulate the catalytic degradation of acid wastewater.Experiments have shown that Fe3O4@hydrogel microspheres have excellent catalytic degradation performance for acid dye wastewater.Through single-factor variable testing,the most economical and reasonable reaction conditions were obtained as follows:pH=3.5,the concentration of H2O2 was 200 mmol/L,and catalyst dosage was 200 mg/L.By adjusting the degree of hydrogel grafting and cross-linking,changing the amount of coating etc.,a method for preparing an organic composite nano-catalyst with controlled cross-linking size and thickness on the surface of Fe3O4 MNPs particles was successfully realized.The AR73 solution was used as a simulated wastewater model to study the catalytic activity of Fe3O4@hydrogel composite catalysts with different coating thicknesses.The results showed that the degradation rate of Fe3O4@lhydrogel in the composite catalyst reached 100%first under different pH conditions.And when the pH is 3.5,the degradation rate is still more than 75%.This degradation effect is significantly better than the other three coating size catalysts(Fe3O4@1/2hydrogel,Fe3O4@3/2hydrogel,Fe3O4@2hydrogel).Fe3O4@lhydrogel composite catalyst has the best catalytic activity.The Fe3O4@hydrogel catalyst was subjected to repeated degradation experiments,and the catalytic degradation experiments were performed in an acidic AR73 solution with univariate analyses.The results show that the degradation reaction is a two-stage quasi-first-order degradation kinetic reaction.The pH value,the amount of catalyst,and the number of catalyst cycles will affect the induction time and kinetic rate(k)of the second stage of the degradation process,while the concentration variable of H2O2 has little effect on it..In addition,compared with the primary catalytic degradation,the degradation rate decreases during the secondary degradation,which may be caused by the small loss of non-magnetic hydrogel components and the loss of iron ion dissolution.Fe3O4@hydrogel was used as a heterogeneous Fenton-like catalyst to demineralize phenol pollutants.The initial pH value of the solution,the initial concentration of H2O2,and the amount of catalyst were single-factor variables to test the mineralization of phenol by the Fenton method.Under the optimal conditions:pH 3.0,H2O2 concentration 200 mmol/L,catalyst dosage 0.4 g/L,80.4%COD in the solution can be removed after 180 min.In addition,Fe3O4@hydrogel has a high catalytic activity in a large pH range of 3.0 to 5.0,and can remove more than 50%of COD at a pH of 5.0,and Fe3O4 MNPs is difficult to degrade phenol under the same conditions.Fe3O4@hydrogel has good dispersibility,hydrophilicity,permeability and mass transfer properties,which enhances its catalytic activity.The degradation principle of heterogeneous Fenton reaction and the analysis of Fe3O4@hydrogel catalyzed reaction were investigated.When the heterogeneous Fenton reaction degrades organic compounds,three kinds of reagents(methanol,tert-butanol,p-benzoquinone)were used to capture the ·OH and O2·-radicals.The EPR test was used to speculate that OH free radicals are oxidatively active species which play a major role in catalytic degradation.In addition,O2·-free radicals also contribute 7 to 12%to the degradation of organic matter.