Treatment Of Dye Wastewater By SiO₂@Fe₃O₄-nZVI-Based Fenton-Like Technology

Dye wastewater is wastewater containing high levels of organic and inorganic pollutants generated during the production,processing and application of dyestuffs.It usually has a high level of colour,COD and BOD,as well as potentially containing toxic and non-degradable organic compounds.The main sources include processes such as washing,dyeing,bleaching and printing during the production of dyestuffs,as well as cleaning and treatment during the application of dyestuffs.The large quantities of water and chemicals used in these processes are discharged into the wastewater,resulting in high concentrations of organic and inorganic pollutants in the wastewater and posing a serious environmental hazard to water bodies.Three dyes,azo dye methyl orange（MO）,anthraquinone dye reactive brilliant blue KN-R（RBKN-R）and triphenylmethane dye methylene blue（MB）,were selected as target pollutants for the study.From the perspective of improving the Fenton reaction process,a new composite material,SiO₂@Fe₃O₄-nZVI,was obtained by coating Fe₃O₄ with SiO₂ loaded with nano zero-valent iron（nZVI）material,which has good stability and oxidation resistance.The composite material was used as a catalyst coupled with the Fenton method for the treatment of three simulated dye wastewaters,and the degradation effect of the dyes in the reaction system as well as the degradation pathway and mechanism were investigated,with the following main conclusions:（1）A nanoscale composite SiO₂@Fe₃O₄-nZVI with good dispersion properties was successfully prepared by co-precipitation,two-step liquid-phase reduction and St?ber hydrolysis.SEM analysis showed that the SiO₂@Fe₃O₄-nZVI particles were irregularly shaped and uniformly dispersed.XRD analysis showed that the composite contained SiO₂,while the material had good crystallinity.EDS and XPS analysis showed that the composites were mainly composed of four elements,Fe,C,O and Si.The results of the split-peak fitting of Fe2p in SiO₂@Fe₃O₄-nZVI indicated that the synthesised material contained Fe,and the results of the split-peak fitting of Si2p indicated that the material contained Si.The saturation magnetisation intensity of the composites was 22.04 emu/g as measured by VSM,indicating that the material has a certain.The BET analysis showed that the specific surface area of the iron nanoparticles increased after the modification of the iron particles by SiO₂ coating,which was beneficial to increase the reactivity of the particles.FTIR analysis showed the presence of Si-O and Si-O-Si bonds on the surface of the composites,indicating that SiO₂ had successfully attached to the catalyst surface and the modified composites The oxidation resistance was good.（2）The oxidative degradation of three dyes,MO,RBKN-R and MB,was carried out using SiO₂@Fe₃O₄-nZVI as the catalyst and coupled with H₂O₂ to construct a Fenton-like system at 25℃,when the concentration of each pollutant was 50 mg/L,SiO₂@Fe₃O₄-nZVI dosing amount was 0.8 g/L,p H=3 and the concentration of H₂O₂ was 15 mmol/L,the degradation rates of all three dyes were above 90%,indicating that SiO₂@Fe₃O₄-nZVI has good catalytic activity.The single-factor experiments showed that the degradation rates of the three dyes increased with the increase of H₂O₂ concentration and SiO₂@Fe₃O₄-nZVI dosage within a certain experimental range,and decreased with the increase of p H and pollutant concentration,and reached the maximum degradation rate at the initial p H value of 3.The effect of temperature on the degradation rates of the three dyes was not obvious;SiO₂@Fe₃O₄-nZVI was repeatedly The degradation of the dyes by the SiO₂@Fe₃O₄-nZVI based Fenton system was in accordance with the proposed primary kinetic process.（3）The results of the radical quenching experiments showed that the reactive oxygen species generated in the SiO₂@Fe₃O₄-nZVI Fenton-like system may include HO·,¹O₂,·O₂^-,and that the Fe₃O₄ and nZVI in the system also degraded the dyes by adsorption and reduction.Analysis of the UV spectrograms before and after comparing the reactions showed that the colour emitting groups of all three types of dyes were degraded,indicating that the SiO₂@Fe₃O₄-nZVI catalyzed H₂O₂ initiated Fenton class reaction degraded the dyes very well.