Degradation Of Methylene Blue And Tetracycline In Water By Activated Peroxymonosulfate With Ammonium Thiomolybdenum And Composite Materials

With the rapid development of industry and agriculture,various dyes and antibiotics are discharged into the water environment through different channels.Most of them are refractory and toxic,which might pose risks to the ecological balance and human health.Among many wastewater treatment technologies,persulfate-based advanced oxidation processes have the advantages of mild reaction conditions,low energy,high efficiency,and environmental protection,which is especially suitable for the treatment of dyes and antibiotics wastewater.In this dissertation,ammonium thiomolybdate(（NH₄）₂Mo₃S₁₃)with high stability and diamagnetism and manganese ferrite（Mn Fe₂O₄）with stable crystal structure and excellent reusability were selected to prepare（NH₄）₂Mo₃S₁₃ and（NH₄）₂Mo₃S₁₃/Mn Fe₂O₄ composite.They were used to activate peroxymonosulfate（PMS）to degrade methylene blue（MB）and tetracycline（TC）.The structure and morphology of the two catalysts were characterized,and the reaction mechanism,the influencing factors and the cyclic stability of the catalysts were studied.Specific research contents and results are as follows:（1）（NH₄）₂Mo₃S₁₃ was prepared by hydrothermal method using thioacetamide（C₂H₅NS）and sodium molybdate（Na₂Mo O₄·2H₂O）.By Fourier transform infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）,and other characterization methods,it was found that（NH₄）₂Mo₃S₁₃ showed a lamellar structure,containing rich Mo-S bond and S₂^2-groups,and the XRD pattern was consistent with the standard cards.When（NH₄）₂Mo₃S₁₃ was prepared by the molar ratio of C₂H₅NS and Na₂Mo O₄·2H₂O of 14:1（AMS-14）,it had the best degradation effect on MB and TC.In AMS-14/PMS system,the degradation rates of MB and TC reached97.3%and 90.4%in 60 min,respectively.Therefore,MB was taken as an example to conduct follow-up experiments.Electron paramagnetic resonance spectroscopy（EPR）,quenching experiment and XPS analysis were used to explore the mechanism of the activation of PMS by AMS-14.It was found that Mo（IV）and S exposed on the surface of AMS-14 were the main active sites for the activation of PMS,and singlet oxygen（¹O₂）was the main active species.In addition,AMS-14 showed good catalytic performance under the influence of initial p H,inorganic anions,humic acids,and simulated wastewater.After three cycles,the catalytic efficiency of AMS-14 on MB decreased slightly,and can be recovered to a higher level after adding hydroxylamine,and the characteristic peaks of AMS-14 in XRD before and after reaction were consistent,indicating that AMS-14 has good cyclic stability.（2）A variety of（NH₄）₂Mo₃S₁₃/MnFe₂O₄ composites（MSMF）were prepared by solvothermal method.It was found that MSMF was spherical and contained characteristic functional groups and crystal surfaces of（NH₄）₂Mo₃S₁₃ and Mn Fe₂O₄,indicating that the composites were successfully prepared.The catalytic performance of MSMF was obviously better than that of（NH₄）₂Mo₃S₁₃ and Mn Fe₂O₄.The MSMF prepared by the mass ratio of（NH₄）₂Mo₃S₁₃ to Mn Fe₂O₄ of 4.0（MSMF4.0）had the best degradation effect on MB and TC.In MSMF4.0/PMS system,the degradation rates of MB and TC reached 90.7%and 93.8%in20 min,respectively.Therefore,TC was taken as an example to conduct subsequent experiments.The comprehensive experimental results showed that Mn（II）/Mn（III）,Fe（II）/Fe（III）,Mo（IV）/Mo（VI）and S^2-/SO_x^2-on the surface of MSMF4.0 all participated in the catalytic process,and^·OH in solution and SO₄^·-and^·OH on the surface were the main active species.In addition,MSMF4.0 also showed good activity and stability after five cycles,and the toxicity of TC degradation intermediates was reduced.The synthesis methods of ammonium thiomolybdate and its composite materials in this dissertation are simple and have superior degradation effect on dyes and antibiotics.This can provide a theoretical reference for the practical application of molybdenum-based catalysts in the field of advanced oxidation processes.