Degradation Of Organic Pollutants Through The Activation Of Peroxymonosulfate And Its Mechanisms

Advanced oxidation processes（AOPs）had gained much attention because of the high efficiency and nonselective degradation.Peroxymonosulfates（PMS）are widely used oxidants in AOPs because they are water-soluble,non-toxic,and easy to store.However,the activation of PMS requires the heavy and transition metals,which may release heavy metals and produce secondary pollution.Therefore,a catalyst with good catalytic activity and persistence is the key to PMS activation and degradation of organic pollutants.In this thesis,rhodamine B（Rh B,a commonly used dye）and metronidazole（MNZ,a nitroimidazole antibiotic）were select as target pollutants,the degradation reaction kinetics and mechanism by peroxymonosulfate（PMS）activated byα-Mn O₂/Palygorskite and Cu Fe₂O₄/Palygorskite,the degradation of MNZ by Fe₃O₄/g-C₃N₄ as a photocatalyst coupling with PMS were seperatedly investigated.The main contents and conclusions of this study are listed as follow:1. The degradation kinetics and mechanisms of Rh B by PMS activated byα-Mn O₂/Pal were studied.Α-Mncomposites were synthesized by hydrothermal method.The analysis of FE-SEM,EDS and XRD confirmed the successful loading ofα-Mn O₂ on Pal.The surface area ofα-Mnwas 159.13 m²/g,which was much higher than that of Pal andα-Mn O2.The 20 mg/L Rh B degradation efficiency reached as high as 100%within 180 min at the conditions of 0.10 g/Lα-Mnand 0.10 g/L PMS.The degradation fitted the pseudo-first-order reaction kinetics well with the rate constant of0.02041 min^-1.The degradation efficiency increased with the increase ofα-Mndosages,PMS dosages and temperatures.The degradation was inhibited at p H>5.5,while was favorable at p H<5.5.The highest 51.2%of Rh B was mineralized by PMS activated byα-Mncomposite under optimized conditions.The dominated radicals for Rh B degradation were O2.^-and ¹O2.Recycling tests showed thatα-Mncomposites possessed an excellent stability even after three successive runs.In summary,the synthesizedα-Mncomposite exhibited remarkable efficiency compared with either raw Pal orα-Mn O₂in activating PMS to degrade Rh B.2. The degradation kinetics and mechanisms of Rh B by PMS activated by Cu Fe₂O₄/Pal were analyzed.CuFe2O4/Pal composites were synthesized by sol-gel combustion method.The results of SEM and EDS confirmed the successful loading of Cu Fe2O4 on Pal.The Rh B degradation by PMS activated by Cu Fe2O4/Pal was studied and several factors influcing the degradation were investigated.The degradation fitted the pseudo-first-order reaction kinetics well with the rate constant of 0.01650 min^-1.The degradation efficiency of Rh B increased from 89.2%to 100%when the dosage of Cu Fe₂O₄/Pal increased from0.10 g/L to 0.30 g/L.When the concentration of PMS increased from 0.05 g/L to 0.10 g/L,the degradation efficiency of Rh B also increased.However,when the dosage exceeded0.20 g/L,the degradation efficiency did not increase further but decreased slightly.The degradation was inhibited at p H>5.5,while was favorable at p H<5.5.An increase in the initial Rh B concentration（10 mg/L to 40 mg/L）would slow its degradation.The dominated radicals for Rh B degradation were O2.^-and ¹O2 from the quenching experiments.The cyclic experiments indicated that the Cu Fe2O4/Pal was stable and can be reused.3. The degradation of MNZ by Fe₃O₄/g-C₃N₄ coupled visible light activated PMS was studied.Fe3O4/g-C3N4 composites were synthesized by situ co-precipitation method.When 0.10 g/L Fe3O4/g-C3N4 and 0.40 g/L PMS were added simultaneously under natural irradiation,20 mg/L MNZ could be completely degraded within 240min,suggesting that the synergistic effects of the photocatalysis of Fe3O4/g-C3N4 composite and the chemical activation of PMS.When the dosage of Fe₃O₄/g-C₃N₄ increased from 0.10 g/L to 0.20g/L,the degradation efficiency of MNZ increased from 59.9%to 100%.When the concentration of PMS increased from 0.20 g/L to 0.40 g/L,the degradation efficiency of MNZ increased significantly,and the overdosage（0.5 g/L）maked the degradation efficiency did not increase but decreased slightly.The dominated radicals for MNZdegradation were O₂^.-,e^-,h⁺,SO₄^.- and.OH from the quenching experiments.