Degradation Of Refractory Organic Pollutants By Different Activated Systems Of Persulfate And Their Mechanisms

Persulfates are widely used oxidants in advanced oxidation processes（AOPs）.Persulfates are stable,water-soluble and easy to store and transport.Therefore,AOPs based on the activation of persulfate have obvious advantages and potential for the degradation of refractory organic pollutants.In this study,thiamphenicol（TAP,a commonly used veterinary antibiotic）,phenol（a main material in industrial wastewater）and rhodamine 6G（Rh6G,a commonly used dye）were selected as model pollutants.The degradation of TAP by UV/S₂O₈^2-（UV/PS）,the degradation of phenol by peroxymonosulfate（PMS）activated by different crystallographic MnO₂,the degradation of Rh6G byγ-MnO₂/PMS and their mechanisms were seperatedly investigated.The main contents and conclusions obtained are listed as follows:1.The degradation and kinetics of TAP by PS activated by UV were studied and compared with UV/H₂O₂.The results showed that the TAP degradation fitted the pseudo-first-order kinetics well.In UV/PS process,the TAP degradation was significantly accelerated under acidic and alkaline conditions,while in UV/H₂O₂process,the neutral and acidic conditions are suitable for the TAP degradation.HCO₃^-inhibited the TAP degradation in both processes;NO₃^-slightly inhibited the TAP degradation in UV/H₂O₂ process;and Cl^-accelerated the TAP degradation in UV/PS process.Humic acid remarkably inhabited TAP degradation.The second-order rate constants for TAP reacting with hydroxyl radicals（HO^·）and sulfate radicals(SO₄^·-)were determined to be 8.3×10⁸ L·mol^-1·s^-1 and 3.1×10⁹ L·mol^-1·s^-1,respectively.Only part of TAP was mineralized in UV/H₂O₂ process,while complete mineralization was achieved in UV/PS process.The possible degradation pathways were proposed based on the identified intermediate products.2.The degradation of phenol by PMS activated by different crystallographic MnO₂was investigated.The MnO₂ nanomaterials with different crystals were prepared and characterized.The phenol degradation by activated PMS was compared,and the effects of various factors on phenol degradation were investigated.Different crystals of MnO₂ had different microscopic morphology.The degradation kinetics were fitted with the pseudo-first-order kinetic model and the catalytic activity abided by the order ofδ-MnO₂>γ-MnO₂>ε-MnO₂.The increase of oxidant and catalyst loading promoted the phenol degradation.The increase of solution pH and the reaction temperature remarkably enhanced the phenol degradation.Activation energy of the phenol degradation inδ-MnO₂/PMS process was determined to be 13.5 kJ·mol^-1.Quenching experiments revealed that superoxide anion radical(O₂^·-)and singlet oxygen（¹O₂）played the main roles in phenol degradation in theδ-MnO₂/PMS system.δ-MnO₂ presented a long-term stability through recycling use in phenol degradation.3.The hydrothermal synthesis ofγ-MnO₂ nanospheres and the degradation of Rh6G by PMS activated byγ-MnO₂ were investigated.The catalytic efficiency ofγ-MnO₂ prepared under different conditions was also evaluated.The catalyst exhibited as a three-dimensional string-like nanosphere with a slight aggregation.The specific surface area and average valence of Mn of the catalyst prepared at 90℃were all higher than that prepared using the autoclave under the same conditions.Rh6G was effectively degraded inγ-MnO₂/PMS process,but the degradation efficiency was affected by the synthesis temperature,Mn²⁺concentration and bath time.γ-MnO₂ nanosphere presented a long-term stability through using the catalyst for multiple in Rh6G degradation.