Degradation Effectiveness Of Organic Pollutants With Peroxymonosulfate Catalyzed By Manganese Oxides

In recent years,Advanced Oxidation Technologies?AOPs?have attracted more and more attention due to their ability to quickly and thoroughly degrade organic pollutants in wastewater.Peroxymonosulfate?PMS?-based oxidation technology becomes one of the emerging AOPs owing to its capability to generate strong oxidizing radicals.Manganese oxide is a kind of environmentally friendly material.Considering its diversity in valence and structure,the activation of PMS by manganese oxide seems theoretically feasible.In this dissertation,acid orange 7?AO7?was used as a typical organic contaminant in simulated wastewater,and its degradation was examined by activating PMS with four kinds of manganese oxides?Mn O,?-Mn O₂,?-Mn₂O₃,Mn₃O₄?.The degradation efficiencies and mechanism in these four systems were compared and discussed.The findings would provide some theoretical references for the treatment of actual industrial dye wastewater.The main conclusions are as follows:?1?In order to compare the effects of Mn_xO_y/PMS system on the degradation of AO7,the effects of AO7 concentration,catalyst concentration,PMS concentration,initial pH value,and sodium chloride concentration on the removal rate of AO7 were investigated.The results show that the effectiveness of the four manganese oxides on the activation of PMS follows this order:?-Mn₂O₃>?-MnO₂>Mn₃O₄>MnO.Under alkaline conditions,all four systems have satisfactory removal rate of AO7,more than 95%at 60 min.Under acidic conditions,only?-MnO₂/PMS,?-Mn₂O₃/PMS systems were able to degrade AO7.The presence of high content of chloride?greater than 10 mM?would promote the degradation of AO7 in the four systems,while degradation of AO7 could be inhibited at low level of chloride?less than 10 mM?.The four systems can not only rapidly degrade AO7,but also partially mineralize it.The extent of mineralization increases with the increase of chloride ion.Recycling experiments show that these four minerals have good catalyst stability.?2?Using free radical trapping experiments with isopropanol?IPA?,methanol?Me?and L-histidine,it is found that there are a small amount of hydroxyl radicals?^·OH?sulfate radical(SO₄^·-)in the four systems.Singlet oxygen?¹O₂?might play an important role in pollutant degradation.Compared to acidic conditions,the inhibition of L-histidine on the system under alkaline conditions is more significant,indicating that these four systems are more likely to generate singlet oxygen under alkaline conditions.In the presence of chloride,L-histidine in the four systems still has a strong inhibitory effect on the system.Finally,a preliminary mechanism of PMS activation by four manganese oxides to degrade AO7.Manganese oxides can form Mn?x?-OH complexes by adsorption of hydroxyl groups in water,which is involved in the activation of PMS to produce a single line Oxygen?¹O₂?.Then AO7 is decomposed into small molecules under the attack of singlet oxygen.