Study On The BPA Removal Over Manganese Oxides Activated Peroxymonosuflate

With the development of modern industry and the increasing problems of water pollution,the exploration of an environmentally friendly,inexpensive and simple-preparation catalytic system is imminent.Advanced oxidation processes（AOPs）with the activation of peroxymonosulfate（PMS）to generate reactive radicals(SO₄^·-and·OH)has attracted much attention.Among the methods of PMS activation,transition metals activation is the most energy-saving and simple method because of their low toxicity,abundant resources,low price,and a variety of mixed valence states and crystalline forms.In this dissertation,four manganese oxide nanoparticles（MnO,Mn₂O₃,Mn₃O₄and MnO₂）were firstly prepared and the catalytic degradation abilities of the four manganese oxides toward bisphenol A（BPA）through PMS activation were investigated.Mn₂O₃ nanoparticles displayed the best degradation efficiency,which could degrade 100%BPA within 5 min.The influence of the changes of valence states and contents for Mnand O elements on the degradation efficiency was studied.It was found that the closer the content of Mn^IV and Mn^II,the higher the catalytic efficiency.In the degradation process,active species·OH and ~1O₂ acted the dominiant role.Then,the rod-like,spherical,flake-like and granular Mn₂O₃ microcrystals exposing different crystal faces were prepared.Using BPA as the target pollutant,the degradation efficiencies of the four catalysts were studied.The effctes of BPA concentration,catalyst dosage,PMS concentration,initial p H value and inorganic ions on the degradation efficiency were explored.In comparison with the other three Mn₂O₃ samples,granular Mn₂O₃（Mn₂O₃-P）with exposing（211）and（222）crystalline facets exhibited the superior removal efficiency of BPA,which could reach 90%within 10 min.The DFT results indicated that the energy barriers oflattice oxygen migration on the（222）and（211）crystalline planes were lower than that on the（400）crystalline planes.Moreover,the adsorption energy of PMS molecules on the（222）and（211）crystalline planes was more negative than that on the（400）crystalline planes.Thus,the higher lattice oxygen mobility and Mn^IV-Mn^III/II conversion of（222）and（211）crystalline planes were favorable for generating oxygen vacancies for the adsorption of PMS and O₂ molecules,which facilitated the production of more active species(SO₄^·-,·OH and ~1O₂)in the catalytic process.Finally,MnO with the poor catalytic performance was calcined to obtain two-phase catalysts MnO/Mn₃O₄（MnO/Mn₃O₄-1,MnO/Mn₃O₄-5 and MnO/Mn₃O₄-10）.The degradation efficiency of MnO calcined at 300℃ for 5 h（MnO/Mn₃O₄-5）toward BPA by activated PMS was 77%within 90 min,which was 2 times higher than that of precursor MnO and 2.6 times than that of Mn₃O₄.Through comparing the redox properties of the catalysts and the changes of valence states and contents for Mnand O elements before and after the catalytic reaction,it was found that the redox properties of the two-phase catalysts with mixed valence was superior,thus it was easier to generate electrons to activate PMS produce more active species,and finally degrade pollutants efficiently.