Preparation Of Novel Co₃O₄-based Catalysts For Peroxymonosulfate Activation:Catalytic Degradation Performance And Mechanism Of Antibiotics

Water pollution of antibiotic wastewater has been considered as a serious environmental problem.Many researchers focused on the treatment of antibiotic and dye wastewater.Compared with other methods,Peroxymonosulfate advanced oxidation technology was considered as the efficient way for organic degradation due to strong oxidation ability,stable chemical properties and long half-life of sulfate radicals.In the present work,we successfully prepared novel Co-based catalysts for improvement of the catalytic activity and stability via doping of nano-carbon-based materials,control of the morphology and crystal surface of Co₃O₄.The manuscript focused on the following aspects and the conclusions were obtained.（1）Novel flower-shape C-dots/Co₃O₄{111} was successfully synthesized by using electrochemical stripping and hydrothermal method.In the composite of flower-shape C-dots/Co₃O₄{111｝,Co₃O₄ exposed {111}high energy crystal surface with exposure of more Co2+,which could provide more active sites for catalytic reaction.In addition,doping of C-dots into Co₃O₄{111} can not only improve the physical and chemical properties of the catalyst prepared,but also promote the transfer of electrons to Co₃O₄,which reduce the deactivation of the catalyst and the invalid decomposition of PMS.High catalytic degradation rate of oxytetracycline,enrofloxacin,rhodamine B and methyl orange were achieved under the suspension of flower like C-dots/Co₃O₄{111}and PMS.Even after 6 cycling runs,flower like C-dots/Co₃O₄{111} still remained high catalytic activity and stability.Furthermore,based on the analysis of HPLC-MS/TOF and calculation of electron cloud density,the possible degradation pathways of the oxidation process of oxytetracycline and enrofloxacin were proposed.Free radical trapping experiments and electron sequential resonance show that sulfate radicals and hydroxyl radicals play the dominant role in catalytic degradation process.（2）In order to further analyze the influence of Co₃O₄ crystal facet on catalytic performance,three kinds of Co₃O₄ single crystals（hexahedron,truncated octahedron and octahedron）were synthesized.However,the degradation experiments showed that the catalytic activity of these three single crystals were low.Thus,the morphology and specific surface area of the catalyst may be the key factors affecting the catalytic performance.（3）Based on the above research,two-dimensional lamellar Co₃O₄{100}/N-rGO catalytic material was successfully synthesized by calcination and hydrothermal method.The absolutely exposure of {100} facet of Co₃O₄ can improve the exposure of active sites of catalysts.The doping of N-rGO can effectively reduce the particle size and agglomeration of Co₃O₄,which making Co₃O₄ uniformly distributed on twodimensional graphene with a diameter of about 5 nm.The modification of graphene oxide by nitrogen atom doping will lead to the polarization difference,which will cause the unstable electrons transformation from graphene to PMS with the generation of singlet oxygen.more than 95%of enrofloxacin can be degraded in 5 minutes under two-dimensional lamellar Co₃O₄｛100}/N-rGO.DFT calculation and experimental results show that different N source calcinations have great influence on the catalytic effect of modified graphene.The activity of catalysts synthesized with different precursors follow the order of Co₃O₄/N-rGO（dicyandiamide）>Co₃O₄/N-rGO（melamine）>Co₃O₄/N-rGO（urea）.Free radical trapping experiments and EPR indicated that the synergistic effects of free radical oxidation and non-free radical oxidation play the dominant role in the degradation process.In summary,this thesis provides the method for improvement of catalytic activity and stability of PMS Co-based activator,which can propel the application of Co-based catalysts as PMS activator for degradation of organic pollutants.