Mechanism Of Antibiotic Degradation By Manganese Oxides Under Microwave Irradiation

This paper investigated microwave adsorption mechanism and microwave induced degradation mechanism of tetracycline（TC）on several typical manganese oxide minerals including:pyrolusite with（1×1）tunnel structure,cryptomelane with（2×2）tunnel structure,birnessite with（1×∞）layer structure and Pb₂Mn O₄ with non-centrosymmetrical structure,and also studied the effect of composition and morphology control on property.Main results are as follows:（1）Pure phased pyrolusite,cryptomelane,birnessite and Co doped birnessite formed by hydrothermal method.Pure phased Pb₂Mn O₄ and Co doped Pb₂Mn O₄formed by high temperature solid state method.Structure of birnessite and Pb₂Mn O₄would stay in Co amount less than 5%and 1%,respectively.Substitution of Mn⁴⁺in birnessite and Pb²⁺in Pb₂Mn O₄ by Co occurred during the doping.Morphology of pyrolusite and cryptomelane were respectively shape of the columnar and needle which had the bigger specific surface area.Actual structural formula of these typical manganese oxide minerals were calculated by results of ICP and XPS,which were similar to their theoretical structural formula.（2）Network analysis showed that typical manganese oxide minerals would produce dielectric loss and magnetic loss during the microwave irradiation.Among them,pyrolusite and cryptomelane relied mainly on dielectric loss,while birnessite and Pb₂Mn O₄ relied mainly on magnetic loss.By characterization and calculation of conductivity,interface,defect,permanent electric dipole moment and spin magnetic moment,we knew that electronic conduction,interface relaxation,defect and permanent electric dipole moment were the main reason for microwave dielectric loss,electronic conduction and interface relaxation were the main reason for microwave dielectric loss of pyrolusite,cryptomelane and birnessite,permanent electric dipole moment was the main reason for microwave dielectric loss of Pb₂Mn O₄;spin magnetic moment was the main reason for magnetic loss.In four types of manganese oxide minerals,cryptomelane had the biggest microwave adsorption,secondly pyrolusite,thirdly birnessite and finally Pb₂Mn O₄.Co doping would contribute to both dielectric loss and magnetic loss.（3）Microwave induced oxidation property of pyrolusite,cryptomelane,birnessite and Co doped birnessite had the positive correlation with their microwave adsorption.However,with lowest microwave adsorption property of Pb₂Mn O₄ with permanent electric dipole moment had the biggest property of microwave induced degradation of TC.This was possibly due to the higher hot spot effect of microwave dielectric loss by permanent electric dipole moment.All in all,permanent electric dipole moment in manganese oxide would make the tremendous contribution on its property of microwave induced degradation of organic,which was the innovation cognition of microwave induced oxidation mechanism.