Atomic Oxygen Radical Anions-Induced Inactivation Of Microorganisms And Surface Modification Of Materials

This dissertation presents a novel approach to the inactivation of microorganisms and surface modification of materials by using atomic oxygen radical anion(O^-)which is prepared by C12A7-O^- material.In this work we mainly focus on the inactivation efficacy and inactivation mechanism of microorganisms induced by O^-,alterations of surface properties of polymers after surface modification via O^-, and oxidation of silicon and formation of SiO₂ on silicon surface by O^-.The major conclusions have been summarized as follows:1.Study of the microorganisms' inactivation and inactivation mechanism induced by O^-1)The preparation of high pure O^- beam:O^- can be stored and emitted by C12A7-O^- material.An O^- generator was prepared through coating with C12A7-O^-material on the surface of ceramic in which was a heater.The maximum intensity of O^- beam emitted from O^- generator was 220μA and the purity of O^- beam was higher than 90%.2)The preparation and characteristics of O^- solution:The O^- solution was prepared by bubbling of the O^- beam into the deionized water for a duration time. The O^- solution was usually acid.The concentrations of active oxygen species such as O^- and H₂O₂ in the O^- solution were investigated by electron paramagnetic resonance(EPR)and ultraviolet-visible spectroscopy(UV-VIS).3)Inactivation of microorganisms with gaseous O^- beam:The inactivation of microorganisms mainly depends on the intensity of O^- beam,treatment temperature, and kinds of microorganism.The results indicate that the O^- beam shows a good ability for microorganisms' inactivation and the cell mortality is enhanced to more than 3-logarithm reduction with O^- beam of 1.5μA/cm² for 120 min.The inactivation efficacy increases with the increases of the intensity of O^- beam and treatment temperature,and independents on the concentration of microorganism.Different mortalities are obtained for different kind of microorganisms due to their different cytoarchitecture.Field emission scanning electron micrographs(FESEM)reveals that the cell structures are destroyed by the exposure to O^- beam.The observed anionic intermediates by a time-of-flight mass spectrometer(TOF-MS)and the neutral volatile products(CO,CO₂)by a Quadruple mass spectrometer(Q-MS)provide an evidence of the reactions between O^- and microorganism.4)Inactivation of microorganism with O^- solution:Effective inactivation of Escherichia coli through O^- solution has been obtained.Escherichia coli cells are reduced by more than 3 logarithm in the O^- solution[pH 4.30±0.20,(2.5±0.8)×10^-2mmol/l O^-;0.5±0.2 mmol/l H₂O₂]within 60 min at 30℃.Significant temperature dependent on the surviving populations is observed within our tested temperature range(15-45℃).Lipid peroxidation reaction and nucleic acid release induced by O^- solution are identified.The treated cells by O^- solution also appear dramatically collapsed by FESEM observation.The release of nucleic acid and the disrepair of cell wall caused by O^- are responsible for the inactivation of Escherichia coli cells.2.Study of the surface modification of polymer materials with O^-1)Surface modification of polystyrene with O^- solution:The O^- solution(0.03±0.01 mmol/l O^-;0.5±0.1 mmol/l H₂O₂)treatment has caused an obvious increase of the surface hydrophilicity,surface energy,surface roughness and also caused an alteration of the surface chemical composition for polystyrene surfaces,which are indicated by the variety of contact angle and material characterization by atomic force microscope(AFM)imaging,FESEM,X-ray photoelectron spectroscopy(XPS),and attenuated total-reflection Fourier transform infrared(ATR-FTIR)measurements. Particularly,it is found that some hydrophilic groups such as hydroxyl(OH)and carbonyl(C=O)groups are introduced onto the polystyrene surfaces via the O^-solution treatment,leading to the increases of surface hydrophilicity and surface energy.2)Surface modification of polytetrafluorethylene with O^- solution:C—O,C—F, and CF₃ chemical bonds have been formed after O^- solution(0.03±0.01 mmol/l O^-; 0.5±0.1 mmol/l H₂O₂)treatment,which indicate O^- solution leads to chain scission and oxidation.At the same time,no hydrophilic groups such as C=O,OH appeared. The contact angle on polytetrafluorethylene surface increases by 14°treated by O^-solution for 48 h at room temperature.The O^- solution treatments lead to the decreases of surface energy and hydrophilicity,the increase of hydrophobicity. FESEM results indicate the surface of polytetrafluorethylene become rougher after O^-solution treatment,which might be the reason for the increase of hydrophobicity.3.Study of the surface oxidation of silicon with O^-Surface oxidation of silicon(Si)wafers by O^- beam and production of metal-oxide-semiconductor(MOS)capacitors with the O^- -oxidized Si substrates were examined.The features of the MOS capacitor were investigated by measuring capacitance-voltage(C-V)and current-voltage(I-V)curves.