Study On The Fabrication Of Layered MnO₂ Nanomaterials And Their Antibacterial Activity In The Dark

With the development of modern technology,conventional semiconductor materials can no longer meet the requirements of various fields.Layered nanomaterials have attracted much attention due to their excellent properties.On the one hand,layered nanomaterials can change the bandgap by doping ions between layers,which enriches the application range.On the other hand,layered nanomaterials usually have large specific surface area,and thus they can be used as adsorbents and catalysts with high activity.MnO₂ is a highly efficient catalyst,which has great potential for environmental protection and biomedical applications due to its low cost,abundant reserves,excellent stability and good biocompatibility.Here,we focus on the properties ofδ-phase MnO₂（δ-MnO₂）layered nanomaterials.The morphology,crystal structure,chemical composition and antibacterial activity are investigated by scanning electron microscopy（SEM）,transmission electron microscope（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,ultraviolet-visible（UV-VIS）spectroscopy,electron spin resonance（ESR）,etc.The main contents are as follows.1.The layeredδ-MnO₂ was synthesized by hydrothermal method.Manganese sulfate（MnSO₄）and permanganate,such as magnesium permanganate（Mg（Mn O₄）₂）,sodium permanganate（Na Mn O₄）,or potassium permanganate（KMn O₄）,were heated in a Teflon-lined stainless steel autoclave.By changing the parameters such as reaction temperature,ratio of reactants and so on,the optimal condition was found for the preparation of MnO₂ nanomaterials with adjustable bandgap.Meanwhile,the ratios between doped ions and Mn were also quantified.It was observed that the bandgap ofδ-MnO₂ nanomaterials decreased with higher doping level.2.The prepared MnO₂ nanomaterials were used for antibacterial test.The antibacterial ability against Streptococcus mutans（S.mutans）was studied within the acceptable limits of cytotoxicity.It was found that all the samples showed spontaneous antibacterial properties in the dark.Moreover,it was observed that MnO₂ with a narrower band gap showed better ability to inhibit bacteria.3.In order to verify the antibacterial mechanism ofδ-MnO₂ nanomaterials,the generation of reactive oxygen species（ROS）was tested by ESR.We found that the samples could spontaneously generate ROS in the dark,such as superoxide anion radicals（·O₂^-）and hydroxyl radicals（·OH）.Since ROS can damage biomolecules,e.g.proteins,vitamins,and lipids of microbial cells by its strong oxidation potential.It was observed that the ESR intensity increased with the doping level,where higher doping level can provide more free electrons,which enhance the antibacterial activity of theδ-MnO₂ nanomaterials4.Finally,the controllable degradation behavior ofδ-MnO₂ nanomaterials was investigated.Following the injection of vitamin C（VC）,the solution with MnO₂ samples started to fade color,indicating that the MnO₂ was degraded into water soluble manganese（Mn）ions,making this approach attractive for in vivo applications,presenting not only an outstanding antibacterial efficacy but also an excellent biosafety...