Effect Of Element Doping And Acid Treatment On Antibacterial Properties Of Nano-MgO

Presently,the world is being affected strongly by COVID-19 virus.As a new antibacterial material,nano-sized magnesium oxide(nano-MgO)has been widely used in the preparation of antibacterial textiles,paper,ceramics and interior wall coatings due to its environmental friendliness,non-discoloration,lack of light induction and ability to inactivate highly,resistant pathogens(such as spores).However,compared with silver antibacterial agents,nano-MgO antibacterial agents generally have low antibacterial activity and high effective concentration.Therefore,in this study,nano-MgO was modified by element doping and acid treatment methods to further improve its antibacterial activity and reduce its effective concentration(E.coli as the microbial model).This thesis choose FeCl2,MgCl2,the mixture of FeCl2 and MgCl2 calcinated with nano-MgO under high temperature,which respectively resulted single doped and co-doped nano-MgO.The influence of element doping on the structure,morphology and antibacterial properties of nano-MgO were studied by scanning electron microscope(SEM),X-ray diffraction(XRD),X-ray electron energy spectrum(XPS),glow light induced fluorescence analysis(PL),inductively coupled plasma emission spectroscopy(ICP).At the same time,the influence of acid treatment on the surface structure and antibacterial properties of nano-MgO was investigated.Fe doped nano-MgO was firstly ground to nanometer size by planetary ball mill,then FeCl2 and nano-MgO were mixed,milled and calcined.The XRD results show that the grain size and crystal spacing of MgO phase increase with Fe doping amount,indicating that iron doping can promote the growth and crystallization of MgO crystals:Grain size of Fe doped sample can reach 57.14 nm(MgO=45.44 nm).Escherichia coli ATCC 25922 was used as the test object.The minimum inhibitory concentration(MIC)and the 4 h total number of bacterial colonies were used as indicators to evaluate the antibacterial properties of nano-MgO.Results showed that samples doped with Fe all showed higher antibacterial activity than the pure nano-MgO and the antibacterial performance was gradually improved with the increasement of Fe quantity,with MIC up to 275ppm,and the total number of colonies in 4 h was 1000 CFU/mL.Possible mechanism:Fe ion replaces Mg ion or enters the gap of MgO generated moredefects and oxygen vacancy in the lattice.XPS results show that with the increasement of Fe quantity,chemosorption oxygen(OA)increases from 13.53%to 48.77%.Oxygen vacancy generates reactive oxygen radicals(ROS)by single electron reduction reaction through adsorption of oxygen.Reactive oxygen species have strong oxidizability to deactivate Escherichia coli.At the same time,iron doping enhanced the alkalinity of nano-MgO powder solution,the pH increased from 10.2 to 11.3,thus providing a more stable environment for ROS and enhancing its antibacterial activity.In addition,SEM characterization indicated that the cell membrane of Escherichia coli was damaged after antibacterial process,which should be caused by mechanical damage of Fe doped riano-MgO.Therefore,the improvement of Fe doping nano-MgO antibacterial activity should be the result of the synergistic effect of ROS increasement and mechanical damage.The Fe-Mg co-doped samples also showed higher antibacterial properties than nano-MgO,but there was no significant improvement compared with Fe doped nano-MgO.Acid can react with MgO to change its surface structure,such as the specific surface area and the number of surface defects.In this paper,the influence of acid impregnation on the structure and antibacterial properties of nano-MgO was studied.Varable acids under different concentration and impregnation time were investigated.The optimal experimental condition was found at pH=1-3,the impregnation time was 1-3 h,and the best acids were hydrochloric acid,acetic acid and oxalic acid.Then the orthogonal experiment was designed to find the best condition of antibacterial agent treatment:in acetic acid solution with pH=2 and impregnated for 3 h.The order of factor influence was:impregnation time>acid concentration>acid species.Various characterization results show that acid treatment can increase the surface defects of nano-MgO and increase the generation of oxygen vacancy.Thus,it is beneficial to increase the generation of ROS and ultimately enhance the antibacterial performance,which is consistent with the conclusion of Fe doped nano-MgO.