Photocatalytic And Antibacterial Properties And Mechanism Of TiO₂@SiO₂ Composites

In recent decades,the continuous increase of organic pollutants in wastewater and the proliferation of microorganisms such as bacteria have posed a huge threat to the ecological environment and people's health.At the same time,the bacterial debris left after by the death of bacteria will also release endotoxin substances that cause typhoid,cholera and other diseases,and then cause secondary pollution.Thus,the problem about how to eliminate the harmful microorganisms while degrading organic pollutants in wastewater has become a hot spot in contemporary scientific research.Therefore,the photocatalysis as a simple and efficient technology for catalytic oxidation of organic matter with antibacterial effect has been developed rapidly.It is well known that TiO₂ is the most widely used semiconductor catalyst in photocatalytic technology because of its excellent properties such as green initiative,no secondary pollution,stable properties,simple preparation and low price.However,the TiO₂ still exist some defects of easy agglomeration of nanoparticles,small surface area,fast recombination of photogenerated electron-hole pairs and poor adsorption performance in application.The photocatalytic activity is usually reduced because of the existence of these defects and then the degradation effects of organic pollutants and the antibacterial effects are influenced.To compensate for these defects,it is one of the effective methods to obtain highly active TiO₂ photocatalytic antibacterial materials by loading technology.In this paper,the micron-sized mesoporous-SiO₂ with stable physicochemical properties,high thermal stability and large specific surface area is used as carrier.And then a new composite photocatalytic antibacterial material is obtained by loading nano-TiO₂ onto SiO₂.In such a way,the defects of TiO₂ about easy agglomeration and poor adsorption can be solved,but also improve the efficiency of photocatalytic degradation of organic pollutants and the antibacterial effect.The carrier SiO₂ was first prepared by sol-gel method,and then the composite material of TiO₂@SiO₂ was obtained by hydrolysis method.The prepared photocatalytic antibacterial composite materials were characterized by the means of SEM,EDS,XRD,XPS,FTIR,BET and particle size analysis.The photocatalytic properties of TiO₂@SiO₂ composite materials were investigated by photocatalytic degradation of methyl orange solution using methyl orange(MO)simulated organic pollutants and high-pressure mercury lamp as ultraviolet light source(UVA).The antibacterial effect of TiO₂@SiO₂ composite material on bacteria was investigated by plate coating,which the Escherichia coli(E.coli)were selected as the source of bacteria and the UVA-ultraviolet lamp and ordinary daylight lamp were selected as light sources.The results show that the best performance of TiO₂@SiO₂ composite materials were obtained when the molar doping capacity of TiO₂ was 4.4%.With the condition of ultraviolet-light(UVA)irradiation for 3 hours,the degradation rate of MO solution was 100%and the antibacterial rate of composite material was 99.3%.Besides,the 4.4%-TiO₂@SiO₂ composite material also exhibits favorable antibacterial properties with an antibacterial rate of up to 90.5%under the visible-light irradiation for 3 hours.The results of detection and analysis of composite materials demonstrated that TiO₂ was successfully loaded onto the micro-SiO₂.Furthermore,the presence of anatase-TiO₂ and amorphous carrier SiO₂ are linked by the formed Ti-O-Si bond,which effectively enhances the photocatalytic activity of TiO₂@SiO₂ composite materials.In addition,the changes of functional group for MO molecules in the degradation process and the photocatalytic degradation mechanism of TiO₂@SiO₂ composite material was deduced by the tests of UV-Vis absorption spectra,FTIR and LC-MS.And the antibacterial mechanism of TiO₂@SiO₂ composite material was investigated by fluorescence detection of the reactive oxygen species(ROS)and SEM images of the changes in bacterial morphology.Results of mechanism revealed that the composite materials can generate amounts of ROS free radicals under the irradiation.During the degradation of organics,the organic macromolecules were attacked by ROS free radicals and degraded into organic small molecules,which were further degraded and eventually mineralized to inorganic compounds such as H₂O,CO₂,NO₃^-and SO₄^2-;during the antibacterial process,the ROS free radicals migrated into the bacterial cells and caused the oxidative damage of cells,resulting in damage to the internal structure of the cells and finally bacterial death.