Construction Of G-C₃N₄ Nanostructure Coatings On Titanium Alloy Surface And Its Photocatalytic Antibacterial Performance

Medical titanium-based alloy materials have found extensive application in orthopedics,dentistry and other biomedical fields.However,titanium implants are always plagued with the problem of bacterial infection after implantation.Implant infections often occur around 4-6 hours after operation,while normal clinical infections take long time.Such bacterial infections cause additional physical pain as well as financial burden for patients,some patients may face the threat of death.Photocatalytic sterilization is an effective way to protect implants from bacterial infection.Graphite carbon nitride(g-C₃N₄)has found extensive application in the field of photocatalysis because of its unique electronic structure,excellent responding to visible light,stable physical and chemical properties.Under light radiation,photoinduced carriers react with adsorbed oxygen and water to generate·O₂^-and·OH,which can enter the inside of bacteria and then inactivate them to achieve the purpose of photocatalytic antimicrobial.The construction of heterojunction and element doping improved visible light photocatalytic activity,and the photocatalytic bacterial inactivation activity.In this paper,TiO₂/g-C₃N₄ Z-scheme heterojunction coating was constructed on the surface of titanium alloy,and metal particles added on the surface and interface of the heterojunction further improve the photocatalytic antibacterial performance,and retain the biocompatibility of the TC4substrate.The photocatalytic antibacterial mechanism of the TiO₂/g-C₃N₄ Z-scheme heterojunction coating with nano-structure was investigated,and the fractional addition of metal particles without affecting the activity of osteoblasts was realized,and the mechanism of photocatalytic antibacterial enhancement of the coating was analyzed.In the first part,the TiO₂/g-C₃N₄ Z-scheme heterojunction coating with nano-structure was constructed in-situ on the surface of the hydrothermal treatment titanium alloy by simple chemical vapor deposition(CVD).TiO₂/g-C₃N₄ heterojunction coating showed excellent hydrophilicity,and its osteoblastic compatibility was better than hydrothermally treated TC4 substrate.TiO₂ mixed phase(rutile and anatase)and g-C₃N₄formed a Z-scheme heterojunction system.Compared with the hydrothermal treatment substrate,the results of co-cultivation with Escherichia coli(E.coli)under natural light showed that the rates of inhibition bacterial adhesion on the surfaces of the 0.2CN and0.4CN heterojunction coating were 67.1%and 84.1%,respectively.Such Z-scheme heterojunction coating can not only improve the separation and transfer of photogenerated carriers,but also increase the number of photogenerated electrons and photogenerated holes,promote the production of reactive oxygen species(ROS)and thus inactivate bacteria.Based on this experiment,the TiO₂/g-C₃N₄ heterojunction coating in-situ constructed on the surface of titanium alloy would have promising prospects for biomedical applications.In the second part,the controllable addition of fractional CuO particles at the interface and surface of the above-mentioned TiO₂/g-C₃N₄ Z-scheme heterojunction coating with nano-structure was synthesised by ion exchange and ultraviolet photoreduction method,and the TiO₂/CuO/g-C₃N₄ with nano-structure was constructed on the surface of titanium alloy.The CuO particles at the interface of the Z-scheme heterojunction becomes the recombination center of photoinduced electrons and holes at the junction of TiO₂ and g-C₃N₄,which improves the whole separation of photoinduced electron-hole pairs in the heterojunction coating;the presence of Cu²⁺on the surface accelerates the electron migration on the surface of heterojunction coating,both of which significantly benefit in improving the photocatalytic antibacterial performance of the heterojunction coating on the surface of titanium alloy.The presence of CuO and the Z-scheme heterojunction coating on the surface of titanium alloy form a dual antibacterial mode of releasing bactericide and contacting bacteria cells.The results of cytocompatibility revealed that the presence of heterojunction coating reduces the cytotoxicity of metal particles and thus maintains the excellent biological activity of titanium alloy.The dual antibacterial mode constructed by a series of processes in this experiment provides a feasible new way for the construction of antibacterial surface of TC4 substrate in the future,and provides a new basis for the application of medical titanium-based alloy implants.In the last part,after optimizing the ion exchange parameters,an appropriate amount of silver nanoparticles(AgNPs)was doped onto the surface and interface of the TiO₂/g-C₃N₄ Z-scheme heterojunction coating by photoreduction method,and the TiO₂/AgNPs/g-C₃N₄ coating with nano-structure was constructed on the surface of titanium alloy.Using reasonably designed process parameters of ion exchange and ultraviolet photoreduction,the synergistic antibacterial performance formed by doped AgNPs and Z-scheme heterojunction coating was excellent,and the antibacterial mechanism was similar to that of TiO₂/CuO/g-C₃N₄ coating.In the presence of a very low content of silver particles,the AgNPs on the surface of the TC4 substrate can achieve high-efficiency antibacterial.The AgNPs at the interface of heterojunction become the recombination center of photogenerated carriers,which enhance the photocatalytic antibacterial ability of TiO₂/AgNPs/g-C₃N₄ coating with nano-structure.At the same time,the constructed coating has excellent osteoblast compatibility and good hydrophilic properties,which proves its great potential in improving the biocompatibility and promoting bone formation of titanium alloys.The experimental results show that the TiO₂/AgNPs/g-C₃N₄ coating with nano-structure constructed on the surface of the TC4substrate enhances the synergistic antibacterial performance formed by contacting bacteria cells and releasing bactericide,and the biological activity of such coating is excellent.This study provides a reference for optimizing the construction of dual antibacterial mode coating on the surface of titanium alloy in the future,showing the great application potential of such antibacterial coating on the surface of TC4 substrate in biomedical fields.The Z-scheme heterojunction coating constructed on the surface of titanium alloy in this study has potential application value in the field of biomedical materials,and the further formed synergistic antibacterial coating has more excellent antibacterial properties,which provides a reference for the development of implant surfaces with a variety of antibacterial mechanisms.