Construction of S-Scheme Heterojunction by TiO₂/rGO Assembled With g-C₃N₄ for Efficient Visible-Light-Driven Antibacterial Activity of Bone Scaffold

The low photogenerated charge carriers and quick complex annihilation of titanium dioxide (TiO₂)/rGO composite leading to an unsatisfactory photocatalysis antibacterial effect limit its application in the bone scaffold. Herein, graphitic carbon nitride (g-C₃N₄) was assembled with TiO₂/rGO via a solvothermal method for enhancing the photocatalysis antibacterial properties of poly (lactic acid) (PLLA) bone scaffold prepared via selective laser sintering. The results revealed that g-C₃N₄ expanded the light absorption range of TiO₂/rGO from blue-violet light to visible light, resulting in the composites having a narrower band gap and producing more photoinduced charge carriers. More importantly, an S-scheme heterojunction was formed between g-C₃N₄ and TiO₂, which promoted the recombination of the electrons in the conduction band of TiO₂ and the holes in the valence band of g-C₃N₄. Meanwhile, rGO with excellent electrical conductivity reduced the interfacial charge transfer resistance and enhanced charge transfer efficiency, thus further avoiding the recombination rate of electrons and holes, whether TiO₂ or g-C₃N₄, and enhancing the photocatalytic properties. Consequently, the holes in the valence band of TiO₂ and the electrons in the conduction band of g-C₃N₄ possessed high oxidation and reduction capacity, which oxidized H₂O and reduced O₂ in the microenvironment, respectively, and generated lots of reactive oxygen species. In vitro antibacterial experiments indicated that the PLLA/TiO₂/g-C₃N₄/rGO scaffold showed a better antibacterial effect, with the bacteriostasis rates of E. coli and S. aureus being 99.1% and 98.9%, respectively. In addition, cell adhesion and fluorescence results indicated that the scaffold had good biocompatibility and could provide a suitable microenvironment for the growth and proliferation of cells.