Photocatalytic pathogen inactivation is gaining increasing importance due to the rising number of microbial species resistant to conventional antibacterial agents. Titanium dioxide (TiO₂)-based photocatalysts have emerged as a promising solution, being not only potent antibacterial agents but also environmentally friendly and capable of simultaneously degrading organic pollutants. This review summarizes recent advances in the antibacterial performance of different TiO₂ modifications, including commercial nanopowders, nanoparticles with various morphologies, thin films, composites, and polymer-supported nanostructures, all primarily activated under UV light. Given the limited ability of pristine TiO₂ to harvest solar radiation, we also highlight the most recent strategies for designing visible-light-responsive TiO₂, such as doping, incorporation of plasmonic metal nanoparticles, formation of heterostructures, and interfacial charge transfer complexes. In addition, we discuss the fundamental structural features of TiO₂, the mechanisms of reactive oxygen species (ROS) generation involved in bacterial inactivation, and kinetic models describing antibacterial efficiency. These insights aim to advance the understanding and development of eco-friendly, cost-effective, and sustainable photocatalytic disinfection technologies.

The biological activities, including cell viability, oxidative stress, genotoxicity/antigenotoxicity, and antimicrobial activity, were evaluated for the visible-light-responsive TiO2-based ICT complex with dihydroquercetin (DHQ) and compared with the pristine TiO2, its inorganic component. Pristine TiO2 did not induce cytotoxicity in MRC-5 or HeLa cells within the tested concentration range (1-20 mg/mL), while TiO2/DHQ displayed a significant reduction in cell viability in both cell lines at higher concentrations (≥10 mg/mL). Analysis of reactive oxygen species (ROS) production revealed that TiO2/DHQ significantly reduced ROS levels in both cell types (MRC-5 and HeLa), with HeLa cells showing a more substantial reduction at lower concentrations. Genotoxicity assessment using the comet assay demonstrated that TiO2 induced DNA damage in MRC-5 cells, while TiO2/DHQ did not, indicating that DHQ mitigates the genotoxic potential of TiO2. Furthermore, TiO2/DHQ exhibited antigenotoxic effects by reducing H2O2-induced DNA damage in MRC-5 cells, supporting its protective role against oxidative stress. Preliminary antimicrobial tests revealed that TiO2/DHQ exhibits antimicrobial activity against E. coli under visible light excitation, while TiO2 does not. These findings suggest that TiO2-based ICT complex with DHQ with enhanced antioxidant properties can potentially serve as a safe, non-toxic biocide agent.

Biological activities, including cell viability, oxidative stress, genotoxicity/antigenotoxicity, and antimicrobial activity, were evaluated for a visible-light-responsive TiO₂-based ICT complex with dihydroquercetin (DHQ) and compared with pristine TiO₂, its inorganic component. Pristine TiO₂ did not induce cytotoxicity in MRC-5 or HeLa cells within the tested concentration range (1–20 mg/mL), while TiO₂/DHQ displayed a significant reduction in cell viability in both cell lines at higher concentrations (≥10 mg/mL). The analysis of reactive oxygen species (ROS) production revealed that TiO₂/DHQ significantly reduced ROS levels in both cell types (MRC-5 and HeLa), with HeLa cells showing a more substantial reduction at lower concentrations. Genotoxicity assessment using the comet assay demonstrated that TiO₂ induced DNA damage in MRC-5 cells, while TiO₂/DHQ did not, indicating that DHQ mitigates the genotoxic potential of TiO₂. Furthermore, TiO₂/DHQ exhibited antigenotoxic effects by reducing H₂O₂-induced DNA damage in MRC-5 cells, supporting its protective role against oxidative stress. Preliminary antimicrobial tests revealed that TiO₂/DHQ exhibits antimicrobial activity against E. coli under visible-light excitation, while TiO₂ does not. These findings suggest that the TiO₂-based ICT complex with DHQ with enhanced antioxidant properties can potentially serve as a safe, non-toxic biocide agent.

Titanium dioxide (TiO₂) is a widely studied semiconductor whose interfacial redox properties strongly influence its photocatalytic and biological performance. In this work, TiO₂ nanomaterials were surface-functionalized with green tea waste extract (GT) and subsequently impregnated with silver to obtain redox-active nanocomposites with tunable optical and biological properties. HPLC, FTIR, diffuse reflectance spectroscopy (DRS), and density functional theory (DFT) analyses demonstrated the formation of an organic–inorganic interface through adsorption of green tea-derived ligands. DFT calculations revealed complementary interfacial roles of the adsorbed constituents, with epigallocatechin gallate (EGCG) inducing interfacial charge-transfer (ICT) states that enable visible-light absorption, as reflected by the decrease in the apparent optical bandgap from ~3.48 eV for pristine TiO₂ to ~1.83 eV for TiO₂/EGCG. ICP-OES analysis further quantified the Ag loading in TiO₂/GT/Ag at 5.1 wt%. Electron paramagnetic resonance (EPR) experiments demonstrated that GT functionalization shifts the interfacial redox balance toward radical scavenging by suppressing excessive radical generation, whereas silver incorporation partially restores oxidative pathways, particularly under irradiation. These differences in interfacial redox behavior directly translate into distinct biological responses. TiO₂/GT/Ag showed the strongest antimicrobial activity, with visible-light enhancement observed predominantly against Staphylococcus aureus, while TiO₂/GT/Ag reduced H₂O₂-induced oxidative stress in non-malignant cells and promoted intracellular reactive oxygen species generation in cancer cells. These findings demonstrate that engineering the organic–inorganic interface through plant-derived ligands and silver incorporation provides an effective strategy for tuning the interfacial redox properties and light-responsive biological performance of TiO₂-based nanomaterials, thereby expanding their potential for antimicrobial and biomedical applications.