Nosocomial infections are a significant concern globally, accounting for a substantial percentage of hospitalizations. Bacteria and fungi can persist on surfaces for extended periods, while viruses, though generally shorter-lived, still pose a transmission risk. The COVID-19 pandemic underscored the urgent need for improved surface disinfection technologies in healthcare facilities and other public spaces. One promising approach involves using photocatalytic nanoparticles, particularly titanium dioxide (TiO2), in paints and coatings. TiO2's low cost and photoreactivity make it attractive; however, its high band gap typically requires high-energy UV light for activation. This limitation restricts its applicability in indoor settings where visible light is more readily available. Therefore, the development of visible-light-activated TiO2-based coatings for frequent-touch surfaces is a crucial area of research, driven by the need for cost-effective and sustainable antimicrobial solutions in various sectors including healthcare and food processing.

The review comprehensively examines existing literature on the use of TiO2 nanoparticles and their modifications for antimicrobial and antiviral applications. It covers various strategies to enhance TiO2's photocatalytic activity under visible light, including doping with transition metals (e.g., Mo, V), rare earth metals, and non-metals (e.g., N, S, P). The literature review also addresses the challenges associated with integrating TiO2 nanoparticles into paints and coatings, such as photodegradation of organic binders and the need for durable coatings. Furthermore, it explores different approaches for creating antimicrobial surfaces, encompassing kill-on-contact mechanisms, the time-released delivery of antimicrobial substances, and surface modifications to influence hydrophilicity or hydrophobicity. The review also considers the incorporation of TiO2 into textiles to create self-cleaning and antimicrobial fabrics.

This is a review article; therefore, it does not employ a specific experimental methodology. Instead, the authors conducted a comprehensive literature review, systematically searching databases for relevant publications on TiO2 nanoparticles, visible-light activation, and their antimicrobial and antiviral applications. The search criteria included keywords such as “TiO2,” “photocatalysis,” “antibacterial,” “coating,” “visible-light activation,” “antiviral,” and combinations thereof. The selected articles were analyzed to extract information on synthesis methods, doping strategies, characterization techniques, photocatalytic performance, antimicrobial efficacy, and durability of the TiO2-based materials. The review focuses on the most recent advancements and research findings reported in the literature, providing a detailed overview of the different approaches and their effectiveness. The authors critically evaluate the strengths and limitations of each strategy and highlight the potential for future development.

The review reveals several key strategies for enhancing the visible-light photocatalytic activity of TiO2 nanoparticles. Doping TiO2 with transition metals like Mo and V alters charge transfer properties, promoting charge separation and red-shifting the band gap. Similarly, rare earth metal doping introduces impurity energy levels, acting as trapping centers for photogenerated species. Non-metal doping, such as with N, S, or P, also narrows the band gap, improving visible-light absorption. The incorporation of carbon dots (CDs) or carbon quantum dots (CQDs) further enhances visible-light absorption and charge separation efficiency. The morphology of TiO2 nanoparticles, particularly the exposed crystal facets, significantly influences photocatalytic activity, with high-energy facets showing superior performance. Combining TiO2 with other materials such as graphene and copper oxide enhances visible-light photocatalysis and stability. The synthesis method significantly impacts the size and properties of the nanoparticles. Biosynthetic approaches using plant extracts offer environmentally friendly alternatives to traditional methods. The review highlights the importance of considering factors like durability and leaching when designing TiO2-based coatings and paints for real-world applications. The studies reviewed demonstrated effective antimicrobial and antiviral activities against various pathogens under visible-light irradiation, indicating the potential for widespread application of these materials in various settings.

The findings of this review demonstrate the significant potential of visible-light-activated TiO2-based materials for preventing the spread of infectious diseases through surface disinfection. The various doping and composite strategies described provide promising avenues for developing cost-effective and sustainable antimicrobial coatings. The review's emphasis on durability and leaching highlights the need for further research to ensure long-term efficacy and environmental safety. The effectiveness of these materials against a broad range of pathogens needs further investigation. The findings contribute significantly to the field by providing a comprehensive overview of recent advancements and highlighting key challenges and opportunities in developing next-generation antimicrobial and antiviral surface coatings.

This review underscores the potential of visible-light-activated TiO2 nanoparticles as a powerful tool for surface disinfection, particularly in healthcare and food processing environments. While significant progress has been made, future research should focus on addressing limitations such as leaching, achieving broad-spectrum antimicrobial activity, and developing standardized testing methods for real-world applications. Green synthesis methods and a greater focus on the long-term durability of these materials are also crucial for successful implementation.

As a review article, this study is limited by the availability and scope of published research. The findings are based on the existing literature and may not encompass all relevant studies. Additionally, the lack of standardized testing methods for evaluating the long-term efficacy and environmental impact of TiO2-based coatings presents a challenge in comparing results across different studies. Further research is needed to standardize testing protocols and establish clear benchmarks for performance and safety.