Using visible light to activate antiviral and antimicrobial properties of TiO2 nanoparticles in paints and coatings: focus on new developments for frequent-touch surfaces in hospitals

Abstract

The COVID-19 pandemic refocused scientists the world over to produce technologies that will be able to prevent the spread of such diseases in the future. One area that deservedly receives much attention is the disinfection of health facilities like hospitals, public areas like bathrooms and train stations, and cleaning areas in the food industry. Microorganisms and viruses can attach to and survive on surfaces for a long time in most cases, increasing the risk for infection. One of the most attractive disinfection methods is paints and coatings containing nanoparticles that act as photocatalysts. Of these, titanium dioxide is appealing due to its low cost and photoreactivity. However, on its own, it can only be activated under high-energy UV light due to the high band gap and fast recombination of photogenerated species. The ideal material or coating should be activated under artificial light conditions to impact indoor areas, especially considering wall paints or frequent-touch areas like door handles and elevator buttons. By introducing dopants to TiO₂ NPs, the bandgap can be lowered to a state of visible-light photocatalysis occurring. Naturally, many researchers are exploring this property now. This review article highlights the most recent advancements and research on visible-light activation of TiO₂-doped NPs in coatings and paints. The progress in fighting air pollution and personal protective equipment is also briefly discussed.

Graphical abstract: Indoor visible-light photocatalytic activation of reactive oxygen species (ROS) over TiO₂ nanoparticles in paint to kill bacteria and coat frequently touched surfaces in the medical and food industries.

Keywords: Antibacterial; Coating; Photocatalysis; TiO2; Visible-light activation.

Fig. 1

Schematic representation of the steps followed during biofilm formation. Reprinted from: Achinas, S. et al. A brief recap of microbial adhesion and biofilms. Appl. Sci. 2019, 9, 2801, with permission from MDPI

Fig. 2

Promising antiviral coatings based on the selection of materials and engineering of surface nanostructures and the antiviral action mechanisms. Reprinted from: Sun, Z. et al. Future antiviral surfaces: Lessons from COVID-19 pandemic. Sustain. Mater. Technol. 2020, 25, e00203,, (copyright 2020) with permission from Elsevier

Fig. 3

Schematic representation of the mechanism followed by TiO₂ for bacterial disinfection using either UV or visible light. Reprinted from Fisher, M.B. et al., Nitrogen and copper doped solar light active TiO₂ photocatalysts for water decontamination, Appl. Catal. B, 2013, 130–131, 8–13. Copyright (2013), with permission from Elsevier

Fig. 4

Diagrams reporting the number of publications per year for the reported time ranges. (adapted from Web of Science, Clarivate Analytics; date of search: May 10, 2022) using the following combinations of topic keywords: (a) TiO₂ or titanium dioxide and coatings or paints and antibacterial or antibacterial or antimicrobial or antimicrobial or antifungal or antifungal or antivirus or antiviral and visible light; the number of publications corresponding to the orange portion of the bar have been obtained narrowing the search adding UV as a topic keyword

Fig. 5

The cell unit of (left) pristine rutile TiO₂ and (right) cell unit where one of the oxygen molecules was replaced with a sulfur molecule. Dark spheres: Ti; white spheres: O; gray spheres: S. Reprinted from Umebayashi, T. et al. Sulfur-doping of rutile-titanium dioxide by ion implantation: Photocurrent spectroscopy and first-principles band calculation studies. J. Appl. Phys. 2003, 93, 5156–5160. Copyright (2003), with permission from the American Institute of Physics

Fig. 6

An illustration of the procedure used to prepare carbon dots/TiO₂ sheets. Reprinted from: Shen, S. et al. Construction of carbon dots-deposited TiO₂ photocatalysts with visible-light-induced photocatalytic activity to eliminate pollutants. Diam. Relat. Mater. 2022, 124, 108,896, (copyright 2022) with permission from Elsevier

Fig. 7

SEM images of T(G-Mn)1 annealed at (a) 550°C and (d) 800°C, T(G-Mn)2 annealed at (b) 550°C and (e) 800°C, and T(G-Mn)3 annealed at (c) 550°C and (f) 800°C, showing the structure manipulation. The graphs indicate the photocatalytic efficiency for the removal of NOx by different T(G-Mn) annealed at (g) 550°C and (h) 800°C. Reprinted from: Lee, J.-C., et al. Manganese and graphene included titanium dioxide composite nanowires: fabrication, characterization and enhanced photocatalytic activities. Nanomaterials 2020, 10, 456, (copyright 2020) with permission from MDPI

Fig. 8

The proposed mechanism of facet-dependent contact 3D/2D heterojunctions for photocatalytic reactions. Reprinted from: Chen, L. et al. One-step solid-state synthesis of facet-dependent contact TiO₂ hollow nano cubes and reduced graphene oxide hybrids with 3D/2D heterojunctions for enhanced visible photocatalytic activity. Appl. Surf. Sci. 2020, 504, 144,353, (copyright 2020) with permission from Elsevier

Fig. 9

The TEM images of E. Coli cells after introducing TiO₂ and CQDs-TiO₂ and irradiation with visible light. Reprinted from: Yan, Y. et al. Carbon quantum dot-decorated TiO₂ for fast and sustainable antibacterial properties under visible light. J. Alloys Compd. 2019, 777, 234–243, (copyright 2019) with permission from Elsevier

Fig. 10

Graphs showing the percentage conversion from NO to NO₂ of several commercial products under visible-light illumination. Adapted from: Kotzias, D. et al. Smart surfaces: photocatalytic degradation of priority pollutants on TiO₂-based coatings in indoor and outdoor environments-principles and mechanisms. Materials (Basel). 2022, 15, 402, (copyright 2022) MDPI

Fig. 11

Graphs showing the normalized UV–vis absorption spectra of (a) the colloidal Au NPs suspensions before (blue curve) and after (red curve) ligand exchange and (b) of the Au NPs modified films on glass with different loadings. A comparison of the two graphs clearly shows the redshift. Reprinted from: Peeters, H. et al. Plasmonic gold-embedded TiO₂ thin films as photocatalytic self-cleaning coatings. Appl. Catal. B Environ. 2020, 267, 118,654, (copyright 2020) with permission from Elsevier (Color figure online)

Fig. 12

Images of the S. aureus cells after irradiation with light from a methane halide lamp radiation (a) the uncoated sample, (b) the undoped coating, and (c) the 0.75% Cu–N-doped coated sample. Reprinted from: Tahmasebizad, N. et al. Photocatalytic activity and antibacterial behavior of TiO₂ coatings co-doped with copper and nitrogen via sol–gel method. J. Sol–Gel Sci. Technol. 2020, 93, 570–578, (copyright 2020) with permission from Springer Link

Fig. 13

The SEM images of polyester–cotton samples, (a and b) untreated, (c and d) treated with TiO₂, and (e and f) treated with TiO₂/SiO₂/graphene oxide. Reprinted from: Gao, J. et al. Durable visible-light self-cleaning surfaces imparted by TiO₂/SiO₂/GO photocatalyst. Text. Res. J. 2019, 89, 517–527, (copyright 2019) with permission from SAGE Journals

Fig. 14

The mechanism proposed for anchoring N-doped TiO₂ nanoparticle fiber was prepared by sonication. Reprinted from Behzadnia, A. et al. Rapid synthesis of N-doped nano TiO₂ on wool fabric at low temperature: introducing self-cleaning, hydrophilicity, antibacterial/antifungal properties with low alkali solubility, yellowness, and cytotoxicity. Photochem. Photobiol. 2014, 90, 1224–1233, (copyright 2014) with permission from Wiley

Fig. 15

(a) The SEM image of the flowerlike TiO₂ particles. (b) Images displaying the water contact angle of (b) pristine cotton, (c) cotton coated with PDMS, and (d) cotton coated with N-doped TiO₂/PDMS. Reprinted from: Pakdel, E. et al. Superhydrophobic and photocatalytic self-cleaning cotton fabric using flowerlike N-doped TiO₂/PDMS coating. Cellulose 2021, 28, 8807–8820, (copyright 2020) with permission from Elsevier

Fig. 16

The SEM images of the bacterial cells treated with Pd-based nanostructures (100 μg/mL). Scale bar: 1 μm. Reprinted from: Cai, T. et al. Optimization of antibacterial efficacy of noble-metal-based core–shell nanostructures and effect of natural organic matter. ACS Nano 2019, 13, 12,694–12,702, (copyright 2019) with permission from ACS

Fig. 17

A schematic illustration of the preparation of C₃N₄:N/TiO_2. Reprinted from: Ashfaq, A. et al. Nitrogen and carbon nitride-doped TiO₂ for multiple catalysis and antimicrobial activity. Nanoscale Res. Lett. 2021, 16, 119, (copyright 2021) with permission from Springer Link

Fig. 18

The SEM images (a) activated carbon (AC), (b) Ag/AC, (c and d) Ag/AC/TiO₂ nanocomposites. Reprinted from: Aravind, M. et al. Enhanced photocatalytic and biological observations of green synthesized activated carbon, activated carbon doped silver and activated carbon/silver/titanium dioxide nanocomposites. J. Inorg. Organomet. Polym. Mater. 2022, 32, 267-279, (copyright 2022) with permission from Springer Link

Fig. 19

(a) Comparative graph showing the survival of the different cells incubated with N–TiO₂ and T–N–TiO₂ under visible-light irradiation. TEM images of S. aureus incubated with N–TiO₂ and T–N–TiO₂ under visible-light irradiation 0 h, 2 h, and 24 h with (a1–a3) N–TiO₂ and (b1-b3) T–N–TiO₂ under visible-light irradiation. Reprinted from: Tzeng, J.-H. et al. Inactivation of pathogens by visible-light photocatalysis with nitrogen-doped TiO₂ and tourmaline-nitrogen co-doped TiO₂. Sep. Purif. Technol. 2021, 274, 118,979, (copyright 2021) with permission from Elsevier

Fig. 20

The SEM image of the TiO₂ nanotubes. Reprinted from: Zhang, Q. et al. Anodic oxidation synthesis of one-dimensional TiO₂ nanostructures for photocatalytic and field emission properties. J. Nanomater. 2014, 2014, 1–14, (copyright 2014) with permission from Hindawi

Fig. 21

Photographic illustration of the concept of bilayer the TiO₂ self-cleaning films. Reprinted from: Song, K. et al. Electro-spray deposited TiO₂ bilayer films and their recyclable photocatalytic self-cleaning strategy. Sci. Rep. 2022, 12, 1582, (copyright 2022) with permission from Springer Nature