Titanium IN interior paint – photocatalysis process and viruses

But what exactly is photocatalysis? What are photocatalysts? 

These questions were answered by Prof. Antoni Morawski, PhD, DSc, Eng., from the Department of Inorganic Chemical Technology and Environmental Engineering at the West Pomeranian University of Technology in Szczecin.

By definition, photocatalysis is the change in the rate of a chemical reaction or its initiation under the influence of ultraviolet and/or visible radiation in the presence of a substance (photocatalyst) that absorbs the radiation and enables an oxidation-reduction chemical reaction on a surface, for example, between oxygen in the air and adsorbed contaminants, which may also be pathogenic microorganisms. Hydroxyl radicals generated on the photocatalyst surface have a higher oxidizing potential than ozone, which is important for disinfection.

Is this a new discovery? Perhaps it hasn't been sufficiently tested yet?

– The ability of titanium dioxide (TiO2 ) to act as a photocatalyst has been known for decades (specifically, since 1921). However, this property was not widely appreciated for many years. Interest in utilizing the photocatalytic properties of TiO2 resurfaced with the publication of a paper on the photoelectrolysis of water by Fujishima and Honda in 1972. This activity was soon exploited for pollutant oxidation, wastewater treatment, drinking water purification, and water treatment for industrial vegetable washing. Titanium dioxide-coated filters were used for air disinfection. Many subsequent studies demonstrated the usefulness of photocatalysis for water disinfection, including the destruction of bacteria. Potential for the destruction of cancer cells was discovered. However, the use of TiO2 in paint coatings became a novelty.

What about viruses? It's such a hot topic right now.

– Recently, there have been numerous publications on this topic. For example, in their work "Photocatalytic inactivation of influenza virus by titanium dioxide thin film," the Japanese demonstrated the deactivation of influenza virus by photocatalysis using TiO2 nanoparticles ₍ R. Nakano, H. Ishiguro, Y. Yao, J. Kajioka, A. Fujishima, K. Sunada, M. Minoshima, K. Hashimoto, Y. Kubota – "Photochemical and Photocatalytical Science", 2012).

Similarly, in the work "Extermination of influenza virus H1N1 by a new visible-light-induced photocatalyst under fluorescent light" (Sei-Young Choi Bongrae Cho – "Virus Research", 2018), a photocatalyst based on TiO2 _with the addition of transition metals (iron, magnesium, and manganese) was confirmed to have antiviral activity against the H1N1 influenza virus. In tests, the virus was eliminated by more than 99% within 30 minutes. It was stated that " it would be desirable to use this photocatalyst for disinfection to reduce virus transmission via droplets and aerosols, as well as via surface contact ." EAKozlov et al. in the publication Inactivation and Mineralization of Aerosol Deposited Model Pathogenic Microorganisms over TiO ₂ and Pt/TiO ₂ (Environmental Science and Technology, 2010, 44, 512-51-26) proved that on pure TiO ₂ after 30 minutes of UVA irradiation 90% inactivation of the influenza A (H3N2) virus is achieved, and on TiO ₂ modified with platinum – 99.8% inactivation of this virus.

Extensive studies in another work were also conducted by R. Nakano, M. Hara, H. Ishiguro, Y. Yao, T. Ochiai, K. Nakata, T. Murakami, J. Kajioka, K. Sunada, K. Hashimoto, A. Fujishima, Y. Kubota ( Broad Spectrum Microbicidal Activity of Photocatalysis by TiO ₂ – Catalysts, 2013). studied Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus vancomycin-resistant Enterococcus faecalis penicillin-resistant Streptococcus pneumoniae Escherichia coli and Pseudomonas aeruginosa, were inactivated gradually. Influenza virus (enveloped virus) and feline calicivirus (non-enveloped virus) were also inactivated during the tests.

The above studies (and many others) clearly confirm that photocatalysts are an effective method against many harmful pathogens and intensive work in this direction is underway worldwide.

You mentioned that painted walls can help protect your health. Isn't that a mistake?

"Surfaces contaminated with microorganisms pose a threat to the people around them. Dust mites, bacteria, viruses, and molds accumulate on walls and in room furnishings. This results in asthma, allergies, and infections. This applies to both residential and healthcare spaces. A wealth of information available in the literature indicates the effectiveness of photocatalytic TiO2 _in deactivating various microorganisms, including bacteria, viruses, fungi, and yeasts.

Infectious diseases caused by antimicrobial-resistant bacteria are becoming a major concern with antibiotic use worldwide. The persistence of these microorganisms on surfaces and medical devices leads to hospital-acquired disease transmission. Hospital-acquired pathogens are believed to contribute to many deaths.

Many advanced technologies are being developed worldwide to reduce the microbial burden in hospital environments. New strategies for preventing related infections are constantly evolving, including hygiene procedures using new liquid biocides or touchless technologies, coating disinfectant surfaces with metals (copper, silver) or light-activated catalysts such as TiO nanoparticles₂.

The challenges of healthcare infections and the increasing spread of antimicrobial-resistant bacteria are driving scientists to explore the field of nanotechnology and photocatalysis as a new source of improving hospital hygiene.

Materials that are inert in their basic form have also been found to be reactive when present in nanoparticle form, and in the case of titanium dioxide, activity is higher under UV and visible radiation. Photocatalysts are expected to be widely used against many harmful pathogens.

Utilizing the excellent photocatalytic effect of TiO ₂ with the generation of a strong oxidant in the form of a hydroxyl radical on the surface is a technologically feasible technology, and its production on an industrial scale is relatively easy and inexpensive.

The simplest and at the same time very effective method is to paint the walls and ceilings with paint containing a photocatalyst.

 But aren't such measures harmful? To humans and the environment?

– Traditional methods, such as disinfection with chlorine compounds, involve the production of carcinogenic disinfection byproducts, Cl2 _. Changes in water quality regulations have led to a greater emphasis on alternative disinfection mechanisms. Using ozone is quite problematic due to the need for a costly ozone generator and the very short "life" of ozone (short half-lives), which does not provide lasting environmental protection.

Titanium dioxide _TiO2 in building materials (walls, ceilings, floors, etc.) is inherently less harmful to the environment. Photoactive materials adsorb pollutants and microorganisms on their surfaces and then inactivate or decompose into carbon dioxide and water under the influence of UV radiation and visible radiation, even from ordinary light bulbs. Photoactive materials do not release toxic byproducts into the environment (like typical chemical preparations) and ensure effective and continuous disinfection of the environment.

How can we benefit from these discoveries in our daily lives? If such surfaces, walls, and ceilings coated with photocatalytic paints, are effective in healthcare, will they be suitable for use in residential spaces? Could they help reduce infections in homes?

Photocatalytic surfaces can be superhydrophilic, meaning water spreads across the surface, allowing dirt to be washed away. Commercial applications include self-cleaning windows (e.g., San Gobain Bioclean™, Pilkington Active™, and Sunclean™) and glass covers for tunnel lighting. Naturally, these coatings are transparent.

The photocatalyst can be used to coat walls, tables, and other surfaces to reduce contact-related infections. Wall tiles (tiles and grout) coated with TiO2 _also provide an effective self-cleaning and disinfecting material. Infection from influenza viruses spread through droplets (coughing, sneezing) can be reduced indoors by adsorbing them onto photoactive surfaces.

Therefore, covering walls and ceilings with paint containing a photocatalyst can effectively limit the spread of microorganisms, including pathogenic ones, as presented in the short list of literature descriptions above.

Aren't such photocatalytic products too complicated to use?

Photocatalytic paints are easy to use. They don't require special application techniques or equipment. Coatings are applied using traditional methods, such as brushes, rollers, or sprays. Because they are water-based, there's no odor issue, and equipment can be washed with water.

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