The reaction of photocatalysis in detail

TiO2 is a semiconductor. Electrons in semiconductors can be in two different states: free and bound. In general, electrons are usually fixed, i.e. they are bound to an ion in a lattice and form a strong chemical bond with such ion.

In order to ‘pull’ an electron out of the lattice, it is necessary to apply at least 3.2 electron volts (eV) of energy (compare: the kinetic energy of a flying mosquito is about a trillion eV). Luckily, this is exactly the amount of energy carried by a quantum of light with a wavelength less than 390 nm. Thus, a quantum of light ‘knocks’ an electron out of the lattice forming an electronic vacancy or simply ‘a hole.’

The electron and the hole move actively inside TiO2 particles. As a result of such movement, they are either recombined (they meet, ‘marry’ each other and return to the bound state) or ejected from the surface and immediately captured by it.

Both the hole and the electron are extremely reactive. The overall surface of the catalyst is a powerful area of oxidation. By contacting the catalyst surface, oxygen receives a free electron and gives rise to an oxidative radical (O•) which is able to destroy (oxidize) any organic compound.

The hole, in its turn, reacts with the first organic compound encountered on the surface. The hole ‘pulls’ its missing electron out of this compound, thereby dissolving it into water and carbon dioxide. Every time an electron-hole pair is used up, a new pair rises to the surface of the catalyst, like bubbles in a glass of champagne. The oxidation process continues as long as light hits the catalyst.

Technological innovations:

The catalyst. The catalyst with the highest photocatalytic activity is TiO2 with a crystalline modification of anatase and minimum impurities. In our devices we use such catalyst in the form of ultrafine powder of our own production. The particle size is about 40 nm. This is the state in which the catalyst is highly active and has the maximum surface area for reaction.

The carrier (the structural component surface covered with TiO2). The requirements to the carrier material are quite strict: it cannot be made of organic materials because any organic matter decomposes when exposed to UV radiation; it needs to transmit UV light which means that it should be transparent; and it must be small but provide a large contact area between the catalyst and air. We know how to make such a carrier: by producing plates or tubes of sintered quartz beads 1 mm in diameter using our own patented technology.

Photocatalysis from a medical point of view, its functionality and the application in “Airguard Immune”

Photocatalytically active materials are used to give surfaces self-cleaning properties, to purify air and water, and to kill bacteria, algae and fungi and viruses in aerosols. Organic pollution is converted into H2O and CO2 by activation by irradiation with light of a suitable wavelength, usually UV light. Here, electron-hole pairs are generated through the absorption of photons, which are available for the necessary reduction or oxidation reactions.

Photocatalysis can not only clean, but under certain conditions also contribute to the environmentally friendly production of hydrogen and the conversion of carbon dioxide (CO2) into higher-value hydrocarbon compounds. In principle, photocatalysis does not use any additional chemical substances and is therefore one of the most environmentally friendly and sustainable technologies. For example, in the field of hygiene and medical technology, photocatalysis is used by antimicrobial finishing of surfaces in order to decontaminate, break down pollutants and sterilize them.

The effectiveness and application advantages of photocatalytic filter technology were finally proven in intensive test phases in Asia. Japanese and South Korean institutes (Korea Conformity Laboratory KCL, JeonBok University, Yonsei University, Japanese Institute for Industrial Engineering Research of Kanagawa Province (KISTEC), Japanese Research Institute for Catalysis (PIRC)) confirm that E. coli, salmonella, bacteriophage, rotavirus, norovirus , Influenza and coronaviruses can be destroyed or rendered harmless by photocatalysis. This applies to MERS coronaviruses, SARS coronaviruses and, as confirmed by the South Korean research institute KICT, photocatalytic filters also eliminate the new corona virus SARS-CoV-2.

Several microbiological tests by recognized laboratories have already been carried out in various EU countries and have confirmed the reduction in germ load.

“Airguard Immune” is currently carrying out a study in cooperation with the Medical University Clinic Graz and the Research Unit for Safety in Health in order to be able to demonstrate a virostatic effect in addition to the other antimicrobial effects. The aim of this in-vivo study is specifically to demonstrate the unique effect of “Airguard Immune” on reducing the viral load of COVID 19 in room air. This promising study is being worked on at full speed and will be published shortly.

“Airguard Immune” uses nanocrystalline titanium oxide and a Philips Cleo UVA lamp, which emits light with a wavelength of 315-400 nm, which prevents the formation of ozone. This effect is used by “Airguard Immune” for decontamination and sterilization.

“Airguard Immune” is a new, innovative product, as it was the first time that a permanently stable photocatalyst was made from titanium oxide. This product offers two major advantages. Firstly, “Airguard Immune” is completely safe and can be used continuously in rooms where people are present. Second, the new technology not only filters the air and absorbs the pathogens, but also inactivates the pathogens through photocatalysis.

Dr.med.univ Bresztowanszky Gerfried