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I was told that I can use an Ozone generator to get rid of fungus (resulting from not enough fresh air I suppose). But I didn't find any reputable source for that claim. Would it work, Chemists of Stackexchange? What should we pay extra attention to?

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  • $\begingroup$ Wow, now that's a particularly bad idea... $\endgroup$
    – Mithoron
    Nov 1 '20 at 19:16
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Here is a good commentary, in my assessment from the National Ozone Association, on which I will review the chemistry latter, to quote:

A debate has swirled about for years about the use of ozone generators for mold infestations. Some mold experts call ozone "useless" for mold treatment, while others strongly insist that ozone will kill mold...The truth will not please either side, but it is clear that high PPM ozone does kill mold and harms mold spores so they cannot reproduce. However, ozone treatments alone are not enough to treat a mold problem. Not only is mold a health concern, but even dead mold and mold spores can be a health threat...The reason that ozone generators are not a full mold solution is that mold is a kind of SYNDROME. Mold does not happen unless there are several factors working in sympathy to provide the conditions mold growth requires. So, an ozone treatment may be like a running a water pump in a basement with a broken water pipe...

Further, an important point, in my opinion, to continue quoting:

So, killing mold with an ozone generator has merit, and it is a proven mold-killing process. I want to add, that we are not talking about many of the ozone generators on the market today. 90% of of these are simply too small to drive the PPM levels needed for an effective ozone treatment...Obviously, ozone levels strong enough to kill mold means you must do this work in an uninhabited/vacated building...We have seen some documentation by groups claiming that ozone treatments that are below EPA or OSHA permitted levels (for occupied areas) are not effective. We agree. You can't have both.

So, high levels of also toxic to humans O3 is required to kill mold, but the gas is not effective on mold hidden behind walls and such, and does not address underlying causative conditions leading to mold formation. Some level of physical removal and exorcism is still likely required as dead mold and mold spores remain potential health issues.

A review of the chemistry of ozone reveals it to be complex, as is noted, for example, in this work: 'OZONE {O3} IN DRINKING WATER TREATMENT a brief overview...', which details possible reaction pathways with ozone, to quote:

Ozone can attack as a dipole, molecule, electrophilicly, or as a nucleophilic agent. Ozone reacts in water, or any aqueous solution, in two ways: DIRECTLY as molecular ozone via three mechanisms; (slow and very selective), forming aldehydes, ketones and carboxylic acids, cyclo addition (+ & -); on unsaturated bonds, as a dipole. ozonide > carbonyl > hydroxy-hydro peroxide > carbonyl & hydrogen peroxide electrophilic (+); on molecular sites with strong electronic density. aromatics (phenol & aniline) nucleophilic (-); on molecular sites with an electronic deficit, usually on carbons carrying electron-withdrawing groups. INDIRECTLY via radicals formed as it decomposes in water; A few such radicals are as follows; hydroxyl radical, .OH, a main reactive ingredient hydroperoxide radical, .HO2 superoxide radical ion, .O2-, ozonide radical ion, .O3- The indirect reactions produced by molecular ozone are limited only by the various radicals it produces, which varies with the initial water quality. The worse the water quality problems are, the more ozone can potentially rise to the occasion.

Also:

Even with the ozone used up quicky, the radicals it forms will continue reacting. One indirect example of ozone molecules contacting water $\ce{ (O3 + H2O = O2 + .OH + .OH)}$...

Technically, the last reaction is not accurate as are some comments in the article (like the hydroxyl ion is a water cleaning agent, it is primarily the hydroxyl radical, but OH- does serve an initiating role, see equations below). My technical assertion on the corrected reaction(s) are as follows:

$\ce{O3 + hv -> O2 + O }$

$\ce{O + H2O -> .OH + .OH }$

Source: GoogleBook

So, the net reaction of ozone with H20 in the necessary presence of UV light is:

$\ce{O3 + H2O + hv -> O2 + .OH + .OH}$

Note, hydroxyl radicals can be created by the action of water on ozone, but the reaction is pH-dependent and is not given by the above equation. In fact, in water with a pH above 7, the reaction can proceed as follows:

$\ce{O3 + OH- -> .O2- + .HO2}$

$\ce{.HO2 = H+ + .O2-}$

$\ce{.O2- + O3 -> O2 + .O3-}$

$\ce{.O3- + H+ = .HO3}$

$\ce{.HO3 -> .OH + O2}$

Source: See, for example, Ozonation of Tris-2-Chloroethyl Phosphate (TCEP) in Water by Michael J. Votruba.

The above approximately (as there are more possible reactions) implies a net reaction in alkaline water of:

$\ce{2 O3 + OH- -> .O2- + .OH + 2 O2}$

where pH cited as 8.5 or higher in applications.

but, in actuality, intermediate reactions and subsequent products are also possible with more ozone.

Note, in atmospheric chemistry, where we are working with aerosols, due to a change in the dielectric constant for the medium (which impacts pKa, see Wikipedia the hydroperoxyl radical), the superoxide is found mostly in the form of $\ce{.HO2}$. The implied approximate net reaction would then be:

$\ce{2 O3 + H2O -> .HO2 + .OH + 2 O2}$

So evidently, the chemistry of ozone can address mold when in contact (especially in the presence of UV light), but many transient (albeit, very powerful) radicals are very short-lived, and this is, by no means, a permanent solution. To the latter, new mold resistance wallboard installed following treatment is likely advisable as is natural sunlight lighting fixtures and a de-humidifier as water presence is also a causative agent for mold growth.

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