What self cleaning windows, deodorizing lights and your skin have in common

Self cleaning windows are a marvel of modern technology. They are capable of breaking down grime and organic matter on their surface, thus reducing the amount of effort you need to spend cleaning them.

This is all achieved through the use of a relatively benign compound: titanium dioxide (or TiO2 for you chemistry freaks).

TiO2 is fairly inert and non-toxic. However, don't push it, everything is toxic in the sufficient amounts or if irresponsibly used - just think of dihydrogen monoxide (H2O). It is used almost everywhere as a whitening agent – toothpaste, icing, paint, plastics, etc – because it is incredibly white and non-toxic.

It does have one interesting property: it is a photocatalyst. That means it interacts with light and facilitates a chemical process, while not actually taking part in the chemical process. For example, nickel is used as a catalyst in the process of hydrogenating margarine (adding an extra hydrogen atom to a liquid fat and making it a not so good solid fat). Other metals like platinum, palladium and rhodium are used in the catalytic converter of your car’s exhaust to make the emissions coming out of your car less toxic) - this is a heat activated process.

TiO2 generates free radicals in the presence of ultraviolet light (UV). These free radicals then oxidize nearby molecules: water, organic molecules, oxygen molecules in the air - thereby breaking them apart. If your dirst and grime gets broken down, it gets cleaned. Simple.

This is achieved by bonding a very, very thin layer of TiO2 to the surface. The UV light is provided courtesy of the sun.

Deodorizing lights work on pretty much the same principle. Except in this case the UV source is a fluorescent light (one of those spiral shaped energy saving ones) - they have a little bit of mercury in them which is arced and this generated UV light, phosphors in the lamps coating absorb the UV and reradiate at a visible wavelength. In this case, the TiO2 is bonded to the outside of the light. The TiO2 catalyzes the oxygen molecules in the air (O2) to produce single oxygen atoms - which are highly reactive. These oxygen atoms then bond with organic molecules (odour molecules) in the air and this oxidation helps eliminate odours.

Since TiO2 is so good at absorbing UV rays, it gets used in sunscreen.

Now, I don't know about you, but I am a little leery of applying a chemical that becomes strongly oxidative in the presence of UV rays on my skin. With all the talk of how we need to eliminate free radicals from our lives (take vitamins C and D, eat leafy green vegetables, don't smoke, get rid of your ozone generator), it is surprising to me that a strong photocatalytic oxidizing substance is approved for use as a skin protector.

Is there is a conspiracy to hide the information. No. I believe it is more likely that people simply have not put the facts together. No lamp has lit in someone’s head.

It reminds about 15-16 years ago when we were eliminating lead (Pb) from everything, and someone asked, "Does the lead in lead crystal leech out?" Surprisingly, up to that time, nobody had even considered that. And yes, the lead in leaded crystal does leech out. So if you store your brandy in it, you are exposing yourself to lead (on a side note, the ancient Romans like the sweetness lead gave to cooking and wines).

Scientists are extremely narrowly focussed in whatever research they do. (I know because a friend of mine is an environmental scientist at McGill and whenever I look over his experiments, my mind simply races over a bazillion things I see he has not considered - to which he wearily replies that he cannot consider every variable because he would never get anything done. He simply controls for one variable at a time.

There are numerous active ingredients used in sunscreen to protect against ultraviolet (UV) exposure. To the best of my knowledge they are zinc oxide, titanium dioxide, octinoxate and oxybenzone.

The one which I have questions about is titanium dioxide and so I do not use sunscreen products containing TiO2. Zinc Oxide (ZnO) also is photocatalyst.

Personally, I think moderate sunlight exposure is good. UV rays produce vitamin D in the skin (which is why vitamin D is often called the sunshine vitamin).

A few days ago, the Canadian Cancer Society said that people should consider limited exposure to natural sunlight.

Disclaimer: I have no direct scientific evidence to back up this claim, nor am I aware of anyone who has done such research. However, a simple thought experiment using available data should prove it to be quite plausible. Yeah, this is me expounding on one of my pet crank theories ;-)

Image taken from here. Maybe the image will post tomorrow, blogger seems to be in one of its "I'm not posting images" moods

You can see more applications of TiO2 here,

Read more on the deodorizing light bulb here.

Read more on catalytic reactions here.

[25-July-2007 @ 09:41, fix typo Deordorizing with correct spelling Deodorizing . Also add labels.]

[Update 13-May-2008 @ 13:15: an article in the Journal of Oleo Science confirms my hypothesis. As it says in the conclusion: "The zinc oxide pigment used in cosmetics and as a sunscreen active agent in commercial formulations causes significant damage to DNA under UV illumination."]


Wow, this is all very interesting. And I have never heard of self-cleaning windows...I didn't realize that there is such a thing. I am also very conscious of what I put on my skin (aside from a small bit of makeup...vanity wins...ugh). A good friend of mine (also an engineer) had a 1-year-old son who was diagnosed with cancer. He immediately began researching all possible causes and therapies, and in the process of watching his family go through this ordeal, he introduced me to the works of Royal Raymond Rife/James Bare and Hulda Clark. There is so much more to say than I could ever fit into this little comment space, but suffice it to say that I have seen some great anecdotal evidence supporting their theories (particularly with the rife machine). But just hearing of Hulda Clark's theories on disease being caused by parasites, toxins and solvents in our bodies, it makes me think twice about slathering on any sort of petroleum-based lotion onto my skin. (And also frightens me, knowing that my maternal aunt, who was diagnosed with breast cancer, has ritualistically rubbed lotion on her skin for as long as I can remember). I'll stick with good old soap and water. :)

P.S. Fortunately for my friend, his story had a happy ending, with his son (who is now 11 years old) making a complete recovery and has been cancer-free for approximately 8 years now.
ghee said…
phew!!this is quite an information.

I stopped using UV sunscreen 2 years ago,as I`ve found out that its not the only solution for not having freckles or taints.Here in Japan,they say that the sunrays are stronger than any other countries,im not sure if that is true.

yeah,cancer is scary..

thanx for the infos! it helps a lot!
Sassy Lady said…
Have to say that Richard have always been considerate enuff to share unknown issues to be known to his readers and for that I thank u Richard...

I feel like I'm back in school learning everyday from u..but in an interesting way..(school's a bore)

I believe to protect ur skin fm UV rays or other diseases..u must treat ur inner body first..like healthy diet, physically and mentally too before u concentrate on the outside.

Its not proven scientifically but in the olden days, ppl live up to 100yrs of age without any kind of illnesses..
Lunafish said…
uh-oh. I used to spend time in the sun and tanning beds lathered up. I'm surprised my skin didn't turn to leather. I do use sunscreen as I am fair with freckles. I never thought of reading the label. I don't tan on purpose anymore but I do spend a great deal of time in the sun at the pool. Thanks for the information. Wow.
Richard said…
Just remember, this is my speculation. As my scientist friends would ask: "Is there any reserach to back it up? No. Then, until there is research, it isn't true."
carra said…
I thought H2O is water. I loved chemistry at school and I know I am not wrong so how water could be used as whitening element? Please explain that!
Richard said…
H2O is water.

Water, in and of itself, is a very good solvent, however, it would not work as a whitening agent. However, if you manage to break the water down (as TiO2 does in the presence of sunlight), then it becomes an oxidizer. Oxidizers are often used for their bleaching capability since they chemically alter most colourants making them clear. As well, oxidants also break down organic bonds, thus leading to biological degradation.

You can read about its photocatalytic properties here.

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