Hydrogen Peroxide and UV

[Andy Perrin]

I've always read that hydrogen peroxide decomposes in sunlight, and particularly in UV. If this is really the case, one would expect the peroxide to be noticeably darker in UV photos than in visible light. I did not find this to be the case, however, with my UV-A setup. Some further reading suggests that the main absorption begins around 310nm:

Quote

The objective of this study was to evaluate the bleaching effect of light sources with various wavelengths using 30% hydrogen peroxide (HP) in vitro. The hematoporphyrin-stained paper was bleached with HP and irradiated for 10 min using LED light sources with 265, 310, 365, 405, or 450 nm respectively. In control group, HP was applied for 10 min without light irradiation. The bleaching procedure was repeated two times. The L*a*b* values of the samples before bleaching and after each bleaching step were measured using a colorimeter. Color changes of specimens were then calculated and statistically analyzed. There was an interaction between light sources and time of irradiation in the color change (p < 0.05). Time and light sources significantly affected ΔE and ΔL (p < 0.05). The light source of 256 nm showed the highest bleaching effect over time followed by that of 310 nm, which were statistically different from other groups (p < 0.001). The 365 nm, 450 nm groups, and control group showed low bleaching effect visually with no significant differences in ΔE and ΔL (p > 0.05). It was concluded that the wavelengths of the light sources affected the bleaching by HP. The 310-nm light can be a potential source for bleaching.

This was consistent with the results I saw in several other papers. Since I do not have a UV-B or UV-C capable setup, I can't test the hypothesis, but those of you who have the ability might have a go at it. In particular, a tri-color with hydrogen peroxide vs a glass of water might be fun.

[colinbm]

Yes, that is why it is usually in brown bottles to block the UV.

[Andy Perrin]

Sure, but the point of the post is that we should do the experiment! 

[colinbm]

I can't photograph it in UVB, But I can record the transmittance with my spectroscope.

 

[Stefano]

I can reach 310 nm, but glass itself looks yellow or orange in my TriColour images. I need a container transparent to UVB.

[dabateman]

Well a quick Google search foud this:

https://www.h2o2.com/technical-library/physical-chemical-properties/radiation-properties/default.aspx?pid=65&name=Ultraviolet-Absorption-Spectrum

 

So you will not see strong darkness of hydrogen peroxide until deeper UVC, kind of like water.

So Colin might be able to image it with his 222nm light, but I don't think he has a UVC capable camera. 

I don't have stock hydrogen peroxide,  only the 3% stuff you buy at the grocery store.  So it would look kind of like water and would mostlybe clear or kind of off clear like isopropyl alcohol,  which starts to peak at 205nm.

 

Acetone you can image into almost UVB, that was dark for me prior to reaching UVC wavelengths. 

 

[Andy Perrin]

Dabateman I think you are reading the graph wrong. It has a LOGARITHMIC scale on the vertical axis and linear on the horizontal, which means absorption shoots up exponentially, starting at the location where it hits 1 which is around 300nm. So way before 205nm and much more like acetone.
 

Colin could definitely image the spectrum of the 3% solution, if there is a quartz container available that wont block the light. 

[dabateman]

@Andy Perrin,

For some reason they are plotting the absorbance coefficient and not the absorbance. 

So its not that strong. Yes absorbance of 1 at 300nm would be quite dark. But thats not on this plot.

See if you can find hydrogen peroxide versus water plot.

 

Ok I'm wrong.  I found this:

https://www.researchgate.net/figure/UV-absorption-spectrum-of-H2O2-showing-that-the-absorption-maximum-was-about-250-nm-This_fig2_7604010

 

If correct than it does spike up after 300nm just like acetone. 

[Andy Perrin]

…yeah, dabateman, I know what they plotted. Every paper I read said the photolysis reaction started around 310nm consistent with the spectrum you showed below.  
 

If stefano or you or Jonathan ever finds a UV-B or UV-C clear container, you could make a time-lapse movie of the decomposition into water. It should gradually turn clear as you irradiate it with UV-B/UV-C.