Test if it is possible to explain the know ORP reduction when adding H2O2 into a saltwater

[HuduVudu]

I have seen this once - a half a year ago - but newer after that - here is the latest additions logged against the pH curve

Sincerely Lasse

My experiment consisted of filling a liter beaker to the 1000ml mark with fresh mixed TM. Then testing for PH and then adding some 3% supermarket H2O2 and then retest for PH. I forget the exact amount of PH rise, but it was significant enough to cause me to scratch my head and do some research.

FWIW

 

[Randy Holmes-Farley]

My experiment consisted of filling a liter beaker to the 1000ml mark with fresh mixed TM. Then testing for PH and then adding some 3% supermarket H2O2 and then retest for PH. I forget the exact amount of PH rise, but it was significant enough to cause me to scratch my head and do some research.

FWIW

Even with no pH issue, hydrogen peroxide reduces copper 9Cu++ to Cu+) and oxidizes iron (Fe++ to Fe+++) in seawater under the same conditions. Thus it can react as both an oxidizer and reducer at the same time.

Different types of chemicals to oxidize and reduce may be why different people see different effects.

 

[taricha]

here is the latest additions logged against the pH

Same here. Peroxide at typical doses doesn't move pH in my tank water.

 

[taricha]

To continue this idea with one more tiny confirmation...

So the slow probe recovery from peroxide seems to be due to the actual continued presence of the peroxide. (In a beaker of just stirred tank water like this test, H2O2 can last much longer than it would in a tank.)

@taricha it is in a more static environment makes sense to me.

indeed if I add a pinch of GHA to the beaker that held the ORP drop from h2o2 for ~7 hours, the rate of ORP recovery upwards increases.

A pinch of GHA was added to the stirred beaker at 460 minutes. After that, the ORP increased (recovered from its H2O2 drop) faster than before.
Since algae getting added to a stirred beaker in the dark is not going to oxidize anything (should be the opposite), the more likely interpretation is that the algae decreased the amount of H2O2 more quickly than the stirring beaker of tank water alone.

 

[Hans-Werner]

In my opinion it might be interesting how alginate may influence the reaction or aging of the probe. Alginate may be a constituent of biofilms and brown algae, but not green algae.

The vast majority of copper ions in saltwater and natural seawater is bound by chelators/ligands excreted by cyanobacteria. I think the proportion of free Cu2+ ions in natural seawater is less than 1 %, in aquaria it might be even much lower than in natural seawater while the total concentration of copper might be several times higher.

 

[Hans-Werner]

I forgot to mention, if someone wants to try sodium alginate, use a very, very dilute solution in RO/DI water, maybe 0,1 g of sodium alginate per liter or less. If lumps form with saltwater, please dilute it more.

 

[Randy Holmes-Farley]

I agree that it would not surprise me if organics on the probe are holding redox active metal ions, and those metal ions are causing the observations.

 

[Lasse]

I still sample and now I have got some very odd result. First - I´ll try to explain my system, Start with the sump. I the apartment for incoming water from the DT - my skimmer and probes are placed. Also the place for my oxidator - it is placed 10 cm from my probes with a steam coming from that direction into the probes. The water goes to the return camber -> DT -> refugium an d back to the probes.

Normally when I have refilled my Oxydator (a type of automatically doser for H2O2. A plastic bottle with a little (very thin ) hole in the bottom filled with H2O2 and x catalysts, The bottle is placed upside down in a chamber of the same material as the catalyst. The catalyst inside the plastic bottle break down the peroxide. Oxygen gas will be formed in the top of the plastic bottle and slowly press out non catalyzed H2O2 into the space there the second catalyze reaction take place and free oxygen radicals and oxygen gas will be transported out into the water.

My is placed in the sump as described above

When I fill the reactor with new H2O2 or move it - there will be some tiny amount of H2O2 spilled out and it has always result in a dip in ORP for my probe placed app 10 cm from the oxydator. For the moment - I have also two probes up in the DT placed there the outlet to the refugium is. This is the curve for my probe A (placed in sump) Blue addition of H2O2 in the DT - normal reaction. Red = refill of Oxydator and black - I was moving and check the oxydator. Yellow - variation depending on automatically feeding. After the refill - ORP is still on a low level - slowly rising and a little more arractic than before. Probably are the probe responding to smaller addition of H2O2 from the oxydator. But I have not seen this before

The probe in the DT - how did it react ? Not the same and it return to normal ORP after a while

The only explanation for this is for me that the oxydator just emits such small amounts of H2O2 that it only becomes a local reaction

Sincerely Lasse

 

[taricha]

This will require a few more rounds of re-checking, but it's promising.

Blue and red show the same h2o2 additions to the tank over 24 hr apart. Blue was first, and before the red data I cleaned the probe with a 30 min soak and brush in detergent (liquinox), and then similar time soak and brush in 1M HCl.
ORP drop went from ~55mV to ~8mv.

I'll re-check to see how close to turning off this effect I can get with a really cleaned ORP probe. (Though I'm still thinking about how to distinguish between scrambling the internal workings rather than removing the active materials on the surface.)

 

[Dan_P]

This will require a few more rounds of re-checking, but it's promising.

Blue and red show the same h2o2 additions to the tank over 24 hr apart. Blue was first, and before the red data I cleaned the probe with a 30 min soak and brush in detergent (liquinox), and then similar time soak and brush in 1M HCl.
ORP drop went from ~55mV to ~8mv.

I'll re-check to see how close to turning off this effect I can get with a really cleaned ORP probe. (Though I'm still thinking about how to distinguish between scrambling the internal workings rather than removing the active materials on the surface.)

Boiled aquarium water could have material for the conditioning film to form but not life to colonize it. Monitoring ORP response as a film forms but does not progress to biofilm might be instructive. Might be a way to observe @Rick Mathew sample storage film formation.

 

[Lasse]

distinguish between scrambling the internal workings rather than removing the active materials on the surface

Yes - in one or another way - I think that all these different experiments highlighted that it has something with age (and/or adaption of the probe) to do. Maybe some with experiences in probe construction could say if it theoretical can be a one month equilibrium period.

I can see 3 main reasons for the "drop" effect

1) A active biofilm
2) a electrochemical layer on the probe (e.g. oxide coating like rust)
3) adaption off equilibrium between external and internal fluids

Sincerely Lasse

 

[Dan_P]

Yes - in one or another way - I think that all these different experiments highlighted that it has something with age (and/or adaption of the probe) to do. Maybe some with experiences in probe construction could say if it theoretical can be a one month equilibrium period.

I can see 3 main reasons for the "drop" effect

1) A active biofilm
2) a electrochemical layer on the probe (e.g. oxide coating like rust)
3) adaption off equilibrium between external and internal fluids

Sincerely Lasse

Do any vendors recommend a conditioning period? I never came across this idea.

We might have to entertain the possibility that the ORP electrode needs more maintenance to provide consistent data. I am also thinking we have observed that H2O2 can change aquarium water in multiple ways depending on several factors.

Since my resolve to not buy an ORP electrode has not wavered, I will just continue to pass along experiment ideas. I would confirm that the dip and slow recovery was correlated to H2O2 concentration. Then, I would catalze the rapid destruction of H2O2 to confirm again that the rise is correlated to its concentration. Having confirmed the event I was monitoring by the ORP dip, I would determine whether transition metals have a concentration dependent effect. Then I would create films on the probe. I would first look at BSA, and boiled skimmate. I might also consider building an ORP electrode of another design to see if electrode construction was a factor.

 

[Randy Holmes-Farley]

Yes - in one or another way - I think that all these different experiments highlighted that it has something with age (and/or adaption of the probe) to do. Maybe some with experiences in probe construction could say if it theoretical can be a one month equilibrium period.

I can see 3 main reasons for the "drop" effect

1) A active biofilm
2) a electrochemical layer on the probe (e.g. oxide coating like rust)
3) adaption off equilibrium between external and internal fluids

Sincerely Lasse

Platinum and gold do not form an oxide layer at room temperature unless placed into a highly oxidizing fluid..

Oxide Films on Platinum Electrodes | Johnson Matthey Technology Review

Johnson Matthey’s international journal of research exploring science and technology in industrial applications

www.technology.matthey.com

Platinum, equally with gold, serves to typify the ideal of a noble metal. It neither rusts nor tarnishes in air whether it is kept for centuries in industrial or marine atmospheres or in clean country air, or whether it is heated in air to high temperatures for long periods. In all these conditions, it is normally considered that a platinum surface will remain clean and bright and free from any tendency to scale, tarnish or develop protective surface oxide films as do the base metals.

Similarly, a platinum anode is commonly considered to present always a clean metallic surface to the electrolyte in which it is immersed, so that electrons can pass freely between the metal and the liquid unimpeded by any oxide barrier.

However, when the conditions at the anode are strongly oxidising, a platinum electrode sometimes behaves as if it were protected by “a film of platinum oxide, which prevents more than superficial oxidation of the platinum and yet permits electron transfer processes”. In a recent contribution from the Department of Chemistry at Harvard University (J. Amer. Chem. Soc., 1957, 79 (18), 4901–4904), F. C. Anson and J. J. Lingane have provided some most convincing evidence that such films really exist. They have succeeded in stripping the films chemically from oxidised anodes and in determining their weight and composition. The films are comprised of PtO and PtO2 in a molar ratio close to 6 to 1.

These data constitute the first direct chemical proof of the formation of platinum oxide films.

 

[taricha]

The only explanation for this is for me that the oxydator just emits such small amounts of H2O2 that it only becomes a local reaction

Thanks for going into the details on the oxydator. I had wondered if what escaped from it was only O2, or also radicals /H2O2 itself.
It seems your data supports the idea that it releases a low slow level of something that acts like the radicals/H2O2 itself.

We might have to entertain the possibility that the ORP electrode needs more maintenance to provide consistent data.

The notion of film formation on clean platinum in seawater in the time frame of hours means that a "clean" probe is only a short term situation, and incompatible with constant ORP monitoring.

Then, I would catalze the rapid destruction of H2O2 to confirm again that the rise is correlated to its concentration.

I don't think I have any inorganic catalysts that would decompose H2O2 without moving the ORP themselves. Platinum is itself a catalyst for H2O2 decomposition. But the extremely long dwell time of H2O2 in a stirred beaker with a probe in it tells me that this process is slow compared to what happens to H2O2 in a tank itself.

It would be interesting for @Lasse to use a hunk of the oxydator catalyst in a container to compare the H2O2 effect time with/without the catalyst. But again, the oxydator is meant to deliver the effect over a long time, so I don't think the catalyst will be super-fast at making the H2O2 disappear.

Then I would create films on the probe. I would first look at BSA, and boiled skimmate.

I was already planning skimmate as a way to rapidly "age" a cleaned probe.
Do we think the organic ligands/ binders in skimmate that govern the metal behavior would survive boiling with therir active effects intact? Or are they more like proteins - denatured by heat?

 

[Dan_P]

Thanks for going into the details on the oxydator. I had wondered if what escaped from it was only O2, or also radicals /H2O2 itself.
It seems your data supports the idea that it releases a low slow level of something that acts like the radicals/H2O2 itself.


The notion of film formation on clean platinum in seawater in the time frame of hours means that a "clean" probe is only a short term situation, and incompatible with constant ORP monitoring.


I don't think I have any inorganic catalysts that would decompose H2O2 without moving the ORP themselves. Platinum is itself a catalyst for H2O2 decomposition. But the extremely long dwell time of H2O2 in a stirred beaker with a probe in it tells me that this process is slow compared to what happens to H2O2 in a tank itself.

It would be interesting for @Lasse to use a hunk of the oxydator catalyst in a container to compare the H2O2 effect time with/without the catalyst. But again, the oxydator is meant to deliver the effect over a long time, so I don't think the catalyst will be super-fast at making the H2O2 disappear.



I was already planning skimmate as a way to rapidly "age" a cleaned probe.
Do we think the organic ligands/ binders in skimmate that govern the metal behavior would survive boiling with therir active effects intact? Or are they more like proteins - denatured by heat?

Good point about denaturing protein, but there are other polymers in aquarium water that might survive a brief heat up to boiling (not long term boiling). So, maybe skip the boiling for now.

 

[Randy Holmes-Farley]

Do we think the organic ligands/ binders in skimmate that govern the metal behavior would survive boiling with therir active effects intact? Or are they more like proteins - denatured by heat?

Some will, some may not. Worth a try.

If the effect remains, it rules out biological effects.

If it disappears, either it was biological, or the heat damaged it.

FWIW, boiling may also alter the oxidation state of trace metals attached to organics on the electrode.

 

[Lasse]

I had wondered if what escaped from it was only O2, or also radicals /H2O2 itself.

In some way you decide by yourself with the chosen concentration and the number of catalyst. I use 12% and 3 catalyst for the moment. The reason for this is that I have bought some new fishes and of "pathogen" reasons - i want free H2O2 in the water that slowly decompose to first active radicals, O2 and water. If I run 6 % and 2 catalyst - most will be O2

inorganic catalysts that would decompose H2O2

Silver or platina. I did a test with the compound that is the normal oxydator catalyst in one of my freshwater tests - no reaction as I saw it.

Sincerely Lasse

 

[Hans-Werner]

Even with no pH issue, hydrogen peroxide reduces copper 9Cu++ to Cu+) and oxidizes iron (Fe++ to Fe+++) in seawater under the same conditions.

Alginate seems to bind copper Cu++ (and here and here).

How would reduction to Cu+ alter adsorption and how does it influence results or ORP measurements?

 

[taricha]

I'll re-check to see how close to turning off this effect I can get with a really cleaned ORP probe.

This was not really replicable. Repeated cycles of cleanings did not turn this off or down.
Dirtying the probe with skimmate gave changes that are hard to interpret.

Conditioning the probe overnight in its proper 3.5M KCl storage solution and then doing several short cycles of detergent and HCl brush cleanings still showed a sizeable ORP drop with H2O2. The effect did not change with repeated rounds of cleaning. I presume this is the "normal" functioning of my probe when clean - like everyone else's.

A 20 min soak in raw skimmate did not change the effect.
An overnight soak in raw skimmate changed the behavior in a confusing way:
From skimmate, rinsing in tank water, then into the tank, and after ORP stabilized ~1 hr, H2O2 caused an ORP rise. (This could be because the skimmate test tube contained lots of metals/organics in a more reduced environment.)
Leaving the probe in the tank for over a day, the ORP was a little higher than normal, and the next H2O2 addition caused the usual ORP drop, then a few min of cleaning the probe and returning, the ORP drop with next H2O2 was still about the same size.

I'll post some charts if I can see the same thing a couple of times and feel it's repeatable.

 

[Randy Holmes-Farley]

Alginate seems to bind copper Cu++ (and here and here).

How would reduction to Cu+ alter adsorption and how does it influence results or ORP measurements?

Both Cu+ and Cu++ can bind strongly to organics.

it is certainly possible to design ligands to be selective for one or the other, as shown below, but I do not know the relative binding of whatever ligands may (or may not lol) be attached naturally to an electrode surface:

Cu2+ selective chelators relieve copper-induced oxidative stress in vivo

https://pubs.rsc.org/en/content/articlepdf/2018/sc/c8sc04041a