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I start by noting that, theoretically starting by the action of oxygen on acidic FeCl2, one can form in situ hydrogen peroxide and other reactive oxygen species, albeit in very small amounts. The latter could then be vented employing microjets. This should result in the formation of powerful (and transient) radicals from the created dilute H2O2.

The underlying chemistry for hydrogen peroxide formation is outlined in this source, see Table S1 here . In the proposed application:

$\ce{ O2 (aq) + Fe^{2+} → Fe^{3+} + .O2− }$ ( moderately fast) )

$\ce{ . O2− + Fe^{2+} + 2 H+ → Fe^{3+} + H2O2}$ (fast )

$\ce{ H2O2 + Fe^{2+} → Fe^{3+} + .OH + OH− }$ ( slow)

However, the slow nature of this last reaction can apparently be overcome (by a factor of a thousand!) per this 2013 paper: 'Fenton chemistry at aqueous interfaces', through the cited employment of microjets.

So, for bleaching, stain removal,..., is this a viable project to examine?

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    $\begingroup$ Slow nature of the last reaction? First reaction is slow, like million times slower, then the last. Seems it's all backwards. Fe is good at catalytically decomposing H2O2 not producing it. $\endgroup$ – Mithoron May 3 '20 at 1:10
  • $\begingroup$ Incorrect, per my reference Table S1, the classic cited Fenton reaction is one of the slowest. See rate for R1 and compare it to Copper chemistry R25, again one of the slower reactions. The metal auto-metal oxidation involving superoxide is reversal. see forward and reverse reaction for Copper R24 & R29. Reverse reaction with superoxide faster than Fenton for iron (see, for example, R7), $\endgroup$ – AJKOER May 3 '20 at 3:17
  • $\begingroup$ Minor reminder: please make sure you don't create tag duplicates. There is no need for h2o2 tag. We already have water tag. $\endgroup$ – andselisk♦ May 4 '20 at 14:34
  • $\begingroup$ It should be clear that my question has an intended broad range of important applications, not confined to any particular iron salt but the whole spectrum of applications that had been forever changed by Fenton chemistry. $\endgroup$ – AJKOER May 4 '20 at 22:27
  • $\begingroup$ My provided answer upon research is a total acknowledgment of this fact, and to the inventors, patent researchers, ,,,,, good news. $\endgroup$ – AJKOER May 4 '20 at 22:29
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So, for bleaching, stain removal,..., is this a viable project to examine?

You may recall that rust stains on clothes or surfaces are one of the worst stains in the world. It is very hard to remove them. It is impossible to use iron salts for bleaching purposes. Those who bleach clothes run away from iron and manganese ions in water like plague or in modern times corona.

Fenton's chemistry is great for environment purposes because iron is among the less harmful elements for the soil & water, and the final product of hydrolysis of iron salts is a great flocculant-great for removing colloidal junk in water.

Instead of these random papers, I would suggest that you start from the very original, 1894, and see what he observed.

Fenton "Oxidation of tartaric acid in presence of iron". J. Chem. Soc., Trans., 1894, 65 (65), 899–911. It is a free access.

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  • $\begingroup$ Iron ion can be chelated, not really employing FeCl2, except for possibly applications other than bleaching. Also, science from 1894 better than 2013 ? $\endgroup$ – AJKOER May 3 '20 at 3:23
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    $\begingroup$ Chelation will not work because the chelate itself is an organic compound. Fenton's reagent or chemistry is used for destroying organic matter by free radicals. As to the comment "Also, science from 1894 better than 2013?" Indeed, reading original paper is often a good starting point for any serious researcher. Like chemistry, many seminal papers in mathematics are to be found in 18th century-19th century. That is why top tier schools often required the reading knowledge of French/Russian/German for math / chem for a PhD. Harvard still requires it for math. $\endgroup$ – M. Farooq May 3 '20 at 3:45
  • $\begingroup$ WRONG on chelation here is one of many many references to quote"The enhancement in Fenton-like is due to the desorption of the entrapped pollutant produced by the addition of the chelating agent and its capability to complex natural metals of the soil" at this Science Direct Source: sciencedirect.com/science/article/abs/pii/S1385894711007492 . $\endgroup$ – AJKOER May 3 '20 at 13:27
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I did find a source confirming the feasibility based apparently on extensive implementation.

It occurred upon my searching for microjets, where I came upon this reference: Tian, Y.; Sun, P.; Wu, H.; Bai, N.; Wang, R.; Zhu, W.; Zhang, J.; Liu, F. ‘Inactivation of Staphylococcus aureus and Enterococcus faecalis by a direct-current, cold atmospheric-pressure air plasma microjet’ in J. Biomed. Res. 2010, 24, 264–269.

It is cited in this 2019 work, published in International Journal of Molecular Science, 2019, 20, 5216; doi: 10.3390/ijms20205216 . To quote pertinent passages from the work: 'Different types of plasma can be used in various biological fields, including disinfection/sterilization' including a type referred to as non-thermal plasma. Here is a pertinent extract from Table I:

Classification:

Non-thermal plasma

Discharge Type:

Glow discharge, Corona discharge, atmospheric pressure plasma jet (APPJ), dielectric barrier discharge (DBD), micro-hollow cathode discharge (MHCD), Plasma needle, (MHCD), Plasma needle, Low-pressure plasma etc.

Examples:

Ozonizer, Plasma medicine, Volatile organic compound (VOC) treatment, Plasma modifications (coating, etching, activation, cleaning, nitration, etc.),

The work notes the following:

The potential of plasma technology in medical and dental applications is extremely broad. As well as disinfection/sterilization of medical and dental devices, the technology could be used to treat beds, desks, and floors [90]. Plasma technology may also have therapeutic potential [91–93]. Therapeutic uses include the treatment of skin diseases [94], blood coagulation [95] as well as dental treatment [96] and applications in dermatology such as chronic wound healing [97].

As to an explanation of underlying mechanics to quote:

Plasma treatment is an especially promising method because the mechanism of bactericidal action is unlikely to differ between multidrug-resistant and normal bacteria. The main mechanisms of bactericidal action in plasma are thought to involve exposure to reactive chemical species for which multidrug-resistant bacteria are unlikely to be resistant [55].

And further:

Reactive chemical species seem to be the principal inactivation factor in most cases, although this may vary depending on the method of plasma generation and whether the sample is exposed to direct or indirect plasma treatment.

Where the reference [55] above, in its extract cites:

Reactive chemical products (hydrogen peroxide-like chemicals), ultraviolet light (UV-A) and slight temperature elevations were observed during the operation of the gas plasma device.

which is also a confirmation of my cited reactive oxygen species (ROS) chemistry where, in the proposed case of wound treatment, for example, we have iron-rich blood with in situ apparently created H2O2, likely forming powerful disinfecting ROSs. Another example, is the more classic Fenton remediation chemistry, removing organic VOCs, with the likes, of yes, perhaps FeCl2.

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