which radical contributes more for dye degradation whether hydroxyl radicals or superoxide radicals? if anyone of those radicals are responsible then what is the method to calculate and determine the quantity of those radical?
Hello. Hydroxyl radical is more produced in aqueous solution than superoxide radical that depended on the potential (low potential to form hydroxyl radicals).
Best regards,
The hydroxyl radical have been considered as the primary oxidants with no selectivity to organic pollutants, the superoxide radical are also vital active
species that could oxidize a wide range of organic pollutants.
Generally, the photocatalytic degradation of organic
compounds proceed via three routes: direct oxidation by the positively
charged holes (h+), oxidation by OH and superoxide (O2
.−) radical. To make sure about the main active species involved in the degradation process, Isopropyl alcohol (IPA), Benzoquinone (BQ) and EDTA-2Na as scavenging species should be used to investigate the role of OH, O2.− and h+, respectively. when these scavengers react with their characteristic ROS, depending on which ROS is mainly involved, the pollutant degradation will efficiently reduce.
Another method is to use probe molecules which react with OH and superoxide radical and form stable compounds. For OH radical, coumarin fluorescent method is used to form 7-hydroxycoumarin as a stable product. Coumarin is non-fluorescent but 7-hydroxycoumarin is a fluorescent specie having emission peak at approximately 456 nm. You can use fluorescence method to measure the formation of product, which is the evidence of OH radical formation. Same principle is used for terepthalic acid probe superoxide measurement. For superoxide radical test, nitroblue tetrazolium a colorless compound is used which form a blue colored formazan product after reaction with superoxide. UV-Visible spectroscopy is used for monitoring formazan formation.
The answer is hydroxyl radicals. You can think also about the use of persulfates to produce sulfate radicals.
Regards
G
Check the listed papers on AOPs:
Article Solar light driven degradation of norfloxacin using as-synth...
Article Wastewater treatment by means of advanced oxidation processe...
Article Wastewater treatment by means of Advanced Oxidation Processe...
regards,
G
Dr. Govindarajan wishes to compare the reactivity of superoxide with that of hydroxyl radicals. Please have a look at the NIST database: Standard Reference Database 17 Version 7. 0 Release 1. 4. 3 (https://kinetics.nist.gov/kinetics/index.jsp), and you will find that superoxide does not react with most compounds and the hydroxyl radical does, and rapidly too. In principle, superoxide is not reactive; it is a mild reductant.
This question was answered many years ago!
Super oxide in fact is a reducing agent but not a strong one while the *OH radical is considered to be non-selective in oxidizing wide variety of organic and inorganic contaminants . The mechanism of oxidation however differs depending on the compound such as addition to a benzene ring or H abstraction (paper 4).
Its quite difficult to get actual concentration of these species as they are short lived (half life :microseconds-milliseconds) and at many times may not be necessary.
One way of quantifying cumulative production of OH rad would be using a known amount of compound such as benzoic acid/sodium benzoate and quantifying the end product of reaction p-hydroxy benzoic acid. I think one of the papers published in 90s shows multiplying the p-HBA yield by ~5 times gives an approximation of OH radical production. (attached paper 2)
Another way it is done is by using a OH radical scavenger such as tert-butanol (TBA) and if it can be demonstrated that the reactivity is reduced substantially in presence of TBA, it verifies that Oh rad is playing a role. (attached paper 1). This paper also shows ways in which you can verify super-oxide radical presence in the system.
If your system is supposed to have some sulfur species, third paper may be helpful that distinguishes Oh rad ans Sulfate rad.
Article 4 provides an excellent review on OH radical.
Best of Luck!
These papers may be a good starting point
Article Mechanistic understanding of polychlorinated biphenyls degra...
Article Reduced Iron-Containing Clay Minerals as Antibacterial Agents
Article Identification of Sulfate and Hydroxyl Radicals in Thermally...
Article Environmental Implications of Hydroxyl Radicals ((•)OH)
one another technique demonstrated to quantify OH radicals with DCFH fluorescence
- Badges
- Science topic
- Similar topics
- Chemistry
- Biochemistry
- Biochemical Techniques
- Blotting Techniques
- Immunoblotting
- Dyes