Is the hydroxyl radical the reactive species towards a target pollutant in all AOP systems?
The answer: not obligatory. A highly reactive "Fe(IV)O" might be generated in the mixture of H2O2 and Fe(II)/Fe(III). Ozone itself is highly reactive. A complete degradation of a pollutant to CO2 involves a sequence of reactions. Peroxyl radicals might be the reactive species towards intermediate products of a pollutant oxidation.
@Yurri V Geletti, thanks for the advise. So, the degradation mechanism and the products generated are all depending on the reactive species generated by the various AOPs? Correct me if I am wrong. So what is the better way to identify the various reactive radicals? On the other hand, is it better to use the HPLC to determine the degradation products first? I would like to have some suggestions. Thanks in advance.
"Correct me if I am wrong." You understand correctly.
"So what is the better way to identify the various reactive radicals?" This is an enormous job not for a single person and for a short time. There are thousands of publications in this area without simple answers.
"to use the HPLC to determine the degradation products." this is one of the best way, but very complex and time consuming.
@Pang Chuan Kian, there are two main techniques to identify reactive species - this includes radical and non-radical reactive species because both can be generated during AOPs. (i) radical scaveneger techinques - here some organic compounds that are highly reactive towards the generated reactive species are added to the treated solution so that immediately the radicals are captured by this scavnegrers. i.e, butyl alcohol for hydroxyl radical, 1,4, benzoquinone for superoxide radicals. When you add a specfic scaveneger say butyl Alcohol and the degradation of your targeted pollutants is reduced, then there is formation and participation of hydroxyl radical. (ii) Electroparamagentic resonance spectrocopy (EPR) detail can be find in the following artice Article Electrochemical advanced oxidation processes for wastewater ...
Article Reactive species in advanced oxidation processes: Formation,...
For the degradation of organic pollutants, we use the oxidizing reagent H2O2 in the presence of clay rich in Fe (as a catalyst). We have not yet come up with a mechanism. However, I thought about the formation of an OH radical. It was while reading your contribution that I asked you the question.
Different AOPs have different mechanisms for the generation of oxidative radicals. The present evolution of AOPs blends different reactors and reactions to produce synergistic reactions that help break down organic contaminants. Would be best to explore review papers on topics that describe mechanisms well. the two review articles by my team describe the key mechanisms of FBR-Fenton process as well as photo processes. Do refer to it for some inspiration and reference.
Article Emerging Contaminants: An Overview of Recent Trends for Thei...
Article Fluidized-bed Fenton technologies for recalcitrant industria...
Safia Taleb The process sounds similar to Fenton-like process that is described in our paper. For Fenton-like process, peroxide interacts with the iron to produce hydroxyl radicals as well as other radicals. It also depends on the pH condition where this reaction occurs. Assuming your reaction is for soil remediation, the pH is likely to be the natural pH, where iron solubility is low. This mechanism is best described as Fenton-like process which is well described in the literature.
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