Hi dear all,
Recently, I am doing research using activated carbon (AC) cathode to reduce O2 for H2O2 generation. However, I found after saturated by reactive blue 19 (a dye), the performance of AC didn't decrease obviously, which confused me.
Therefore, I was wondering is it because the active sites for O2 reduction and adsorption are different?
Generally, the active sites include defects, surface functional groups, heteratom. Can I understand the difference from this aspects?
Thanks in advance!
Along with the specific surface area, the nature of the surface is important for the catalytic activity of carbon. Some reactions may occur with the presence of oxygen complexes (alkylation, hydrolysis, esterification) on the surface, others in the presence of dissociating groups (H-B exchange, isomerization, hydrogenation) or surface active centers (dehydration). There is a direct correlation of the catalytic activity of oxidized coals with the amount and acidity of surface proton donor groups. With the presence of oxygen functional groups on the surface of carbon materials, as a rule of acid nature, not only catalytic, but adsorptive and oxidizing properties are associated. The type of functional groups and their acid strength depend on the type of oxidizer and the conditions of the oxidation process. Nitric acid, hydrogen peroxide, as well as permanganates and bichromates are most often used as oxidants.
Wei,
there are mainly carboxylic and phenolic groups. Remember that their form depends on the pH of solution.
regards,
G
Dear Wei,
The reactivity of an adsorbent towards the adsorbate depends on the applied working conditions (such as pH) and on the characteristics of the adsorbate (i.e., charge, size, solubility...). Same adsorbent can fix different adsorbates differently. The adsorption could be chemisorption or physisorption.
The size and the weight of reactive blue 19 dye are much higher than those of O2, therefore, their adsorption and reaction mechanisms on the AC surface should be completely different. I believe that, even after saturation of AC by reactive blue 19, the O2 can access to the surface of AC to be reduced due to its higher mobility (small size). Experimentally, it is difficult to cover fully the surface of an adsorbent such as AC (due to its high specific surface area) by dye molecules; some parts of the AC surface are still active and O2 molecules can penetrate and react.
- How you can assume that the surface of AC is fully saturated by the reactive blue 19 dye? I think it is only the maximum adsorption of reactive blue 19 dye by AC under your working conditions; and the term ‘’saturation of AC’’ is inappropriate. If you change some parameters such as pH or the type of dye, you can find different amount of adsorbed dye by the same AC.
Regards
R.Djellabi
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