I have been doing lit. survey on the above mentioned topic, particularly polymer membranes for water treatment and I have some questions...
1) If I understand correctly polymers consist of some functional groups such as amine or hydroxyl groups that serve as functional groups in removing different heavy metals...
Now my question is what causes the binding between a functional group and a heavy metal ion? Secondly, if i have a heavy metal in mind such as Pb how can i determine which functional group will be most effective in removing it?
Apologies if the question is silly, water treatment is a very new topic for me...
Dr. Ahmad,
This is a very mature research area There are a lot of research and many papers have been published in this area. The attached is just one of the papers published in this area. Hope that it can help you.
Good luck
Maohong Fan
Sorry to say, but the cited example previously is not the best example in my opinion, as the results are rather poor.
Membranes are for separating by filtration, not for adsorbing ions, because the amount of product in a membrane is minimal.
To capture metals two concepts are used: first have an anion to attract cations, then have complexing ligands to chelate the metals.
Ion exchange resins are the best example of functional materials that are actually in use. If the pH is right, then the organic part (resin polymer) will have the anions (like for example carboxylate of sulfonate), and the rest has to be engineerd in, for instance, having oxygen, nitrogen or other donnor groups to make donor-acceptor bonds for chelating the metals. (polyethylene glycol seems to work well in this respect, but few introduce this in their resins, mostly because inorganic substances are less costly and take down more amounts of metals for less.
The ligand to metal stability constants are a good indicator of reactivity with metals, there are plenty of them around, so much that the journal of inorganic and nuclear chemistry decided long ago to stop publishing any more!
some groups have worked on cloth to filter and sequester some metals, usually when the dilution is such that it takes something special to complex the metal and modify the cloth accordingly.
The mechanism of heavy metal adsorption by functional groups is called "chelation". This mechanism connects to electric charge, binding capability, surface forces and so on. Nitrogen-containing functional groups like amines are more capable to adsorb heavy metals. Beside functionality of polymer sorbents, their morphology play pivotal role in heavy metal removal from water...........
I agree wiht Ehsan Salehi, that morphology is pivotal. Indeed, metals bound to ligands embedded inside polymers resist attack by acids that would remove them (or prevent their capture) on surfaces, so that porosisty plays an important rôle...taht cannot be done by thin membranes
It is worthy of mention that thin membrane sorbents can support faster removal rate compared to routine adsorbents. Control of morphology in thin membrane is rather an art!
I'm currently studying microplastic/plastic fragments debris in coastal and estuarines ecosystem. It is said that such plastics are able to adsorb-desorb as well as leach out heavy metals in the environment. I wonder if the adsorption and desorption part have the same idea/concept as the question.
The reference given by Sharon is a very good example of a short presentation summarizing the concepts of chelation.
On the other hand, Victor proposes adsorption on plastics, but this is negligible, but can be done, and has been done: trash polystyrene (like waste cups) can be sulfonated in sulfuric acid to give sulfonated polystyrene, which acts as a good ion exchange resin, but less costly than pure ion exchange resins.
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