There are three important characteristics of adsorbents to be considered for the removal of metal ions. One is capacity, which is related to specific surface area. The realistic surface area for CNT is around 1000 m2/g (theoretical maximum is 1315 m2/g). For comparison charcoal has 1500-1600 m2/g. Of course, oxidation degree of the surface of carbonaceous adsorbents should be taken into account here. Second is selectivity, which is associated with presence of negatively charged carboxylic groups. For some metals the presence of pi-electronic system in CNT could be significant, but in waste waters these reactive sites will be blocked by organic molecules. Finally, the cost of adsorbent - compare cost of charcoal and CNT. I think the answer is pretty obvious.

yes possible as well as graphene graphene oxide

osmosis system or distiller system

The cost of CNT's make any conceived project as totally uneconomical.

That is a broad question. If you look into the effeciency the small tubes may achieve the goal due to few factors specific surface area, curvature effect, etc..

On the other hand, single or multi tubes still to be activated via some oxidants which make the process not enviromentlly effective. Another thig single tubes when they oxidaized the pristine backbone will be damaged..

Econmically, they cost a lot.

Another thing which heavy metal do you need to tackle with? Which ionic charge status you want ( anionic, cations)

So many factors to be considered!

But, yes they can be..

There are some other adorbents better than CNT, though.

Cation exchangers are still the most economical materials. The key problem with carbon is that it extremely difficult to functionalize it with cation or anion exchange groups with a high ion exchange capacity. Heavy metals in water exist as ions (cationic or anionic complexes). If you can invent a way to functionalize carbon nanotubes with desired functional groups then it would be a good service to science.

There are more than oxidant to deal with the CNT oxidation, H2SO4:HNO3 (3:1) Vol ration at 8 mole/ L.

H2O2+ H2SO4 can be also a good choice and can introduce mainly -COOH>OH>C=O.

COOH is the most active group due to the close moiety of C=O and OH at the same spot leading to a strong polarization which lead to adsorb or bind with two bonds (or two cations).

Ahmed mohammed Jasim , you are right about -COOH, but the capacity (millimole/g) is so small that it is negligible. Oxidation does make carbon hydrophilic but practical cation exchange would be nil.

Mohamed Bayati link was indeed helpful. Thank you.

Ahmed mohammed Jasim you have given some nice inputs in the discussion. Can you name some adsorbents better than CNT as you mentioned in your answer.

Alan F Rawle sir, As you mentioned CNT's are uneconomical. So do you think heavy metal removal from wastewater with CNT as an adsorbent will be worth exploring as a major project. I fear there won't be any industrial application as such.

M. Farooq Wahab sir, if anyhow we succeeded in functionalizing CNT with suitable reagents. Is the project (removal of heavy metal from wastewater by CNT) worth exploring considering high cost of CNT and presence of so many low cost adsorbent. I am interested in socio- economic analysis.

There are different types of CNTs and their Prices based on their specifications.

If you want an effecient you may need small tubes which are very expensive.

CNTs have problem economically.

Carbon black is very very cheap you may use it.

Practically, People have started avoiding CNTs.

Pradeep Saw, may I suggest that you leave the idea of metal ion sorption by carbon nanotubes. I have done this type of modification for several years for metals ions without much success. On the other hand, you might use the modified carbons for removing organic pollutants. That might be a far more useful idea than removing metal ions. Note that activated carbons will indiscrimately adsorb organics, by modifications you can make them selective.

The comparison point should be with another form of carbon - carbon black. Inexpensive as used in road tires, high surface area, and can be functionalized for heavy metal adsorption.

M. Farooq Wahab , Let him try he may get good results noting is impossible

Off course can but that depends on the size of the particle and the time need for thst

M. Farooq Wahab sir, thank you for inputs. I think i should go for more literature reading before coming to any conclusion

First thing to consider, can you regenerate the CNT from the heavy metal ions, efficientlly?

Carbon black by itself is holding oxygen groups since it is produced from buring.

One bad thing with carbon black is the aggregation which limit the exposed surface area.

Ahmed mohammed Jasim Can't we increase available surface area for adsorption by some methods.

There are three important characteristics of adsorbents to be considered for the removal of metal ions. One is capacity, which is related to specific surface area. The realistic surface area for CNT is around 1000 m2/g (theoretical maximum is 1315 m2/g). For comparison charcoal has 1500-1600 m2/g. Of course, oxidation degree of the surface of carbonaceous adsorbents should be taken into account here. Second is selectivity, which is associated with presence of negatively charged carboxylic groups. For some metals the presence of pi-electronic system in CNT could be significant, but in waste waters these reactive sites will be blocked by organic molecules. Finally, the cost of adsorbent - compare cost of charcoal and CNT. I think the answer is pretty obvious.

Hi,

CNTs are excellent absorbents and you can apply them for many adsorption purposes. However, selectivity is what you have to focus on and considering what you are going to modify, you need to modify your CNTs.

Dear Vahid,

CNT is good adsorbent but original question was about socio economic scenario of using CNT. Cost of 1 g CNT is about 8-10 USD, cost charcoal - 500-600 USD per metric ton. The ratio is 20000. Guess how much adsorbent is required for water plant treatment?

You can follow this paper. May come in your work.

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