Based on my reading, HNO3 treated AC gives more functional group content including (oxygen and nitrate functional group) compared to NaOH (only single bonded OH group). but somehow, I observed that most of research on heavy metals adsorption on AC uses NaOH as activating agent. I'm very curious on this matter :) Hope you guys can help me out
"Pretreatment with detergent and alkali chemicals such as NaOH, Na2CO3, and NaHCO3 were found to improve or maintain the bioadsorption capacity in comparison with live M. rouxii biomass. Acid pretreatment using HCl, H2SO4, and C2H4O2 resulted in a significant reduction in the bioadsorption capacity while alkali pretreatment was found to be more effective."
You can check the paper below for more information
Regards,
K
Based on that paper: It was observed that the amount of lead adsorbed by activated carbon, activated with nitric acid (HNO3), H2SO4, and HCL was significantly higher than carbons activated with ZnCl2, NaOH, and H3PO4. This shows that adsorption of Pb2+ ions requires chemisorption than physical adsorption. Activation with HNO3, H2SO4, and HCL created more reactive sites for adsorption.
HNO3, H2SO4, and HCL increase the concentration of surface oxygen groups which reacts easily with lead and iron ions than ZnCl2, NaOH, and H3PO4.
Why does the study stated that if AC with ZnCl2, NaOH and H3PO4 will have bigger surface area and less than functional groups? How does these chemicals effect differently from HNO3, H2SO4, HCL.
I would really appreciate if you could give opinions based on your understanding on this matter :) Kien Vu
It is true that treatment of carbon by acids leads to create more functional groups on its surface, but the surface area is reduced due to the absence of pores, and acid treatment may lead to destroy porous structure of carbon. On the other hand, treatment of carbon by NaOH, KOH Or ZnCl2 leads to an increase in the surface area because the metal will be incorporated into the carbon composition, and after removing it by dilute acid, it leads to the formation of pores on the surface.
Badr M. Thamer Thank you sir for the explanation. Based on your explanation, it means that if using acid the functional group increases but surface area might be lower due to acidic properties (corrosion). But as for alkali, less functional group but larger surface area. Is my understanding true? :)
Badr M. Thamer Based on my reading on one reference i found recently, NaOH gives larger surface area since when NaOH with carbon sample, Na2CO3 will produced or form under thermal decomposition that give gases CO2 and H2O that responsible for burst pre-cursor and results in wider holes:
2C + 6NaOH -> 2Na + 2Na2CO3+3H2
Is this true due to gas formation hence that is the reason for higher surface area when we're using NaOH. and what is your opinion sir?
I really appreciate your thoughts on this matter Badr M. Thamer :)