Electromagnetic Interference Shielding Properties of CO2 Activated Carbon Black Filled Polymer Coating Materials

Carbon Letters Vol. 9, No. 4 December 2008 pp. 298-302

The activation was performed by treating the carbon blacks in CO2, Hope you can find some information.

Ok, CO2 is a stable gas, I think that the mechanism is the same, to clean and activate the surface. 

To activate carbon, you typically use steam and/or heat. Depending upon the type of carbon, one can use hot CO2 or N2 (or other reasonably inert gas) to help activate or regenerate activated carbon without oxidizing it. Obviously, using steam will add moisture to the activated carbon which is undesirable for some applications, so some hot gas is frequently used.

Hi Abdulkreem, ....CO2 is chemically a weak acid (weak electrophile). So it can be used to remove organic impurities on activated carbon, such as organic sulphur - containing compound (remnant) that is possible existed in activated carbon. As you know that CO2 can react with Hidrogen, it means CO2  can act as an oxidant in certain temperature. Hope this will be useful. 

Regard,

Rudy

Thanks all for the answer 

this one of the journals:

"Activated carbons were prepared by a combined method of

activation from coconut shell. The detailed experimental proce- dure was reported in our previous work [33]. AC samples were prepared based on the experimental design procedure using the Taguchi method. In brief, the dried coconut shell powder (1.0–2.0 mm) was impregnated with various mass ratios of ZnCl2 solution to raw material. After dehydration of mixtures at moderate temperature, samples were pyrolyzed at 800 1Cin a tube furnace under nitrogen gas flow. Then, N2 was switched to CO2 and activation process was continued for certain times"

But he did not explain why all the journals like that

Thanks all for the answer 

this one of the journals:

"Activated carbons were prepared by a combined method of

activation from coconut shell. The detailed experimental proce- dure was reported in our previous work [33]. AC samples were prepared based on the experimental design procedure using the Taguchi method. In brief, the dried coconut shell powder (1.0–2.0 mm) was impregnated with various mass ratios of ZnCl2 solution to raw material. After dehydration of mixtures at moderate temperature, samples were pyrolyzed at 800 1Cin a tube furnace under nitrogen gas flow. Then, N2 was switched to CO2 and activation process was continued for certain times"

But he did not explain why all the journals like that

To remove the organic moeity which were used during the synthetic procedure

The main use of CO2 during thermal activation of carbon is to have an inert atmosphere to avoid its oxidation, as far as I know...

Using tubular furnace, add certain weight in the tube and allow the passage of CO2 gas in through the tube in absence of any air and raise the temperature gradually by about 10 oC /min up to the required temperature for about 4 hours(or any required time) then cool it and remove the activated sample   

The reverse Boudouard reaction (CO2 + C 2 CO) can be used to reconstruct the surface of graphite.  This reaction is thermodynamically favored at temperatures > 975 K.  Several publications suggest that graphite can be reconstructed into nanotubes and other C structures, some having enhanced surface areas.  This enhanced surface areas could be helpful in forming a more active carbon. 

Baird, T.; Fryer, J. R.; Grant, B. (Oct 1974). "Carbon" 12. pp. 591–602. doi:10.1016/0008-6223(74)90060-8.

Trimm, D. L. (1977). "Catalysis Reviews: Science and Engineering" 16. pp. 155–189. doi:10.1080/03602457708079636.

Dal, H. J.; Rinzler, A. G.; Nikolaev, P.; Thess, A.; Colbert, D. T.; Smalley, R. E. (1996). "Chem. Phys. Lett." 260. pp. 471–475. 

Chen, P.; Zhang, H. B.; Lin, G. D.; Hong, Q.; Tsai, K. R. (1997). "Carbon" 35. pp. 1495–1501. doi:10.1016/S0008-6223(97)00100-

Hi,

After producing activated carbon, it needs to be modified for enhanced performance. Here comes the Physical (using steam or CO2, singly or both together) and Chemical (chemical activation agents, ZnCl2, H3PO4 etc.) treatments which are widely practiced by industries.

The purpose of using CO2 during activation is to extract carbon atoms from the structure of the carbon species/compounds being produced/experimented. When the carbon species react with CO2 in the furnace, there evolves the formation of ‘Surface Oxygen Complexes’ which act in two ways: either as a reaction intermediate or inhibitor to the reaction rate.

C + CO2 = CO + C(O), where the second product is the surface oxygen complex mentioned above.

This C(O) becomes stable with the furnace conditions gradually and starts to inhibit the reaction by blocking active sites of the carbon species,

C(O) = C-O [reversible process];

There is also a proposition that C(O) may be decomposed by leaving the surface of the carbon species as CO:

C(O) = CO.

In both the cases, we find a ‘free’ reactive carbon atom which is desired for subsequent applications of the final activated carbon.

NOTE: There are many other aspects to consider in order to get a better picture of the chemistry of using CO2 during activation of carbon such as: temperature range (800-1000 oC most common), the nature of the parent material whether it is Graphitized or Non-graphitized because this feature brings the symmetry and arrangement of constituent molecules which play significant roles in the chemistry of the activation.

 Thanks,

Sirajus Salehin.

During heating processes, N2 and CO2 are used for two different things:

• N2 (or any other inert gas, such as Ar or He) is used to convert the carbonaceous raw material into another more stable and heat resistant compound that consists mainly of carbon (C). Oxygen and hydrogen are largely eliminated, thus leaving a carbonaceous framework with low surface area. This process is named PYROLYSIS.
• CO2, in contrast, reacts with the carbon (is not inert) at around 800 ºC according to C+CO2 --> 2CO. As you can see, you remove some carbon from the solid, and convert it to CO that goes away in the gas. This process of 'gasification' develops porosity by removing carbon atoms. This is one of the methods to produce active carbon. It is active because it can adsorb a lot due to its great surface area (say, from 100 to 2000 m2/g). This process is named ACTIVATION. You can also do it with other oxidizing agents such as H2O or O2 too.

Greetings, Abdulkreem Ghassan Alsultan

 CO2 has been used due to its availability and also it produces larger meso plus macropore surface area. This occurs when the CO2, while diffusing through the carbon matrix, drills, deepens, clears out and volatizes the impurities.

Through this process numerous types of carbon can be produced that give a range of adsorption capacities. The development of high adsorptive power is accompanied by a loss of mechanical strength and density, therefore some comprise is needed in selecting the degree to which the activation is conducted.

Humphrey

You may have read about activation of carbons in nitrogen flow. N2 is an inert gas, and activations in nitrogen flow can be conducted after impregnation of your carbon with an activation agent (for example KOH). In this case the N2 flow is only used to create an inert atmosphere to avoid combustion and remove the reaction products.

Physical activation of carbons (without being previously impregnateed with any activating agent) can be performed by heating in CO2 or steam flow. In this case, the gas or gas mixture is the activation agent.

There is a very nice piece of work dealing with the physical and chemical activation of carbon fibers: Carbon 2004, 42(7), 1367.

Due to its both more easily accessible and cheaper, and also to achieve a relatively large pores

Division proposed by Fernando is very adequate. In the case of mechanism of the Boudouard-Bell's reaction and Ergun (1956), you should read our paper.

Best regards

C + H2 O → CO + H2 (29 kcal),

C + CO2 → 2CO (39 kcal),

CO + H2 O → CO2 + H2 (10 kcal).

Hello,

If You want to enhance the activated carbon efficacy, you can do the post oxidation treatment, by using air stream at a temperature around 280 degrees Celsius, during one or two hours.  

To prepare activated carbons you should use weak oxidants like CO2 and H2O. The N2 is not an oxidant so it not an activating agent. The use of nitrogen is common in the pyrolysis process previous to activation and the objective of N2 use is to guarantee an inert atmosphere. Sincerely yours, Dr. Pedro Villegas.

Dear Abdul Kareem,

In addition to previous answers, Carbon dioxides (CO2) is a weak acid, like other acids act usually as oxidant so it could use for activating carbon. While preparing active carbon , there is still some impurities which cover the pores  (of course, there is a weak  and strong linkages between impurities and carbon pores  so that in eliminating them, someone can use Nitrogen and CO2, respectively due to obtain active carbon having a great pores.

Best regard,

Rudy Situmeang

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