In my opinion, the surface area will remain the same, but the quality of the surface will be problematic - on the surface functional groups will undergo different chemical reactions and this may lead to unwanted activity. The activation may be carried also in the presence of other inert gas

Dear Mihir,

In chemical activation, inert gas is used to reduce the liberation of carbon from the material under heating, thereby reducing it yield. Nitrogen gas is mainly used because it is cheap. Carbonization can also be done under other inert gases such as helium and hydrogen. At same heating temperature, such gases will provide only slight changes in surface area. Moreover these gases are not categorized under agents of activation.

Regards,

abbas

The inert gas like nitrogen remove oxygen from the system because the oxygen burn the sample and finaly the obtained carbon is with a large rate of ash and is not activated so no/or very low porosity or surface area

Dear,

Activation is not necessarily done using inert atmosphere though it is recommended, but can also be done in atmospheric condition. However, inert atmosphere is more suitable to reduce the carbon being burnt off as carbon dioxide, decreasing the carbon yield and increasing the ash content. Though, activation can be still be achieved in atmospheric conditions at lower temperatures such as 400 - 500 C depending on the source of the carbon.

Hi Mihir,

I assume that when you say 'in the absence of nitrogen', you mean in the absence of 'pure nitrogen' and I assume that the purpose of the question is to balance any reduction in surface area (as a measure of the effectiveness of the activated carbon) against the cost of carrying out the activation process in the presence of air. If surface area were our only consideration, then based on the following two reports, it would seem that since the presence of oxygen reduces the PH of the carbonized charcoal (http://sciencelinks.jp/j-east/article/200320/000020032003A0606421.php), and since "A direct correlation was found between pH ... and surface area" with "an inhibition effect on gasification at low pH" (http://www.sciencedirect.com/science/article/pii/000862239190173G), I would expect there to be a reduction in surface area in the presence of oxygen.

On the other hand, as these reports (and some of the comments of other colleagues, here) also imply, when deciding on an activation method, the resulting surface area is not the only criterion for effectiveness since the extent to which different materials are adsorbed onto the carbon depends on its chemical structure which in turn depends on the activation method.

In summary, the type of gas(es) used in activation affects surface area, one of the mechanisms being through PH. The presence of oxygen reduces PH and reduces surface area. The method of activation also affects the quality of the activated carbon in ways which are not related to surface area alone.

Good luck with whatever it is that you are trying to do :-)

Bijan.

Actually, I am planning to prepare activated carbon using fruit peel. I want to use this activated carbon as a support medium for impregnating iron oxide nanoparticles.

My main concern is how the presence or absence of nitrogen gas during combustion (during activated carbon preparation) will affect the properties of this nanocomposite?

Of course, the answer would depend on which properties of the nanocomposite you are interested in preserving or enhancing; nevertheless, the following may be helpful:

From the second reference I linked to earlier, "The charcoal carbonized under oxygen-nitrogen atmosphere adsorbed higher amount of alkali (NaOH,NaHCO3), benzylamine, ammonia gas, methylamine gas than charcoal carbonized under nitrogen atmosphere." So, I would expect other metal oxides to exhibit similar behaviour, being better adsorbed if the activation is done in the presence of oxygen (albeit to a lesser extent for Iron due to its lower position in the activity series). But this an get very complicated due to the multiple valency of iron and you may get either reduction or oxidation of your nanocomposite depending on the type(s) of oxide present. This evidence suggests that it may be safer for you to stick to a nitrogen atmosphere.

If you are going to impregnate the iron oxide with something, then, presumably, you also need to think about the mechanism by which you are going to subsequently free your composite from the carbon which might have a more important effect on the resultant isolated impregnated composite. It may be that weaker adsorption, whilst reducing the yield per gram of carbon, may improve the yield of in-tact impregnated composite after release.

I think from here on, you'll need to experiment and see what actually happens (but, of course, hopefully, your experimental design will be better informed by questions such as these).

Have fun!

Bijan.

Thanks to all of you for the reply to my query

No oxidation of material from oxygen in the air will take place in nitrogen atmosphere.

Islamic University of Indonesia, Jogjakarta, Indonesia

Chemical activation is one of the important process in preparation of activated carbon. The chemical can change the structure of precursor in order to be easy the conversion process from carbonaceous to carbon . Insertion of chemical such as phosphoric acid into the precursor may increase the conversion or accelerate the evaporation of unwanted materials. Purified nitrogen is an inert gas that can decrease the burn off precursor or formation of ash during pyrolysis process. The nitrogen may also function for accelerate the evaporation of unwanted materials. Beside that it may be able to support the formation of a new pore for increasing the surface area of activated carbon. It may be also better to study the characteristics of precursor before preparation of activated carbon. . The determination of condition pyrolysis process such as impregnated agent, gas and temperature is very important for producing the maximum results.

The application of a gaseous stream such as air, nitrogen, or argon is a common practice during pyrolysis, which generates a better development of the internal porosity in the material (González, 2018)

doi: 10.1016/j.rser.2017.04.117

When the pyrolysis without nitrogen gas, the pores could be closed, broken/britle or shringkage and finally, the surface area will be significantly reduced. Pyrolysis using nitrogen gas may support to reduce over heating and ash contents. And aldo to increase the evaporation of unusable compunds for pore formation.

Sir I have done this. No special effect I got surface area upto 1300 m2/g