The pH has a very important effect for adsorption processes in the liquid phase. The pH indeed has an influence on surface chemistry and on surface charge. For instance, at low pH, the surface is positively charged, so the performances for adsorbing cations will be low because of the corresponding electrostatic repulsion. Having a pH lower than 1 after activation is normal if, for instance, your date seeds were activated with a strong acid (among them orthophosphoric acid is very efficient). But so low pH is not good for applications and even for handling the material as it will be very corrosive. You have to wash it until neutral pH, better in a Soxhlet extractor filled with distilled water so that you can save a significant amount of water.

Alain

It is generally recommended to neutralize the pH of the adsorbent after its preparation. The adsorption process is highly pH sensitive and pH driven. Thus, before using your activated carbon as an adsorbent in any process it should be neutralized. If you use the same adsorbent, then it will be difficult to distinguish, whether the adsorption phenomenon is  affected by adsorbent pH or pH of the solution. The effect of alkalinity and acidity of the working solution affects the adsorption process remarkably, but it solely depends on the adsorbate. Generally, it is observed that maximum adsorption takes place in acidic medium and in same cases like fluoride it is maximum at neutral pH.

Thanks

Regards

Sumit

The pH has a very important effect for adsorption processes in the liquid phase. The pH indeed has an influence on surface chemistry and on surface charge. For instance, at low pH, the surface is positively charged, so the performances for adsorbing cations will be low because of the corresponding electrostatic repulsion. Having a pH lower than 1 after activation is normal if, for instance, your date seeds were activated with a strong acid (among them orthophosphoric acid is very efficient). But so low pH is not good for applications and even for handling the material as it will be very corrosive. You have to wash it until neutral pH, better in a Soxhlet extractor filled with distilled water so that you can save a significant amount of water.

Alain

The pH of the activated carbon is dependent on the chemical agent you used for the activation. For such a low pH that you got, i am thinking you did not wash the activated carbon with deionized/distilled water, hence such a low pH. You should wash the activated carbon with deionized water until the pH comes to neutral. 

The pH of the absorbent has a very important effect on the adsorption properties. You should determine the pH  (pzc), the point of zero charge of your AC. 

I think the following papers can help :

Carbon, 32 (1994) 759-769.

Brazilian J. Chem. English.  27 (2010) 183-193.

PZC is very important  when you choose  metal-complex compound for preparation supported Me/C catalyst with nanoparticles of metal

there is no normal range of pH and you have to nuetralize your AC before you used it by deionized or double distilled water.

The pH is always low after activation and a lot of distilled/deionized water is required to bring it to neutral pH. It also depends on the intended use of the medium

The pH of activated carbon is influenced with chemical activation using acid ( for example; H3PO4) or base activator (for example KOH) that can be removed by washing with distilled water. However, the acid or base characterization of activated carbon might occur due to the presence of functional group such as O, N on the surface.