The following review paper may be helpful as it provide a comprehensive list of literatures on chemical, physical and biological modification techniques of activated carbon (AC) pertaining to enhancement of contaminant removal from aqueous solutions was compiled and reviewed.  Types of microorganism adsorbed on AC and chemical species removed include copper, zinc, nickel, lead, cadmium

Reference

Chun Yang Yin, Mohd Kheireddine Aroua, Wan Mohd Ashri Wan Daud. 2007.Review of modifications of activated carbon for enhancing contaminant uptakes from aqueous solutions. Separation and Purification Technology 52: 403–415. http://www.sciencedirect.com/science/article/pii/S1383586606002024

Dear Abdulkreem, from my experience I can tell that physical or thermal activation method (in the range of 850-950 degree Celsius) with controlled gasification (steam, CO2, or both together) can give you the best activated carbon, in terms of  both surface area and porosity. Microporosity development is one of the key factors for better adsorption capacity with activated carbon. The uses of gasification agents mentioned above will initiate complex heterogenous reactions involving the transportation of the gaseous agents into the carbon surfaces and upon their diffusion, the porosity in carbons develops at its best (I have done this in my experiment). 

You can also try Physico-chemical activation method using any of the gasification agents with KOH or ZnCl2 impregnated samples which has been reported for producing better activated carbons with high surface areas compared to the commercially available ones. If you want, I can give you the papers as attachments. 

All the best with your experiments.

Salehin.

If you already have an activated carbon, and want to modify it for increasing its surface area, you have to pay attention to 3 things:

1. which kind of porosity do you want ? If your material is already highly microporous, a further activation may create more mesopores and make its surface area decrease. This may happen with physical activation, e.g. with steam.

2. do you mind having impurities inside ? Chemical activation, e.g. with KOH, may create much more micropores, but even after extensive washing, traces of K may remain.

3. is the pH important ? KOH and H3PO4 activation will lead to basic and acid carbons, respectively. Therefore, their point of zero charge will be different and, depending on the pH at which you'll do the metal impregnation, the ions may be preferentially adsorbed or not by the carbon surface.

Alain

It depends also on the nature of the raw material used, the activated carbon coconut-base, is different to the carbon seed-base, and so on...