The general titration procedure was carried out based on Boehm’s method.

A known mass of carbon. 1.5 g carbon was added to 50.00 mL of one of three reaction bases of 0.05 M concentration: (NaHCO3, Na2CO3 and NaOH).

The samples were agitated by shaking for 24 h and then filtered to remove the carbon, and 10.00 mL aliquots were taken by pipette from the samples.

The aliquots of the reaction base NaHCO3 were then acidified by the addition of 20.00 mL of 0.05 M HCl.

The aliquots of the reaction base Na2CO3 were acidified by the addition of 30.00 mL of 0.05 M HCl,

The acidified solutions were then back-titrated with 0.05 M NaOH, the titrator base.

The aliquots of the NaOH reaction base were acidified by the addition of 20.00 mL of 0.05 M HCl and the sample was back-titrated with 0.05 M NaOH;

----------------------

Calculations

The equations used to determine the quantity of surface groups depends on the titration method: back-titration or direct titration. For a back-titration, amounts of the acidic groups on carbon were determined by: equation 1 and 2

where [B] and VB are the concentration and volume of the reaction base mixed with the carbon, providing the number of moles of reaction base that was available to the carbon surface for reaction with the surface functionalities. nCSF denotes the moles of carbon surface functionalities on the surface of the carbon that reacted with the base during the mixing step. Va is the volume of the aliquot taken from the VB, and [HCl] and VHCl are the concentration and volume of the acid added to the aliquot taken from the original sample. This gives the number of moles of acid added to the aliquot, and available for reaction with the remaining reaction base. The remaining moles of acid are then determined through the titration using [NaOH] and VNaOH, the concentration and volume of the titrant in the back-titration. Thus, through the knowledge of the remaining moles of acid, leading to the amount of reaction base remaining after reaction, and by difference (knowing the total amount of reaction base available initially) the amount of base reacted with the surface functionalities, the surface functionalities can be quantified.

These equations are based on the calculations from Chen and Wu [21] but modified to take the molar ratio of acid to base (nHCl/ nB) into account to allow for monoprotic vs. diprotic reaction bases.