All the activated carbons were washed with d-H2O then poured into
1 mol/L HCl solution. Then, the samples were washed with d-H2O until
the silver nitrate test became negative. The activated carbons produced
were then dried at 110 °C. In the second step, the samples were treated
with a 6 N nitric acid solution. For this purpose, 10 mL of HNO3 solution
was mixed with 1 g of activated carbons and the mixture was boiled for
3 h. Then, the oxidized activated carbons were washed, with hot d-H2O
until the pH of the filtrating solution was neutral, and finally were dried
overnight at 110 °C.