Activated Carbon Surface Modifications by Nitric Acid, Hydrogen Peroxide, and Ammonium Peroxydisulfate Treatments

A series of activated carbons with different degrees of activation was treated with HNO 3 , H 2 O 2 , and (NH 4 ) 2 S 2 O 8 in order to introduce oxygen surface complexes. The effects of the oxidizing treatments on the surface area, the pore texture, and the surface chemical nature were analyzed by means of N 2 and CO 2 adsorption, mercury porosimetry, FTIR, TPD, electrophoretic, and mass titration measurements. Results obtained show that the HNO 3 treatment affects the surface area and the porosity of the samples to a greater extent than the other treatments. Carboxyl groups were essentially fixed after the three treatments, although ketone and ether groups, as detected by FTIR, were also fixed after the treatments with peroxides. The most important conclusion was that the stronger acid groups were fixed after the (NH4) 2 S 2 O 5 treatment rather than after the HNO 3 treatment, in spite of the fact that this latter treatment fixed the largest number of oxygen complexes that evolved as CO 2 .