**2.1.1 Surface modification**

Commercial activated charcoals GR MERCK 2518 and GAC Norit 1240 Plus (A– 10128) have been subjected to the post-chemical treatment with 1 М nitric acid at boiling temperature during 6 h. The oxidized materials, were subsequently washed with distilled water until neutral media, and dried in an oven at 110 0C for 24 h.
