Modification of carbons with acids, salts, and hydrogen peroxide for the adsorption of anionic and cationic dyes in single and binary systems with Cd2+ and CrO42-

This article reports the modification of 17 different kinds of carbons with H2SO4, HNO3, H2O2, KCl, and NaCl for the removal of anionic dyes, reactive red 2 (RR2) and reactive black 5 (RB5), and cationic dyes, basic blue 9 (BB9) and basic brilliant green (BBG), in single and binary solutions with Cd2+ and CrO42-. The results show that the better carbon for the removal of the dyes is a bone char modified with HNO3. This carbon was modified according to the Taguchi method in order to optimize the carbon surface modification process and to reduce its cost. The better results of adsorption of RR2, BBG, BB9, and RB5 dyes were 147.2, 247.7, 248.2 and 133.0 mg/g respectively, according to Taguchi design. The results revealed the optimal conditions to prepare an efficient carbon for the adsorption of the dyes. Three carbons were then obtained using these factors' combination, where a slight increase was observed with respect to the results of the Taguchi design and a considerable increase according to original conditions. Thus, we decided to choose experiment 4 because the modification conditions were optimized and this represents a decrease in the cost of modifying. Then, we carried out adsorption studies of RR2 and BBG in single and binary solutions with Cd2+ and CrO42- and synergistic and non-interaction effects were observed. Finally, the carbon modified was characterized by several analytical techniques to understand the adsorption mechanism.