Enhanced adsorption of metal ions onto functionalized granular activated carbons prepared from cherry stones

Some granular activated carbons (GACs) were prepared from cherry stones (CS), an agricultural waste, by thermal methods following pyrolysis in nitrogen and subsequent activation (with air, carbon dioxide and steam) or single-step activation in steam. A GAC prepared by activation with carbon dioxide was further treated with several oxidizing agents (air, air-ozone mixture, nitric acid and hydrogen peroxide). The non-oxidized GACs produced have surface areas ranged from 508 to 901m(2)/g and show a predominantly micro- and macropores structure. Oxidation treatments, especially with nitric acid and ozone, led to the fixation of high amounts of acidic surface oxygen complexes (SOCs), thus making the carbon surface more hydrophilic. Contrary to oxidation with the other agents, the ozone treatment, at the conditions applied in this work, does not decrease the GAC surface area. Both, the non-oxidized and the oxidized GACs were used as adsorbent to study the adsorption of Cu(II) from aqueous solution. Adsorption isotherms were obtained at 25 degrees C and data were well fitted to the Langmuir equation. The results show that the Cu(II) uptake of the non-oxidized GACs is not great, but similar to that of the commercial grade Filtrasorb 400. The adsorption capacity for Cu(II) could be greatly enhanced by GAC oxidation, especially with nitric acid and ozone treatments. The larger adsorption capacity of the oxidized GACs has been attributed to oxygen functionalities (mainly carboxylic) fixed on the GAC surface, which can remove Cu(II) species from water by both ion-exchange and surface complexation mechanisms. The ozonated GAC was also evaluated for the adsorption of Co(II) species from single solute and Cu(II)-Co(II) binary mixture solutions. The functionalization of GAC by the ozone treatment improved the adsorption of both Cu(II) and Co(II) regardless of the fact that they were in single solute or binary systems.