Effect of the porous texture and surface chemistry of activated carbons on the adsorption of a germanium complex from dilute aqueous solutions

The effect of the adsorption properties and surface chemistry of activated carbons on the adsorption of germanium (IV) from dilute aqueous solutions (50 ppm) was investigated. A large number of activated carbons were obtained by activating three precursors, one coal and two lignocellulosic chars, with alkaline hydroxides, NaOH and KOH, and different activating agent/precursor ratios (from 1/1 to 5/1). The characterization of their textural properties, assessed by N2 and CO2 isotherms, and their oxygen surface chemistry, assessed by temperature-programmed desorption experiments, confirm that a large variety of materials with different surface areas, pore size distributions and surface chemistries are available for this study. To increase the Ge adsorption, an organic compound (catechol) was used as a ligand in order to form a germanium complex. Such a complex works very well, allowing its good adsorption on the activated carbons. The results showed that to achieve the highest Ge adsorption, the activated carbon should show a high apparent surface area, a wide microporosity and a moderate oxygen surface content that may assure the wettability of the solution but that does not produce large repulsive interactions.