Effect of steam activation on the porosity and chemical nature of activated carbons from Eucalyptus globulus and peach stones

The effect of steam activation of chars prepared from Eucalyptus globulus (EU) and peach stones (PS) on both the porosity development and the amount of oxygen surface groups is presented. The N-2 (77 K) and CO2 (273 K) adsorption isotherms and the mercury intrusion measurements show that, apart from the differences in macroporosity caused by the different texture of the original precursors, the development of porosity upon activation is small for the EU char and important for the PS char. A somewhat parallel behaviour is found for the oxygen surface groups, as determined by infrared spectroscopy and temperature programmed decomposition (TPD): the development of microporosity for PS chars is accompanied by an increase in the number of oxygen surface groups stable at the activation temperature, the number being low for activated carbons from EU chars. This behaviour indicates the more important role of diffusion control of the water molecule to the interior of the particle when activating the EU char in respect to the PS char.