Influence of activation atmosphere used in the chemical activation of almond shell on the characteristics and adsorption performance of activated carbons

• High toluene adsorption capacities are obtained on almond shell based AC prepared under different activating atmospheres.
• A compromise between physical and chemical characteristics is needed to maximize adsorption.
• Deviation of linearity of D–R plots is used as a parameter to describe toluene adsorption.

The aim of this work was to compare the effect of different activating atmospheres on the final properties and adsorption performance of activated carbons. Almond shell based activated carbons have been obtained by chemical activation with phosphoric acid. Two sets of activated carbons were prepared. First set was prepared under inert atmosphere at different impregnation ratios, temperatures and times of activation. Second set of activated carbons was prepared at the same activating conditions except the activating atmosphere using an oxidant one. Activated carbons prepared under both activation atmospheres were characterized by elemental analysis (EA), thermogravimetry (TGA), temperature programmed desorption (TPD), point zero charge (PZC), Boehm titration and N2 physisorption. To study the adsorption performance of the activated carbons toluene adsorption–desorption isotherms were determined gravimetrically. The results obtained confirm that the activating atmosphere has a strong influence on the final characteristics of the activated carbons. Activated carbons with higher oxygen content and more negative surface charge have been obtained by changing the activating atmosphere by an oxidant one. Surface area is also higher for activated carbons prepared under oxidant atmosphere. However toluene adsorption capacity is lower for activated carbons prepared under oxidant atmosphere due to their surface chemistry.