Arundo donax-Based Activated Carbons for Aqueous-Phase Adsorption of Volatile Organic Compounds

A series of activated carbons with similar surface properties (BET surface area of 1100 m2/g, total pore volume of 1 cm3/g) were developed by H3PO4 acid activation of Arundo donax L. stems, under four different atmospheres. Their ability to adsorb individual benzene and toluene from dilute aqueous solutions was comparatively examined at preestablished equilibrium conditions. All the samples showed appreciable uptakes of both compounds, though the carbons obtained under flowing N2 were most effective due to their smallest total content of polar/acidic surface oxygen functional groups. An empirical pseudo-second-order expression and conventional adsorption isotherm models represented properly kinetic and equilibrium data for adsorption of the organics on the N2-derived carbons, respectively. Competing adsorption effects were found for the carbons developed under flowing N2 and air using binary solutions of benzene and toluene and of the organics in the presence of Ni(II) ions. Besides, low-temperature thermal desorption proved effective to regenerate the spent carbons loaded with the organics keeping unchanged their original adsorptive capacity, while treatment with dilute HCl acid allowed regeneration of the carbons after being loaded from a ternary solution of benzene, toluene, and Ni(II) ions.