Adsorption of fulvic acids from aqueous solutions by carbon nanotubes

Carbon nanotubes (CNTs) were used as adsorbent to remove fulvic acids (FA) from aqueous solutions. The adsorption capacity of CNTs for FA can reach 24 mg g −1 at 5 °C and equilibrium concentration of 18 mg dm −3 . The kinetic and thermodynamic parameters, such as rate of adsorption, standard free energy changes (Δ G 0 ), standard enthalpy change (Δ H 0 ) and standard entropy change (Δ S 0 ), have been obtained. Acidic conditions (pH = 2–5) favor FA removal. An increase in the ionic strength or the addition of divalent cations increase the adsorption of FA dramatically (FA = 60 mg dm −3 ). An increase in the maximum adsorbed amount of FA was observed when treating FA in synthetic seawater. Desorption studies reveal that FA can be easily and quickly removed from CNTs by altering the pH values of the solution. Good adsorption capacity and quick desorption indicate that CNTs are a promising adsorbent to remove FA from aqueous solutions.