Influence of mesopore volume and adsorbate size on adsorption capacities of activated carbons in aqueous solutions

Liquid-phase adsorption of phenol, iodine and tannic acid onto commercial grade granular activated carbons and activated carbon fabric was conducted to explore the influence of the mesopore volume and the size of adsorbates on the adsorption capacity. These carbons have different mesopore volumes, while possessing similar surface areas and micropore volumes, which are believed to determine the adsorption capacity in the liquid phase. The adsorption isotherms reflect that the adsorption capacity is an increasing function of the mesopore volume. Further analysis using the Langmuir and the Dubinin-Radushkevich equations shows increases of both the equilibrium constant and the adsorption energy with the mesopore volume, indicating that mesopores facilitate the adsorption of the adsorbates in the inner and narrow micropores, which contain adsorptive sites with higher adsorption energies. It was also found that the influence of mesopore volume on the capacity was enhanced by the increase in the adsorbate size. The results of the present study have demonstrated the importance of mesopores in enhancing the adsorption capacity of microporous carbons in aqueous solutions, especially for the adsorption of large adsorbates.