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 g rade granular activated carbons and activated carbon fabric was conducted t o explore the influence of the mesopore volume and the size of adsorbates o n the adsorption capacity. These carbons have different mesopore volumes, w hile possessing similar surface areas and micropore volumes, which are beli eved to determine the adsorption capacity in the liquid phase. The adsorpti on isotherms reflect that the adsorption capacity is an increasing function of the mesopore volume. Further analysis using the Langmuir and the Dubini n-Radushkevich equations shows increases of both the equilibrium constant a nd the adsorption energy with the mesopore volume, indicating that mesopore s facilitate the adsorption of the adsorbates in the inner and narrow micro pores, which contain adsorptive sites with higher adsorption energies. It w as also found that the influence of mesopore volume on the capacity was enh anced by the increase in the adsorbate size. The results of the present stu dy have demonstrated the importance of mesopores in enhancing the adsorptio n capacity of microporous carbons in aqueous solutions, especially for the adsorption of large adsorbates. (C) 2000 Elsevier Science Ltd. All rights r eserved.