Comparison study of naphthalene adsorption on activated carbons prepared from different raws

Abstract

Five activated carbons (ACs) from apricot shells (ACAS), mixture of lignin and cellulose (ACLC), wood (ACW), walnut shells (ACWS), and coal (CAC) were prepared and used as adsorbents to study the adsorption behavior of naphthalene. All ACs were characterized by scanning electron microscopy, N2 adsorption-desorption method, Xray photoelectron spectroscopy, and elemental analysis. The effects of initial concentration, contact time, ionic strength, pH, and temperature on the adsorption of ACs for naphthalene were examined. Results show that CAC exhibit higher micropore specific surface area and contain more C-O bond than other ACs. Except for ACW, CAC is the least polar or the most hydrophobic adsorbent among ACs. This finding may be helpful in the formation of hydrogen bonding between CAC and naphthalene. The adsorption quantity of CAC was 227.03mg g-1 at 303 K, which was considerably higher compared with that of other ACs. The kinetics process of naphthalene on all ACs was controlled by pseudo-second-order kinetic model. The adsorption equilibrium of naphthalene on ACs was reached at 40min. The adsorption isotherms of naphthalene to ACs were consistent with the Freundlich isotherm model. The result of thermodynamic analysis shows that the adsorption occurs spontaneously. Moreover, the higher starting naphthalene concentration and lower adsorption temperature significantly can enhance the adsorption capacity of CAC. The maximum adsorption value of naphthalene on ACs was also observed at pH 4 under the same conditions. Moreover, the increase in ionic strength slightly promotes the adsorption of naphthalene on ACs. The microporous structure, element content and surface functional group of ACs affect its adsorption capacity.