Adsorption kinetics of phenol from water on Fe/AC

Abstract

Activated carbon (AC)-supported iron adsorbents (Fe/AC) were prepared using pore volume impregnation with ferric nitrate. The effect of iron doping on the physicochemical properties of AC as well as the effects of the contact time, initial phenol concentration, and Fe doping mass fraction on phenol adsorption by AC and Fe/AC from water were investigated. The adsorption kinetics was also analyzed using pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The adsorbents were characterized using elemental analysis, X-ray diffraction, N2 adsorption, and Boehm titration. The results show that the AC pore properties after Fe doping were not significantly changed. But Fe doping introduced a significant number of acidic oxygenated groups (mainly carboxylic groups, phenolic groups, and lactones) onto the AC surface. In addition, the number of acidic O-containing groups of Fe/AC increased with increasing doped Fe mass fraction. The adsorption of phenol on the adsorbents can be separated into rapid adsorption, slow adsorption, and equilibrium periods. Fe doping did not significantly affect the adsorption capacity of a low-concentration phenol solution. However, the adsorption of high-concentration phenol showed that Fe doping clearly reduced the phenol uptake and that the uptake decreased with increasing doped Fe mass fraction because of the decrease in the dispersive interaction between phenol and AC surface. The uptake of each adsorbent increases with increasing the initial phenol concentration. A pseudo-second-order model better describes the adsorption of low-concentration phenol on AC and Fe1/AC (AC doped with low-mass fraction Fe). The adsorption of low-concentration phenol by Fe5/AC (AC with high-mass fraction doped Fe) is consistent with the Elovich model due to a major decrease in the adsorption sites on the AC surface after Fe doping. The AC adsorption before and after Fe doping followed the Elovich model when high-concentration phenol was adsorbed. The rate-controlling steps during early and middle adsorption are primarily intraparticle and film diffusions, respectively.