Behavior of phenol adsorption on thermal modified activated carbon

Adsorption process is acknowledged as an effective option for phenolic wastewater treatment. In this work, the activated carbon (AC) samples after thermal modification were prepared by using muffle furnace. The phenol adsorption kinetics and equilibrium measurements were carried out under static conditions at temperature ranging from 25 to 55 °C. The test results show that the thermal modification can enhance phenol adsorption on AC samples. The porous structure and surface chemistry analyses indicate that the decay in pore morphology and decrease of total oxygen-containing functional groups are found for the thermal modified AC samples. Thus, it can be further inferred that the decrease of total oxygen-containing functional groups on the modified AC samples is the main reason for the enhanced phenol adsorption capacity. For both the raw sample and the optimum modified AC sample at 900 °C, the pseudo-second order kinetics and Langmuir models are found to fit the experimental data very well. The maximum phenol adsorption capacity of the optimum modified AC sample can reach 144.93 mg·g− 1 which is higher than that of the raw sample, i.e. 119.53 mg·g− 1. Adsorption thermodynamics analysis confirms that the phenol adsorption on the optimum modified AC sample is an exothermic process and mainly via physical adsorption.

Graphical abstractAs shown in the graphical abstract, thermal modification for activated carbon operated at 900 °C can result in the decrease of pore morphology and total oxygen-containing functional groups (phenolic hydroxyl, lactone base and carboxyl). Experimental data show that the modified sample designated as AC2 has the superior phenol adsorption capacity than the raw sample (AC0). The mechanism of thermal modification can be explained by the π-π dispersive force interaction. The lower content of total oxygen-containing functional groups on AC2 sample will strengthen the π-π dispersive force interaction between phenol molecule and AC sample, which leads to higher phenol adsorption capacity.Figure optionsDownload full-size imageDownload as PowerPoint slide