Adsorption and correlations of selected aromatic compounds on a KOH-activated carbon with large surface area

Knowledge of adsorption mechanism and behavior of organic compounds by KOH-activated carbons (KOH-ACs) from wastewater is crucial to its environmental application in wastewater treatment as adsorbent. A superior adsorbent, KOH-activated carbon (KOH-AC), with large surface area (3143m²/g), total pore volume of 2.03cm³/g, relatively low micropore fraction of 53.2%, and having adsorption capacities of organic compounds up to >1000mg/g, was prepared. It is an adsorbent significantly different with common ACs because the molecular sieving effect, widely observed for common ACs, is insignificant for KOH-AC. This difference could be attributed to the lower micropore fraction of KOH-AC than common ACs. A negative relationship of adsorption capacity of 25 aromatic compounds (including phenols, anilines, nitrobenzenes and polycyclic aromatic hydrocarbons) with chemical melting point was observed, suggesting that adsorption is dependent on the packing efficiency and stacking density of molecules on KOH-AC. A linear solvation energy relationships of adsorption affinity of 25 aromatic compounds with solute solvatochromic parameters was also observed, that can be used to quantify the contributions of π-π interaction, hydrogen-bonding interaction and hydrophobic effect to adsorption on KOH-AC. Combined with the reported results of adsorption of organic compounds on carbon nanotubes and biochars, it was also observed that external surface area of adsorbents is controlling the packing efficiency and stacking density of molecules on adsorbents and thus affecting adsorption capacity of organic compounds. Moreover, micropore surface area and the fraction of micropores are the adsorbent properties mainly affecting adsorption affinity of organic compounds. The observations and the developed correlations in this study would be helpful in the application of KOH-AC as superior adsorbent by enhancing the understanding of adsorption mechanisms of organic compounds on KOH-AC and by giving a method to predict the adsorption behaviors.