The Adsorption of Acetylsalicylic Acid on Carbon Black: The Influence of Adsorbent Porosity and Its Surface Chemistry

This study investigated the influence of physicochemical properties of carbon black (porosity and surface chemistry) on the adsorption of acetylsalicylic acid (ASA) from aqueous solutions. Three unmodified carbon blacks (XC72, N220, and N550) with different specific surface areas, as well as two surface-modified carbon blacks (oxidized carbon black (N220-Ox) and 3-aminopropyltriethoxysilane-modified carbon black (N220-APTES)), were used in the study. The kinetics and equilibrium of adsorption were studied, along with the effects of the initial adsorbent mass, solution pH, and ionic strength on adsorption efficiency. The results showed that the adsorption equilibrium for acetylsalicylic acid was reached after 30–60 min, with the adsorption kinetics being well characterized by a pseudo-second-order equation. Under equilibrium conditions, the adsorption of acetylsalicylic acid on carbon blacks followed the Langmuir isotherm model. The best adsorption capacity was observed for XC72 carbon black, which has the highest BET area, while the lowest was observed for N550 carbon black. For unmodified carbon blacks, adsorption was found to be correlated with their porous structure. Functionalization of the surface with APTES increased the carbon black’s adsorption capacity, whereas surface oxidation reduced its effectiveness. Additionally, it was found that adsorption depended on solution pH: acetylsalicylic acid was adsorbed most efficiently in an acidic environment (pH ~3.5), and the solution ionic strength had no effect on its adsorption onto the tested carbon blacks.