Equilibrium Adsorption of Single Component and Binary Mixtures of Aromatic Compounds onto a Polyfunctional Hypercrosslinked Polymeric Adsorbent

A polyfunctional hypercrosslinked polymeric adsorbent, LA-8, was synthesized and characterized. It was first used to investigate the adsorption properties of 1-amino-2-naphthol-4-sulphonic acid (1,2,4-acid), including the corresponding adsorption isotherms, thermodynamics and binary competitive adsorption with 2-naphthol. The Freundlich model gave good fits to both the single and binary adsorption isotherms, indicating an endothermic and favourable adsorption process. The positive value of ΔH⁰ for the single solute system was in the range of 30–60 kJ/mol showing the existence of integrated processes involving chemical interaction. The values of ΔG⁰ demonstrated the spontaneous nature of the adsorption process while the value of ΔS⁰ showed increased randomness at the solid–solution interface, thereby indicating the presence of stoichiometric displacement. Both ΔH⁰ and ΔS⁰ appeared to vary linearly with increased solid loading, q_e.

Pre-adsorbed 2-naphthol molecules supplied another adsorption site for 1,2,4-acid, despite the existence of an antagonistic interaction with 2-naphthol. In simultaneous processes, the mechanism for 1,2,4-acid adsorption probably mainly involved van der Waals forces and hydrogen-bonding interaction. Furthermore, the adsorption of a greater amount of 2-naphthol onto the solid phase demonstrated the occurrence of interaction between the tested binary solutes. It was concluded that direct competition for adsorption sites was the dominant competitive mechanism.