Equilibrium adsorption of single component and binary mixtures of aromatic compounds onto a polyfunctional hypercrosslinked polymeric adsorbent

Abstract

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, qe. 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.