Effective removal of salicylic and gallic acids from single component and impurity-containing systems using an isatin-modified adsorption resin

Abstract

In this study, an isatin-modified adsorption resin named HF-02, which effectively adsorbs and removes salicylic acid (SA) and gallic acid (GA) from aqueous phase, was prepared and characterized. Its adsorption capacity towards these two adsorbates was higher than for the commercial hyper-crosslinked resins H103 and CHA-111, and the macroporous resins HPD 500, Amberlite XAD-7 and XAD-4. This is attributed to its superior porous structure and modified groups. The adsorption capacity of HF-02 towards SA is higher than for GA and its uptake amounts for SA and GA calculated by Freundlich isotherm were 350.7 mg g⁻¹ and 160.8 mg g⁻¹, respectively. The difference is mainly because the utilization ratio of adsorption sites in resins is lower when adsorbing GA and the hydrophilicity of GA is stronger than SA. The thermodynamic parameters in single component systems indicated that the two adsorption processes are exothermic and physical in nature. Furthermore, the molecular structure, initial concentration and temperature determine the uptake amounts and adsorption rate of HF-02. It is noteworthy that 1% NaOH aqueous solution and absolute ethanol gave a more efficient desorption effect in the dynamic experiment than 363 K pure water. The salt-promoting effect of NaCl, the complex-forming effect of Ni(II) and the ionization-inhibiting effect of H⁺ would enhance the uptake amounts of HF-02 in impurity-containing systems.