Ultra-highly selective adsorption of Methylene blue and Congo red by pH-responsive glutathione-modified magnetic nanoparticles

Wastewater that contains highly toxic and carcinogenic organic dyes is harmful to the environment. Herein, a novel magnetic multifunctional pH-responsive adsorbent (Fe₃O₄@UiO-66-NH₂/GSH) was developed, which showed excellent adsorption properties for both anionic and cationic dyes at different pH values. The adsorption capacities for CR (pH = 2) and MB (pH = 11) at 298.15 K were achieved at 1609.73 mg/g and 1827.24 mg/g, respectively. The effect of pH on the adsorption capacity was discussed experimentally and theoretically. Moreover, the uptake of four additional dyes (MO, AB, NR, and MV) was determined to test the application properties of the prepared particles. The influence of the salt concentration was also studied. The results showed that the prepared adsorbents can be applied in the treatment of complex dye wastewater. At the end of this work, the adsorption mechanism was investigated systematically by adsorption thermodynamics and hydrodynamics, as well as by comparing the FTIR and XPS results before and after adsorption. This demonstrated that electrostatic interactions played an essential role in the adsorption process. Last but not least, the regeneration rate of Fe₃O₄@UiO-66-NH₂/GSH remained above 90 % after four consecutive adsorption-desorption cycles in 10 % and 20 % ethanol solutions, which indicated that it had good reusability and recyclability and was an economical material. Thus, the synthesized Fe₃O₄@UiO-66-NH₂/GSH is a promising adsorbent that can be used for dye removal.