Removal of methylene blue from aqueous solution by magnetic hydrogel nanocomposite absorbents

Currently reported adsorbents for wastewater purification generally have only limited adsorption capacity and low adsorption rate towards dye contaminants. In this work, KH570-modified magnetic hydrogel nanocomposites (KH570-mHNCs) with semi-IPNs structure were prepared based on poly (acrylamide-co-acrylic acid), polyvinyl pyrrolidone (PVP), and KH570-modified magnetic nanoparticles, and it exhibited high absorption capacity and absorption rate for methylene blue dye. KH570-mHNCs had a rough surface with many porous and gully structures, and FTIR results preliminarily confirmed the target structure of KH570-mHNCs. KH570-mHNCs could rapidly absorb methylene blue by approaching absorption equilibrium at 90 min. Dye absorption of KH570-mHNCs had maximum dye absorption capacity at pH = 8, and methylene blue adsorption capacity was 255.4 mg/g, 326.3 mg/g, and 418.5 mg/g in the condition of initial dye concentrations of 700 mg/L, 900 mg/L, and 1100 mg/L, respectively. Methylene blue adsorption isotherms and kinetics conformed to the Langmuir model and pseudo-second-order kinetic model, respectively. Methylene blue adsorption for KH570-mHNCs was a spontaneous, exothermal, and entropy reduction process. In addition, KH570-mHNCs had good magnetic response, desorption, and reusability, which made it a potential application in the field of methylene blue removal from the aqueous solution.