A Novel Magnetic Nano-Adsorbent Functionalized with Green Tea Extract and Magnesium Oxide to Remove Methylene Blue from Aqueous Solutions: Synthesis, Characterization, and Adsorption Behavior

In this study, a novel green tea/Mg-functionalized magnetic nano-adsorbent, denoted as GTE-MgO-Fe3O4 NPs, was developed and applied to the extraction of Methylene Blue (MB) from water-based solutions. The GTE-MgO-Fe3O4 NPs were synthesized by incorporating green tea extracts (GTE) and Mg species onto the surface of Fe3O4 nanoparticles using a hydrothermal method. Characterization analyses corroborated the successful functionalization of the Fe3O4 surface with GTE and Mg species, resulting in a superparamagnetic adsorbent equipped with abundant surface functional groups, which promoted MB adsorption and facilitated magnetic separation. Batch experiments revealed that different operating parameters had an impact on the adsorption behavior, such as adsorbent dosage, pH, coexisting ions, contact time, the initial MB concentration, and temperature. The investigations of adsorption kinetics and isotherms emphasized that the MB adsorption onto GTE-MgO-Fe3O4 NPs was an exothermic process dominated by chemisorption. The experimental adsorption capacity of GTE-MgO-Fe3O4 NPs for MB surpassed 174.93 mg g−1, markedly superior to the performance of numerous other adsorbents. Ultimately, the utilized GTE-MgO-Fe3O4 NPs could be effectively regenerated through acid pickling, retaining over 76% of its original adsorption capacity after six adsorption–desorption cycles, which suggested that GTE-MgO-Fe3O4 NPs was a suitable adsorbent for eliminating MB from effluent.