Facile one-step synthesis of 3D honeycomb-like porous chitosan bead inlaid with Mn-Fe bimetallic oxide nanoparticles for enhanced degradation of dye pollutant

Developing a sustainable, efficient and recyclable heterogeneous Fenton-like catalyst is important to wastewater treatment. Herein, well-dispersed MnO2 and Fe3O4 nanoparticles inlaid in chitosan beads (MnO2-Fe3O4/CH) was firstly fabricated and employed in the degradation of methylene blue (MB). The bead was prepared via a facile one-step method by dropwise addition of chitosan-metal salt solution into alkaline solution. Comparing with monometallic chitosan beads (MnO2/CH, Fe3O4/CH) and naked MnO2-Fe3O4, MnO2-Fe3O4/CH displayed significantly higher activity for MB degradation with the assistance of hydrogen peroxide (H2O2), finally removing 96.8% MB under the optimal conditions (50 mg L-1 MB, 4.0 g L-1 catalyst, 30 g L-1 H2O2, pH = 7, 60 min). Based on a series of characterizations, the large surface area (60.1 m2 g-1), well-developed porosity (0.3 cm3 g-1), and intensified electron transport of MnO2-Fe3O4/CH consequently enhanced the catalytic performance via a synergistic effect. Because the specific porous structure of MnO2-Fe3O4/CH facilitated the adsorption/diffusion of reactants and exposure of active sites. Meanwhile, the electron transfer from Mn3+ to Fe3+ accelerated the Fe3+/Fe2+ cycle, which favored the production of dominant reactive species hydroxyl radical for MB degradation. Besides, the magnetic beads could be easily collected from the solution and reused for five times with a negligible leaching.