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.