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.

Automated summary

In this study, a sustainable and efficient heterogeneous Fenton-like catalyst comprising well-dispersed MnO2 and Fe3O4 nanoparticles in chitosan beads was developed for wastewater treatment. The MnO2-Fe3O4/CH catalyst showed a significantly higher activity for methylene blue degradation due to its large surface area, developed porosity, and enhanced electron transport. The catalyst facilitated the adsorption and diffusion of reactants, exposed active sites, and accelerated the Fe3+/Fe2+ cycle, ultimately favoring the production of hydroxyl radicals for efficient pollutant removal. Moreover, the magnetic beads exhibited easy collection and reusable properties with minimal leaching.