Fabrication of a compressible PU@RGO@MnO2 hybrid sponge for efficient removal of methylene blue with an excellent recyclability

Abstract

To enhance the recyclability while maintaining the high efficiency for the removal of organic dyes, monolithic polyurethane@reduced graphene oxide@manganese dioxide (PU@RGO@MnO₂) hybrid sponge with a hierarchical structure and satisfactory flexibility is fabricated by self-assembly of RGO on a PU sponge followed by uniform coating of MnO₂ nanoparticles onto RGO by means of an in situ redox reaction between RGO and KMnO₄. RGO acts as an ideal substrate to accommodate MnO₂ nanoparticles and prevents their aggregation, whereas the numerous hydrophilic MnO₂ nanoparticles play dual roles of adsorption and catalytic degradation of methylene blue (MB) dye. The resultant hybrid sponge shows a hierarchical porous structure that provides fast transport channels and abundant active sites, benefiting the diffusion and removal of MB. By enhancing the mass transfer with the help of a micro-pump, the monolithic hybrid sponge acts as a filter for dye removal. Under the dynamic mode, the adsorption efficiency of the PU@RGO@MnO₂ hybrid sponge for MB (50 ppm, 30 mL) reaches 94% after 20 min, whereas it is as low as 5% under the static mode. With the assistance of H₂O₂, the removal efficiency of the hybrid sponge is 96% at first time under the dynamic mode, whereas it is only 14% in the static mode. The monolithic hybrid sponge is highly efficient in adsorption and catalytic degradation of MB based on an adsorption–oxidation–desorption process. Even after being used 4 times, it still maintains excellent removal efficiency and recyclability.