Removal and recycling of aqueous selenite anions using cobalt-based metal-organic-framework coated on multi-walled carbon nanotubes composite membrane.

The utilization of selenium as a novel functional material is rapidly expanding, and the retrieval of selenium from waste containing selenium is gaining recognition in the industry. This study prepared a novel composite membrane coated with the cobalt-based metal-organic framework coated on multi-walled carbon nanotubes (Co-MOF@MWCNTs). The MWCNTs served as the skeleton to support the active components of Co-MOF, which enabled efficient removal and resource utilization of liquid selenite (SeO). The morphology, structure, and composition of the prepared membrane were characterized using field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), etc.. Applying a permeate flux of 67.08 L m h, the SeO removal efficiency of the composite membrane reached up to 92.2%. The composite membrane containing CoSeO can be used as an electrocatalytic oxygen evolution catalyst. Density functional theory calculations and electrochemical analysis showed that the conversion from O* to OOH* was a rate-determining step. Under 1.0 M KOH conditions, the lowest overpotential for Co-MOF@MWCNTs-40 at 10 mA cm was 360 mV. In this study, the process of selenium resource utilization and the mechanism of SeO removal by Co-MOF@MWCNTs are revealed. It demonstrates that membrane-based sequestration of SeO can provide a viable approach for SeO removal and utilization in wastewater.