Preparation of superhydrophilic functionalized nZVI-MOF-74(Co)-PDA@PVDF composite membranes for enhanced Cr(VI) removal.

Nano-zero-valent iron (nZVI) is widely employed in heavy metal wastewater treatment; however, it oxidizes and agglomerates readily, forming dense oxide shells that significantly diminish its effectiveness and reduction efficiency. Furthermore, the complete recovery of nZVI from water remains challenging. To address these issues, we successfully integrated nZVI onto the metal-organic framework Co-MOF-74. The framework, rich in pore channels, facilitates the uniform dispersion of nZVI, while open metal sites provide electrons crucial for the reduction of Cr(VI). Subsequently, we synthesized superhydrophilic nZVI-MOF-74(Co)-PDA@PVDF composite membranes (FMPP membranes) by incorporating nZVI-MOF-74(Co) particles into poly(dopamine) (PDA)-modified poly(vinylidene difluoride) (PVDF) powders. These nZVI-MOF-74(Co)-PDA@PVDF composite membranes feature abundant PDA functional groups, such as -OH, -NH, and -NH2, which enhance membrane hydrophilicity and significantly improve oxidation resistance. The equilibrium adsorption capacity for Cr(VI) was 83.12 mg/g at 25 °C. The Cr(VI) removal behavior of the FMPP membrane aligns with the pseudo-second-order kinetic model and the Weber-Morris model. The FMPP membrane offers advantages of high efficiency, stability, and reusability. This study demonstrates that FMPP membranes hold great potential for broad application in heavy metal wastewater treatment.