Self-cleaning of metal-organic framework membranes achieved by photocatalytic ZIFs for dye and antibiotic separation

Abstract

The progress of membrane-based applications is hindered by widespread membrane fouling, which leads to a significant decrease in separation effectiveness and lifespan, even though membrane separations have shown great potential in the treatment of dye wastewater. The metal-organic framework MOFs (ZIF-8) display strong thermal and chemical stability and an exceptional capacity to degrade organic molecules under visible light, making them extremely promising for the development of self-cleaning membranes. In this investigation, a ZIF-8/L-DOPA/PVDF mixed matrix membrane with excellent self-cleaning properties was constructed using the in-situ growth technique. The characterization results confirmed the formation of a continuous ZIF-8 coating layer, considerably increasing the surface roughness of the composite membrane from 22.9 nm to 76.3 nm compared to L-DOPA/PVDF substrates. The ZIF-8 layer deposited on the L-DOPA/PVDF membrane surface reduced the contact angle from 75.71° to 40.94°. The highest-performing ZIF-8/L-DOPA/PVDF membranes show a higher water permeability of 159.63 (L·m−2 h−1 bar−1) and superior dye rejection rates (Congo red: 97.3 %, Methylene Blue: 98.32 %, Methyl Blue: 98.62 %), along with enhanced removal of antibiotics (e.g., Tetracycline: 95.3 % and Ciprofloxacin: 93.34 %), and long-term nanofiltration stability. Furthermore, the treated membrane recovers almost all of its initial separation efficacy after exposure to visible light due to the successful removal of attached dyes from the membrane surface through photocatalysis. This work presents the potential to fabricate membranes with advantageous photocatalytic properties and effectively treat dye wastewater using self-cleaning membranes.