High performance bimetallic ZIF-CoZn@PVDF-HFP composite nanofiber membrane for membrane distillation based on coaxial electrospinning technology

Abstract

Membrane Distillation (MD) technology stands out for its cost-effectiveness and sustainability in diverse applications, such as high-salinity wastewater treatment and seawater desalination. However, conventional MD membranes frequently encounter challenges associated with inadequate permeate flux and insufficient anti-wetting performance. In the present study, we fabricated a series of ZIF-CoZn@PVDF-HFP composite nanofiber membranes with a core–shell structure via coaxial electrospinning. Here, PVDF-HFP functions as the core, while a blend of bimetallic Zeolitic imidazolate framework ZIF-CoZn nanoparticles and PVDF-HFP constitutes the shell. Through the utilization of the coaxial technology, functional nanoparticles achieve uniform and stably dispersed on the nanofiber surface, leading to the creation of a secondary rough structure in addition to the inherent roughness of single-nozzle electrospinning. This results in a surface with a 3D-hierarchical structure. The significantly amplifies the evaporation area on the surface of the composite nanofiber membrane, thereby bolstering the permeate flux in the MD process. Additionally, the incorporation of bimetallic ZIF-CoZn nanoparticles, recognized for their superior hydrophobicity and low thermal conductivity, improves the anti-wetting and heat-insulating properties of the composite nanofiber membrane, further advancing permeate flux performance. Using a 35 g L−1 NaCl as the feed solution, the optimal 1 % ZIF-CoZn@PVDF-HFP composite nanofiber membrane demonstrated a permeate flux of 21.8 L m−2 h−1, coupled with a salt rejection rate exceeding 99.9 %. Even during long-term MD testing, it maintained excellent insulation and anti-wetting capabilities. Our research offers a convenient and effective approach for fabricating anti-wetting composite nanofiber membranes.