Metal–Organic Frameworks Supported on Nanofiber for Desalination by Direct Contact Membrane Distillation

Abstract

Among other applications, metal–organic frameworks (MOFs) are slowly gaining grounds as fillers for desalination composite membranes. In this study, superhydrophobic poly(vinylidene fluoride) nanofibrous membranes were fabricated with MOF (iron 1,3,5-benzenetricarboxylate) loading of up to 5 wt % via electrospinning on a nonwoven substrate. To improve the attachment of nanofibers onto the substrate, a substrate pretreatment method called “solvent basing” was employed. The iron content in the nanofiber, measured by energy-dispersive X-ray spectroscopy, increased proportionally with the increase of the MOF concentration in the spinning dope, indicating a uniform distribution of MOF in the nanofiber. The water contact angle increased up to 138.06 ± 2.18° upon the incorporation of 5 wt % MOF, and a liquid entry pressure of 82.73 kPa could be maintained, making the membrane useful for direct contact membrane distillation experiments. The membrane was stable for the entire operating period of 5 h, exhibiting 2.87 kg/m 2 ·h of water vapor flux and 99.99% NaCl (35 g/L) rejection when the feed and permeate temperature were 48 and 16 °C, respectively. Immobilization of MOF on nanofibers with the enhanced attachment was proven by inductively coupled mass spectrometry analysis, by which no Fe 2+ could be found in the permeate to the detection limit of ppt.