ABSTRACT
High-performance thin film nanocomposite (TFN) hollow fiber (HF) membranes, with MIL-101(Cr) MOF nanoparticles (52 ± 13 nm) embedded, have been synthesized with the polyamide layer formed either on the outer or inner surface of a polysulfone HF (250 and 380 µm ID and OD, respectively). The TFN_out membrane was developed using the conventional interfacial polymerization method, typically applied to obtain TFN flat membranes (MOF particles added to the thin layer by deposition). This membrane gave a water permeance value of 1.0 ± 0.7 L·m-2·h-1·bar-1 and a rejection of 90.9 ± 1.2% of acridine orange (AO, 265 Da). In contrast, the TFN_in membrane was synthesized by microfluidic means and gave a significantly higher water permeance of 2.8 ± 0.2 L·m-2·h-1·bar-1 and a slightly lower rejection of 87.4 ± 2.5% of the same solute. This remarkable increase of flux obtained with small solute AO suggests that the HF membranes developed in this work would exhibit good performance with other typical solutes with higher molecular weight than AO. The differences between the performances of both TFN_in and TFN_out membranes lay on the distinct superficial physicochemical properties of the support, the synthesis method, and the different concentrations of MOF present in the polyamide films of both membranes. The TFN_in is more desirable due to its potential advantages, and more effortless scalability due to the microfluidic continuous synthesis. In addition, the TFN_in membrane needs much fewer quantities of reactants to be synthesized than the TFN_out or the flat membrane version.
ABSTRACT
The MOFs Cr carboxylate MIL-101(Cr) and Zn imidazolate ZIF-11 have different chemical and textural properties. These properties have been combined to prepare thin film nanocomposite (TFN) membranes for organic solvent nanofiltration (OSN) with the two MOFs simultaneously embedded in the same membrane. The TFN membrane containing only ZIF-11 permeated faster than that with only MIL-101(Cr) when filtering sunset yellow (SY) (4.9 L m-2 h-1 bar-1) and acridine orange (AO) (3.2 L m-2 h-1 bar-1), although MIL-101(Cr) alone gave rise in both cases to better rejections (above 90%). The combination of the two MOFs led to a versatile TFN membrane that showed an intermediate performance that improved the rejections given by the TFN membrane synthesized with ZIF-11 and the permeances corresponding to the TFN membrane synthesized with MIL-101(Cr). The effect of the temperature on the TFN membranes designed for this work has also been studied, obtaining apparent activation energies of 13.2 ± 2.1 and 8.3 ± 1.1 kJ mol-1 for the OSN of pure methanol and SY-methanol, respectively.
