Synthesis and fabrication of nanostructured hydrophobic polyazole membranes for low-energy water recovery

Aromatic fluorinated polyoxadiazoles (F-POD) and polytriazoles (F-PT) were synthesized and for the first time manufactured into porous membranes by phase inversion and by electrospinning. The phase inversion F-POD membranes had a mean flow pore size (MFP) of 51 nm, while for F-PT it was around 74 nm. The electrospun membranes had a much larger pore size, the MFP for F-POD membrane was around 1.7 μm and for F-PT it was 2.7 μm. The membranes were tested for desalination of Red Sea water using direct contact membrane distillation (DCMD). By combining the high polymer hydrophobicity and high porosity, apparent contact angles up to 162° were obtained, assuring the operation with practically no liquid water leakage under pressure up to 0.9 bar. Salt selectivity as high as 99.95% and water fluxes as high as 85 L m−2 h−1 were demonstrated, operating at 80 °C feed temperature and 22 °C permeate.