Layered double hydroxides (LDHs) as novel macropore-templates: The importance of porous structures for forward osmosis desalination

Abstract To minimize the effect of the internal concentration polarization (ICP) in the substrates of the forward osmosis (FO) membranes, higher overall porosity and interconnected pore network was engineered into the substrates by erosion of the three-dimensional layered double hydroxides (LDHs) with “sand rose” morphology. As expected, the substrates showed high porosity and macropore structure in the pore-wall after erosion of the LDH nanoparticles by HCl washing, which potentially promoted connectivity of the finger-like pores in the substrates. Therefore, the promising water flux for as-obtained FO membrane prepared from the typical interfacial polymerization was observed. The obtained TFN 7.5 -HCl membranes displayed the highest water flux up to 47.2 L m −2  h −1 at PRO mode (1 M NaCl as draw solution and DI-water as feed solution) and the water permeability coefficient reaching 7.29 L m −2  h −1 bar −1 at RO mode (DI-water as feed solution, Δ P  = 5 bar). These values were much higher than that of the commercial FO membranes. Counterintuitively, the obtained TFN 7.5 -HCl membrane disentangled successfully the dilemma of permeability–selectivity, e.g. improved selectivity between water and NaCl was achieved. Thus, it is believed that the designation strategy provides a simple and promising method to fabricate the enabled high-performance FO membranes.