Layered double hydroxide-modified thin-film composite membranes with remarkably enhanced chlorine resistance and anti-fouling capacity

Polyamide (PA)-based thin-film composite (TFC) membranes prepared via interfacial polymerization have been widely applied in nanofiltration, reverse osmosis and forward osmosis (FO). However, a major issue facing practical applications of PA-TFC membranes remained the irreversible degradation and fouling of PA upon long-term exposure to aqueous environments. In this study, layered double hydroxides (LDHs) as inorganic additives were incorporated into PA matrices as well as polysulfone (PSf) substrates in attempt to alleviate the membrane degradation and fouling. The effect of location of LDHs on the physicochemical property and separation performance of FO membranes was investigated in detail. Four different FO membranes, including TFC (PA membrane on PSf substrate), TFC-LDH (PA membrane on PSf substrate blended with LDHs), LDH@TFC (LDH post-modified PA membrane on PSf substrate) and LDH@TFC-LDH (LDH post-modified PA membrane on PSf substrate blended with LDHs) were prepared. The water flux followed the sequence TFC-LDH > TFC LDH@TFC-LDH approximate to LDH@TFC, while the reverse salt flux showed the opposite trend. Moreover, it was observed that compared with pure TFC membrane, not only the surface of LDH@TFC-LDH membrane became more hydrophilic, but also porosity of the substrate became higher, therefore endowing the LDH@TFCLDH membrane with superior anti-fouling capacity. Moreover, the LDH@TFC-LDH membrane remained stable during long-term chlorination tests under alkaline conditions. To summarize, post-modifying the PA active layer with LDH nanocrystals and blending the PSf substrate with LDH nanocrystals significantly enhanced both antifouling capacity and chlorine resistance of prepared membranes without sacrificing the water flux during the FO process.