From micro to nano: Polyamide thin film on microfiltration ceramic tubular membranes for nanofiltration

Interfacial polymerization is an effective technique to synthesize high performance polyamide thin film membranes. However, it is still very challenging to apply this technique on ceramic hollow fibres or tubular membranes, especially when the substrate pore size is in the microfiltration range. In this study, we demonstrated that thin polyamide layer can be synthesized directly on microfiltration ceramic tubular membranes with a surface pore size of 0.1-0.2 mu m via interfacial polymerization without an intermediate layer. A thin polyamide layer with a thickness 30-40 nm was coated on the inner surface of the ceramic substrate by circulating the monomers of branched polyethyleneimine (PEI), piperazine (PIP), and trimesoyl chloride (TMC) through the membrane lumen. The thin film layer showed good integration with the ceramic substrate and could withstand high pressure of at least 10 bar. The mechanical property of the polyamide layer was examined using AFM and the modulus was measured. The thin film composite membranes demonstrated excellent nanofiltration performance with a pure water permeability of 16-18 LMH bar(-1) and a molecular weight cut-off of similar to 250 Da. The membranes also showed good salt rejections (>90%) to CaCl2, MgCl2 and MgSO4, and still maintained high rejections of MgCl2 and sucrose at elevated temperature of 80 degrees C. The use of highly inert ceramic substrates has enabled the application of polyamide membranes under more challenging conditions.