In-situ growth of metal-organic framework film on a polydopamine-modified flexible substrate for antibacterial and forward osmosis membranes

Metal-organic frameworks (MOFs), being a type of the most representative porous nanomaterials, have been regarded as a promising candidate to fabricate antibacterial separation membrane attributing to their high porosity, tunable pore size and chemical functionality. Comparing with the traditional blending techniques, depositing a continuous and coherent MOF crystal layer on top of the membrane can fully exploit the functionality of the materials. In this study, we constructed a continuous zeolite imidazole framework-8 (ZIF-8) crystal layer on the surface of flexible polysulfone (PS) membrane pre-modified by polydopamine (PDA) via a facile immersion strategy. The characterization results confirmed the formation of a continuous ZIF-8 coating layer, which significantly increases the roughness of composite membrane from 17.2 nm to 154.0 nm compared with PDA/PS substrates. The ZIF-8 layer deposited on the surface of the PDA/PS membrane reduced the contact angle value from 45.4 degrees to 38.6 degrees based on the properties of Janus membrane. As a result, the ZIF-8/PDA/PS composite membranes showed a high water flux of 9.6 L/m(2).h and a low solute reverse flux of 3.8 g/m(2).h using 1 M MgCl2 as draw solution and DI water as feed solution under forward osmosis mode. In addition, the composite membranes also exhibited a satisfactory antimicrobial performance against Escherichia coli (E. coli) with antibacterial efficiency almost 99%, which is much higher than PDA/PS membrane (64%). This work demonstrates a facile way to ZIF-8/PDA/PS composite membranes with good FO performance and excellent antibacterial capacities.