Novel ultrafiltration membrane fabricated using nanofiber layer as integral filler: Taking PAN and C3N4 as example

This study introduces a novel ultrafiltration (UF) membrane, called NFFM, which utilizes a nanofiber (NF) layer as an integral filler during the phase inversion process. The photoactive NFFM was prepared using photoactive PAN-C3N4 (PCN) NF, which is made using C3N4 nanosheets as a visible light responsive photocatalyst with a loading ratio of up to 20%. NFFM membranes made using PAN NF, hydrophilic modified PAN-C3N4 (HPC) NF as filler, and PAN-C3N4 blend membrane were also prepared for comparison. NFFMs showed special morphologies, such as porous surfaces, selective layer located at the internal interface in cross-section, diverse pore sizes and pore size distribution, which are different from that of the traditional blend membrane made with the same ratio of components. Because the dissolving of NF layer into the casting solution changes the composition, polymer distribution, and property of the casting solution, thus change the membrane property. Thickness, composition and surface states of NF Layer can influence its dissolution process. Membrane filled with PCN NF (NFFM-PCN) showed a smaller pore size than membrane filled with HPC (NFFM-HPC), due to the low solubility of HPC. Moreover, a longer contacting time can cause the casting solution penetrate into the surface of the HPC layer, leading to a smooth surface. Finally, dye rejection and photoactivity test showed that NFFM-PCN showed better dye rejection property and photoactivity than other membranes, despite the lower photoactivity of C3N4 due to the coverage effect of PAN. Overall, this primitive study provides a new method for preparing a new type of membrane for some potential applications.