Fabrication of highly permeable PVDF loose nanofiltration composite membranes for the effective separation of dye/salt mixtures

The separation of dyes and salts is very challenging in regards to treating high salinity textile wastewater. To effectively dispose dye/salt mixtures, it has become urgent to develop highly permeable and antifouling nanofiltration membranes. Herein, a novel loose nanofiltration membrane was fabricated by combining blending with interfacial polymerisation. Polyvinylidene fluoride (PVDF)/styrene-maleic anhydride (SMA) copolymer membranes with uniform microstructures were achieved via phase inversion by controlling the miscibility. Numerous carboxyl groups were gathered on the surface due to the amphiphilic SMA segregation during the membrane formation. Carboxylated carbon nanotubes (CNT-COOH) were used to further tune the membrane microstructures and promote the carboxyl groups segregation onto the surface. Ultimately, polyethylenimine (PEI) and triethanolamine (TEA) were co-deposited on the membrane surface by the amidation reaction and hydrogen bonding to form a loose structure. The optimized membrane exhibited high dye rejections to Congo red (99.9%), methyl blue (96.7%), acid fuchsin (96.1%), and low salt rejections to NaCl (1.7%), MgCl2 (4.5%), MgSO4 (1.2%). Significantly, it possessed a permeate flux of up to 251.6 L/m2·h·bar during the dye/salt mixtures filtration. Moreover, the optimized membrane also performed excellent antifouling properties toward proteins and dyes. Overall, this work provides a promising loose nanofiltration membrane for textile wastewater treatment.