Separation of anionic dye mixtures b y Al-metal-organic framework filled polyacrylonitrile-ethanolamine membrane and its modified product

Molecular separation of dye mixtures containing the same charge remains a challenge. In the present study, we prepared a composite membrane that could efficiently separate anionic dye mixtures. Briefly, Al-Metal-organic framework (Al-MOF) nanoparticles synthesized by the ion-exchange method were used as fillers during the in-situ synthesis of ethanolamine (ETA) grafted polyacrylonitrile (PAN) membrane. The optimized composite membrane showed a high rejection of congo red (CR) from a single solution (96% rejection) and the CR/methyl orange (MO) mixture (93%/18%) solution. The flux of dye mixture solution reached 180 L m −2  h −1 , higher than many reports in the literature. The further modification on pore size (heat treatment) or surface charge (hydrolysis treatment) improved the membrane performance to separate smaller dye mixture of methyl blue (MB)/MO. Both modified membranes showed a good MB rejection (93%) and flux of 70–85 L m −2  h −1 . While for the separation of the MB/MO mixture, the heat-treated membrane showed the lowest flux and a middling rejection. The surface hydrolyzed membrane showed a better selectivity (96% MB/32% MO) and a higher flux (127 L m −2  h −1 ) than that of the entirety hydrolyzed membrane (93% MB/58% MO and flux of 78 L m −2  h −1 ), which was attributed to their different charge distribution.