Nano-scale modification of polysulfone membrane matrix and the surface for the separation of chromium ions from water

• Four different bulk and surface modified polysulfone (PSf) membranes were prepared.
• SiO2 nanoparticles and polydopamine (PDA) were used for the modification.
• PSf/SiO2/PDA membrane showed smoother surface and more hydrophilic behavior.
• PSf/SiO2/PDA membrane exhibited quite stable solution flux and robust structure.
• PSf/SiO2/PDA membrane exhibited the best performance in the Cr(VI) removal.

In this study, aiming at hexavalent chromium removal from aqueous solutions, different strategies were proposed for developing hydrophilic and surface functional polysulfone (PSf) membrane. In addition to PSf membrane, three different types of membranes were prepared by addition of SiO2 nano-particles to the dope solution and/or by deposition of polydopamine (PDA) layer on the surface of the membranes. The membranes (i.e. PSf, PSf/PDA, PSf/SiO2 and PSf/SiO2/PDA) were characterized by different techniques. The membranes’ transport properties and the separation performance were studied using a filtration unit operated at a continuous dead-end flow mode. The kinetics and the separation mechanism of Cr(VI) were investigated by tracing the effect of pH, initial chromium concentration and operation time. It was found that the surface and adsorption property of PDA layer is dependent on the substrate (PSf or PSf/SiO2) on which it is grown. Reusability of the membranes was studied by repeating consecutive adsorption/desorption cycles. NaOH (0.05 M) showed the highest stripping capability. Among the membranes, PSf/SiO2/PDA membrane with relatively smooth surface and robust structure over the operation time exhibited quite stable water flux (at 13 L m−2 h−1) and superior separation performance (94% at pH = 3), which is quite encouraging from practical and industrial points of view.

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