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Metal-organic frameworks (MOFs) are studied for the design of advanced nanocomposite membranes, primarily due to their ultrahigh surface area, regular and highly tunable pore structures, and favorable polymer affinity. However, the development of engineered MOF-based membranes for water treatment lags behind. Here, thin-film nanocomposite (TFN) membranes containing poly(sodium 4-styrenesulfonate) (PSS) modified ZIF-8 (mZIF) in a polyamide (PA) layer were constructed via a facile interfacial polymerization (IP) method. The modified hydrophilic mZIF nanoparticles were evenly dispersed into an aqueous solution comprising piperazine (PIP) monomers, followed by polymerizing with trimesoyl chloride (TMC) to form a composite PA film. FT-IR spectroscopy and XPS analyses confirm the presence of mZIF nanoparticles on the top layer of the membranes. SEM and AFM images evince a retiform morphology of the TFN-mZIF membrane surface, which is intimately linked to the hydrophilicity and adsorption capacity of mZIF nanoparticles. Furthermore, the effect of different ZIF-8 loadings on the overall membrane performance was studied. Introducing the hydrophilizing mZIF nanoparticles not only furnishes the PA layer with a better surface hydrophilicity and more negative charge but also more than doubles the original water permeability, while maintaining a high retention of NaSO. The ultrahigh retentions of reactive dyes (e.g., reactive black 5 and reactive blue 2, >99.0%) for mZIF-functionalized PA membranes ensure their superior nanofiltration performance. This facile, cost-effective strategy will provide a useful guideline to integrate with other modified hydrophilic MOFs to design nanofiltration for water treatment.

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Surface zwitterionization of graphene oxide (GO) was firstly conducted by grafting poly(sulfobetaine methacrylate) (PSBMA) onto the GO surface via reverse atom transfer radical polymerization (RATRP).

Use of tight ultrafiltration (UF) membranes has created a new pathway in fractionation of dye/salt mixtures from textile wastewater for sustainable resource recovery. Unexpectedly, a consistently high rejection for the dyes with smaller sizes related to the pore sizes of tight UF membranes is yielded. The potential mechanism involved in this puzzle remains unclear. In this study, seven tailored UF membranes with molecular weight cut-offs (MWCOs) from 6050 to 17530 Da were applied to separate dye/salt mixtures. These UF membranes allowed a complete transfer for NaCl and NaSO, due to large pore sizes. Additionally, these UF membranes had acceptably high rejections for direct and reactive dyes, due to the aggregation of dyes as clusters for enhanced sizes and low diffusivity. Specifically, the membrane with an MWCO of 7310 Da showed a complete rejection for reactive blue 2 and direct dyes. An integrated UF-diafiltration process was subsequently designed for fractionation of reactive blue 2/NaSO mixture, achieving 99.84% desalination efficiency and 97.47% dye recovery. Furthermore, reactive blue 2 can be concentrated from 2.01 to 31.80 g·L. These results indicate that UF membranes even with porous structures are promising for effective fractionation of dyes and salts in sustainable textile wastewater treatment.