Selective Adsorption and Separation through Molecular Filtration by Hyperbranched Poly(ether amine)/Carbon Nanotube Ultrathin Membranes.

In response to the increasing public awareness of serious dye-contained wastewater contamination, we herein fabricated a novel anthracene-containing hyperbranched poly(ether amine) (hPEA-AN)/carbon nanotube (CNT) ultrathin membrane (UTM), which combined both the merits of the conventional dye adsorption strategy and membrane filtration process, to implement efficient selective adsorption of dye molecules and also the separation of dye mixtures by molecular filtration. Taking advantage of the π-π stacking interactions between anthracene and CNT sidewalls and hydrophobic interactions, CNTs were coated tightly with hPEA-AN to form the hPEA-AN@CNT complex, which can be well-dispersed very stably in water. The formation of the hPEA-AN@CNT complex was confirmed using X-ray photoelectron spectroscopy, Raman spectra, fluorescence spectra, and thermogravimetric analysis. Meanwhile, a simple filtration process was applied to prepare hPEA-AN@CNT UTMs with a thickness of 1.5 μm, which can be further cross-linked through photodimerization of anthracene moieties. The UTMs represented selective adsorption behaviors toward hydrophilic dyes even with similar backbones and the same charge states, namely, they showed high adsorption capacities (Qeq) toward eosin B, erythrosin B (ETB), 4',5'-dibromofluorescein, and Evans blue (EVB) dyes up to 300 μmol/g while showing low adsorption capacities toward calcein (Cal), methyl red, and Ponceau S dyes. On the basis of this unique selective adsorption, molecular filtration was then realized toward mixed ETB/Cal and EVB/Cal dyes, with a separation efficiency of up to 100% and regeneration without an obvious efficiency decrease.