Charge-selective separation and recovery of organic ions by polymeric micelles

Dendritic Macrosurfactant Assembly for Physical Functionalization of HIPE-Templated Polymers

High-internal-phase emulsion-templated macroporous polymers (polyHIPEs) have attracted much interest, but their surface functionalization remains a primary concern. Thus, competitive surface functionalization via physical self-assembly of macrosurfactants was reviewed. Dendritic and diblock-copolymer macrosurfactants were tested, and the former appeared to be more topologically competitive in terms of solubility, viscosity, and versatility. In particular, hyperbranched polyethyleneimine (PEI) was transformed into dendritic PEI macrosurfactants through click-like N-alkylation with epoxy compounds. Free-standing PEI macrosurfactants were used as molecular nanocapsules for charge-selective guest encapsulation and robustly dictated the surface of a macroporous polymer through the HIPE technique, in which the macroporous polymer could act as a well-recoverable adsorbent. Metal nanoparticle-loaded PEI macrosurfactants could similarly lead to polyHIPE, whose surface was dictated by its catalytic component. Unlike conventional Pickering stabilizer, PEI macrosurfactant-based metal nanocomposite resulted in open-cellular polyHIPE, rendering the catalytic sites well accessible. The active amino groups on the polyHIPE could also be transformed into functional groups of aminopolycarboxylic acids, which could efficiently eliminate trace and heavy metal species in water.

Biorenewable triblock copolymers consisting of l-lactide and ε-caprolactone for removing organic pollutants from water: a lifecycle neutral solution

Background

Current methods of removing organic pollutants from water are becoming ineffective as the world population increases. In this study, a series of biorenewable triblock copolymers with hydrophobic poly(ε-caprolactone) block and hydrophilic poly(l-lactide) blocks were synthesized and tested as agents to remove environmental pollutants from an aqueous solution. The percent of pollutant removed and equilibrium inclusion constants were calculated for the polymers. These values were compared to previously known removal agents for their effectiveness.

Results

Triblock copolymer samples removed over 70% of the polycyclic aromatic hydrocarbon (PAH) phenanthrene from an aqueous solution, with selectivity for the adsorption of phenanthrene over other PAHs tested. The inclusion constant was 7.4 × 10⁵ M⁻¹ and adsorption capacity was 5.8 × 10⁻⁷ mol phenanthrene/g polymer. Rose Bengal was used to further probe the nature of interactions between the copolymers and a small molecule guest. Solid samples of the block-poly(l-lactide)–block-poly(ε-caprolactone)–block-poly(l-lactide) (PLLA–PCL–PLLA) systems were found to rapidly remove over 90% of Rose Bengal from aqueous solution, resulting in a complete disappearance of the characteristic pink color. Solutions of the copolymers in dichloromethane also removed Rose Bengal from water with a similar level of efficiency. Large inclusion constant values were obtained, ranging from 1.0 × 10⁵ to 7.9 × 10⁵ M⁻¹, and the average adsorption capacity value of 6.2 × 10⁻⁷ mol/g polymer was determined. Aged polymer samples exhibited different adsorption characteristics and mechanistic theories for the removal of Rose Bengal were determined.

Conclusion

The triblock copolymer consisting of l-lactide and ε-caprolactone was effective in removing various organic pollutants in aqueous environments. It is a biorenewable material which leads to minimal waste production during its lifecycle. These polymers were in general more effective in removing organic pollutants than commercially available pollution removal systems.

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 (Q_eq) 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.

Linear polymeric ionic liquids as phase-transporters for both cationic and anionic dyes with synergic effects

Linear polymeric ionic liquids were synthesized and demonstrated to be very effective transporters for both anionic dye methyl orange (MO) and cationic dye methylene blue (MB) from water to chloroform individually as well as simultaneously.