Supramolecular Networks of Hyperbranched Poly(ether amine) (hPEA) Nanogel/Chitosan (CS) for the Selective Adsorption and Separation of Guest Molecules

Abstract

Supramolecular networks with selective adsorption for guest molecules were formed via dynamic hydrogenbonding interactions between the carboxyl group-containing hyperbranched poly(ether amine) nanogels (hPEA-NG) and chitosan (CS). The hPEA-NG/CS supramolecular networks were physically cross-linked and were composed of hPEA-NGs dispersed within a crystallized CS matrix. An increasing CS content enhanced the mechanical properties of the hPEA-NG/ CS supramolecular networks. The transparent hPEA-NG supramolecular networks did not disassemble in aqueous solutions with different pH values and organic solvents and were swollen with high weight fractions of water (W H 2 O = 0.95) in less than 30 s. The adsorptive behavior of seven fluorescein dyes and five azobenzene (azo) dyes onto the hPEA-NG/CS supramolecular networks was investigated. These hPEA-NG/CS supramolecular networks showed rapid adsorption for Rose Bengal (RB), Erythrosin B (ETB), Eosin B (EB), 4′,5′-dibromofluorescein (DBF), Ponceau S (PS) and Evans blue (EVB) dyes with high adsorption capacities (Q eq ). The networks showed very low adsorption for calcein (Cal), fluorescein (FR), 4,5,6,7-tetrachlorofluorescein (TCF), and Bismarck brown (BBY) dyes. The adsorption process was found to follow pseudo-second-order kinetics. The different adsorptive behaviors for different dyes indicated the selective adsorption of the hPEA-NG/CS supramolecular networks for the azo and fluorescein dyes despite similar backbone structures and charge states. On the basis of the unique selective adsorption, the separation of mixtures of fluorescein dyes, such as RB/Cal, RB/FR, and PS/MR, was achieved using the hPEA-NG/CS supramolecular network as an adsorbent. ■ INTRODUCTIONSupramolecular polymer networks are cross-linked threedimensional assemblies with noncovalent and intermolecular bonds. 1−4 They have gained considerable attention because of their intrinsic self-healing, 5,6 shape memory, 6−8 and stimuliresponse properties 6 and potential applications in controlled drug delivery, 9,10 and smart materials and water treatment. 11,12 The supramolecular polymer networks are typically cross-linked by transient physical interactions, including hydrogen bonding, 13−20 halogen bonding, 14,21 ionic interactions, 3,22 host− guest interactions, 23,24 π−π stacking, 13,25−28 and transition metal complexation. 29−31 Because of the directional property and versatility, the supramolecular interaction via hydrogen bonding has been intensively studied in the construction of supramolecular polymer networks. Lehn and co-workers generated mesoscopic molecules by the assembly of bifunctional heterocyclic chiral and achiral organic compounds (as the backbone) and uracil derivatives (as side-chains) through hydrogen bonds. 32 Using triuret blocks, controlled conformation and temperature-dependent hydrogen bonding, Ni and coworkers prepared supramolecular thermo-reversible polyureaurethane networks. 33 In these studies, the building blocks were usually polymers or oligomers. However, nanogels (NGs) as ...

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