No abstract

The grafting from approach was used to prepare pH-responsive polyacid brushes using poly(itaconic acid) (PIA) and poly(acrylic acid) (PAA) at the amine functional groups of chitosan. Hybrid materials consisting of polymer brushes and magnetite nanoparticles (MNPs) were also prepared. The products were structurally characterized and displayed reversible pH-responsive behavior and controlled adsorption/desorption of methylene blue (MB). Switchable binding of MB involves cooperative effects due to conformational changes of brushes and swelling phenomena in solution which arise from response to changes in pH. Above the pKa, magnetic nanocomposites (MNCs) are deprotonated and display enhanced electrostatic interactions with high MB removal efficiency (>99%). Below the pKa, MNCs undergo self-assembly and release the cationic dye. The switchable binding of MB and the structure of the polymer brush between collapsed and extended forms relate to changes in osmotic pressure due to reversible ionization of acid groups at variable pH. Reversible adsorption-desorption with variable binding affinity and regeneration ability was demonstrated after five cycles.

Hybridization of metal nanoparticles (NPs) with redox-switchable polymer supports not only mitigates their aggregation, but also introduces interfacial electron pathways desirable for catalysis and numerous other applications. The large surface area and surface accessible atoms for noble metal nanoparticles (e.g., Ag, Au, Pt) offer promising opportunities to address challenges in catalysis and environmental remediation. Herein, AgNPs were supported onto redox-switchable polyaniline that acts as an advanced multifunctional conducting template for enhanced catalytic activity. At the initial stage of reduction of Ag, leucoemeraldine is oxidized in situ to pernigraniline (PG), which acts as interfacial pathway between NPs for electron transport. With the contribution of BH, PG acts as an electron-acceptor site, which creates interfacial electron-hole pairs, serving as additional active catalytic reduction sites. The use of a redox-responsive composite system as a template enhances catalyst performance through adjustable charge injection across interfacial sites, along with catalyst reusability for the reduction of 4-nitrophenol (4-NPh). Strikingly, from X-ray photoelectron spectroscopy results it was observed that in situ reduction of Ag onto the conductive polymer alters the electronic character of the catalyst. The unique multielectronic effects of such Ag-supported NPs enrich the scope of such catalytic systems via a tunable interface, diversified catalytic activity, fast kinetics, minimization of AgNPs aggregation, and maintenance of high stability under multiple reaction cycles.

Various structural forms of poly(aniline) (PANI) were synthesized in aqueous solution with different acids and/or a chitosan template support to afford nanoparticle PANI (NP; synthesized in water), bulk-PANI (aqueous acetic acid (HAc), hydrochloric acid (HCl) and sulfuric acid (SA) and a chitosan-PANI composite (CH) material. The polymer materials were characterized using spectroscopy ( 1 H NMR, FT-IR, UV-vis), TGA and P-XRD. The polymer materials were structurally diverse according to their unique morphology related to the ratio between quinoid and benzenoid monomer units of PANI. The sorption and kinetic uptake properties of PANI materials with methylene blue (MB) in aqueous solution were studied where variable sorption capacity was observed, as follows: NP > HAc > HCl > SA > CH. The Sips isotherm model describes the adsorptive equilibrium uptake while the pseudo-second order kinetic model describes the time dependent uptake of MB. The monolayer sorption capacities (Q m ) reported herein are among the highest (ca. 6-fold greater) relative to other Q m values reported for PANI materials in the literature.

The ability to achieve exquisite control over polymer building blocks within multicompartment magnetite nanocomposites (NCs) to afford predictable and ordered packing hierarchical structures remains a significant challenge for the design of NCs. Thus, there is an urgent need to develop new types of nano-dimensional assemblies that undergo responsive shape shift, size, phase, and morphological transitions, especially for processes that are triggered by biologically relevant stimuli such as ionic gradients to meet the demand for diverse applications. Accordingly, we report an unprecedented concept for the preparation of salt-responsive magnetite/polyaniline composite nanoassemblies with chemically distinct dual-compartment structures. The size, shape, and nano-dimensional phase separation of the PANI assemblies within NCs were adjusted in a facile manner with incremental changes in salt gradients using NaCl(aq). Composition effects bestow desirable diversiform shape, size, and phase behavior of the incorporated conductive polymer via dynamic H-bonding. The size, shape, and superparamagnetic character of iron oxide nanoparticles (IONPs) are unaffected by a "salting-in" process. The mechanism, gradual morphological evolution, interchangeable nanophase separation, and ion-stimulated disassembly of PANI building blocks for these magneto/ion-responsive polymer-composites at elevated ionic strength are strongly supported by DLS, Raman spectroscopy, TEM, and equilibrium dye (MB/MO) recognition studies.

Stimuli-responsive microcapsules that can release encapsulated small molecules under external environmental stimuli have been extensively employed in delivering small molecules to targeted sites. Here, salt-activated hydrogen bonding chemistry was exploited to develop responsive release systems for self-healing (guest) molecules from capsular polyaniline (PANI) particles. Payloads were physically entrapped within PANI nanoparticles constructed by interface-templated polymerization, where responsive payload release was achieved by using saltdependent (sodium chloride) gradients. We propose a coactivation mechanism for release of guest molecules attributed to hydrogen bonding and polymer osmotic expansion. The release mechanism relies on a salt activator with cleavage of saline-responsive noncovalent interactions within the mesoporous particles. The responsiveness and guest release are coactivated by changes in polymer shell permeability, expansion, and polymer shell hydrophobicity. Anion hydration and its concentration (degree of doping) play a pivotal role for the ion responsiveness. NaCl stimuli offer a versatile and simple method for triggering sustained release of self-healing materials which hold enormous potential for applications in enhanced anticorrosion protection in harsh salt-attacking environments.